Publication Search Results

ID: 159283
Type: article
Authors: de Kleer, Katherine; Butler, Bryan; de Pater, Imke; Gurwell, Mark A.; Moullet, Arielle; Trumbo, Samantha; Spencer, John
Abstract: We present thermal observations of Ganymede from the Atacama Large Millimeter Array (ALMA) in 2016-2019 at a spatial resolution of 300-900 km (0"1-0"2 angular resolution) and frequencies of 97.5, 233, and 343.5 GHz (wavelengths of 3, 1.3, and 0.87 mm); the observations collectively covered all Ganymede longitudes. We determine the global thermophysical properties using a thermal model that considers subsurface emission and depth- and temperature-dependent thermophysical and dielectric properties, in combination with a retrieval algorithm. The data are sensitive to emission from the upper ∼0.5 m of the surface, and we find a millimeter emissivity of 0.75-0.78 and (sub)surface porosities of 10%-40%, corresponding to effective thermal inertias of 400-800 J m^-2 K^-1 s^-1/2. Combined with past infrared results, as well as modeling presented here of a previously unpublished night-time infrared observation from Galileo's photopolarimeter-radiometer instrument, the multiwavelength constraints are consistent with a compaction profile whereby the porosity drops from ∼85% at the surface to ${10}_{-10}^{+30}{\rm{ \% }}$ at depth over a compaction length scale of tens of centimeters. We present maps of temperature residuals from the best-fit global models, which indicate localized variations in thermal surface properties at some (but not all) dark terrains and at impact craters, which appear 5-8 K colder than the model. Equatorial regions are warmer than predicted by the model, in particular near the centers of the leading and trailing hemispheres, while the midlatitudes (∼30°-60°) are generally colder than predicted; these trends are suggestive of an exogenic origin.

ID: 159286
Type: article
Authors: Event Horizon Telescope Collaboration; Akiyama, Kazunori; Algaba, Juan Carlos; Alberdi, Antxon; Alef, Walter; Anantua, Richard; Asada, Keiichi; Azulay, Rebecca; Baczko, Anne-Kathrin; Ball, David; Baloković, Mislav; Barrett, John; Benson, Bradford A.; Bintley, Dan; Blackburn, Lindy; Blundell, Raymond; Boland, Wilfred; Bouman, Katherine L.; Bower, Geoffrey C.; Boyce, Hope; Bremer, Michael; Brinkerink, Christiaan D.; Brissenden, Roger; Britzen, Silke; Broderick, Avery E.; Broguiere, Dominique; Bronzwaer, Thomas; Byun, Do-Young; Carlstrom, John E.; Chael, Andrew; Chan, Chi-kwan; Chatterjee, Shami; Chatterjee, Koushik; Chen, Ming-Tang; Chen, Yongjun; Chesler, Paul M.; Cho, Ilje; Christian, Pierre; Conway, John E.; Cordes, James M.; Crawford, Thomas M.; Crew, Geoffrey B.; Cruz-Osorio, Alejandro; Cui, Yuzhu; Davelaar, Jordy; De Laurentis, Mariafelicia; Deane, Roger; Dempsey, Jessica; Desvignes, Gregory; Dexter, Jason; Doeleman, Sheperd S.; Eatough, Ralph P.; Falcke, Heino; Farah, Joseph; Fish, Vincent L.; Fomalont, Ed; Ford, H. Alyson; Fraga-Encinas, Raquel; Freeman, William T.; Friberg, Per; Fromm, Christian M.; Fuentes, Antonio; Galison, Peter; Gammie, Charles F.; García, Roberto; Gentaz, Olivier; Georgiev, Boris; Goddi, Ciriaco; Gold, Roman; Gómez, José L.; Gómez-Ruiz, Arturo I.; Gu, Minfeng; Gurwell, Mark; Hada, Kazuhiro; Haggard, Daryl; Hecht, Michael H.; Hesper, Ronald; Ho, Luis C.; Ho, Paul; Honma, Mareki; Huang, Chih-Wei L.; Huang, Lei; Hughes, David H.; Ikeda, Shiro; Inoue, Makoto; Issaoun, Sara; James, David J.; Jannuzi, Buell T.; Janssen, Michael; Jeter, Britton; Jiang, Wu; Jimenez-Rosales, Alejandra; Johnson, Michael D.; Jorstad, Svetlana; Jung, Taehyun; Karami, Mansour; Karuppusamy, Ramesh; Kawashima, Tomohisa; Keating, Garrett K.; Kettenis, Mark; Kim, Dong-Jin; Kim, Jae-Young; Kim, Jongsoo; Kim, Junhan; Kino, Motoki; Koay, Jun Yi; Kofuji, Yutaro; Koch, Patrick M.; Koyama, Shoko; Kramer, Michael; Kramer, Carsten; Krichbaum, Thomas P.; Kuo, Cheng-Yu; Lauer, Tod R.; Lee, Sang-Sung; Levis, Aviad; Li, Yan-Rong; Li, Zhiyuan; Lindqvist, Michael; Lico, Rocco; Lindahl, Greg; Liu, Jun; Liu, Kuo; Liuzzo, Elisabetta; Lo, Wen-Ping; Lobanov, Andrei P.; Loinard, Laurent; Lonsdale, Colin; Lu, Ru-Sen; MacDonald, Nicholas R.; Mao, Jirong; Marchili, Nicola; Markoff, Sera; Marrone, Daniel P.; Marscher, Alan P.; Martí-Vidal, Iván; Matsushita, Satoki; Matthews, Lynn D.; Medeiros, Lia; Menten, Karl M.; Mizuno, Izumi; Mizuno, Yosuke; Moran, James M.; Moriyama, Kotaro; Moscibrodzka, Monika; Müller, Cornelia; Musoke, Gibwa; Mejías, Alejandro Mus; Michalik, Daniel; Nadolski, Andrew; Nagai, Hiroshi; Nagar, Neil M.; Nakamura, Masanori; Narayan, Ramesh; Narayanan, Gopal; Natarajan, Iniyan; Nathanail, Antonios; Neilsen, Joey; Neri, Roberto; Ni, Chunchong; Noutsos, Aristeidis; Nowak, Michael A.; Okino, Hiroki; Olivares, Héctor; Ortiz-León, Gisela N.; Oyama, Tomoaki; Özel, Feryal; Palumbo, Daniel C. M.; Park, Jongho; Patel, Nimesh; Pen, Ue-Li; Pesce, Dominic W.; Piétu, Vincent; Plambeck, Richard; PopStefanija, Aleksandar; Porth, Oliver; Pötzl, Felix M.; Prather, Ben; Preciado-López, Jorge A.; Psaltis, Dimitrios; Pu, Hung-Yi; Ramakrishnan, Venkatessh; Rao, Ramprasad; Rawlings, Mark G.; Raymond, Alexander W.; Rezzolla, Luciano; Ricarte, Angelo; Ripperda, Bart; Roelofs, Freek; Rogers, Alan; Ros, Eduardo; Rose, Mel; Roshanineshat, Arash; Rottmann, Helge; Roy, Alan L.; Ruszczyk, Chet; Rygl, Kazi L. J.; Sánchez, Salvador; Sánchez-Arguelles, David; Sasada, Mahito; Savolainen, Tuomas; Schloerb, F. Peter; Schuster, Karl-Friedrich; Shao, Lijing; Shen, Zhiqiang; Small, Des; Sohn, Bong Won; SooHoo, Jason; Sun, He; Tazaki, Fumie; Tetarenko, Alexandra J.; Tiede, Paul; Tilanus, Remo P. J.; Titus, Michael; Toma, Kenji; Torne, Pablo; Trent, Tyler; Traianou, Efthalia; Trippe, Sascha; van Bemmel, Ilse; van Langevelde, Huib Jan; van Rossum, Daniel R.; Wagner, Jan; Ward-Thompson, Derek; Wardle, John; Weintroub, Jonathan; Wex, Norbert; Wharton, Robert; Wielgus, Maciek; Wong, George N.; Wu, Qingwen; Yoon, Doosoo; Young, André; Young, Ken; Younsi, Ziri; Yuan, Feng; Yuan, Ye-Fei; Zensus, J. Anton; Zhao, Guang-Yao; Zhao, Shan-Shan
Abstract: In 2017 April, the Event Horizon Telescope (EHT) observed the near-horizon region around the supermassive black hole at the core of the M87 galaxy. These 1.3 mm wavelength observations revealed a compact asymmetric ring-like source morphology. This structure originates from synchrotron emission produced by relativistic plasma located in the immediate vicinity of the black hole. Here we present the corresponding linear-polarimetric EHT images of the center of M87. We find that only a part of the ring is significantly polarized. The resolved fractional linear polarization has a maximum located in the southwest part of the ring, where it rises to the level of ∼15%. The polarization position angles are arranged in a nearly azimuthal pattern. We perform quantitative measurements of relevant polarimetric properties of the compact emission and find evidence for the temporal evolution of the polarized source structure over one week of EHT observations. The details of the polarimetric data reduction and calibration methodology are provided. We carry out the data analysis using multiple independent imaging and modeling techniques, each of which is validated against a suite of synthetic data sets. The gross polarimetric structure and its apparent evolution with time are insensitive to the method used to reconstruct the image. These polarimetric images carry information about the structure of the magnetic fields responsible for the synchrotron emission. Their physical interpretation is discussed in an accompanying publication.

