Publication Search Results

ID: 159436
Type: article
Authors: Binder, Breanna A.; Sy, Janelle M.; Eracleous, Michael; Christodoulou, Dimitris M.; Bhattacharya, Sayantan; Cappallo, Rigel; Laycock, Silas; Plucinsky, Paul P.; Williams, Benjamin F.
Abstract: We present new X-ray and UV observations of the Wolf-Rayet + black hole (BH) binary system NGC 300 X-1 with the Chandra X-ray Observatory and the Hubble Space Telescope Cosmic Origins Spectrograph. When combined with archival X-ray observations, our X-ray and UV observations sample the entire binary orbit, providing clues to the system geometry and interaction between the BH accretion disk and the donor star wind. We measure a binary orbital period of 32.7921 ± 0.0003 hr, in agreement with previous studies, and perform phase-resolved spectroscopy using the X-ray data. The X-ray light curve reveals a deep eclipse, consistent with inclination angles of i = 60°-75°, and a pre-eclipse excess consistent with an accretion stream impacting the disk edge. We further measure radial velocity variations for several prominent far-UV spectral lines, most notably H II λ1640 and C IV λ1550. We find that the He II emission lines systematically lag the expected Wolf-Rayet star orbital motion by a phase difference of Δφ ∼ 0.3, while C IV λ1550 matches the phase of the anticipated radial velocity curve of the Wolf-Rayet donor. We assume the C IV λ1550 emission line follows a sinusoidal radial velocity curve (semi-amplitude = 250 km s^-1) and infer a BH mass of 17 ± 4 M_⊙. Our observations are consistent with the presence of a wind-Roche lobe overflow accretion disk, where an accretion stream forms from gravitationally focused wind material and impacts the edge of the BH accretion disk.

ID: 159350
Type: article
Authors: Lazzarini, Margaret; Williams, Benjamin F.; Durbin, Meredith; Dalcanton, Julianne; Antoniou, Vallia; Binder, Breanna A.; Eracleous, Michael; Plucinsky, Paul P.; Sasaki, Manami; Vulic, Neven
Abstract: We present our analysis of high-quality high-mass X-ray binary (HMXB) candidates in M31 selected from point-source optical counterpart candidates from the Chandra-PHAT survey catalog. We fit the spectral energy distributions of optical counterpart candidates using the Bayesian Extinction and Stellar Tool. We used the best-fit luminosity, effective temperature, radius, and dust reddening for the companion stars in combination with the local star formation history, dust maps of M31, published X-ray spectral fits from XMM-Newton observations, IR colors, and Chandra X-ray hardness ratios to determine our best sample of HMXB candidates. The age distribution of the HMXB sample appears peaked between 10 and 50 Myr, consistent with findings in other nearby galaxies. Using the age distribution and mean star formation rate (SFR), we find that 80-136 HMXBs were produced per unit of SFR over the last 50 Myr and 89-163 HMXBs were produced per unit of SFR over the last 80 Myr, if we expand the assumed age limit beyond the lifetimes of single massive stars. We also calculate the HMXB production rate (HMXBs/M_⊙) over time, which ranges from 7 × 10^-7 to 4 × 10^-6 HMXBs/M_⊙ over the last 80 Myr, in agreement with both theoretical predictions and measured production rates in other galaxies.

ID: 159437
Type: article
Authors: Sano, Hidetoshi; Tsuge, Kisetsu; Tokuda, Kazuki; Muraoka, Kazuyuki; Tachihara, Kengo; Yamane, Yumiko; Kohno, Mikito; Fujita, Shinji; Enokiya, Rei; Rowell, Gavin; Maxted, Nigel; Filipović, Miroslav D.; Knies, Jonathan; Sasaki, Manami; Onishi, Toshikazu; Plucinsky, Paul P.; Fukui, Yasuo
Abstract: We report the first evidence for high-mass star formation triggered by collisions of molecular clouds in M 33. Using the Atacama Large Millimeter/submillimeter Array, we spatially resolved filamentary structures of giant molecular cloud 37 in M 33 using ¹²CO(J = 2-1), ¹³CO(J = 2-1), and C¹⁸O(J = 2-1) line emission at a spatial resolution of ∼2 pc. There are two individual molecular clouds with a systematic velocity difference of ∼6 km s^-1. Three continuum sources representing up to ∼10 high-mass stars with spectral types of B0V-O7.5V are embedded within the densest parts of molecular clouds bright in the C¹⁸O(J = 2-1) line emission. The two molecular clouds show a complementary spatial distribution with a spatial displacement of ∼6.2 pc, and show a V-shaped structure in the position-velocity diagram. These observational features traced by CO and its isotopes are consistent with those in high-mass star-forming regions created by cloud-cloud collisions in the Galactic and Magellanic Cloud H II regions. Our new finding in M 33 indicates that cloud-cloud collision is a promising process for triggering high-mass star formation in the Local Group.

