Publication Search Results

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: 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: 149401
Type: article
Authors: Slane, Patrick; Lovchinsky, I.; Kolb, C.; Snowden, S. L.; Temim, T.; Blondin, J.; Bocchino, F.; Miceli, M.; Chevalier, R. A.; Hughes, J. P.; Patnaude, Daniel J.; Gaetz, Terrance
Abstract: Vela X is a prototypical example of a pulsar wind nebula whose morphology and detailed structure have been affected by interaction with the reverse shock of its host supernova remnant. The resulting complex of filamentary structure and mixed-in ejecta embedded in a nebula that is offset from the pulsar provides the best example we have of this middle-age state that characterizes a significant fraction of composite supernova remnants (SNRs), and perhaps all of the large-diameter pulsar wind nebulae (PWNe) seen as TeV sources. Here, we report on an XMM-Newton (hereafter XMM) Large Project study of Vela X, supplemented by additional Chandra observations. Through broad spectral modeling, as well as detailed spectral investigations of discrete emission regions, we confirm previous studies that report evidence for ejecta material within Vela X, and show that equivalent-width variations of O VII and O VIII are consistent with temperature maps within the PWN that show low-temperature regions where the projected SNR emission appears to dominate emission from the ejecta. We identify spectral variations in the nonthermal emission, with hard emission being concentrated near the pulsar. We carry out investigations of the Vela X “cocoon” structure, and with hydrodynamical simulations, show that its overall properties are consistent with structures formed in the late-phase evolution of a composite SNR expanding into a surrounding medium with a density gradient, with ejecta material being swept beyond the pulsar and compressed into an elongated structure in the direction opposite the high external density.

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: 139609
Type: article
Authors: Binder, B.; Williams, B. F.; Kong, A. K. H.; Gaetz, T. J.; Plucinsky, Paul P.; Skillman, E. D.; Dolphin, A.
Abstract: We present new observations of the `supernova impostor' SN 2010da using the Chandra X-ray Observatory and the Hubble Space Telescope. During the initial 2010 outburst, the 0.3-10 keV luminosity was observed by Swift to be ~5 × 10³⁸ erg s^-1 and faded by a factor of ~25 in a four month period. Our two new Chandra observations show a factor of ~10 increase in the 0.35-8 keV X-ray luminosity, from ~4 × 10³⁶ to 4 × 10³⁷ erg s^-1 in ~6 months, and the X-ray spectrum is consistent in both observations with a power-law with a photon index of ? ~ 0. We find evidence of X-ray spectral state changes: when SN 2010da is in a high-luminosity state, the X-ray spectrum is harder (? ~0) compared to the low-luminosity state (? ~ 1.2 ± 0.8). Using our Hubble observations, we fit the colour-magnitude diagram of the coeval stellar population to estimate a time since formation of the SN 2010da progenitor system of ?5 Myr. Our observations are consistent with SN 2010da being a high-mass X-ray binary (HMXB) composed of a neutron star and a luminous blue variable-like companion, although we cannot rule out the possibility that SN 2010da is an unusually X-ray bright massive star. The ?5 Myr age is consistent with the theoretically predicted delay time between the formation of a massive binary and the onset of the HMXB phase. It is possible that the initial 2010 outburst marked the beginning of X-ray production in the system, making SN 2010da possibly the first massive progenitor binary ever observed to evolve into an HMXB.