ID: 159442
Type: article
Authors: Event Horizon Telescope Collaboration; Akiyama, Kazunori; Algaba, Juan Carlos; Alberdi, Antxon; Alef, Walter; Anantua, Richard; Asada, Keiichi; Azulay, Rebecca; Baczko, Anne-Kathrin; Ball, David; Baloković, Mislav; Barrett, John; Benson, Bradford A.; Bintley, Dan; Blackburn, Lindy; Blundell, Raymond; Boland, Wilfred; Bouman, Katherine L.; Bower, Geoffrey C.; Boyce, Hope; Bremer, Michael; Brinkerink, Christiaan D.; Brissenden, Roger; Britzen, Silke; Broderick, Avery E.; Broguiere, Dominique; Bronzwaer, Thomas; Byun, Do-Young; Carlstrom, John E.; Chael, Andrew; Chan, Chi-kwan; Chatterjee, Shami; Chatterjee, Koushik; Chen, Ming-Tang; Chen, Yongjun; Chesler, Paul M.; Cho, Ilje; Christian, Pierre; Conway, John E.; Cordes, James M.; Crawford, Thomas M.; Crew, Geoffrey B.; Cruz-Osorio, Alejandro; Cui, Yuzhu; Davelaar, Jordy; De Laurentis, Mariafelicia; Deane, Roger; Dempsey, Jessica; Desvignes, Gregory; Dexter, Jason; Doeleman, Sheperd S.; Eatough, Ralph P.; Falcke, Heino; Farah, Joseph; Fish, Vincent L.; Fomalont, Ed; Ford, H. Alyson; Fraga-Encinas, Raquel; Friberg, Per; Fromm, Christian M.; Fuentes, Antonio; Galison, Peter; Gammie, Charles F.; García, Roberto; Gelles, Zachary; Gentaz, Olivier; Georgiev, Boris; Goddi, Ciriaco; Gold, Roman; Gómez, José L.; Gómez-Ruiz, Arturo I.; Gu, Minfeng; Gurwell, Mark; Hada, Kazuhiro; Haggard, Daryl; Hecht, Michael H.; Hesper, Ronald; Himwich, Elizabeth; Ho, Luis C.; Ho, Paul; Honma, Mareki; Huang, Chih-Wei L.; Huang, Lei; Hughes, David H.; Ikeda, Shiro; Inoue, Makoto; Issaoun, Sara; James, David J.; Jannuzi, Buell T.; Janssen, Michael; Jeter, Britton; Jiang, Wu; Jimenez-Rosales, Alejandra; Johnson, Michael D.; Jorstad, Svetlana; Jung, Taehyun; Karami, Mansour; Karuppusamy, Ramesh; Kawashima, Tomohisa; Keating, Garrett K.; Kettenis, Mark; Kim, Dong-Jin; Kim, Jae-Young; Kim, Jongsoo; Kim, Junhan; Kino, Motoki; Koay, Jun Yi; Kofuji, Yutaro; Koch, Patrick M.; Koyama, Shoko; Kramer, Michael; Kramer, Carsten; Krichbaum, Thomas P.; Kuo, Cheng-Yu; Lauer, Tod R.; Lee, Sang-Sung; Levis, Aviad; Li, Yan-Rong; Li, Zhiyuan; Lindqvist, Michael; Lico, Rocco; Lindahl, Greg; Liu, Jun; Liu, Kuo; Liuzzo, Elisabetta; Lo, Wen-Ping; Lobanov, Andrei P.; Loinard, Laurent; Lonsdale, Colin; Lu, Ru-Sen; MacDonald, Nicholas R.; Mao, Jirong; Marchili, Nicola; Markoff, Sera; Marrone, Daniel P.; Marscher, Alan P.; Martí-Vidal, Iván; Matsushita, Satoki; Matthews, Lynn D.; Medeiros, Lia; Menten, Karl M.; Mizuno, Izumi; Mizuno, Yosuke; Moran, James M.; Moriyama, Kotaro; Moscibrodzka, Monika; Müller, Cornelia; Musoke, Gibwa; Mus Mejías, Alejandro; Michalik, Daniel; Nadolski, Andrew; Nagai, Hiroshi; Nagar, Neil M.; Nakamura, Masanori; Narayan, Ramesh; Narayanan, Gopal; Natarajan, Iniyan; Nathanail, Antonios; Neilsen, Joey; Neri, Roberto; Ni, Chunchong; Noutsos, Aristeidis; Nowak, Michael A.; Okino, Hiroki; Olivares, Héctor; Ortiz-León, Gisela N.; Oyama, Tomoaki; Özel, Feryal; Palumbo, Daniel C. M.; Park, Jongho; Patel, Nimesh; Pen, Ue-Li; Pesce, Dominic W.; Piétu, Vincent; Plambeck, Richard; PopStefanija, Aleksandar; Porth, Oliver; Pötzl, Felix M.; Prather, Ben; Preciado-López, Jorge A.; Psaltis, Dimitrios; Pu, Hung-Yi; Ramakrishnan, Venkatessh; Rao, Ramprasad; Rawlings, Mark G.; Raymond, Alexander W.; Rezzolla, Luciano; Ricarte, Angelo; Ripperda, Bart; Roelofs, Freek; Rogers, Alan; Ros, Eduardo; Rose, Mel; Roshanineshat, Arash; Rottmann, Helge; Roy, Alan L.; Ruszczyk, Chet; Rygl, Kazi L. J.; Sánchez, Salvador; Sánchez-Arguelles, David; Sasada, Mahito; Savolainen, Tuomas; Schloerb, F. Peter; Schuster, Karl-Friedrich; Shao, Lijing; Shen, Zhiqiang; Small, Des; Sohn, Bong Won; SooHoo, Jason; Sun, He; Tazaki, Fumie; Tetarenko, Alexandra J.; Tiede, Paul; Tilanus, Remo P. J.; Titus, Michael; Toma, Kenji; Torne, Pablo; Trent, Tyler; Traianou, Efthalia; Trippe, Sascha; van Bemmel, Ilse; van Langevelde, Huib Jan; van Rossum, Daniel R.; Wagner, Jan; Ward-Thompson, Derek; Wardle, John; Weintroub, Jonathan; Wex, Norbert; Wharton, Robert; Wielgus, Maciek; Wong, George N.; Wu, Qingwen; Yoon, Doosoo; Young, André; Young, Ken; Younsi, Ziri; Yuan, Feng; Yuan, Ye-Fei; Zensus, J. Anton; Zhao, Guang-Yao; Zhao, Shan-Shan
Abstract: Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around the supermassive black hole in M87 on event-horizon scales. This polarized synchrotron radiation probes the structure of magnetic fields and the plasma properties near the black hole. Here we compare the resolved polarization structure observed by the EHT, along with simultaneous unresolved observations with the Atacama Large Millimeter/submillimeter Array, to expectations from theoretical models. The low fractional linear polarization in the resolved image suggests that the polarization is scrambled on scales smaller than the EHT beam, which we attribute to Faraday rotation internal to the emission region. We estimate the average density n_e ∼ 10^4-7 cm^-3, magnetic field strength B ∼ 1-30 G, and electron temperature T_e ∼ (1-12) × 10¹⁰ K of the radiating plasma in a simple one-zone emission model. We show that the net azimuthal linear polarization pattern may result from organized, poloidal magnetic fields in the emission region. In a quantitative comparison with a large library of simulated polarimetric images from general relativistic magnetohydrodynamic (GRMHD) simulations, we identify a subset of physical models that can explain critical features of the polarimetric EHT observations while producing a relativistic jet of sufficient power. The consistent GRMHD models are all of magnetically arrested accretion disks, where near-horizon magnetic fields are dynamically important. We use the models to infer a mass accretion rate onto the black hole in M87 of (3-20) × 10^-4 M_⊙ yr^-1.

ID: 159441
Type: article
Authors: Goddi, Ciriaco; Martí-Vidal, Iván; Messias, Hugo; Bower, Geoffrey C.; Broderick, Avery E.; Dexter, Jason; Marrone, Daniel P.; Moscibrodzka, Monika; Nagai, Hiroshi; Algaba, Juan Carlos; Asada, Keiichi; Crew, Geoffrey B.; Gómez, José L.; Impellizzeri, C. M. Violette; Janssen, Michael; Kadler, Matthias; Krichbaum, Thomas P.; Lico, Rocco; Matthews, Lynn D.; Nathanail, Antonios; Ricarte, Angelo; Ros, Eduardo; Younsi, Ziri; Akiyama, Kazunori; Alberdi, Antxon; Alef, Walter; Anantua, Richard; Azulay, Rebecca; Baczko, Anne-Kathrin; Ball, David; Baloković, Mislav; Barrett, John; Benson, Bradford A.; Bintley, Dan; Blackburn, Lindy; Blundell, Raymond; Boland, Wilfred; Bouman, Katherine L.; Boyce, Hope; Bremer, Michael; Brinkerink, Christiaan D.; Brissenden, Roger; Britzen, Silke; Broguiere, Dominique; Bronzwaer, Thomas; Byun, Do-Young; Carlstrom, John E.; Chael, Andrew; Chan, Chi-kwan; Chatterjee, Shami; Chatterjee, Koushik; Chen, Ming-Tang; Chen, Yongjun; Chesler, Paul M.; Cho, Ilje; Christian, Pierre; Conway, John E.; Cordes, James M.; Crawford, Thomas M.; Cruz-Osorio, Alejandro; Cui, Yuzhu; Davelaar, Jordy; De Laurentis, Mariafelicia; Deane, Roger; Dempsey, Jessica; Desvignes, Gregory; Doeleman, Sheperd S.; Eatough, Ralph P.; Falcke, Heino; Farah, Joseph; Fish, Vincent L.; Fomalont, Ed; Ford, H. Alyson; Fraga-Encinas, Raquel; Freeman, William T.; Friberg, Per; Fromm, Christian M.; Fuentes, Antonio; Galison, Peter; Gammie, Charles F.; García, Roberto; Gentaz, Olivier; Georgiev, Boris; Gold, Roman; Gómez-Ruiz, Arturo I.; Gu, Minfeng; Gurwell, Mark; Hada, Kazuhiro; Haggard, Daryl; Hecht, Michael H.; Hesper, Ronald; Ho, Luis C.; Ho, Paul; Honma, Mareki; Huang, Chih-Wei L.; Huang, Lei; Hughes, David H.; Inoue, Makoto; Issaoun, Sara; James, David J.; Jannuzi, Buell T.; Jeter, Britton; Jiang, Wu; Jimenez-Rosales, Alejandra; Johnson, Michael D.; Jorstad, Svetlana; Jung, Taehyun; Karami, Mansour; Karuppusamy, Ramesh; Kawashima, Tomohisa; Keating, Garrett K.; Kettenis, Mark; Kim, Dong-Jin; Kim, Jae-Young; Kim, Jongsoo; Kim, Junhan; Kino, Motoki; Koay, Jun Yi; Kofuji, Yutaro; Koch, Patrick M.; Koyama, Shoko; Kramer, Michael; Kramer, Carsten; Kuo, Cheng-Yu; Lauer, Tod R.; Lee, Sang-Sung; Levis, Aviad; Li, Yan-Rong; Li, Zhiyuan; Lindqvist, Michael; Lindahl, Greg; Liu, Jun; Liu, Kuo; Liuzzo, Elisabetta; Lo, Wen-Ping; Lobanov, Andrei P.; Loinard, Laurent; Lonsdale, Colin; Lu, Ru-Sen; MacDonald, Nicholas R.; Mao, Jirong; Marchili, Nicola; Markoff, Sera; Marscher, Alan P.; Matsushita, Satoki; Medeiros, Lia; Menten, Karl M.; Mizuno, Izumi; Mizuno, Yosuke; Moran, James M.; Moriyama, Kotaro; Müller, Cornelia; Musoke, Gibwa; Mejías, Alejandro Mus; Nagar, Neil M.; Nakamura, Masanori; Narayan, Ramesh; Narayanan, Gopal; Natarajan, Iniyan; Neilsen, Joey; Neri, Roberto; Ni, Chunchong; Noutsos, Aristeidis; Nowak, Michael A.; Okino, Hiroki; Olivares, Héctor; Ortiz-León, Gisela N.; Oyama, Tomoaki; Özel, Feryal; Palumbo, Daniel C. M.; Park, Jongho; Patel, Nimesh; Pen, Ue-Li; Pesce, Dominic W.; Piétu, Vincent; Plambeck, Richard; PopStefanija, Aleksandar; Porth, Oliver; Pötzl, Felix M.; Prather, Ben; Preciado-López, Jorge A.; Psaltis, Dimitrios; Pu, Hung-Yi; Ramakrishnan, Venkatessh; Rao, Ramprasad; Rawlings, Mark G.; Raymond, Alexander W.; Rezzolla, Luciano; Ripperda, Bart; Roelofs, Freek; Rogers, Alan; Rose, Mel; Roshanineshat, Arash; Rottmann, Helge; Roy, Alan L.; Ruszczyk, Chet; Rygl, Kazi L. J.; Sánchez, Salvador; Sánchez-Arguelles, David; Sasada, Mahito; Savolainen, Tuomas; Schloerb, F. Peter; Schuster, Karl-Friedrich; Shao, Lijing; Shen, Zhiqiang; Small, Des; Sohn, Bong Won; SooHoo, Jason; Sun, He; Tazaki, Fumie; Tetarenko, Alexandra J.; Tiede, Paul; Tilanus, Remo P. J.; Titus, Michael; Toma, Kenji; Torne, Pablo; Trent, Tyler; Traianou, Efthalia; Trippe, Sascha; van Bemmel, Ilse; van Langevelde, Huib Jan; van Rossum, Daniel R.; Wagner, Jan; Ward-Thompson, Derek; Wardle, John; Weintroub, Jonathan; Wex, Norbert; Wharton, Robert; Wielgus, Maciek; Wong, George N.; Wu, Qingwen; Yoon, Doosoo; Young, André; Young, Ken; Yuan, Feng; Yuan, Ye-Fei; Zensus, J. Anton; Zhao, Guang-Yao; Zhao, Shan-Shan; Bruni, Gabriele; Gopakumar, A.; Hernández-Gómez, Antonio; Herrero-Illana, Ruben; Ingram, Adam; Komossa, S.; Kovalev, Y. Y.; Muders, Dirk; Perucho, Manel; Rösch, Florian; Valtonen, Mauri
Abstract: We present the results from a full polarization study carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) during the first Very Long Baseline Interferometry (VLBI) campaign, which was conducted in 2017 April in the λ3 mm and λ1.3 mm bands, in concert with the Global mm-VLBI Array (GMVA) and the Event Horizon Telescope (EHT), respectively. We determine the polarization and Faraday properties of all VLBI targets, including Sgr A*, M87, and a dozen radio-loud active galactic nuclei (AGNs), in the two bands at several epochs in a time window of 10 days. We detect high linear polarization fractions (2%-15%) and large rotation measures (RM > 10^3.3-10^5.5 rad m^-2), confirming the trends of previous AGN studies at millimeter wavelengths. We find that blazars are more strongly polarized than other AGNs in the sample, while exhibiting (on average) order-of-magnitude lower RM values, consistent with the AGN viewing angle unification scheme. For Sgr A* we report a mean RM of (-4.2 ± 0.3) × 10⁵ rad m^-2 at 1.3 mm, consistent with measurements over the past decade and, for the first time, an RM of (-2.1 ± 0.1) × 10⁵ rad m^-2 at 3 mm, suggesting that about half of the Faraday rotation at 1.3 mm may occur between the 3 mm photosphere and the 1.3 mm source. We also report the first unambiguous measurement of RM toward the M87 nucleus at millimeter wavelengths, which undergoes significant changes in magnitude and sign reversals on a one year timescale, spanning the range from -1.2 to 0.3 × 10⁵ rad m^-2 at 3 mm and -4.1 to 1.5 × 10⁵ rad m^-2 at 1.3 mm. Given this time variability, we argue that, unlike the case of Sgr A*, the RM in M87 does not provide an accurate estimate of the mass accretion rate onto the black hole. We put forward a two-component model, comprised of a variable compact region and a static extended region, that can simultaneously explain the polarimetric properties observed by both the EHT (on horizon scales) and ALMA (which observes the combined emission from both components). These measurements provide critical constraints for the calibration, analysis, and interpretation of simultaneously obtained VLBI data with the EHT and GMVA.

