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Late-time Observations of Calcium-rich Transient SN 2019ehk Reveal a Pure Radioactive Decay Power SourceJacobson-Galán, Wynn V.Margutti, RaffaellaKilpatrick, Charles D.Raymond, JohnBerger, EdoBlanchard, Peter K.Bobrick, AlexeyFoley, Ryan J.Gomez, SebastianHosseinzadeh, GriffinMilisavljevic, DannyPerets, HagaiTerreran, GiacomoZenati, YossefDOI: info:10.3847/2041-8213/abdebcv. 908L32
Jacobson-Galán, Wynn V., Margutti, Raffaella, Kilpatrick, Charles D., Raymond, John, Berger, Edo, Blanchard, Peter K., Bobrick, Alexey, Foley, Ryan J., Gomez, Sebastian, Hosseinzadeh, Griffin, Milisavljevic, Danny, Perets, Hagai, Terreran, Giacomo, and Zenati, Yossef. 2021. "Late-time Observations of Calcium-rich Transient SN 2019ehk Reveal a Pure Radioactive Decay Power Source." The Astrophysical Journal 908:L32. https://doi.org/10.3847/2041-8213/abdebc
ID: 159342
Type: article
Authors: Jacobson-Galán, Wynn V.; Margutti, Raffaella; Kilpatrick, Charles D.; Raymond, John; Berger, Edo; Blanchard, Peter K.; Bobrick, Alexey; Foley, Ryan J.; Gomez, Sebastian; Hosseinzadeh, Griffin; Milisavljevic, Danny; Perets, Hagai; Terreran, Giacomo; Zenati, Yossef
Abstract: We present multiband Hubble Space Telescope imaging of the calcium-rich supernova (SN) SN 2019ehk at 276-389 days after explosion. These observations represent the latest B-band to near-IR photometric measurements of a calcium-rich transient to date and allow for the first opportunity to analyze the late-time bolometric evolution of an object in this observational SN class. We find that the late-time bolometric light curve of SN 2019ehk can be described predominantly through the radioactive decay of 56Co for which we derive a mass of M(56Co) = (2.8 ± 0.1) × 10-2 M. Furthermore, the rate of decline in bolometric luminosity requires the leakage of γ-rays on timescale tγ = 53.9 ± 1.30 days, but we find no statistical evidence for incomplete positron trapping in the SN ejecta. While our observations cannot constrain the exact masses of other radioactive isotopes synthesized in SN 2019ehk, we estimate a mass ratio limit of M(57Co)/M(56Co) ≤ 0.030. This limit is consistent with the explosive nucleosynthesis produced in the merger of low-mass white dwarfs, which is one of the favored progenitor scenarios in early-time studies of SN 2019ehk.
Measured Lightcurves and Rotational Periods of 3122 Florence, 3830 Trelleborg, and (131077) 2000 YH105Abrams, Natasha S.Bieryla, AllysonGomez, SebastianHuang, JaneLewis, John ArbanGarrison, Lehman H.Carmichael, Theronv. 473–4
Abrams, Natasha S., Bieryla, Allyson, Gomez, Sebastian, Huang, Jane, Lewis, John Arban, Garrison, Lehman H., and Carmichael, Theron. 2020. "Measured Lightcurves and Rotational Periods of 3122 Florence, 3830 Trelleborg, and (131077) 2000 YH105." Minor Planet Bulletin 47:3– 4.
ID: 158251
Type: article
Authors: Abrams, Natasha S.; Bieryla, Allyson; Gomez, Sebastian; Huang, Jane; Lewis, John Arban; Garrison, Lehman H.; Carmichael, Theron
Abstract: We determined the rotational periods of 3122 Florence, 3830 Trelleborg, and (131077) 2000 YH105 with the Harvard Clay Telescope and KeplerCam at the Fred L. Whipple Observatory. We found the rotational periods to be 2.3580 ± 0.0015 h, 17.059 ± 0.017 h, and 1.813 ± 0.00003 h, respectively. Our measurement of 3122 Florence's period agrees with Warner (2016), who reported 2.3580 ± 0.0002 h.
Measured Lightcurves and Rotational Periods of (16579) 1992 GO (25660) 2000 AO88, And (37652) 1994 JS1Abrams, Natasha S.Gomez, SebastianBieryla, Allysonv. 47168–169
Abrams, Natasha S., Gomez, Sebastian, and Bieryla, Allyson. 2020. "Measured Lightcurves and Rotational Periods of (16579) 1992 GO (25660) 2000 AO88, And (37652) 1994 JS1." Minor Planet Bulletin 47:168– 169.