ID: 157708
Type: article
Authors: Fukushima, Kotaro; Yamaguchi, Hiroya; Slane, Patrick O.; Park, Sangwook; Katsuda, Satoru; Sano, Hidetoshi; Lopez, Laura A.; Plucinsky, Paul P.; Kobayashi, Shogo B.; Matsushita, Kyoko
Abstract: Despite their importance, a detailed understanding of Type Ia supernovae (SNe Ia) remains elusive. X-ray measurements of the element distributions in supernova remnants (SNRs) offer important clues for understanding the explosion and nucleosynthesis mechanisms for SNe Ia. However, it is challenging to observe the entire ejecta mass in X-rays for young SNRs, because the central ejecta may not have been heated by the reverse shock yet. Here we present over 200 kilosecond Chandra observations of the Type Ia SNR G344.7-0.1, whose age is old enough for the reverse shock to have reached the SNR center, providing an opportunity to investigate the distribution of the entire ejecta mass. We reveal a clear stratification of heavy elements with a centrally peaked distribution of the Fe ejecta surrounded by intermediate-mass elements (IMEs: Si, S, Ar Ca) with an arc-like structure. The centroid energy of the Fe K emission is marginally lower in the central Fe-rich region than in the outer IME-rich regions, suggesting that the Fe ejecta were shock-heated more recently. These results are consistent with the prediction for standard SN Ia models, where the heavier elements are synthesized in the interior of an exploding white dwarf. We find, however, that the peak location of the Fe K emission is slightly offset to the west with respect to the geometric center of the SNR. This apparent asymmetry is likely due to the inhomogeneous density distribution of the ambient medium, consistent with our radio observations of the ambient molecular and neutral gas.

ID: 156972
Type: article
Authors: Kavanagh, Patrick J.; Sasaki, Manami; Breitschwerdt, Dieter; de Avillez, Miguel A.; Filipović, Miroslav D.; Galvin, Timothy; Haberl, Frank; Hatzidimitriou, Despina; Henze, Martin; Plucinsky, Paul P.; Saeedi, Sara; Sokolovsky, Kirill V.; Williams, Benjamin F.
Abstract:
Aims: We use new deep XMM-Newton observations of the northern disc of M31 to trace the hot interstellar medium (ISM) in unprecedented detail and to characterise the physical properties of the X-ray emitting plasmas.
Methods: We used all XMM-Newton data up to and including our new observations to produce the most detailed image yet of the hot ISM plasma in a grand design spiral galaxy such as our own. We compared the X-ray morphology to multi-wavelength studies in the literature to set it in the context of the multi-phase ISM. We performed spectral analyses on the extended emission using our new observations as they offer sufficient depth and count statistics to constrain the plasma properties. Data from the Panchromatic Hubble Andromeda Treasury were used to estimate the energy injected by massive stars and their supernovae. We compared these results to the hot gas properties.
Results: The brightest emission regions were found to be correlated with populations of massive stars, notably in the 10 kpc star-forming ring. The plasma temperatures in the ring regions are ~0.2 up to ~0.6 keV. We suggest this emission is hot ISM heated in massive stellar clusters and superbubbles. We derived X-ray luminosities, densities, and pressures for the gas in each region. We also found large extended emission filling low density gaps in the dust morphology of the northern disc, notably between the 5 and 10 kpc star-forming rings. We propose that the hot gas was heated and expelled into the gaps by the populations of massive stars in the rings.
Conclusions: It is clear that the massive stellar populations are responsible for heating the ISM to X-ray emitting temperatures, filling their surroundings, and possibly driving the hot gas into the low density regions. Overall, the morphology and spectra of the hot gas in the northern disc of M31 is similar to other galaxy discs.
FITS files for Figs. 1 and 2 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/637/A12
Based on observations obtained with XMM- Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