ID: 159285
Type: article
Authors: Lavvas, P.; Lellouch, E.; Strobel, D. F.; Gurwell, Mark A.; Cheng, A. F.; Young, L. A.; Gladstone, G. R.
Abstract: Pluto, Titan and Triton all have low-temperature environments with an N₂, CH₄ and CO atmospheric composition in which solar radiation drives an intense organic photochemistry. Titan is rich in atmospheric hazes, and Cassini-Huygens observations showed that their formation is initiated with the production of large molecules through ion-neutral reactions. New Horizons revealed that optical hazes are also ubiquitous in Pluto's atmosphere, and it is thought that similar haze formation pathways are active in this atmosphere as well. However, we show here that Pluto's hazes may contain a major organic ice component (dominated by C₄H₂ ice) from the direct condensation of the primary photochemical products in this atmosphere. This contribution may imply that haze has a less important role in controlling Pluto's atmospheric thermal balance compared to Titan. Moreover, we expect that the haze composition of Triton is dominated by C₂H₄ ice.

ID: 159284
Type: article
Authors: Readhead, A. C. S.; Ravi, V.; Liodakis, I.; Lister, M. L.; Singh, V.; Aller, M. F.; Blandford, R. D.; Browne, I. W. A.; Gorjian, V.; Grainge, K. J. B.; Gurwell, Mark A.; Hodges, M. W.; Hovatta, T.; Kiehlmann, S.; Lähteenmäki, A.; Mcaloone, T.; Max-Moerbeck, W.; Pavlidou, V.; Pearson, T. J.; Peirson, A. L.; Perlman, E. S.; Reeves, R. A.; Soifer, B. T.; Taylor, G. B.; Tornikoski, M.; Vedantham, H. K.; Werner, M.; Wilkinson, P. N.; Zensus, J. A.
Abstract: PKS 1413+135 is one of the most peculiar blazars known. Its strange properties led to the hypothesis almost four decades ago that it is gravitationally lensed by a mass concentration associated with an intervening galaxy. It exhibits symmetric achromatic variability, a rare form of variability that has been attributed to gravitational milli-lensing. It has been classified as a BL Lac object, and is one of the rare objects in this class with a visible counterjet. BL Lac objects have jet axes aligned close to the line of sight. It has also been classified as a compact symmetric object-objects that have jet axes not aligned close to the line of sight. Intensive efforts to understand this blazar have hitherto failed to resolve even the questions of the orientation of the relativistic jet and the host galaxy. Answering these two questions is important because they challenge our understanding of jets in active galactic nuclei and the classification schemes we use to describe them. We show that the jet axis is aligned close to the line of sight and PKS 1413+135 is almost certainly not located in the apparent host galaxy, but is a background object in the redshift range 0.247 < z < 0.5. The intervening spiral galaxy at z = 0.247 provides a natural host for the putative lens responsible for symmetric achromatic variability and is shown to be a Seyfert 2 galaxy. We also show that, as for the radio emission, a "multizone" model is needed to account for the high-energy emission.

ID: 157837
Type: article
Authors: Broderick, Avery E.; Gold, Roman; Karami, Mansour; Preciado-López, Jorge A.; Tiede, Paul; Pu, Hung-Yi; Akiyama, Kazunori; Alberdi, Antxon; Alef, Walter; Asada, Keiichi; Azulay, Rebecca; Baczko, Anne-Kathrin; Baloković, Mislav; Barrett, John; Bintley, Dan; Blackburn, Lindy; Boland, Wilfred; Bouman, Katherine L.; Bower, Geoffrey C.; Bremer, Michael; Brinkerink, Christiaan D.; Brissenden, Roger; Britzen, Silke; Broguiere, Dominique; Bronzwaer, Thomas; Byun, Do-Young; Carlstrom, John E.; Chael, Andrew; Chatterjee, Shami; Chatterjee, Koushik; Chen, Ming-Tang; Chen, Yongjun; Cho, Ilje; Conway, John E.; Cordes, James M.; Crew, Geoffrey B.; Cui, Yuzhu; Davelaar, Jordy; De Laurentis, Mariafelicia; Deane, Roger; Dempsey, Jessica; Desvignes, Gregory; Doeleman, Sheperd S.; Eatough, Ralph P.; Falcke, Heino; Fish, Vincent L.; Fomalont, Ed; Fraga-Encinas, Raquel; Friberg, Per; Fromm, Christian M.; Galison, Peter; Gammie, Charles F.; García, Roberto; Gentaz, Olivier; Georgiev, Boris; Goddi, Ciriaco; Gómez, José L.; Gu, Minfeng; Gurwell, Mark; Hada, Kazuhiro; Hecht, Michael H.; Hesper, Ronald; Ho, Luis C.; Ho, Paul; Honma, Mareki; Huang, Chih-Wei L.; Huang, Lei; Hughes, David H.; Inoue, Makoto; Issaoun, Sara; James, David J.; Janssen, Michael; Jeter, Britton; Jiang, Wu; Jiménez-Rosales, Alejandra; Johnson, Michael D.; Jorstad, Svetlana; Jung, Taehyun; Karuppusamy, Ramesh; Kawashima, Tomohisa; Keating, Garrett K.; Kettenis, Mark; Kim, Jae-Young; Kim, Jongsoo; Kino, Motoki; Koay, Jun Yi; Koch, Patrick M.; Koyama, Shoko; Kramer, Michael; Kramer, Carsten; Krichbaum, Thomas P.; Kuo, Cheng-Yu; Lee, Sang-Sung; Li, Yan-Rong; Li, Zhiyuan; Lindqvist, Michael; Lico, Rocco; Liu, Kuo; Liuzzo, Elisabetta; Lo, Wen-Ping; Lobanov, Andrei P.; Loinard, Laurent; Lonsdale, Colin; Lu, Ru-Sen; MacDonald, Nicholas R.; Mao, Jirong; Marscher, Alan P.; Martí-Vidal, Iván; Matsushita, Satoki; Matthews, Lynn D.; Menten, Karl M.; Mizuno, Yosuke; Mizuno, Izumi; Moran, James M.; Moriyama, Kotaro; Moscibrodzka, Monika; Müller, Cornelia; Nagai, Hiroshi; Nagar, Neil M.; Nakamura, Masanori; Narayan, Ramesh; Narayanan, Gopal; Natarajan, Iniyan; Neri, Roberto; Ni, Chunchong; Noutsos, Aristeidis; Okino, Hiroki; Olivares, Héctor; Ortiz-León, Gisela N.; Oyama, Tomoaki; Palumbo, Daniel C. M.; Park, Jongho; Pen, Ue-Li; Pesce, Dominic W.; Piétu, Vincent; Plambeck, Richard; PopStefanija, Aleksandar; Porth, Oliver; Prather, Ben; Ramakrishnan, Venkatessh; Rao, Ramprasad; Rawlings, Mark G.; Raymond, Alexander W.; Rezzolla, Luciano; Ripperda, Bart; Roelofs, Freek; Rogers, Alan; Ros, Eduardo; Rose, Mel; Rottmann, Helge; Ruszczyk, Chet; Ryan, Benjamin R.; Rygl, Kazi L. J.; Sánchez, Salvador; Sánchez-Arguelles, David; Sasada, Mahito; Savolainen, Tuomas; Schloerb, F. Peter; Schuster, Karl-Friedrich; Shao, Lijing; Shen, Zhiqiang; Small, Des; Sohn, Bong Won; SooHoo, Jason; Tazaki, Fumie; Tilanus, Remo P. J.; Titus, Michael; Toma, Kenji; Torne, Pablo; Traianou, Efthalia; Trippe, Sascha; Tsuda, Shuichiro; van Bemmel, Ilse; van Langevelde, Huib Jan; van Rossum, Daniel R.; Wagner, Jan; Wardle, John; Weintroub, Jonathan; Wex, Norbert; Wharton, Robert; Wielgus, Maciek; Wong, George N.; Wu, Qingwen; Yoon, Doosoo; Young, André; Young, Ken; Younsi, Ziri; Yuan, Feng; Yuan, Ye-Fei; Zensus, J. Anton; Zhao, Guangyao; Zhao, Shan-Shan; Zhu, Ziyan; Event Horizon Telescope Collaboration
Abstract: The Event Horizon Telescope (EHT) provides the unprecedented ability to directly resolve the structure and dynamics of black hole emission regions on scales smaller than their horizons. This has the potential to critically probe the mechanisms by which black holes accrete and launch outflows, and the structure of supermassive black hole spacetimes. However, accessing this information is a formidable analysis challenge for two reasons. First, the EHT natively produces a variety of data types that encode information about the image structure in nontrivial ways; these are subject to a variety of systematic effects associated with very long baseline interferometry and are supplemented by a wide variety of auxiliary data on the primary EHT targets from decades of other observations. Second, models of the emission regions and their interaction with the black hole are complex, highly uncertain, and computationally expensive to construct. As a result, the scientific utilization of EHT observations requires a flexible, extensible, and powerful analysis framework. We present such a framework, THEMIS, which defines a set of interfaces between models, data, and sampling algorithms that facilitates future development. We describe the design and currently existing components of THEMIS, how THEMIS has been validated thus far, and present additional analyses made possible by THEMIS that illustrate its capabilities. Importantly, we demonstrate that THEMIS is able to reproduce prior EHT analyses, extend these, and do so in a computationally efficient manner that can efficiently exploit modern high-performance computing facilities. THEMIS has already been used extensively in the scientific analysis and interpretation of the first EHT observations of M87.