ID: 140229
Type: article
Authors: Hong, Jaesub; Antoniou, Vallia; Zezas, Andreas; Haberl, Frank; Drake, Jeremy J.; Plucinsky, Paul P.; Gaetz, Terrance; Sasaki, Manami; Williams, Benjamin; Long, Knox S.; Blair, William P.; Winkler, P. Frank; Wright, Nicholas J.; Laycock, Silas; Udalski, Andrzej
Abstract: Located in the Small Magellanic Cloud (SMC), SXP 214 is an X-ray pulsar in a high mass X-ray binary system with a Be-star companion. A recent survey of the SMC under a Chandra X-ray Visionary program found that the source was in a transition when the X-ray flux was on a steady rise. The Lomb-Scargle periodogram revealed a pulse period of 211.49 ± 0.42 s, which is significantly (>5?) shorter than the previous measurements made with XMM-Newton and RXTE. This implies that the system has gone through sudden spin-up episodes recently. The pulse profile shows a sharp eclipse-like feature with a modulation amplitude of >95%. The linear rise of the observed X-ray luminosity from ?2× to 7× {10}³⁵ erg s^-1 is correlated with a steady softening of the X-ray spectrum, which can be described by the changes in the local absorption from N _H ~ 10²⁴ to ?10²⁰ cm^-2 for an absorbed power-law model. The soft X-ray emission below 2 keV was absent in the early part of the observation when only the pulsating hard X-ray component was observed, whereas at later times, both soft and hard X-ray components were observed to be pulsating. A likely explanation is that the neutron star was initially hidden in the circumstellar disk of the companion, and later came out of the disk with the accreted material that continued fueling the observed pulsation.

ID: 140494
Type: article
Authors: Binder, B.; Williams, B. F.; Eracleous, M.; Plucinsky, Paul P.; Gaetz, T. J.; Anderson, S. F.; Skillman, E. D.; Dalcanton, J. J.; Kong, A. K. H.; Weisz, D. R.
Abstract: We present comprehensive X-ray point source catalogs of NGC 55, NGC 2403, and NGC 4214 as part of the Chandra Local Volume Survey. The combined archival observations have effective exposure times of 56.5 ks, 190 ks, and 79 ks for NGC 55, NGC 2403, and NGC 4214, respectively. When combined with our published catalogs for NGC 300 and NGC 404, our survey contains 629 X-ray sources total down to a limiting unabsorbed luminosity of ~ 5× {10}³⁵ erg s^-1 in the 0.35-8 keV band in each of the five galaxies. We present X-ray hardness ratios, spectral analysis, radial source distributions, and an analysis of the temporal variability for the X-ray sources detected at high significance. To constrain the nature of each X-ray source, we carried out cross-correlations with multi-wavelength data sets. We searched overlapping Hubble Space Telescope observations for optical counterparts to our X-ray detections to provide preliminary classifications for each X-ray source as a likely X-ray binary, background active galactic nucleus, supernova remnant, or foreground star.

ID: 136406
Type: article
Authors: Williams, Benjamin F.; Wold, Brian; Haberl, Frank; Garofali, Kristen; Blair, William P.; Gaetz, Terrance J.; Kuntz, K. D.; Long, Knox S.; Pannuti, Thomas G.; Pietsch, Wolfgang; Plucinsky, Paul P.; Winkler, P. Frank
Abstract: We have obtained a deep 8 field XMM-Newton mosaic of M33 covering the galaxy out to the D₂₅ isophote and beyond to a limiting 0.2-4.5 keV unabsorbed flux of 5 × 10^-16 erg cm^-2 s^-1 (L \gt 4 × 10³⁴ erg s^-1 at the distance of M33). These data allow complete coverage of the galaxy with high sensitivity to soft sources such as diffuse hot gas and supernova remnants (SNRs). Here, we describe the methods we used to identify and characterize 1296 point sources in the 8 fields. We compare our resulting source catalog to the literature, note variable sources, construct hardness ratios, classify soft sources, analyze the source density profile, and measure the X-ray luminosity function (XLF). As a result of the large effective area of XMM-Newton below 1 keV, the survey contains many new soft X-ray sources. The radial source density profile and XLF for the sources suggest that only ~15% of the 391 bright sources with L \gt 3.6 × 10³⁵ erg s^-1 are likely to be associated with M33, and more than a third of these are known SNRs. The log(N)-log(S) distribution, when corrected for background contamination, is a relatively flat power law with a differential index of 1.5, which suggests that many of the other M33 sources may be high-mass X-ray binaries. Finally, we note the discovery of an interesting new transient X-ray source, which we are unable to classify.