ID: 158252
Type: article
Authors: Abrams, Natasha S.; Gomez, Sebastian; Bieryla, Allyson
Abstract: We determined the rotational periods of (16579) 1992 GO, (25660) 2000 AO88 and (37652) 1994 JS1, with the 1.2 m telescope at the Fred L. Whipple Observatory. We found the rotational periods to be 10.9887 ± 0.0004 h, 2.63705 ± 0.00004 h, and 17.4433 ± 0.0007 h, respectively. The former two were previously undetermined periods. The period that we determined for 1994 JS1 agrees well with the previously measured periods of 17.4501 ± 0.0014 (Noschese et al., 2019) and 17.459 ± 0.002 h (Marchini et al., 2019).
The Tidal Disruption Event AT 2018hyz II: Light-curve modelling of a partially disrupted starGomez, SebastianNicholl, MattShort, PhilipMargutti, RaffaellaAlexander, Kate D.Blanchard, Peter K.Berger, EdoEftekhari, TarranehSchulze, SteveAnderson, JosephArcavi, IairChornock, RyanCowperthwaite, Philip S.Galbany, LluísHerzog, Laura J.Hiramatsu, DaichiHosseinzadeh, GriffinLaskar, TanmoyMüller Bravo, Tomás E.Patton, LockeTerreran, GiacomoDOI: info:10.1093/mnras/staa2099v. 4971925–1934
Gomez, Sebastian, Nicholl, Matt, Short, Philip, Margutti, Raffaella, Alexander, Kate D., Blanchard, Peter K., Berger, Edo, Eftekhari, Tarraneh, Schulze, Steve, Anderson, Joseph, Arcavi, Iair, Chornock, Ryan, Cowperthwaite, Philip S., Galbany, Lluís, Herzog, Laura J., Hiramatsu, Daichi, Hosseinzadeh, Griffin, Laskar, Tanmoy, Müller Bravo, Tomás E., Patton, Locke, and Terreran, Giacomo. 2020. "The Tidal Disruption Event AT 2018hyz II: Light-curve modelling of a partially disrupted star." Monthly Notices of the Royal Astronomical Society 497:1925– 1934. https://doi.org/10.1093/mnras/staa2099
ID: 158102
Type: article
Authors: Gomez, Sebastian; Nicholl, Matt; Short, Philip; Margutti, Raffaella; Alexander, Kate D.; Blanchard, Peter K.; Berger, Edo; Eftekhari, Tarraneh; Schulze, Steve; Anderson, Joseph; Arcavi, Iair; Chornock, Ryan; Cowperthwaite, Philip S.; Galbany, Lluís; Herzog, Laura J.; Hiramatsu, Daichi; Hosseinzadeh, Griffin; Laskar, Tanmoy; Müller Bravo, Tomás E.; Patton, Locke; Terreran, Giacomo
Abstract: AT 2018hyz (= ASASSN-18zj) is a tidal disruption event (TDE) located in the nucleus of a quiescent E+A galaxy at a redshift of z = 0.04573, first detected by the All-Sky Automated Survey for Supernovae (ASAS-SN). We present optical+UV photometry of the transient, as well as an X-ray spectrum and radio upper limits. The bolometric light curve of AT 2018hyz is comparable to other known TDEs and declines at a rate consistent with a t-5/3 at early times, emitting a total radiated energy of E = 9 × 1050 erg. An excess bump appears in the UV light curve about 50 d after bolometric peak, followed by a flattening beyond 250 d. We detect a constant X-ray source present for at least 86 d. The X-ray spectrum shows a total unabsorbed flux of ∼4 × 10-14 erg cm-2 s-1 and is best fit by a blackbody plus power-law model with a photon index of Γ = 0.8. A thermal X-ray model is unable to account for photons >1 keV, while a radio non-detection favours inverse-Compton scattering rather than a jet for the non-thermal component. We model the optical and UV light curves using the Modular Open-Source Fitter for Transients (MOSFiT) and find a best fit for a black hole of 5.2 × 106 M disrupting a 0.1 M star; the model suggests the star was likely only partially disrupted, based on the derived impact parameter of β = 0.6. The low optical depth implied by the small debris mass may explain how we are able to see hydrogen emission with disc-like line profiles in the spectra of AT 2018hyz (see our companion paper).