ID: 157835
Type: article
Authors: Gold, Roman; Broderick, Avery E.; Younsi, Ziri; Fromm, Christian M.; Gammie, Charles F.; Mościbrodzka, Monika; Pu, Hung-Yi; Bronzwaer, Thomas; Davelaar, Jordy; Dexter, Jason; Ball, David; Chan, Chi-kwan; Kawashima, Tomohisa; Mizuno, Yosuke; Ripperda, Bart; Akiyama, Kazunori; Alberdi, Antxon; Alef, Walter; Asada, Keiichi; Azulay, Rebecca; Baczko, Anne-Kathrin; Baloković, Mislav; Barrett, John; Bintley, Dan; Blackburn, Lindy; Boland, Wilfred; Bouman, Katherine L.; Bower, Geoffrey C.; Bremer, Michael; Brinkerink, Christiaan D.; Brissenden, Roger; Britzen, Silke; Broguiere, Dominique; Byun, Do-Young; Carlstrom, John E.; Chael, Andrew; Chatterjee, Koushik; Chatterjee, Shami; Chen, Ming-Tang; Chen, Yongjun; Cho, Ilje; Christian, Pierre; Conway, John E.; Cordes, James M.; Crew, Geoffrey B.; Cui, Yuzhu; De Laurentis, Mariafelicia; Deane, Roger; Dempsey, Jessica; Desvignes, Gregory; Doeleman, Sheperd S.; Eatough, Ralph?P; Falcke, Heino; Fish, Vincent L.; Fomalont, Ed; Fraga-Encinas, Raquel; Freeman, Bill; Friberg, Per; Gómez, José L.; Galison, Peter; García, Roberto; Gentaz, Olivier; Georgiev, Boris; Goddi, Ciriaco; Gu, Minfeng; Gurwell, Mark; Hada, Kazuhiro; Hecht, Michael H.; Hesper, Ronald; Ho, Luis C.; Ho, Paul; Honma, Mareki; Huang, Chih-Wei L.; Huang, Lei; Hughes, David H.; Inoue, Makoto; Issaoun, Sara; James, David J.; Jannuzi, Buell T.; Janssen, Michael; Jeter, Britton; Jiang, Wu; Jimenez-Rosales, Alejandra; Johnson, Michael D.; Jorstad, Svetlana; Jung, Taehyun; Karami, Mansour; Karuppusamy, Ramesh; Keating, Garrett K.; Kettenis, Mark; Kim, Jae-Young; Kim, Junhan; Kim, Jongsoo; Kino, Motoki; Koay, Jun Yi; Koch, Patrick M.; Koyama, Shoko; Kramer, Michael; Kramer, Carsten; Krichbaum, Thomas P.; Kuo, Cheng-Yu; Lauer, Tod R.; Lee, Sang-Sung; Li, Yan-Rong; Li, Zhiyuan; Lico, Rocco; Lindqvist, Michael; Liu, Kuo; Liuzzo, Elisabetta; Lo, Wen-Ping; Lobanov, Andrei P.; Loinard, Laurent; Lonsdale, Colin; Lu, Ru-Sen; MacDonald, Nicholas R.; Markoff, Sera; Mao, Jirong; Marrone, Daniel P.; Marscher, Alan P.; Martí-Vidal, Iván; Matsushita, Satoki; Matthews, Lynn D.; Medeiros, Lia; Menten, Karl M.; Mizuno, Izumi; Moran, James M.; Moriyama, Kotaro; Müller, Cornelia; Nagai, Hiroshi; Nakamura, Masanori; Nagar, Neil M.; Narayan, Ramesh; Narayanan, Gopal; Natarajan, Iniyan; Neri, Roberto; Ni, Chunchong; Noutsos, Aristeidis; Okino, Hiroki; Ortiz-León, Gisela N.; Oyama, Tomoaki; Özel, Feryal; Palumbo, Daniel C. M.; Park, Jongho; Patel, Nimesh; Pen, Ue-Li; Pesce, Dominic W.; Plambeck, Richard; Piétu, Vincent; PopStefanija, Aleksandar; Porth, Oliver; Preciado-López, Jorge A.; Psaltis, Dimitrios; Ramakrishnan, Venkatessh; Rao, Ramprasad; Rawlings, Mark G.; Raymond, Alexander W.; Rezzolla, Luciano; Roelofs, Freek; Rogers, Alan; Ros, Eduardo; Rose, Mel; Roshanineshat, Arash; Rottmann, Helge; Roy, Alan L.; Ruszczyk, Chet; Rygl, Kazi L. J.; Sánchez, Salvador; Sánchez-Arguelles, David; Sasada, Mahito; Savolainen, Tuomas; Schuster, Karl-Friedrich; Schloerb, F. Peter; Shao, Lijing; Shen, Zhiqiang; Small, Des; Sohn, Bong Won; SooHoo, Jason; Tiede, Paul; Tazaki, Fumie; Tilanus, Remo P. J.; Titus, Michael; Toma, Kenji; Torne, Pablo; Trent, Tyler; Traianou, Thalia; Trippe, Sascha; Tsuda, Shuichiro; van Langevelde, Huib Jan; van Bemmel, Ilse; van Rossum, Daniel R.; Wagner, Jan; Wardle, John; Wex, Norbert; Weintroub, Jonathan; Wharton, Robert; Wielgus, Maciek; Wong, George N.; Wu, Qingwen; Yoon, Doosoo; Young, Ken; Young, André; Yuan, Feng; Yuan, Ye-Fei; Zensus, J. Anton; Zhao, Guangyao; Zhao, Shan-Shan; Zhu, Ziyan; Event Horizon Telescope Collaboration
Abstract: The Event Horizon Telescope (EHT) Collaboration has recently produced the first resolved images of the central supermassive black hole in the giant elliptical galaxy M87. Here we report on tests of the consistency and accuracy of the general relativistic radiative transfer codes used within the collaboration to model M87* and Sgr A*. We compare and evaluate (1) deflection angles for equatorial null geodesics in a Kerr spacetime; (2) images calculated from a series of simple, parameterized matter distributions in the Kerr metric using simplified emissivities and absorptivities; (3) for a subset of codes, images calculated from general relativistic magnetohydrodynamics simulations using different realistic synchrotron emissivities and absorptivities; (4) observables for the 2017 configuration of EHT, including visibility amplitudes and closure phases. The error in total flux is of order 1% when the codes are run with production numerical parameters. The dominant source of discrepancies for small camera distances is the location and detailed setup of the software "camera" that each code uses to produce synthetic images. We find that when numerical parameters are suitably chosen and the camera is sufficiently far away the images converge and that for given transfer coefficients, numerical uncertainties are unlikely to limit parameter estimation for the current generation of EHT observations. The purpose of this paper is to describe a verification and comparison of EHT radiative transfer codes. It is not to verify EHT models more generally.

ID: 157610
Type: article
Authors: Kim, Jae-Young; Krichbaum, Thomas P.; Broderick, Avery E.; Wielgus, Maciek; Blackburn, Lindy; Gómez, José L.; Johnson, Michael D.; Bouman, Katherine L.; Chael, Andrew; Akiyama, Kazunori; Jorstad, Svetlana; Marscher, Alan P.; Issaoun, Sara; Janssen, Michael; Chan, Chi-kwan; Savolainen, Tuomas; Pesce, Dominic W.; Özel, Feryal; Alberdi, Antxon; Alef, Walter; Asada, Keiichi; Azulay, Rebecca; Baczko, Anne-Kathrin; Ball, David; Baloković, Mislav; Barrett, John; Bintley, Dan; Boland, Wilfred; Bower, Geoffrey C.; Bremer, Michael; Brinkerink, Christiaan D.; Brissenden, Roger; Britzen, Silke; Broguiere, Dominique; Bronzwaer, Thomas; Byun, Do-Young; Carlstrom, John E.; Chatterjee, Shami; Chatterjee, Koushik; Chen, Ming-Tang; Chen, Yongjun; Cho, Ilje; Christian, Pierre; Conway, John E.; Cordes, James M.; Crew, Geoffrey B.; Cui, Yuzhu; Davelaar, Jordy; De Laurentis, Mariafelicia; Deane, Roger; Dempsey, Jessica; Desvignes, Gregory; Dexter, Jason; Doeleman, Sheperd S.; Eatough, Ralph P.; Falcke, Heino; Fish, Vincent L.; Fomalont, Ed; Fraga-Encinas, Raquel; Friberg, Per; Fromm, Christian M.; Galison, Peter; Gammie, Charles F.; García, Roberto; Gentaz, Olivier; Georgiev, Boris; Goddi, Ciriaco; Gold, Roman; Gómez-Ruiz, Arturo I.; Gu, Minfeng; Gurwell, Mark; Hada, Kazuhiro; Hecht, Michael H.; Hesper, Ronald; Ho, Luis C.; Ho, Paul; Honma, Mareki; Huang, Chih-Wei L.; Huang, Lei; Hughes, David H.; Ikeda, Shiro; Inoue, Makoto; James, David J.; Jannuzi, Buell T.; Jeter, Britton; Jiang, Wu; Jimenez-Rosales, Alejandra; Jung, Taehyun; Karami, Mansour; Karuppusamy, Ramesh; Kawashima, Tomohisa; Keating, Garrett K.; Kettenis, Mark; Kim, Junhan; Kim, Jongsoo; Kino, Motoki; Koay, Jun Yi; Koch, Patrick M.; Koyama, Shoko; Kramer, Michael; Kramer, Carsten; Kuo, Cheng-Yu; Lauer, Tod R.; Lee, Sang-Sung; Li, Yan-Rong; Li, Zhiyuan; Lindqvist, Michael; Lico, Rocco; Liu, Kuo; Liuzzo, Elisabetta; Lo, Wen-Ping; Lobanov, Andrei P.; Loinard, Laurent; Lonsdale, Colin; Lu, Ru-Sen; MacDonald, Nicholas R.; Mao, Jirong; Markoff, Sera; Marrone, Daniel P.; Martí-Vidal, Iván; Matsushita, Satoki; Matthews, Lynn D.; Medeiros, Lia; Menten, Karl M.; Mizuno, Yosuke; Mizuno, Izumi; Moran, James M.; Moriyama, Kotaro; Moscibrodzka, Monika; Musoke, Gibwa; Müller, Cornelia; Nagai, Hiroshi; Nagar, Neil M.; Nakamura, Masanori; Narayan, Ramesh; Narayanan, Gopal; Natarajan, Iniyan; Neri, Roberto; Ni, Chunchong; Noutsos, Aristeidis; Okino, Hiroki; Olivares, Héctor; Ortiz-León, Gisela N.; Oyama, Tomoaki; Palumbo, Daniel C. M.; Park, Jongho; Patel, Nimesh; Pen, Ue-Li; Piétu, Vincent; Plambeck, Richard; PopStefanija, Aleksandar; Porth, Oliver; Prather, Ben; Preciado-López, Jorge A.; Psaltis, Dimitrios; Pu, Hung-Yi; Ramakrishnan, Venkatessh; Rao, Ramprasad; Rawlings, Mark G.; Raymond, Alexander W.; Rezzolla, Luciano; Ripperda, Bart; Roelofs, Freek; Rogers, Alan; Ros, Eduardo; Rose, Mel; Roshanineshat, Arash; Rottmann, Helge; Roy, Alan L.; Ruszczyk, Chet; Ryan, Benjamin R.; Rygl, Kazi L. J.; Sánchez, Salvador; Sánchez-Arguelles, David; Sasada, Mahito; Schloerb, F. Peter; Schuster, Karl-Friedrich; Shao, Lijing; Shen, Zhiqiang; Small, Des; Sohn, Bong Won; SooHoo, Jason; Tazaki, Fumie; Tiede, Paul; Tilanus, Remo P. J.; Titus, Michael; Toma, Kenji; Torne, Pablo; Trent, Tyler; Traianou, Efthalia; Trippe, Sascha; Tsuda, Shuichiro; van Bemmel, Ilse; van Langevelde, Huib Jan; van Rossum, Daniel R.; Wagner, Jan; Wardle, John; Ward-Thompson, Derek; Weintroub, Jonathan; Wex, Norbert; Wharton, Robert; Wong, George N.; Wu, Qingwen; Yoon, Doosoo; Young, André; Young, Ken; Younsi, Ziri; Yuan, Feng; Yuan, Ye-Fei; Zensus, J. Anton; Zhao, Guangyao; Zhao, Shan-Shan; Zhu, Ziyan; Algaba, Juan-Carlos; Allardi, Alexander; Amestica, Rodrigo; Anczarski, Jadyn; Bach, Uwe; Baganoff, Frederick K.; Beaudoin, Christopher; Benson, Bradford A.; Berthold, Ryan; Blanchard, Jay M.; Blundell, Ray; Bustamente, Sandra; Cappallo, Roger; Castillo-Domínguez, Edgar; Chang, Chih-Cheng; Chang, Shu-Hao; Chang, Song-Chu; Chen, Chung-Chen; Chilson, Ryan; Chuter, Tim C.; Rosado, Rodrigo Córdova; Coulson, Iain M.; Crowley, Joseph; Derome, Mark; Dexter, Matthew; Dornbusch, Sven; Dudevoir, Kevin A.; Dzib, Sergio A.; Eckart, Andreas; Eckert, Chris; Erickson, Neal R.; Everett, Wendeline B.; Faber, Aaron; Farah, Joseph R.; Fath, Vernon; Folkers, Thomas W.; Forbes, David C.; Freund, Robert; Gale, David M.; Gao, Feng; Geertsema, Gertie; Graham, David A.; Greer, Christopher H.; Grosslein, Ronald; Gueth, Frédéric; Haggard, Daryl; Halverson, Nils W.; Han, Chih-Chiang; Han, Kuo-Chang; Hao, Jinchi; Hasegawa, Yutaka; Henning, Jason W.; Hernández-Gómez, Antonio; Herrero-Illana, Rubén; Heyminck, Stefan; Hirota, Akihiko; Hoge, James; Huang, Yau-De; Violette Impellizzeri, C. M.; Jiang, Homin; John, David; Kamble, Atish; Keisler, Ryan; Kimura, Kimihiro; Kono, Yusuke; Kubo, Derek; Kuroda, John; Lacasse, Richard; Laing, Robert A.; Leitch, Erik M.; Li, Chao-Te; Lin, Lupin C. -C; Liu, Ching-Tang; Liu, Kuan-Yu; Lu, Li-Ming; Marson, Ralph G.; Martin-Cocher, Pierre L.; Massingill, Kyle D.; Matulonis, Callie; McColl, Martin P.; McWhirter, Stephen R.; Messias, Hugo; Meyer-Zhao, Zheng; Michalik, Daniel; Montaña, Alfredo; Montgomerie, William; Mora-Klein, Matias; Muders, Dirk; Nadolski, Andrew; Navarro, Santiago; Neilsen, Joseph; Nguyen, Chi H.; Nishioka, Hiroaki; Norton, Timothy; Nowak, Michael A.; Nystrom, George; Ogawa, Hideo; Oshiro, Peter; Oyama, Tomoaki; Parsons, Harriet; Peñalver, Juan; Phillips, Neil M.; Poirier, Michael; Pradel, Nicolas; Primiani, Rurik A.; Raffin, Philippe A.; Rahlin, Alexandra S.; Reiland, George; Risacher, Christopher; Ruiz, Ignacio; Sáez-Madaín, Alejandro F.; Sassella, Remi; Schellart, Pim; Shaw, Paul; Silva, Kevin M.; Shiokawa, Hotaka; Smith, David R.; Snow, William; Souccar, Kamal; Sousa, Don; Sridharan, Tirupati K.; Srinivasan, Ranjani; Stahm, William; Stark, Antony A.; Story, Kyle; Timmer, Sjoerd T.; Vertatschitsch, Laura; Walther, Craig; Wei, Ta-Shun; Whitehorn, Nathan; Whitney, Alan R.; Woody, David P.; Wouterloot, Jan G. A.; Wright, Melvin; Yamaguchi, Paul; Yu, Chen-Yu; Zeballos, Milagros; Zhang, Shuo; Ziurys, Lucy; Event Horizon Telescope Collaboration
Abstract: 3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique - global Very Long Baseline Interferometry (VLBI) at 1.3 mm (230 GHz) - to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable γ-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array (ALMA), at an angular resolution of ∼20 μas (at a redshift of z = 0.536 this corresponds to ∼0.13 pc ∼ 1700 Schwarzschild radii with a black hole mass M_BH = 8 × 10⁸ M_☉). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation. We find a multicomponent inner jet morphology with the northernmost component elongated perpendicular to the direction of the jet, as imaged at longer wavelengths. The elongated nuclear structure is consistent on all four observing days and across different imaging methods and model-fitting techniques, and therefore appears robust. Owing to its compactness and brightness, we associate the northern nuclear structure as the VLBI "core". This morphology can be interpreted as either a broad resolved jet base or a spatially bent jet. We also find significant day-to-day variations in the closure phases, which appear most pronounced on the triangles with the longest baselines. Our analysis shows that this variation is related to a systematic change of the source structure. Two inner jet components move non-radially at apparent speeds of ∼15 c and ∼20 c (∼1.3 and ∼1.7 μas day^-1, respectively), which more strongly supports the scenario of traveling shocks or instabilities in a bent, possibly rotating jet. The observed apparent speeds are also coincident with the 3C 279 large-scale jet kinematics observed at longer (cm) wavelengths, suggesting no significant jet acceleration between the 1.3 mm core and the outer jet. The intrinsic brightness temperature of the jet components are ≲10¹⁰ K, a magnitude or more lower than typical values seen at ≥7 mm wavelengths. The low brightness temperature and morphological complexity suggest that the core region of 3C 279 becomes optically thin at short (mm) wavelengths.
The data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A69 and at http://https://eventhorizontelescope.org/for-astronomers/data