ID: 156970
Type: article
Authors: Law, Charles J.; Milisavljevic, Dan; Patnaude, Daniel J.; Plucinsky, Paul P.; Gladders, Michael D.; Schmidt, Judy; Sravan, Niharika; Banovetz, John; Sano, Hidetoshi; McGraw, Jordan M.; Takahashi, George; Orlando, Salvatore
Abstract: We present a three-dimensional kinematic reconstruction of the optically emitting, oxygen-rich ejecta of supernova remnant N132D in the Large Magellanic Cloud (LMC). Data were obtained with the 6.5 m Magellan telescope in combination with the IMACS+GISMO instrument and survey [O III] λλ4959, 5007 line emission in a ∼3' × 3' region centered on N132D. The spatial and spectral resolutions of our data enable detailed examination of the optical ejecta structure. The majority of N132D's optically bright oxygen ejecta are arranged in a torus-like geometry tilted approximately 28° with respect to the plane of the sky. The torus has a radius of 4.4 pc (D_LMC/50 kpc), exhibits a blueshifted radial velocity asymmetry of -3000 to +2300 km s^-1, and has a conspicuous break in its circumference. Assuming homologous expansion from the geometric center of O-rich filaments, the average expansion velocity of 1745 km s^-1 translates to an age since explosion of 2450 ± 195 yr. A faint, spatially separated "runaway knot" (RK) with total space velocity of 3650 km s^-1 is nearly perpendicular to the torus plane and coincident with X-ray emission that is substantially enhanced in Si relative to the LMC and N132D's bulk ejecta. These kinematic and chemical signatures suggest that the RK may have had its origin deep within the progenitor star. Overall, the main- shell morphology and high-velocity, Si-enriched components of N132D have remarkable similarity with those of Cassiopeia A, which was the result of a Type IIb supernova explosion. Our results underscore the need for further observations and simulations that can robustly reconcile whether the observed morphology is dominated by explosion dynamics or shaped by interaction with the environment.

ID: 158816
Type: article
Authors: Sano, H.; Plucinsky, Paul P.; Bamba, A.; Sharda, P.; Filipovic, M. D.; Law, Charles J.; Alsaberi, R. Z. E.; Yamane, Y.; Tokuda, K.; Acero, F.; Sasaki, M.; Vink, J.; Inoue, T.; Inutsuka, S.; Shimoda, J.; Tsuge, K.; Fujii, K.; Voisin, F.; Maxted, N.; Rowell, G.; Onishi, T.; Kawamura, A.; Mizuno, N.; Yamamoto, H.; Tachihara, K.; Fukui, Y.
Abstract: N132D is the brightest gamma-ray supernova remnant (SNR) in the Large Magellanic Cloud (LMC). We carried out ¹²CO(J = 1-0, 3-2) observations toward the SNR using the Atacama Large Millimeter/submillimeter Array (ALMA) and Atacama Submillimeter Telescope Experiment. We find diffuse CO emission not only at the southern edge of the SNR as previously known, but also inside the X-ray shell. We spatially resolved nine molecular clouds using ALMA with an angular resolution of 5", corresponding to a spatial resolution of ˜1 pc at the distance of the LMC. Typical cloud sizes and masses are ˜2.0 pc and ˜100 M_?, respectively. High intensity ratios of CO J = 3-2/1-0 > 1.5 are seen toward the molecular clouds, indicating that shock heating has occurred. Spatially resolved X-ray spectroscopy reveals that thermal X-rays in the center of N132D are produced not only behind a molecular cloud but also in front of it. Considering the absence of a thermal component associated with the forward shock toward one molecular cloud located along the line of sight to the center of the remnant, this suggests that this particular cloud is engulfed by shock waves and is positioned on the near side of the remnant. If the hadronic process is the dominant contributor to the gamma-ray emission, the shock-engulfed clouds play a role as targets for cosmic rays. We estimate the total energy of cosmic-ray protons accelerated in N132D to be ˜0.5-3.8 × 10⁴⁹ erg as a conservative lower limit, which is similar to that observed in Galactic gamma-ray SNRs.