SN 2019ehk: A Double-peaked Ca-rich Transient with Luminous X-Ray Emission and Shock-ionized Spectral FeaturesJacobson-Galán, Wynn V.Margutti, RaffaellaKilpatrick, Charles D.Hiramatsu, DaichiPerets, HagaiKhatami, DavidFoley, Ryan J.Raymond, JohnYoon, Sung-ChulBobrick, AlexeyZenati, YossefGalbany, LluísAndrews, JenniferBrown, Peter J.Cartier, RégisCoppejans, Deanne L.Dimitriadis, GeorgiosDobson, MatthewHajela, AprajitaHowell, D. AndrewKuncarayakti, HanindyoMilisavljevic, DannyRahman, MohammedRojas-Bravo, CésarSand, David J.Shepherd, JoelSmartt, Stephen J.Stacey, HollandStroh, MichaelSwift, Jonathan J.Terreran, GiacomoVinko, JozsefWang, XiaofengAnderson, Joseph P.Baron, Edward A.Berger, EdoBlanchard, Peter K.Burke, JamisonCoulter, David A.DeMarchi, LindsayDerkacy, James M.Fremling, ChristofferGomez, SebastianGromadzki, MariuszHosseinzadeh, GriffinKasen, DanielKriskovics, LeventeMcCully, CurtisMüller-Bravo, Tomás E.Nicholl, MattOrdasi, AndrásPellegrino, CraigPiro, Anthony L.Pál, AndrásRen, JuanjuanRest, ArminRich, R. MichaelSai, HannaSárneczky, KrisztiánShen, Ken J.Short, PhilipSiebert, Matthew R.Stauffer, CandiceSzakáts, RóbertZhang, XinhanZhang, JujiaZhang, KaichengDOI: info:10.3847/1538-4357/ab9e66v. 898166
Jacobson-Galán, Wynn V., Margutti, Raffaella, Kilpatrick, Charles D., Hiramatsu, Daichi, Perets, Hagai, Khatami, David, Foley, Ryan J., Raymond, John, Yoon, Sung-Chul, Bobrick, Alexey, Zenati, Yossef, Galbany, Lluís, Andrews, Jennifer, Brown, Peter J., Cartier, Régis, Coppejans, Deanne L., Dimitriadis, Georgios, Dobson, Matthew, Hajela, Aprajita, Howell, D. Andrew, Kuncarayakti, Hanindyo, Milisavljevic, Danny, Rahman, Mohammed, Rojas-Bravo, César, Sand, David J. et al. 2020. "SN 2019ehk: A Double-peaked Ca-rich Transient with Luminous X-Ray Emission and Shock-ionized Spectral Features." The Astrophysical Journal 898:166. https://doi.org/10.3847/1538-4357/ab9e66
ID: 157818
Type: article
Authors: Jacobson-Galán, Wynn V.; Margutti, Raffaella; Kilpatrick, Charles D.; Hiramatsu, Daichi; Perets, Hagai; Khatami, David; Foley, Ryan J.; Raymond, John; Yoon, Sung-Chul; Bobrick, Alexey; Zenati, Yossef; Galbany, Lluís; Andrews, Jennifer; Brown, Peter J.; Cartier, Régis; Coppejans, Deanne L.; Dimitriadis, Georgios; Dobson, Matthew; Hajela, Aprajita; Howell, D. Andrew; Kuncarayakti, Hanindyo; Milisavljevic, Danny; Rahman, Mohammed; Rojas-Bravo, César; Sand, David J.; Shepherd, Joel; Smartt, Stephen J.; Stacey, Holland; Stroh, Michael; Swift, Jonathan J.; Terreran, Giacomo; Vinko, Jozsef; Wang, Xiaofeng; Anderson, Joseph P.; Baron, Edward A.; Berger, Edo; Blanchard, Peter K.; Burke, Jamison; Coulter, David A.; DeMarchi, Lindsay; Derkacy, James M.; Fremling, Christoffer; Gomez, Sebastian; Gromadzki, Mariusz; Hosseinzadeh, Griffin; Kasen, Daniel; Kriskovics, Levente; McCully, Curtis; Müller-Bravo, Tomás E.; Nicholl, Matt; Ordasi, András; Pellegrino, Craig; Piro, Anthony L.; Pál, András; Ren, Juanjuan; Rest, Armin; Rich, R. Michael; Sai, Hanna; Sárneczky, Krisztián; Shen, Ken J.; Short, Philip; Siebert, Matthew R.; Stauffer, Candice; Szakáts, Róbert; Zhang, Xinhan; Zhang, Jujia; Zhang, Kaicheng