ID: 156378
Type: article
Authors: Larionov, V. M.; Jorstad, S. G.; Marscher, A. P.; Villata, M.; Raiteri, C. M.; Smith, P. S.; Agudo, I.; Savchenko, S. S.; Morozova, D. A.; Acosta-Pulido, J. A.; Aller, M. F.; Aller, H. D.; Andreeva, T. S.; Arkharov, A. A.; Bachev, R.; Bonnoli, G.; Borman, G. A.; Bozhilov, V.; Calcidese, P.; Carnerero, M. I.; Carosati, D.; Casadio, C.; Chen, W. -P; Damljanovic, G.; Dementyev, A. V.; Di Paola, A.; Frasca, A.; Fuentes, A.; Gómez, J. L.; Gónzalez-Morales, P.; Giunta, A.; Grishina, T. S.; Gurwell, Mark A.; Hagen-Thorn, V. A.; Hovatta, T.; Ibryamov, S.; Joshi, M.; Kiehlmann, S.; Kim, J. -Y; Kimeridze, G. N.; Kopatskaya, E. N.; Kovalev, Yu A.; Kovalev, Y. Y.; Kurtanidze, O. M.; Kurtanidze, S. O.; Lähteenmäki, A.; Lázaro, C.; Larionova, L. V.; Larionova, E. G.; Leto, G.; Marchini, A.; Matsumoto, K.; Mihov, B.; Minev, M.; Mingaliev, M. G.; Mirzaqulov, D.; Muñoz Dimitrova, R. V.; Myserlis, I.; Nikiforova, A. A.; Nikolashvili, M. G.; Nizhelsky, N. A.; Ovcharov, E.; Pressburger, L. D.; Rakhimov, I. A.; Righini, S.; Rizzi, N.; Sadakane, K.; Sadun, A. C.; Samal, M. R.; Sanchez, R. Z.; Semkov, E.; Sergeev, S. G.; Sigua, L. A.; Slavcheva-Mihova, L.; Sola, P.; Sotnikova, Yu V.; Strigachev, A.; Thum, C.; Traianou, E.; Troitskaya, Yu V.; Troitsky, I. S.; Tsybulev, P. G.; Vasilyev, A. A.; Vince, O.; Weaver, Z. R.; Williamson, K. E.; Zhekanis, G. V.
Abstract: We report the results of decade-long (2008-2018) γ-ray to 1 GHz radio monitoring of the blazar 3C 279, including GASP/WEBT, Fermi and Swift data, as well as polarimetric and spectroscopic data. The X-ray and γ-ray light curves correlate well, with no delay ≳ 3 h, implying general cospatiality of the emission regions. The γ-ray-optical flux-flux relation changes with activity state, ranging from a linear to a more complex dependence. The behaviour of the Stokes parameters at optical and radio wavelengths, including 43 GHz Very Long Baseline Array images, supports either a predominantly helical magnetic field or motion of the radiating plasma along a spiral path. Apparent speeds of emission knots range from 10 to 37c, with the highest values requiring bulk Lorentz factors close to those needed to explain γ-ray variability on very short time-scales. The Mg II emission line flux in the `blue' and `red' wings correlates with the optical synchrotron continuum flux density, possibly providing a variable source of seed photons for inverse Compton scattering. In the radio bands, we find progressive delays of the most prominent light-curve maxima with decreasing frequency, as expected from the frequency dependence of the τ = 1 surface of synchrotron self- absorption. The global maximum in the 86 GHz light curve becomes less prominent at lower frequencies, while a local maximum, appearing in 2014, strengthens toward decreasing frequencies, becoming pronounced at ∼5 GHz. These tendencies suggest different Doppler boosting of stratified radio-emitting zones in the jet.

ID: 158812
Type: article
Authors: Lee, Jee Won; Lee, Sang-Sung; Algaba, Juan-Carlos; Hodgson, Jeffrey; Kim, Jae-Young; Park, Jongho; Kino, Motoki; Kim, Dae-Won; Kang, Sincheol; Yoo, Sungmin; Kim, Sang Hyun; Gurwell, Mark
Abstract: We present the results of simultaneous multifrequency imaging observations at 22, 43, 86, and 129 GHz of OJ 287. We used the Korean Very Long Baseline Interferometry Network as part of the Interferometric Monitoring of Gamma-ray Bright active galactic nuclei (iMOGABA). The iMOGABA observations were performed during 31 epochs from 2013 January 16 to 2016 December 28. We also used 15 GHz OVRO and 225 GHz SMA flux density data. We analyzed four flux enhancements in the light curves. The estimated timescales of three flux enhancements were similar with timescales of ˜50 days at two frequencies. A fourth flux enhancement had a variability timescale approximately twice as long. We found that 225 GHz enhancements led the 15 GHz enhancements by a range of 7-30 days in the time delay analysis. We found the fractional variability did not change with frequency between 43 and 86 GHz. We could reliably measure the turnover frequency, ${\nu }_{{\rm{c}}}$ , of the core of the source in three epochs. This was measured to be in a range from 27 to 50 GHz and a flux density at the turnover frequency, ${S}_{{\rm{m}}}$ , ranging from 3 to 6 Jy. The derived SSA magnetic fields, ${B}_{\mathrm{SSA}}$ , are in a range from 0.157 ± 0.104 to 0.255 ± 0.146 mG. We estimated the equipartition magnetic field strengths to be in a range from 0.95 ± 0.15 to 1.93 ± 0.30 mG. The equipartition magnetic field strengths are up to a factor of 10 higher than the values of ${B}_{\mathrm{SSA}}$ . We conclude that the downstream jet may be more particle energy dominated.