ID: 156978
Type: article
Authors: Sharda, Piyush; Gaetz, Terrance J.; Kashyap, Vinay L.; Plucinsky, Paul P.
Abstract: We perform detailed spectroscopy of the X-ray-brightest supernova remnant in the Large Magellanic Cloud (LMC), N132D, using Chandra archival observations. By analyzing the spectra of the entire well- defined rim, we determine the mean abundances for O, Ne, Mg, Si, S, and Fe for the local LMC environment. We find evidence of enhanced O on the northwestern and S on the northeastern blast wave. By analyzing spectra interior to the remnant, we confirm the presence of a Si-rich, relatively hot plasma (≳1.5 keV) that is also responsible for the Fe K emission. Chandra images show that the Fe K emission is distributed throughout the interior of the southern half of the remnant but does not extend out to the blast wave. We estimate the progenitor mass to be 15 ± 5 M_☉ using abundance ratios in different regions that collectively cover a large fraction of the remnant, as well as from the radius of the forward shock compared with models of an explosion in a cavity created by stellar winds. We fit ionizing and recombining plasma models to the Fe K emission and find that the current data cannot distinguish between the two, so the origin of the high-temperature plasma remains uncertain. Our analysis is consistent with N132D being the result of a core-collapse supernova in a cavity created by its intermediate-mass progenitor.

ID: 157300
Type: article
Authors: Suzuki, Hiromasa; Bamba, Aya; Enokiya, Rei; Yamaguchi, Hiroya; Plucinsky, Paul P.; Odaka, Hirokazu
Abstract: We report on the results of our detailed analyses on the peculiar recombining plasma of the supernova remnant (SNR) G359.1-0.5, and the interacting CO clouds. Combining Chandra and Suzaku data, we estimated the ionization state of the plasma with a careful treatment of the background spectrum. The average spectrum showed a remarkably large deviation of the electron temperature (∼0.17 keV) from the initial temperature (>16 keV), indicating that the plasma is in a highly recombination-dominant state. On the other hand, the recombination timescale (n_et) is comparable to those of the other recombining SNRs (∼4.2 × 10¹¹ cm^-3 s). We also searched for spatial variation of the plasma parameters, but found no significant differences. Using ¹²CO(J = 2-1) data obtained with NANTEN2, we found a new, plausible candidate for the interacting CO cloud, which has a line-of-sight velocity of ∼ -20 km s^-1. This indicates that the SNR is located at a distance of ∼4 kpc, which is the foreground of the Galactic center, as previously reported. The associated CO cloud does not show clear spatial coincidence with the nearby GeV/TeV emission, indicating that the origins of the GeV/TeV emission are likely unrelated to G359.1-0.5.

ID: 157707
Type: article
Authors: Suzuki, Hitomi; Yamaguchi, Hiroya; Ishida, Manabu; Uchida, Hiroyuki; Plucinsky, Paul P.; Foster, Adam R.; Miller, Eric D.
Abstract: We present XMM-Newton observations of N132D, the X-ray brightest supernova remnant in the Large Magellanic Cloud, using the Reflection Grating Spectrometer (RGS), which enables high-resolution spectroscopy in the soft X-ray band. A dozen emission lines from L-shell transitions of Si, S, Ar, Ca, and Fe at intermediate charge states are newly detected in the RGS data integrating the ∼200 ks on-axis observations. This enables accurate abundance measurements of these elements, whose K-shell emission is out of the RGS bandpass. The 0.3-2.0-keV spectra require at least three components of thermal plasmas with different electron temperatures and indicate clear evidence of non-equilibrium ionization (NEI). Our detailed spectral diagnostics further reveal that the forbidden-to-resonance line ratios of O VII and Ne IX are both higher than expected for typical NEI plasmas. This enhancement could be attributed to either resonance scattering or emission induced by charge exchange in addition to a possible contribution from the superposition of multiple-temperature components, although the lack of spatial information prevents us from concluding which is most likely.