Abstract: We present panchromatic observations and modeling of the Calcium-rich supernova (SN) 2019ehk in the star-forming galaxy M100 (d ≍ 16.2 Mpc) starting 10 hr after explosion and continuing for ∼300 days. SN 2019ehk shows a double-peaked optical light curve peaking at t = 3 and 15 days. The first peak is coincident with luminous, rapidly decaying Swift-XRT-discovered X-ray emission ( ${L}_{{\rm{x}}}\approx {10}^{41}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ at 3 days; Lx ∝ t-3), and a Shane/Kast spectral detection of narrow Hα and He II emission lines (v ≍ 500 $\mathrm{km}\,{{\rm{s}}}^{-1}$ ) originating from pre-existent circumstellar material (CSM). We attribute this phenomenology to radiation from shock interaction with extended, dense material surrounding the progenitor star at r ), and a Shane/Kast spectral detection of narrow Hα and He II emission lines (v ≍ 500 $\mathrm{km}\,{{\rm{s}}}^{-1}$ ) originating from pre-existent circumstellar material (CSM). We attribute this phenomenology to radiation from shock interaction with extended, dense material surrounding the progenitor star at r 15 cm and the resulting cooling emission. We calculate a total CSM mass of ∼7 × 10-3 ${M}_{\odot }$ (MHe/MH ≍6) with particle density n ≍ 109 cm-3. Radio observations indicate a significantly lower density n . Radio observations indicate a significantly lower density n 4 cm-3 at larger radii r > (0.1-1) × 1017 cm. The photometric and spectroscopic properties during the second light-curve peak are consistent with those of Ca-rich transients (rise-time of tr = 13.4 ± 0.210 days and a peak B-band magnitude of MB = -15.1 ± 0.200 mag). We find that SN 2019ehk synthesized (3.1 ± 0.11) × 10-2 ${M}_{\odot }$ of ${}^{56}\mathrm{Ni}$ and ejected Mej = (0.72 ± 0.040) ${M}_{\odot }$ total with a kinetic energy Ek = (1.8 ± 0.10) × 1050 erg. Finally, deep HST pre-explosion imaging at the SN site constrains the parameter space of viable stellar progenitors to massive stars in the lowest mass bin (∼10 ${M}_{\odot }$ ) in binaries that lost most of their He envelope or white dwarfs (WDs). The explosion and environment properties of SN 2019ehk further restrict the potential WD progenitor systems to low-mass hybrid HeCO WD+CO WD binaries.
An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qizNicholl, M.Wevers, T.Oates, S. R.Alexander, K. D.Leloudas, G.Onori, F.Jerkstrand, A.Gomez, SebastianCampana, S.Arcavi, I.Charalampopoulos, P.Gromadzki, M.Ihanec, N.Jonker, P. G.Lawrence, A.Mandel, I.Schulze, S.Short, P.Burke, J.McCully, C.Hiramatsu, D.Howell, D. A.Pellegrino, C.Abbot, H.Anderson, J. P.Berger, EdoBlanchard, P. K.Cannizzaro, G.Chen, T. -WDennefeld, M.Galbany, L.González-Gaitán, S.Hosseinzadeh, GriffinInserra, C.Irani, I.Kuin, P.Müller-Bravo, T.Pineda, J.Ross, N. P.Roy, R.Smartt, S. J.Smith, K. W.Tucker, B.Wyrzykowski, L.Young, D. R.DOI: info:10.1093/mnras/staa2824v. 499482–504
Nicholl, M., Wevers, T., Oates, S. R., Alexander, K. D., Leloudas, G., Onori, F., Jerkstrand, A., Gomez, Sebastian, Campana, S., Arcavi, I., Charalampopoulos, P., Gromadzki, M., Ihanec, N., Jonker, P. G., Lawrence, A., Mandel, I., Schulze, S., Short, P., Burke, J., McCully, C., Hiramatsu, D., Howell, D. A., Pellegrino, C., Abbot, H., Anderson, J. P. et al. 2020. "An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz." Monthly Notices of the Royal Astronomical Society 499:482– 504. https://doi.org/10.1093/mnras/staa2824
ID: 158741
Type: article