ID: 158749
Type: article
Authors: Psaltis, Dimitrios; Medeiros, Lia; Christian, Pierre; Özel, Feryal; Akiyama, Kazunori; Alberdi, Antxon; Alef, Walter; Asada, Keiichi; Azulay, Rebecca; Ball, David; Balokovic, Mislav; Barrett, John; Bintley, Dan; Blackburn, Lindy; Boland, Wilfred; Bower, Geoffrey C.; Bremer, Michael; Brinkerink, Christiaan D.; Brissenden, Roger; Britzen, Silke; Broguiere, Dominique; Bronzwaer, Thomas; Byun, Do-Young; Carlstrom, John E.; Chael, Andrew; Chan, Chi-kwan; Chatterjee, Shami; Chatterjee, Koushik; Chen, Ming-Tang; Chen, Yongjun; Cho, Ilje; Conway, John E.; Cordes, James M.; Crew, Geoffrey B.; Cui, Yuzhu; Davelaar, Jordy; De Laurentis, Mariafelicia; Deane, Roger; Dempsey, Jessica; Desvignes, Gregory; Dexter, Jason; Eatough, Ralph P.; Falcke, Heino; Fish, Vincent L.; Fomalont, Ed; Fraga-Encinas, Raquel; Friberg, Per; Fromm, Christian M.; Gammie, Charles F.; García, Roberto; Gentaz, Olivier; Goddi, Ciriaco; Gómez, José L.; Gu, Minfeng; Gurwell, Mark; Hada, Kazuhiro; Hesper, Ronald; Ho, Luis C.; Ho, Paul; Honma, Mareki; Huang, Chih-Wei L.; Huang, Lei; Hughes, David H.; Inoue, Makoto; Issaoun, Sara; James, David J.; Jannuzi, Buell T.; Janssen, Michael; Jiang, Wu; Jimenez-Rosales, Alejandra; Johnson, Michael D.; Jorstad, Svetlana; Jung, Taehyun; Karami, Mansour; Karuppusamy, Ramesh; Kawashima, Tomohisa; Keating, Garrett K.; Kettenis, Mark; Kim, Jae-Young; Kim, Junhan; Kim, Jongsoo; Kino, Motoki; Koay, Jun Yi; Koch, Patrick M.; Koyama, Shoko; Kramer, Michael; Kramer, Carsten; Krichbaum, Thomas P.; Kuo, Cheng-Yu; Lauer, Tod R.; Lee, Sang-Sung; Li, Yan-Rong; Li, Zhiyuan; Lindqvist, Michael; Lico, Rocco; Liu, Jun; Liu, Kuo; Liuzzo, Elisabetta; Lo, Wen-Ping; Lobanov, Andrei P.; Lonsdale, Colin; Lu, Ru-Sen; Mao, Jirong; Markoff, Sera; Marrone, Daniel P.; Marscher, Alan P.; Martí-Vidal, Iván; Matsushita, Satoki; Mizuno, Yosuke; Mizuno, Izumi; Moran, James M.; Moriyama, Kotaro; Moscibrodzka, Monika; Müller, Cornelia; Musoke, Gibwa; Mus Mejías, Alejandro; Nagai, Hiroshi; Nagar, Neil M.; Narayan, Ramesh; Narayanan, Gopal; Natarajan, Iniyan; Neri, Roberto; Noutsos, Aristeidis; Okino, Hiroki; Olivares, Héctor; Oyama, Tomoaki; Palumbo, Daniel C. M.; Park, Jongho; Patel, Nimesh; Pen, Ue-Li; Piétu, Vincent; Plambeck, Richard; PopStefanija, Aleksandar; Prather, Ben; Preciado-López, Jorge A.; Ramakrishnan, Venkatessh; Rao, Ramprasad; Rawlings, Mark G.; Raymond, Alexander W.; Ripperda, Bart; Roelofs, Freek; Rogers, Alan; Ros, Eduardo; Rose, Mel; Roshanineshat, Arash; Rottmann, Helge; Roy, Alan L.; Ruszczyk, Chet; Ryan, Benjamin R.; Rygl, Kazi L. J.; Sánchez, Salvador; Sánchez-Arguelles, David; Sasada, Mahito; Savolainen, Tuomas; Schloerb, F. Peter; Schuster, Karl-Friedrich; Shao, Lijing; Shen, Zhiqiang; Small, Des; Sohn, Bong Won; SooHoo, Jason; Tazaki, Fumie; Tilanus, Remo P. J.; Titus, Michael; Torne, Pablo; Trent, Tyler; Traianou, Efthalia; Trippe, Sascha; van Bemmel, Ilse; van Langevelde, Huib Jan; van Rossum, Daniel R.; Wagner, Jan; Wardle, John; Ward-Thompson, Derek; Weintroub, Jonathan; Wex, Norbert; Wharton, Robert; Wielgus, Maciek; Wong, George N.; Wu, Qingwen; Yoon, Doosoo; Young, André; Young, Ken; Younsi, Ziri; Yuan, Feng; Yuan, Ye-Fei; Zhao, Shan-Shan; EHT Collaboration
Abstract: The 2017 Event Horizon Telescope (EHT) observations of the central source in M87 have led to the first measurement of the size of a black-hole shadow. This observation offers a new and clean gravitational test of the black-hole metric in the strong-field regime. We show analytically that spacetimes that deviate from the Kerr metric but satisfy weak-field tests can lead to large deviations in the predicted black-hole shadows that are inconsistent with even the current EHT measurements. We use numerical calculations of regular, parametric, non-Kerr metrics to identify the common characteristic among these different parametrizations that control the predicted shadow size. We show that the shadow-size measurements place significant constraints on deviation parameters that control the second post-Newtonian and higher orders of each metric and are, therefore, inaccessible to weak-field tests. The new constraints are complementary to those imposed by observations of gravitational waves from stellar-mass sources.

ID: 157120
Type: article
Authors: Roelofs, F.; Janßen, M.; Natarajan, I.; Deane, R.; Davelaar, J.; Olivares, H.; Porth, O.; Paine, Scott N.; Bouman, Katherine L.; Tilanus, R. P. J.; van Bemmel, I. M.; Falcke, H.; Akiyama, K.; Alberdi, A.; Alef, W.; Asada, K.; Azulay, R.; Baczko, A.; Ball, D.; Baloković, Mislav; Barrett, J.; Bintley, D.; Blackburn, Lindy; Boland, W.; Bower, G. C.; Bremer, M.; Brinkerink, C. D.; Brissenden, Roger; Britzen, S.; Broderick, A. E.; Broguiere, D.; Bronzwaer, T.; Byun, D.; Carlstrom, J. E.; Chael, A.; Chan, C.; Chatterjee, S.; Chatterjee, K.; Chen, M.; Chen, Y.; Cho, I.; Christian, P.; Conway, J. E.; Cordes, J. M.; Crew, G. B.; Cui, Y.; De Laurentis, M.; Dempsey, J.; Desvignes, G.; Dexter, J.; Doeleman, Sheperd S.; Eatough, R. P.; Fish, V. L.; Fomalont, E.; Fraga-Encinas, R.; Friberg, P.; Fromm, C. M.; Gómez, J. L.; Galison, P.; Gammie, C. F.; García, R.; Gentaz, O.; Georgiev, B.; Goddi, C.; Gold, R.; Gu, M.; Gurwell, Mark; Hada, K.; Hecht, M. H.; Hesper, R.; Ho, L. C.; Ho, P.; Honma, M.; Huang, C. L.; Huang, L.; Hughes, D. H.; Ikeda, S.; Inoue, M.; Issaoun, S.; James, David J.; Jannuzi, B. T.; Jeter, B.; Jiang, W.; Johnson, M. D.; Jorstad, S.; Jung, T.; Karami, M.; Karuppusamy, R.; Kawashima, T.; Keating, Garrett K.; Kettenis, M.; Kim, J.; Kim, J.; Kim, J.; Kino, M.; Koay, J. Y.; Koch, P. M.; Koyama, S.; Kramer, M.; Kramer, C.; Krichbaum, T. P.; Kuo, C.; Lauer, T. R.; Lee, S.; Li, Y.; Li, Z.; Lindqvist, M.; Lico, R.; Liu, K.; Liuzzo, E.; Lo, W.; Lobanov, A. P.; Loinard, L.; Lonsdale, C.; Lu, R.; MacDonald, N. R.; Mao, J.; Markoff, S.; Marrone, D. P.; Marscher, A. P.; Martí-Vidal, I.; Matsushita, S.; Matthews, L. D.; Medeiros, L.; Menten, K. M.; Mizuno, Y.; Mizuno, I.; Moran, James M.; Moriyama, K.; Moscibrodzka, M.; Müller, C.; Nagai, H.; Nagar, N. M.; Nakamura, M.; Narayan, Ramesh; Narayanan, G.; Neri, R.; Ni, C.; Noutsos, A.; Okino, H.; Olivares, H.; Ortiz-León, G. N.; Oyama, T.; Özel, F.; Palumbo, Daniel C. M.; Patel, Nimesh; Pen, U.; Pesce, Dominic W.; Piétu, V.; Plambeck, R.; PopStefanija, A.; Prather, B.; Preciado-López, J. A.; Psaltis, D.; Pu, H.; Ramakrishnan, V.; Rao, R.; Rawlings, M. G.; Raymond, Alexander W.; Rezzolla, L.; Ripperda, B.; Rogers, A.; Ros, E.; Rose, M.; Roshanineshat, A.; Rottmann, H.; Roy, A. L.; Ruszczyk, C.; Ryan, B. R.; Rygl, K. L. J.; Sánchez, S.; Sánchez-Arguelles, D.; Sasada, M.; Savolainen, T.; Schloerb, F. P.; Schuster, K.; Shao, L.; Shen, Z.; Small, D.; Won Sohn, B.; SooHoo, J.; Tazaki, F.; Tiede, P.; Titus, M.; Toma, K.; Torne, P.; Traianou, E.; Trent, T.; Trippe, S.; Tsuda, S.; van Langevelde, H. J.; van Rossum, D. R.; Wagner, J.; Wardle, J.; Weintroub, Jonathan; Wex, N.; Wharton, R.; Wielgus, Maciek; Wong, G. N.; Wu, Q.; Young, A.; Young, K.; Younsi, Z.; Yuan, F.; Yuan, Y.; Zensus, J. A.; Zhao, G.; Zhao, S.; Zhu, Z.
Abstract: Context. Realistic synthetic observations of theoretical source models are essential for our understanding of real observational data. In using synthetic data, one can verify the extent to which source parameters can be recovered and evaluate how various data corruption effects can be calibrated. These studies are the most important when proposing observations of new sources, in the characterization of the capabilities of new or upgraded instruments, and when verifying model-based theoretical predictions in a direct comparison with observational data.
Aims: We present the SYnthetic Measurement creator for long Baseline Arrays (SYMBA), a novel synthetic data generation pipeline for Very Long Baseline Interferometry (VLBI) observations. SYMBA takes into account several realistic atmospheric, instrumental, and calibration effects.
Methods: We used SYMBA to create synthetic observations for the Event Horizon Telescope (EHT), a millimetre VLBI array, which has recently captured the first image of a black hole shadow. After testing SYMBA with simple source and corruption models, we study the importance of including all corruption and calibration effects, compared to the addition of thermal noise only. Using synthetic data based on two example general relativistic magnetohydrodynamics (GRMHD) model images of M 87, we performed case studies to assess the image quality that can be obtained with the current and future EHT array for different weather conditions.
Results: Our synthetic observations show that the effects of atmospheric and instrumental corruptions on the measured visibilities are significant. Despite these effects, we demonstrate how the overall structure of our GRMHD source models can be recovered robustly with the EHT2017 array after performing calibration steps, which include fringe fitting, a priori amplitude and network calibration, and self-calibration. With the planned addition of new stations to the EHT array in the coming years, images could be reconstructed with higher angular resolution and dynamic range. In our case study, these improvements allowed for a distinction between a thermal and a non-thermal GRMHD model based on salient features in reconstructed images.