ID: 158830
Type: article
Authors: Xi, Long; Gaetz, Terrance J.; Plucinsky, Paul P.
Abstract: We have analyzed the archival Chandra X-ray Observatory observations of the compact feature in the Small Magellanic Cloud supernova remnant 1E 0102.2-7219, which has recently been suggested to be the central compact object remaining after the supernova explosion. In our analysis, we have used appropriate, time-dependent responses for each of the archival observations, have modeled the background instead of subtracting it, and have fit unbinned spectra to preserve the maximal spectral information. The spectrum of this feature is similar to the spectrum of the surrounding regions that have significantly enhanced abundances of O, Ne, and Mg. We find that the previously suggested blackbody model is inconsistent with the data, as Monte Carlo simulations indicate that more than 99% of the simulated data sets have a test statistic value lower than that of the data. The spectrum is described adequately by a nonequilibrium ionization thermal model with two classes of models that fit the data equally well. One class of models has a temperature of kT ˜ 0.79 keV, an ionization timescale of ˜3 × 10¹¹ cm^-3 s, and marginal evidence for enhanced abundances of O and Ne, and the other has a temperature of kT ˜ 0.91 keV, an ionization timescale of ˜7 × 10¹⁰ cm^-3 s, and abundances consistent with local interstellar medium values. We also performed an image analysis and find that the spatial distribution of the counts is not consistent with that of a point source. The hypothesis of a point-source distribution can be rejected at the 99.9% confidence level. Therefore, this compact feature is most likely a knot of O- and Ne-rich ejecta associated with the reverse shock.

ID: 154539
Type: article
Authors: Antoniou, Vallia; Zezas, Andreas; Drake, Jeremy J.; Badenes, Carles; Haberl, Frank; Wright, Nicholas J.; Hong, Jaesub; Di Stefano, Rosanne; Gaetz, Terrance J.; Long, Knox S.; Plucinsky, Paul P.; Sasaki, Manami; Williams, Benjamin F.; Winkler, P. Frank; SMC XVP collaboration
Abstract: We have compiled the most complete census of high-mass X-ray binaries (HMXBs) in the Small Magellanic Cloud with the aim to investigate the formation efficiency of young accreting binaries in its low-metallicity environment. In total, we use 123 X-ray sources with detections in our Chandra X-ray Visionary Program (XVP), supplemented by 14 additional (likely and confirmed) HMXBs identified by Haberl & Sturm that fall within the XVP area, but are neither detected in our survey (nine sources) nor matched with any of the 127 sources identified in the XVP data (five sources). Specifically, we examine the number ratio of the HMXBs [N(HMXBs)] to (a) the number of OB stars, (b) the local star formation rate (SFR), and (c) the stellar mass produced during the specific star formation burst, all as a function of the age of their parent stellar populations. Each of these indicators serves a different role, but in all cases we find that the HMXB formation efficiency increases as a function of time (following a burst of star formation) up to ∼40─60 Myr, and then gradually decreases. The formation efficiency peaks at ∼30─40 Myr with average rates of {\text{}}{{N}}({HMXB})/{SFR}={339}_-83⁺⁷⁸ {({M}_ȯ /{yr})}^-1, and N(HMXB)/M \star =({8.74}_-0.92^+1.0)× {10}^-6 {M}_ȯ ^-1, in good agreement with previous estimates of the average formation efficiency in the broad ∼20─60 Myr age range.

ID: 155407
Type: article
Authors: Xi, Long; Gaetz, Terrance J.; Plucinsky, Paul P.; Hughes, John P.; Patnaude, Daniel J.
Abstract: We measure the expansion of the forward shock of the Small Magellanic Cloud supernova remnant 1E 0102.2-7219 in X-rays using Chandra X-Ray Observatory on-axis Advanced CCD Imaging Spectrometer observations from 1999 to 2016. We estimate an expansion rate of 0.025% ± 0.006% yr^-1 and a blast wave velocity of (1.61+/- 0.37)× {10}³ {km} {{{s}}}^-1. Assuming partial electron- ion equilibration via Coulomb collisions and cooling due to adiabatic expansion, this velocity implies a post-shock electron temperature of 0.84 ± 0.20 keV, which is consistent with the estimate of 0.68 ± 0.05 keV based on the X-ray spectral analysis. We combine the expansion rate with the blast wave and reverse shock radii to generate a grid of one- dimensional models for a range of ejecta masses (2{--}6 {M}_☉ ) to constrain the explosion energy, age, circumstellar density, swept-up mass, and unshocked-ejecta mass. We find acceptable solutions for a constant-density ambient medium and for an r ^-2 power- law profile (appropriate for a constant progenitor stellar wind). For the constant-density case, we find an age of ∼1700 yr, explosion energies (0.87-2.61) × 10⁵¹ erg, ambient densities 0.85-2.54 amu cm^-3, swept-up masses 22{--}66 {M}_☉ , and unshocked-ejecta masses 0.05{--}0.16 {M}_☉ . For the power-law density profile, we find an age of ∼2600 yr, explosion energies (0.34-1.02) × 10⁵¹ erg, densities 0.22{--}0.66 {amu} {cm}}^-3 at the blast wave, swept-up masses 17{--}52 {M}_☉ , and unshocked-ejecta masses 0.06{--}0.18 {M}_☉ . Assuming that the true explosion energy was (0.5-1.5) × 10⁵¹ erg, ejecta masses 2{--}3.5 {M}_☉ are favored for the constant-density case and 3{--}6 {M}_☉ for the power-law case. The unshocked-ejecta mass estimates are comparable to Fe masses expected in core-collapse supernovae with progenitor mass 15.0{--}40.0 {M}_☉ , offering a possible explanation for the lack of Fe emission observed in X-rays.