Authors: Nicholl, M.; Wevers, T.; Oates, S. R.; Alexander, K. D.; Leloudas, G.; Onori, F.; Jerkstrand, A.; Gomez, Sebastian; Campana, S.; Arcavi, I.; Charalampopoulos, P.; Gromadzki, M.; Ihanec, N.; Jonker, P. G.; Lawrence, A.; Mandel, I.; Schulze, S.; Short, P.; Burke, J.; McCully, C.; Hiramatsu, D.; Howell, D. A.; Pellegrino, C.; Abbot, H.; Anderson, J. P.; Berger, Edo; Blanchard, P. K.; Cannizzaro, G.; Chen, T. -W; Dennefeld, M.; Galbany, L.; González-Gaitán, S.; Hosseinzadeh, Griffin; Inserra, C.; Irani, I.; Kuin, P.; Müller-Bravo, T.; Pineda, J.; Ross, N. P.; Roy, R.; Smartt, S. J.; Smith, K. W.; Tucker, B.; Wyrzykowski, L.; Young, D. R.
Abstract: At 66-=Mpc, AT2019qiz is the closest optical tidal disruption event (TDE) to date, with a luminosity intermediate between the bulk of the population and the faint-and-fast event iPTF16fnl. Its proximity allowed a very early detection and triggering of multiwavelength and spectroscopic follow-up well before maximum light. The velocity dispersion of the host galaxy and fits to the TDE light curve indicate a black hole mass ?106-=M?, disrupting a star of ?1-=M?. By analysing our comprehensive UV, optical, and X-ray data, we show that the early optical emission is dominated by an outflow, with a luminosity evolution L ? t2, consistent with a photosphere expanding at constant velocity (?2000-=km-=s-1), and a line-forming region producing initially blueshifted H and He-=II profiles with v = 3000-10-=000-=km-=s-1. The fastest optical ejecta approach the velocity inferred from radio detections (modelled in a forthcoming companion paper from K. D. Alexander et al.), thus the same outflow may be responsible for both the fast optical rise and the radio emission - the first time this connection has been observed in a TDE. The light-curve rise begins 29 ± 2 d before maximum light, peaking when the photosphere reaches the radius where optical photons can escape. The photosphere then undergoes a sudden transition, first cooling at constant radius then contracting at constant temperature. At the same time, the blueshifts disappear from the spectrum and Bowen fluorescence lines (N-=III) become prominent, implying a source of far-UV photons, while the X-ray light curve peaks at ?1041-=erg-=s-1. Assuming that these X-rays are from prompt accretion, the size and mass of the outflow are consistent with the reprocessing layer needed to explain the large optical to X-ray ratio in this and other optical TDEs, possibly favouring accretion-powered over collision-powered outflow models.
An extremely energetic supernova from a very massive star in a dense mediumNicholl, MattBlanchard, Peter K.Berger, EdoChornock, RyanMargutti, RaffaellaGomez, SebastianLunnan, RagnhildMiller, Adam A.Fong, Wen-faiTerreran, GiacomoVigna-Gómez, AlejandroBhirombhakdi, KornpobBieryla, AllysonChallis, PeteLaher, Russ R.Masci, Frank J.Paterson, KerryDOI: info:10.1038/s41550-020-1066-7v. 4893–899
Nicholl, Matt, Blanchard, Peter K., Berger, Edo, Chornock, Ryan, Margutti, Raffaella, Gomez, Sebastian, Lunnan, Ragnhild, Miller, Adam A., Fong, Wen-fai, Terreran, Giacomo, Vigna-Gómez, Alejandro, Bhirombhakdi, Kornpob, Bieryla, Allyson, Challis, Pete, Laher, Russ R., Masci, Frank J., and Paterson, Kerry. 2020. "An extremely energetic supernova from a very massive star in a dense medium." Nature Astronomy 4:893– 899. https://doi.org/10.1038/s41550-020-1066-7