ID: 156702
Type: article
Authors: Traianou, E.; Krichbaum, T. P.; Boccardi, B.; Angioni, R.; Rani, B.; Liu, J.; Ros, E.; Bach, U.; Sokolovsky, K. V.; Lisakov, M. M.; Kiehlmann, S.; Gurwell, Mark; Zensus, J. A.
Abstract: Aims: The γ-ray production mechanism and its localization in blazars are still a matter of debate. The main goal of this paper is to constrain the location of the high-energy emission in the blazar TXS 2013+370 and to study the physical and geometrical properties of the inner jet region on sub-pc scales. Methods: TXS 2013+370 was monitored during 2002-2013 with VLBI at 15, 22, 43, and 86 GHz, which allowed us to image the jet base with an angular resolution of ≥0.4 pc. By employing CLEAN imaging and Gaussian model-fitting, we performed a thorough kinematic analysis at multiple frequencies, which provided estimates of the jet speed, orientation, and component ejection times. Additionally, we studied the jet expansion profile and used the information on the jet geometry to estimate the location of the jet apex. VLBI data were combined with single-dish measurements to search for correlated activity between the radio, mm, and γ-ray emission. For this purpose, we employed a cross-correlation analysis, supported by several significance tests. Results: The high-resolution VLBI imaging revealed the existence of a spatially bent jet, described by co- existing moving emission features and stationary features. New jet features, labeled as A1, N, and N1, are observed to emerge from the core, accompanied by flaring activity in radio/mm- bands and γ-rays. The analysis of the transverse jet width profile constrains the location of the mm core to lie ≤2 pc downstream of the jet apex, and also reveals the existence of a transition from parabolic to conical jet expansion at a distance of ∼54 pc from the core, corresponding to ∼1.5 × 10⁶ Schwarzschild radii. The cross-correlation analysis of the broad-band variability reveals a strong correlation between the radio-mm and γ-ray data, with the 1 mm emission lagging ∼49 days behind the γ-rays. Based on this, we infer that the high energy emission is produced at a distance of the order of ∼1 pc from the jet apex, suggesting that the seed photon fields for the external Compton mechanism originate either in the dusty torus or in the broad-line region. Reduced images of Figs. 1-3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/634/A112

ID: 157688
Type: article
Authors: Wielgus, Maciek; Akiyama, Kazunori; Blackburn, Lindy; Chan, Chi-kwan; Dexter, Jason; Doeleman, Sheperd S.; Fish, Vincent L.; Issaoun, Sara; Johnson, Michael D.; Krichbaum, Thomas P.; Lu, Ru-Sen; Pesce, Dominic W.; Wong, George N.; Bower, Geoffrey C.; Broderick, Avery E.; Chael, Andrew; Chatterjee, Koushik; Gammie, Charles F.; Georgiev, Boris; Hada, Kazuhiro; Loinard, Laurent; Markoff, Sera; Marrone, Daniel P.; Plambeck, Richard; Weintroub, Jonathan; Dexter, Matthew; MacMahon, David H. E.; Wright, Melvyn; Alberdi, Antxon; Alef, Walter; Asada, Keiichi; Azulay, Rebecca; Baczko, Anne-Kathrin; Ball, David; Baloković, Mislav; Barausse, Enrico; Barrett, John; Bintley, Dan; Boland, Wilfred; Bouman, Katherine L.; Bremer, Michael; Brinkerink, Christiaan D.; Brissenden, Roger; Britzen, Silke; Broguiere, Dominique; Bronzwaer, Thomas; Byun, Do-Young; Carlstrom, John E.; Chatterjee, Shami; Chen, Ming-Tang; Chen, Yongjun; Cho, Ilje; Christian, Pierre; Conway, John E.; Cordes, James M.; Crew, Geoffrey B.; Cui, Yuzhu; Davelaar, Jordy; De Laurentis, Mariafeliciae; Deane, Roger; Dempsey, Jessica; Desvignes, Gregory; Dzib, Sergio A.; Eatough, Ralph P.; Falcke, Heino; Fomalont, Ed; Fraga-Encinas, Raquel; Friberg, Per; Fromm, Christian M.; Galison, Peter; García, Roberto; Gentaz, Olivier; Goddi, Ciriaco; Gold, Roman; Gómez, José L.; Gómez-Ruiz, Arturo I.; Gu, Minfeng; Gurwell, Mark; Hecht, Michael H.; Hesper, Ronald; Ho, Luis C.; Ho, Paul; Honma, Mareki; Huang, Chih-Wei L.; Huang, Lei; Hughes, David H.; Inoue, Makoto; James, David J.; Jannuzi, Buell T.; Janssen, Michael; Jeter, Britton; Jiang, Wu; Jimenez-Rosales, Alejandra; Jorstad, Svetlana; Jung, Taehyun; Karami, Mansour; Karuppusamy, Ramesh; Kawashima, Tomohisa; Keating, Garrett K.; Kettenis, Mark; Kim, Jae-Young; Kim, Junhan; Kim, Jongsoo; Kino, Motoki; Koay, Jun Yi; Koch, Patrick M.; Koyama, Shoko; Kramer, Michael; Kramer, Carsten; Kuo, Cheng-Yu; Lauer, Tod R.; Lee, Sang-Sung; Li, Yan-Rong; Li, Zhiyuan; Lindqvist, Michael; Lico, Rocco; Liu, Kuo; Liuzzo, Elisabetta; Lo, Wen-Ping; Lobanov, Andrei P.; Lonsdale, Colin; MacDonald, Nicholas R.; Mao, Jirong; Marchili, Nicola; Marscher, Alan P.; Martí-Vidal, Iván; Matsushita, Satoki; Matthews, Lynn D.; Medeiros, Lia; Menten, Karl M.; Mizuno, Yosuke; Mizuno, Izumi; Moran, James M.; Moriyama, Kotaro; Moscibrodzka, Monika; Müller, Cornelia; Musoke, Gibwa; Nagai, Hiroshi; Nagar, Neil M.; Nakamura, Masanori; Narayan, Ramesh; Narayanan, Gopal; Natarajan, Iniyan; Nathanail, Antonios; Neri, Roberto; Ni, Chunchong; Noutsos, Aristeidis; Okino, Hiroki; Olivares, Héctor; Ortiz-León, Gisela N.; Oyama, Tomoaki; Özel, Feryal; Palumbo, Daniel C. M.; Park, Jongho; Patel, Nimesh; Pen, Ue-Li; Piétu, Vincent; PopStefanija, Aleksandar; Porth, Oliver; Prather, Ben; Preciado-López, Jorge A.; Psaltis, Dimitrios; Pu, Hung-Yi; Ramakrishnan, Venkatessh; Rao, Ramprasad; Rawlings, Mark G.; Raymond, Alexander W.; Rezzolla, Luciano; Ripperda, Bart; Roelofs, Freek; Rogers, Alan; Ros, Eduardo; Rose, Mel; Roshanineshat, Arash; Rottmann, Helge; Roy, Alan L.; Ruszczyk, Chet; Ryan, Benjamin R.; Rygl, Kazi L. J.; Sánchez, Salvador; Sánchez-Arguelles, David; Sasada, Mahito; Savolainen, Tuomas; Schloerb, F. Peter; Schuster, Karl-Friedrich; Shao, Lijing; Shen, Zhiqiang; Small, Des; Sohn, Bong Won; SooHoo, Jason; Tazaki, Fumie; Tiede, Paul; Tilanus, Remo P. J.; Titus, Michael; Toma, Kenji; Torne, Pablo; Trent, Tyler; Traianou, Efthalia; Trippe, Sascha; Tsuda, Shuichiro; van Bemmel, Ilse; van Langevelde, Huib Jan; van Rossum, Daniel R.; Wagner, Jan; Wardle, John; Ward-Thompson, Derek; Wex, Norbert; Wharton, Robert; Wu, Qingwen; Yoon, Doosoo; Young, André; Young, Ken; Younsi, Ziri; Yuan, Feng; Yuan, Ye-Fei; Zensus, J. Anton; Zhao, Guangyao; Zhao, Shan-Shan; Zhu, Ziyan
Abstract: The Event Horizon Telescope (EHT) has recently delivered the first resolved images of M87*, the supermassive black hole in the center of the M87 galaxy. These images were produced using 230 GHz observations performed in 2017 April. Additional observations are required to investigate the persistence of the primary image feature-a ring with azimuthal brightness asymmetry-and to quantify the image variability on event horizon scales. To address this need, we analyze M87* data collected with prototype EHT arrays in 2009, 2011, 2012, and 2013. While these observations do not contain enough information to produce images, they are sufficient to constrain simple geometric models. We develop a modeling approach based on the framework utilized for the 2017 EHT data analysis and validate our procedures using synthetic data. Applying the same approach to the observational data sets, we find the M87* morphology in 2009-2017 to be consistent with a persistent asymmetric ring of ∼40 μas diameter. The position angle of the peak intensity varies in time. In particular, we find a significant difference between the position angle measured in 2013 and 2017. These variations are in broad agreement with predictions of a subset of general relativistic magnetohydrodynamic simulations. We show that quantifying the variability across multiple observational epochs has the potential to constrain the physical properties of the source, such as the accretion state or the black hole spin.

ID: 154559
Type: article
Authors: D'Ammando, F.; Raiteri, C. M.; Villata, M.; Acosta-Pulido, J. A.; Agudo, I.; Arkharov, A. A.; Bachev, R.; Baida, G. V.; Benítez, E.; Borman, G. A.; Boschin, W.; Bozhilov, V.; Butuzova, M. S.; Calcidese, P.; Carnerero, M. I.; Carosati, D.; Casadio, C.; Castro-Segura, N.; Chen, W. -P; Damljanovic, G.; Di Paola, A.; Echevarría, J.; Efimova, N. V.; Ehgamberdiev, Sh A.; Espinosa, C.; Fuentes, A.; Giunta, A.; Gómez, J. L.; Grishina, T. S.; Gurwell, Mark A.; Hiriart, D.; Jermak, H.; Jordan, B.; Jorstad, S. G.; Joshi, M.; Kimeridze, G. N.; Kopatskaya, E. N.; Kuratov, K.; Kurtanidze, O. M.; Kurtanidze, S. O.; Lähteenmäki, A.; Larionov, V. M.; Larionova, E. G.; Larionova, L. V.; Lázaro, C.; Lin, C. S.; Malmrose, M. P.; Marscher, A. P.; Matsumoto, K.; McBreen, B.; Michel, R.; Mihov, B.; Minev, M.; Mirzaqulov, D. O.; Molina, S. N.; Moody, J. W.; Morozova, D. A.; Nazarov, S. V.; Nikiforova, A. A.; Nikolashvili, M. G.; Ohlert, J. M.; Okhmat, N.; Ovcharov, E.; Pinna, F.; Polakis, T. A.; Protasio, C.; Pursimo, T.; Redondo-Lorenzo, F. J.; Rizzi, N.; Rodriguez-Coira, G.; Sadakane, K.; Sadun, A. C.; Samal, M. R.; Savchenko, S. S.; Semkov, E.; Sigua, L.; Skiff, B. A.; Slavcheva-Mihova, L.; Smith, P. S.; Steele, I. A.; Strigachev, A.; Tammi, J.; Thum, C.; Tornikoski, M.; Troitskaya, Yu V.; Troitsky, I. S.; Vasilyev, A. A.; Vince, O.; WEBT Collaboration; Hovatta, T.; Kiehlmann, S.; Max-Moerbeck, W.; Readhead, A. C. S.; Reeves, R.; Pearson, T. J.; OVRO Team; Mufakharov, T.; Sotnikova, Yu V.; Mingaliev, M. G.
Abstract: We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and X-rays) and Fermi (γ-rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented γ-ray flaring activity was observed during 2016 November-2017 February, with four major outbursts. A peak flux of (2158 ± 63) × 10^-8 ph cm^-2 s^-1, corresponding to a luminosity of (2.2 ± 0.1) × 10⁵⁰ erg s^-1, was reached on 2016 December 28. These four γ-ray outbursts have corresponding events in the near- infrared, optical, and UV bands, with the peaks observed at the same time. A general agreement between X-ray and γ-ray activity is found. The γ-ray flux variations show a general, strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This γ-ray/optical relationship is in agreement with the geometrical model that has successfully explained the low- energy flux and spectral behaviour, suggesting that the long-term flux variations are mainly due to changes in the Doppler factor produced by variations of the viewing angle of the emitting regions. The difference in behaviour between radio and higher energy emission would be ascribed to different viewing angles of the jet regions producing their emission.