ID: 147889
Type: article
Authors: Knies, Jonathan R.; Sasaki, Manami; Plucinsky, Paul P.
Abstract: We present the analysis of Suzaku X-ray observations of the Galactic supernova remnant (SNR) `Monogem Ring', a large structure observed in X-rays with an extent of ≈25°, located at an anticentre position. One observation close to the shock also coincides with a large ring-like structure observed in H alpha, which is called the `Gemini H alpha ring'. We investigate the origin of the ring-like structure and also possible interactions with the SNR. We show that the SNR is expanding in a region with a density gradient, which has an effect on the morphology of the SNR and the properties of the plasma. The X-ray spectra fit well with a collisional ionization equilibrium model with a temperature of kT ≈ 0.3 keV. The spectra obtained at a position where the SNR coincides with the Gemini H alpha ring are better described with non-equilibrium ionization with a temperature of kT ≈ 1.0 keV. Based on the spectral analysis results, we estimate an age of t ≈ 6.8 × 10⁴ yr for a distance of ≈300 pc, using the Sedov-Taylor solution. We have identified several early-type stars in the Hipparcos catalogue at a distance of 200-300 pc, which have most likely formed the `Gemini H alpha ring' by their powerful stellar winds.

ID: 150223
Type: article
Authors: West, Lacey A.; Lehmer, Bret D.; Wik, Daniel; Yang, Jun; Walton, Dominic J.; Antoniou, Vallia; Haberl, Frank; Hornschemeier, Ann; Maccarone, Thomas J.; Plucinsky, Paul P.; Ptak, Andrew; Williams, Benjamin F.; Vulic, Neven; Yukita, Mihoko; Zezas, Andreas
Abstract: We present nearly simultaneous NuSTAR and XMM-Newton observations of the nearby (832 kpc) ultraluminous X-ray source (ULX) M33 X-8. M33 X-8 has a 0.3–10 keV luminosity of L _X ≈ 1.4 × 10³⁹ erg s^‑1, near the boundary of the “ultraluminous” classification, making it an important source for understanding the link between typical Galactic X-ray binaries and ULXs. Past studies have shown that the 0.3–10 keV spectrum of X-8 can be characterized using an advection-dominated accretion disk model. We find that when fitting to our NuSTAR and XMM-Newton observations, an additional high-energy (≳10 keV) Comptonization component is required, which allows us to rule out single advection-dominated disk and classical sub-Eddington models. With our new constraints, we analyze XMM-Newton data taken over the last 17 yr to show that small (≈30%) variations in the 0.3–10 keV flux of M33 X-8 result in spectral changes similar to those observed for other ULXs. The two most likely phenomenological scenarios suggested by the data are degenerate in terms of constraining the nature of the accreting compact object (i.e., black hole versus neutron star). We further present a search for pulsations using our suite of data; however, no clear pulsations are detected. Future observations designed to observe M33 X-8 at different flux levels across the full 0.3–30 keV range would significantly improve our constraints on the nature of this important source.