ID: 158742
Type: article
Authors: Nicholl, Matt; Blanchard, Peter K.; Berger, Edo; Chornock, Ryan; Margutti, Raffaella; Gomez, Sebastian; Lunnan, Ragnhild; Miller, Adam A.; Fong, Wen-fai; Terreran, Giacomo; Vigna-Gómez, Alejandro; Bhirombhakdi, Kornpob; Bieryla, Allyson; Challis, Pete; Laher, Russ R.; Masci, Frank J.; Paterson, Kerry
Abstract: The interaction of a supernova with a circumstellar medium (CSM) can dramatically increase the emitted luminosity by converting kinetic energy to thermal energy. In `superluminous' supernovae of type IIn-named for narrow hydrogen lines1 in their spectra-the integrated emission can reach2-6 ~1051 erg, attainable by thermalizing most of the kinetic energy of a conventional supernova. A few transients in the centres of active galaxies have shown similar spectra and even larger energies7,8, but are difficult to distinguish from accretion onto the supermassive black hole. Here we present a new event, SN2016aps, offset from the centre of a low-mass galaxy, that radiated ?5 × 1051 erg, necessitating a hyper-energetic supernova explosion. We find a total (supernova ejecta + CSM) mass likely exceeding 50-100 M?, with energy ?1052 erg, consistent with some models of pair-instability supernovae or pulsational pair-instability supernovae-theoretically predicted thermonuclear explosions from helium cores >50 M?. Independent of the explosion mechanism, this event demonstrates the existence of extremely energetic stellar explosions, detectable at very high redshifts, and provides insight into dense CSM formation in the most massive stars.
The tidal disruption event AT 2018hyz - I. Double-peaked emission lines and a flat Balmer decrementShort, P.Nicholl, M.Lawrence, A.Gomez, SebastianArcavi, I.Wevers, T.Leloudas, G.Schulze, S.Anderson, J. P.Berger, EdoBlanchard, P. K.Burke, J.Segura, N. CastroCharalampopoulos, P.Chornock, R.Galbany, L.Gromadzki, M.Herzog, L. J.Hiramatsu, D.Horne, KeithHosseinzadeh, GriffinHowell, D. AndrewIhanec, N.Inserra, C.Kankare, E.Maguire, K.McCully, C.Müller Bravo, T. E.Onori, F.Sollerman, J.Young, D. R.DOI: info:10.1093/mnras/staa2065v. 4984119–4133
Short, P., Nicholl, M., Lawrence, A., Gomez, Sebastian, Arcavi, I., Wevers, T., Leloudas, G., Schulze, S., Anderson, J. P., Berger, Edo, Blanchard, P. K., Burke, J., Segura, N. Castro, Charalampopoulos, P., Chornock, R., Galbany, L., Gromadzki, M., Herzog, L. J., Hiramatsu, D., Horne, Keith, Hosseinzadeh, Griffin, Howell, D. Andrew, Ihanec, N., Inserra, C., Kankare, E. et al. 2020. "The tidal disruption event AT 2018hyz - I. Double-peaked emission lines and a flat Balmer decrement." Monthly Notices of the Royal Astronomical Society 498:4119– 4133. https://doi.org/10.1093/mnras/staa2065
ID: 158740
Type: article
Authors: Short, P.; Nicholl, M.; Lawrence, A.; Gomez, Sebastian; Arcavi, I.; Wevers, T.; Leloudas, G.; Schulze, S.; Anderson, J. P.; Berger, Edo; Blanchard, P. K.; Burke, J.; Segura, N. Castro; Charalampopoulos, P.; Chornock, R.; Galbany, L.; Gromadzki, M.; Herzog, L. J.; Hiramatsu, D.; Horne, Keith; Hosseinzadeh, Griffin; Howell, D. Andrew; Ihanec, N.; Inserra, C.; Kankare, E.; Maguire, K.; McCully, C.; Müller Bravo, T. E.; Onori, F.; Sollerman, J.; Young, D. R.