ID: 149176
Type: article
Authors: Fazio, G. G.; Hora, J. L.; Witzel, G.; Willner, S. P.; Ashby, M. L. N.; Baganoff, F.; Becklin, E.; Carey, S.; Haggard, D.; Gammie, C.; Ghez, A.; Gurwell, M. A.; Ingalls, J.; Marrone, D.; Morris, M. R.; Smith, H. A.
Abstract: Sgr A*, the supermassive black hole (SMBH) at the center of our Milky Way Galaxy, is known to be a variable source of X-ray, near-infrared (NIR), and submillimeter radiation and therefore a prime candidate to study the electromagnetic radiation generated by mass accretion flow onto a black hole and/or a related jet. Disentangling the power source and emission mechanisms of this variability is a central challenge to our understanding of accretion flows around SMBHs. Simultaneous multiwavelength observations of the flux variations and their time correlations can play an important role in obtaining a better understanding of possible emission mechanisms and their origin. This paper presents observations of two flares that both apparently violate the previously established patterns in the relative timing of submillimeter/NIR/X-ray flares from Sgr A*. One of these events provides the first evidence of coeval structure between NIR and submillimeter flux increases, while the second event is the first example of the sequence of submillimeter/X-ray/NIR flux increases all occurring within ∼1 hr. Each of these two events appears to upend assumptions that have been the basis of some analytic models of flaring in Sgr A*. However, it cannot be ruled out that these events, even though unusual, were just coincidental. These observations demonstrate that we do not fully understand the origin of the multiwavelength variability of Sgr A* and show that there is a continued and important need for long-term, coordinated, and precise multiwavelength observations of Sgr A* to characterize the full range of variability behavior.

ID: 154410
Type: article
Authors: Lacaille, Kevin M.; Chapman, Scott C.; Smail, Ian; Steidel, C. C.; Blain, A. W.; Geach, J.; Golob, A.; Gurwell, Mark; Ivison, R. J.; Reddy, N.; Sawicki, M.
Abstract: We present James Clerk Maxwell Telescope Submillimetre Common-User Bolometer Array 2 (SCUBA-2) 850 and 450 μm observations (σ₈₅₀ ̃ 0.5 mJy, σ₄₅₀ ̃ 5 mJy) of the HS1549+19 and HS1700+64 survey fields containing two of the largest known galaxy overdensities at z = 2.85 and 2.30, respectively. We detect 56 sub-millimetre galaxies (SMGs) with SNR > 4 over ̃50 arcmin² at 850 μm with flux densities of 3-17 mJy. The number counts indicate overdensities in the 3-arcmin diameter core region (̃1.5 Mpc at z = 2.5) of 6^{+4}_{-2}× (HS1549) and 4^{+6}_{-2}× (HS1700) compared to blank field surveys. Within these core regions, we spectroscopically confirm that approximately one-third of the SMGs lie at the protocluster redshifts for both HS1549 and HS1700. We use statistical identifications of other SMGs in the wider fields to constrain an additional four candidate protocluster members in each system. We combine multiwavelength estimates of the star-formation rates (SFRs) from Lyman-break dropout- and narrow-band-selected galaxies, and the SCUBA-2 SMGs, to estimate total SFRs of 12 500 ± 2800 M_☉ yr^-1 (4900 ± 1200 M_☉ yr^-1) in HS1549 (HS1700), and SFR densities (SFRDs) within the central 1.5-Mpc diameter of each protocluster to be 3000 ± 900 M_☉ yr^-1 Mpc^-3 (1300 ± 400 M_☉ yr^-1 Mpc^-3) in the HS1549 (HS1700) protocluster, ̃10⁴ × larger than the global SFRDs found at their respective epochs, due to the concentration of star-forming galaxies in the small volume of the dense cluster cores. Our results suggest centrally concentrated starbursts within protoclusters may be a relatively common scenario for the build-up of mass in rich clusters assembling at z ≳ 2.

ID: 152899
Type: article
Authors: Park, Jongho; Lee, Sang-Sung; Kim, Jae-Young; Hodgson, Jeffrey A.; Trippe, Sascha; Kim, Dae-Won; Algaba, Juan-Carlos; Kino, Motoki; Zhao, Guang-Yao; Lee, Jee Won; Gurwell, Mark A.
Abstract: PKS 1510–089 is a bright and active γ-ray source that showed strong and complex γ-ray flares in mid-2015 during which the Major Atmospheric Gamma Imaging Cerenkov telescopes detected variable very high energy (photon energies >100 GeV) emission. We present long-term multifrequency radio, optical, and γ-ray light curves of PKS 1510–089 from 2013 to 2018, and results of an analysis of the jet kinematics and linear polarization using 43 GHz Very Long Baseline Array data observed between late 2015 and mid-2017. We find that a strong radio flare trails the γ-ray flares in 2015, showing an optically thick spectrum at the beginning and becoming optically thin over time. Two laterally separated knots of emission are observed to emerge from the radio core nearly simultaneously during the γ-ray flares. We detect an edge-brightened linear polarization near the core in the active jet state in 2016, similar to the quiescent jet state in 2008–2013. These observations indicate that the γ-ray flares may originate from compression of the knots by a standing shock in the core and the jet might consist of multiple complex layers showing time-dependent behavior, rather than of a simple structure of a fast jet spine and a slow jet sheath.

ID: 154281
Type: article
Authors: Porth, Oliver; Chatterjee, Koushik; Narayan, Ramesh; Gammie, Charles F.; Mizuno, Yosuke; Anninos, Peter; Baker, John G.; Bugli, Matteo; Chan, Chi-kwan; Davelaar, Jordy; Del Zanna, Luca; Etienne, Zachariah B.; Fragile, P. Chris; Kelly, Bernard J.; Liska, Matthew; Markoff, Sera; McKinney, Jonathan C.; Mishra, Bhupendra; Noble, Scott C.; Olivares, Héctor; Prather, Ben; Rezzolla, Luciano; Ryan, Benjamin R.; Stone, James M.; Tomei, Niccolò; White, Christopher J.; Younsi, Ziri; Akiyama, Kazunori; Alberdi, Antxon; Alef, Walter; Asada, Keiichi; Azulay, Rebecca; Baczko, Anne-Kathrin; Ball, David; Baloković, Mislav; Barrett, John; Bintley, Dan; Blackburn, Lindy; Boland, Wilfred; Bouman, Katherine L.; Bower, Geoffrey C.; Bremer, Michael; Brinkerink, Christiaan D.; Brissenden, Roger; Britzen, Silke; Broderick, Avery E.; Broguiere, Dominique; Bronzwaer, Thomas; Byun, Do-Young; Carlstrom, John E.; Chael, Andrew; Chatterjee, Shami; Chen, Ming-Tang; Chen, Yongjun; Cho, Ilje; Christian, Pierre; Conway, John E.; Cordes, James M.; Geoffrey; Crew, B.; Cui, Yuzhu; De Laurentis, Mariafelicia; Deane, Roger; Dempsey, Jessica; Desvignes, Gregory; Doeleman, Sheperd S.; Eatough, Ralph P.; Falcke, Heino; Fish, Vincent L.; Fomalont, Ed; Fraga-Encinas, Raquel; Freeman, Bill; Friberg, Per; Fromm, Christian M.; Gómez, José L.; Galison, Peter; García, Roberto; Gentaz, Olivier; Georgiev, Boris; Goddi, Ciriaco; Gold, Roman; Gu, Minfeng; Gurwell, Mark; Hada, Kazuhiro; Hecht, Michael H.; Hesper, Ronald; Ho, Luis C.; Ho, Paul; Honma, Mareki; Huang, Chih-Wei L.; Huang, Lei; Hughes, David H.; Ikeda, Shiro; Inoue, Makoto; Issaoun, Sara; James, David J.; Jannuzi, Buell T.; Janssen, Michael; Jeter, Britton; Jiang, Wu; Johnson, Michael D.; Jorstad, Svetlana; Jung, Taehyun; Karami, Mansour; Karuppusamy, Ramesh; Kawashima, Tomohisa; Keating, Garrett K.; Kettenis, Mark; Kim, Jae-Young; Kim, Junhan; Kim, Jongsoo; Kino, Motoki; Koay, Jun Yi; Patrick; Koch, M.; Koyama, Shoko; Kramer, Michael; Kramer, Carsten; Krichbaum, Thomas P.; Kuo, Cheng-Yu; Lauer, Tod R.; Lee, Sang-Sung; Li, Yan-Rong; Li, Zhiyuan; Lindqvist, Michael; Liu, Kuo; Liuzzo, Elisabetta; Lo, Wen-Ping; Lobanov, Andrei P.; Loinard, Laurent; Lonsdale, Colin; Lu, Ru-Sen; MacDonald, Nicholas R.; Mao, Jirong; Marrone, Daniel P.; Marscher, Alan P.; Martí-Vidal, Iván; Matsushita, Satoki; Matthews, Lynn D.; Medeiros, Lia; Menten, Karl M.; Mizuno, Izumi; Moran, James M.; Moriyama, Kotaro; Moscibrodzka, Monika; Müller, Cornelia; Nagai, Hiroshi; Nagar, Neil M.; Nakamura, Masanori; Narayanan, Gopal; Natarajan, Iniyan; Neri, Roberto; Ni, Chunchong; Noutsos, Aristeidis; Okino, Hiroki; Oyama, Tomoaki; Özel, Feryal; Palumbo, Daniel C. M.; Patel, Nimesh; Pen, Ue-Li; Pesce, Dominic W.; Piétu, Vincent; Plambeck, Richard; PopStefanija, Aleksandar; Preciado-López, Jorge A.; Psaltis, Dimitrios; Pu, Hung-Yi; Ramakrishnan, Venkatessh; Rao, Ramprasad; Rawlings, Mark G.; Raymond, Alexander W.; Ripperda, Bart; Roelofs, Freek; Rogers, Alan; Ros, Eduardo; Rose, Mel; Roshanineshat, Arash; Rottmann, Helge; Roy, Alan L.; Ruszczyk, Chet; Rygl, Kazi L. J.; Sánchez, Salvador; Sánchez-Arguelles, David; Sasada, Mahito; Savolainen, Tuomas; Schloerb, F. Peter; Schuster, Karl-Friedrich; Shao, Lijing; Shen, Zhiqiang; Small, Des; Sohn, Bong Won; SooHoo, Jason; Tazaki, Fumie; Tiede, Paul; Tilanus, Remo P. J.; Titus, Michael; Toma, Kenji; Torne, Pablo; Trent, Tyler; Trippe, Sascha; Tsuda, Shuichiro; van Bemmel, Ilse; van Langevelde, Huib Jan; van Rossum, Daniel R.; Wagner, Jan; Wardle, John; Weintroub, Jonathan; Wex, Norbert; Wharton, Robert; Wielgus, Maciek; Wong, George N.; Wu, Qingwen; Young, Ken; Young, André; Yuan, Feng; Yuan, Ye-Fei; Zensus, J. Anton; Zhao, Guangyao; Zhao, Shan-Shan; Zhu, Ziyan; Event Horizon Telescope Collaboration
Abstract: Recent developments in compact object astrophysics, especially the discovery of merging neutron stars by LIGO, the imaging of the black hole in M87 by the Event Horizon Telescope, and high- precision astrometry of the Galactic Center at close to the event horizon scale by the GRAVITY experiment motivate the development of numerical source models that solve the equations of general relativistic magnetohydrodynamics (GRMHD). Here we compare GRMHD solutions for the evolution of a magnetized accretion flow where turbulence is promoted by the magnetorotational instability from a set of nine GRMHD codes: Athena++, BHAC, Cosmos++, ECHO, H-AMR, iharm3D, HARM-Noble, IllinoisGRMHD, and KORAL. Agreement among the codes improves as resolution increases, as measured by a consistently applied, specially developed set of code performance metrics. We conclude that the community of GRMHD codes is mature, capable, and consistent on these test problems.