ID: 142326
Type: article
Authors: Binder, B.; Gross, J.; Williams, B. F.; Eracleous, M.; Gaetz, T. J.; Plucinsky, Paul P.; Skillman, E. D.
Abstract: We have obtained three epochs of Chandra ACIS-I observations (totaling ~184 ks) of the nearby spiral galaxy NGC 300 to study the logN-logS distributions of its X-ray point-source population down to ~2 × 10^-15 erg s^-1 cm^-2 in the 0.35-8 keV band (equivalent to ~10³⁶ erg s^-1). The individual epoch logN-logS distributions are best described as the sum of a background active galactic nucleus (AGN) component, a simple power law, and a broken power law, with the shape of the logN-logS distributions sometimes varying between observations. The simple power law and AGN components produce a good fit for "persistent" sources (i.e., with fluxes that remain constant within a factor of ~2). The differential power-law index of ~1.2 and high fluxes suggest that the persistent sources intrinsic to NGC 300 are dominated by Roche-lobe-overflowing low-mass X-ray binaries. The variable X-ray sources are described by a broken power law, with a faint-end power-law index of ~1.7, a bright-end index of ~2.8-4.9, and a break flux of ~ 8× {10}^-15 erg s^-1 cm^-2 (~4 × 10³⁶ erg s^-1), suggesting that they are mostly outbursting, wind-fed high-mass X-ray binaries, although the logN-logS distribution of variable sources likely also contains low-mass X-ray binaries. We generate model logN-logS distributions for synthetic X-ray binaries and constrain the distribution of maximum X-ray fluxes attained during outburst. Our observations suggest that the majority of outbursting X-ray binaries occur at sub-Eddington luminosities, where mass transfer likely occurs through direct wind accretion at ~1%-3% of the Eddington rate.

ID: 144794
Type: article
Authors: Garofali, Kristen; Williams, Benjamin F.; Plucinsky, Paul P.; Gaetz, Terrance J.; Wold, Brian; Haberl, Frank; Long, Knox S.; Blair, William P.; Pannuti, Thomas G.; Winkler, P. Frank; Gross, Jacob
Abstract: We have carried out a study of the X-ray properties of the supernova remnant (SNR) population in M33 with XMM-Newton, comprising deep observations of eight fields in M33 covering all of the area within the D₂₅ contours, and with a typical luminosity of 7.1 × 10³⁴ erg s^-1 (0.2-2.0 keV). Here, we report our work to characterize the X-ray properties of the previously identified SNRs in M33, as well as our search for new X-ray detected SNRs. With our deep observations and large field of view we have detected 105 SNRs at the 3? level, of which 54 SNRs are newly detected in X-rays, and three are newly discovered SNRs. Combining XMM-Newton data with deep Chandra survey data allows detailed spectral fitting of 15 SNRs, for which we have measured temperatures, ionization time-scales and individual abundances. This large sample of SNRs allows us to construct an X-ray luminosity function, and compare its shape to luminosity functions from host galaxies of differing metallicities and star formation rates to look for environmental effects on SNR properties. We conclude that while metallicity may play a role in SNR population characteristics, differing star formation histories on short time-scales, and small-scale environmental effects appear to cause more significant differences between X-ray luminosity distributions. In addition, we analyse the X-ray detectability of SNRs, and find that in M33 SNRs with higher [S II]/H ? ratios, as well as those with smaller galactocentric distances, are more detectable in X-rays.

ID: 144706
Type: article
Authors: Hong, Jaesub; Antoniou, Vallia; Zezas, Andreas; Haberl, Frank; Sasaki, Manami; Drake, Jeremy J.; Plucinsky, Paul P.; Laycock, Silas
Abstract: We report the timing analysis results of X-ray pulsars from a recent deep Chandra survey of the Small Magellanic Cloud (SMC). We analyzed a total exposure of 1.4 Ms from 31 observations over a 1.2 deg² region in the SMC under a Chandra X-ray Visionary Program. Using the Lomb-Scargle and epoch-folding techniques, we detected periodic modulations from 20 pulsars and a new candidate pulsar. The survey also covered 11 other pulsars with no clear sign of periodic modulation. The 0.5-8 keV X-ray luminosity (L _X ) of the pulsars ranges from 10³⁴ to 10³⁷ erg s^-1 at 60 kpc. All of the Chandra sources with L _X ? 4 × 10³⁵ erg s^-1 exhibit X-ray pulsations. The X-ray spectra of the SMC pulsars (and high-mass X-ray binaries) are in general harder than those of the SMC field population. All but SXP 8.02 can be fitted by an absorbed power-law model with a photon index of ? ? 1.5. The X-ray spectrum of the known magnetar SXP 8.02 is better fitted with a two-temperature blackbody model. Newly measured pulsation periods of SXP 51.0, SXP 214, and SXP 701, are significantly different from the previous XMM-Newton and RXTE measurements. This survey provides a rich data set for energy-dependent pulse profile modeling. Six pulsars show an almost eclipse-like dip in the pulse profile. Phase-resolved spectral analysis reveals diverse spectral variations during pulsation cycles: e.g., for an absorbed power-law model, some exhibit an (anti)-correlation between absorption and X-ray flux, while others show more intrinsic spectral variation (I.e., changes in photon indices).