Abstract: We present results from spectroscopic observations of AT 2018hyz, a transient discovered by the All-Sky Automated Survey for Supernova survey at an absolute magnitude of MV ˜ -20.2 mag, in the nucleus of a quiescent galaxy with strong Balmer absorption lines. AT 2018hyz shows a blue spectral continuum and broad emission lines, consistent with previous TDE candidates. High cadence follow-up spectra show broad Balmer lines and He I in early spectra, with He II making an appearance after ˜70-100 d. The Balmer lines evolve from a smooth broad profile, through a boxy, asymmetric double-peaked phase consistent with accretion disc emission, and back to smooth at late times. The Balmer lines are unlike typical active galactic nucleus in that they show a flat Balmer decrement (Ha/Hß ˜ 1.5), suggesting the lines are collisionally excited rather than being produced via photoionization. The flat Balmer decrement together with the complex profiles suggests that the emission lines originate in a disc chromosphere, analogous to those seen in cataclysmic variables. The low optical depth of material due to a possible partial disruption may be what allows us to observe these double-peaked, collisionally excited lines. The late appearance of He II may be due to an expanding photosphere or outflow, or late-time shocks in debris collisions.
Follow-up of the Neutron Star Bearing Gravitational-wave Candidate Events S190425z and S190426c with MMT and SOARHosseinzadeh, GriffinCowperthwaite, P. S.Gomez, SebastianVillar, Victoria AshleyNicholl, M.Margutti, R.Berger, EdoChornock, R.Paterson, K.Fong, W.Savchenko, V.Short, P.Alexander, K. D.Blanchard, Peter K.Braga, J.Calkins, Michael L.Cartier, R.Coppejans, D. L.Eftekhari, TarranehLaskar, T.Ly, C.Patton, LockePelisoli, I.Reichart, D. E.Terreran, G.Williams, Peter K. G.DOI: info:10.3847/2041-8213/ab271cv. 880L4
Hosseinzadeh, Griffin, Cowperthwaite, P. S., Gomez, Sebastian, Villar, Victoria Ashley, Nicholl, M., Margutti, R., Berger, Edo, Chornock, R., Paterson, K., Fong, W., Savchenko, V., Short, P., Alexander, K. D., Blanchard, Peter K., Braga, J., Calkins, Michael L., Cartier, R., Coppejans, D. L., Eftekhari, Tarraneh, Laskar, T., Ly, C., Patton, Locke, Pelisoli, I., Reichart, D. E., Terreran, G. et al. 2019. "Follow-up of the Neutron Star Bearing Gravitational-wave Candidate Events S190425z and S190426c with MMT and SOAR." The Astrophysical Journal 880:L4. https://doi.org/10.3847/2041-8213/ab271c
ID: 155119
Type: article
Authors: Hosseinzadeh, Griffin; Cowperthwaite, P. S.; Gomez, Sebastian; Villar, Victoria Ashley; Nicholl, M.; Margutti, R.; Berger, Edo; Chornock, R.; Paterson, K.; Fong, W.; Savchenko, V.; Short, P.; Alexander, K. D.; Blanchard, Peter K.; Braga, J.; Calkins, Michael L.; Cartier, R.; Coppejans, D. L.; Eftekhari, Tarraneh; Laskar, T.; Ly, C.; Patton, Locke; Pelisoli, I.; Reichart, D. E.; Terreran, G.; Williams, Peter K. G.
Abstract: On 2019 April 25.346 and 26.640 UT the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo gravitational-wave (GW) observatory announced the detection of the first candidate events in Observing Run 3 that contained at least one neutron star (NS). S190425z is a likely binary neutron star (BNS) merger at d L = 156 ± 41 Mpc, while S190426c is possibly the first NS-black hole (BH) merger ever detected, at d L = 377 ± 100 Mpc, although with marginal statistical significance. Here we report our optical follow-up observations for both events using the MMT 6.5 m telescope, as well as our spectroscopic follow-up of candidate counterparts (which turned out to be unrelated) with the 4.1 m SOAR telescope. We compare to publicly reported searches, explore the overall areal coverage and depth, and evaluate those in relation to the optical/near-infrared (NIR) kilonova emission from the BNS merger GW170817, to theoretical kilonova models, and to short gamma-ray burst (SGRB) afterglows. We find that for a GW170817-like kilonova, the partial volume covered spans up to about 40% for S190425z and 60% for S190426c. For an on-axis jet typical of SGRBs, the search effective volume is larger, but such a configuration is expected in at most a few percent of mergers. We further find that wide- field γ-ray and X-ray limits rule out luminous on-axis SGRBs, for a large fraction of the localization regions, although these searches are not sufficiently deep in the context of the γ-ray emission from GW170817 or off-axis SGRB afterglows. The results indicate that some optical follow-up searches are sufficiently deep for counterpart identification to about 300 Mpc, but that localizations better than 1000 deg2 are likely essential.