ID: 142340
Type: article
Authors: Plucinsky, Paul P.; Beardmore, Andrew P.; Foster, Adam; Haberl, Frank; Miller, Eric D.; Pollock, Andrew M. T.; Sembay, Steve
Abstract: Context. The flight calibration of the spectral response of charge-coupled device (CCD) instruments below 1.5 keV is difficult in general because of the lack of strong lines in the on-board calibration sources typically available. This calibration is also a function of time due to the effects of radiation damage on the CCDs and/or the accumulation of a contamination layer on the filters or CCDs.
Aims: We desire a simple comparison of the absolute effective areas of the current generation of CCD instruments onboard the following observatories: Chandra ACIS-S3, XMM-Newton (EPIC-MOS and EPIC-pn), Suzaku XIS, and Swift XRT and a straightforward comparison of the time-dependent response of these instruments across their respective mission lifetimes.
Methods: We have been using 1E 0102.2-7219, the brightest supernova remnant in the Small Magellanic Cloud, to evaluate and modify the response models of these instruments. 1E 0102.2-7219 has strong lines of O, Ne, and Mg below 1.5 keV and little or no Fe emission to complicate the spectrum. The spectrum of 1E 0102.2-7219 has been well-characterized using the RGS gratings instrument on XMM-Newton and the HETG gratings instrument on Chandra. As part of the activities of the International Astronomical Consortium for High Energy Calibration (IACHEC), we have developed a standard spectral model for 1E 0102.2-7219 and fit this model to the spectra extracted from the CCD instruments. The model is empirical in that it includes Gaussians for the identified lines, an absorption component in the Galaxy, another absorption component in the SMC, and two thermal continuum components with different temperatures. In our fits, the model is highly constrained in that only the normalizations of the four brightest lines/line complexes (the O vii He? triplet, O viii Ly? line, the Ne ix He? triplet, and the Ne x Ly? line) and an overall normalization are allowed to vary, while all other components are fixed. We adopted this approach to provide a straightforward comparison of the measured line fluxes at these four energies. We have examined these measured line fluxes as a function of time for each instrument after applying the most recent calibrations that account for the time-dependent response of each instrument.
Results: We performed our effective area comparison with representative, early mission data when the radiation damage and contamination layers were at a minimum, except for the XMM-Newton EPIC-pn instrument which is stable in time. We found that the measured fluxes of the O vii He?r line, the O viii Ly? line, the Ne ix He?r line, and the Ne x Ly? line generally agree to within ±10% for all instruments, with 38 of our 48 fitted normalizations within ± 10% of the IACHEC model value. We then fit all available observations of 1E 0102.2-7219 for the CCD instruments close to the on-axis position to characterize the time dependence in the 0.5-1.0 keV band. We present the measured line normalizations as a function of time for each CCD instrument so that the users may estimate the uncertainty in their measured line fluxes for the epoch of their observations.

ID: 145644
Type: article
Authors: Temim, Tea; Slane, Patrick; Plucinsky, Paul P.; Gelfand, Joseph; Castro, Daniel; Kolb, Christopher
Abstract: We present a measurement of the proper motion of the presumed pulsar in the evolved composite supernova remnant (SNR) MSH 15-56 whose pulsar wind nebula (PWN) has been disrupted by the supernova (SN) reverse shock. Using Chandra X-ray observations acquired over a baseline of 15 years, we measure a pulsar velocity of {720}_-215⁺²⁹⁰ {km} {{{s}}}^-1 and a direction of motion of 14° ± 22° west of south. We use this measurement to constrain a hydrodynamical (HD) model for the evolution of this system, and find that its morphology is well-described by an SNR expanding in an ambient density gradient that increases from east to west. The effect of the density gradient and the pulsar's motion is an asymmetric interaction between the SN reverse shock and the PWN that displaces the bulk of the PWN material away from the pulsar toward the northeast. The simulation is consistent with an SNR age of 11,000 years, an SN ejecta mass of 10 M _⊙, and an average surrounding density of 0.4 cm^‑3, but a combination of a higher SN ejecta mass and ambient density can produce a similar SNR morphology at a later age.