ID: 123019
Type: article
Authors: Sankrit, Ravi; Raymond, John C.; Bautista, Manuel; Gaetz, Terrance J.; Williams, Brian J.; Blair, William P.; Borkowski, Kazimierz J.; Long, Knox S.
Abstract: We report on spectra of two positions in the XA region of the Cygnus Loop supernova remnant obtained with the InfraRed Spectrograph on the Spitzer Space Telescope. The spectra span the 10-35 μm wavelength range, which contains a number of collisionally excited forbidden lines. These data are supplemented by optical spectra obtained at the Whipple Observatory and an archival UV spectrum from the International Ultraviolet Explorer. Coverage from the UV through the IR provides tests of shock wave models and tight constraints on model parameters. Only lines from high ionization species are detected in the spectrum of a filament on the edge of the remnant. The filament traces a 180 km s^-1 shock that has just begun to cool, and the oxygen to neon abundance ratio lies in the normal range found for Galactic H II regions. Lines from both high and low ionization species are detected in the spectrum of the cusp of a shock-cloud interaction, which lies within the remnant boundary. The spectrum of the cusp region is matched by a shock of about 150 km s^-1 that has cooled and begun to recombine. The post-shock region has a swept-up column density of about 1.3 × 10¹⁸ cm^-2, and the gas has reached a temperature of 7000-8000 K. The spectrum of the Cusp indicates that roughly half of the refractory silicon and iron atoms have been liberated from the grains. Dust emission is not detected at either position. Based on observations made with the Spitzer Space Telescope.

ID: 114791
Type: article
Authors: Binder, B.; Williams, B. F.; Eracleous, M.; Gaetz, T. J.; Kong, A. K. H.; Skillman, E. D.; Weisz, D. R.
Abstract: We present a comprehensive X-ray point-source catalog of NGC 404 obtained as part of the Chandra Local Volume Survey. A new 97 ks Chandra ACIS-S observation of NGC 404 was combined with archival observations for a total exposure of ~123 ks. Our survey yields 74 highly significant X-ray point sources and is sensitive to a limiting unabsorbed luminosity of ~6 × 10³⁵ erg s^-1 in the 0.35-8 keV band. To constrain the nature of each X-ray source, cross-correlations with multi-wavelength data were generated. We searched overlapping Hubble Space Telescope observations for optical counterparts to our X-ray detections, but find only two X-ray sources with candidate optical counterparts. We find 21 likely low-mass X-ray binaries (LMXBs), although this number is a lower limit due to the difficulties in separating LMXBs from background active galactic nuclei. The X-ray luminosity functions (XLFs) in both the soft and hard energy bands are presented. The XLFs in the soft band (0.5-2 keV) and the hard band (2-8 keV) have a limiting luminosity at the 90% completeness limit of 10³⁵ erg s^-1 and 10³⁶ erg s^-1, respectively, significantly lower than previous X-ray studies of NGC 404. We find the XLFs to be consistent with those of other X-ray populations dominated by LMXBs. However, the number of luminous (>10³⁷ erg s^-1) X-ray sources per unit stellar mass in NGC 404 is lower than is observed for other galaxies. The relative lack of luminous XRBs may be due to a population of LMXBs with main-sequence companions formed during an epoch of elevated star formation ~0.5 Gyr ago.

ID: 118386
Type: article
Authors: Raymond, John C.; Ghavamian, Parviz; Williams, Brian J.; Blair, William P.; Borkowski, Kazimierz J.; Gaetz, Terrance J.; Sankrit, Ravi
Abstract: Dust grains are sputtered away in the hot gas behind shock fronts in supernova remnants (SNRs), gradually enriching the gas phase with refractory elements. We have measured emission in C IV ?1550 from C atoms sputtered from dust in the gas behind a non-radiative shock wave in the northern Cygnus Loop. Overall, the intensity observed behind the shock agrees approximately with predictions from model calculations that match the Spitzer 24 µm and the X-ray intensity profiles. Thus, these observations confirm the overall picture of dust destruction in SNR shocks and the sputtering rates used in models. However, there is a discrepancy in that the C IV intensity 10'' behind the shock is too high compared with the intensities at the shock and 25'' behind it. Variations in the density, hydrogen neutral fraction, and the dust properties over parsec scales in the pre-shock medium limit our ability to test dust destruction models in detail.

ID: 115652
Type: article
Authors: Sasaki, M.; Plucinsky, Paul P.; Gaetz, T. J.; Bocchino, F.
Abstract: Context. We study the X-ray emission of the Galactic supernova remnant (SNR) CTB 109 (G109.1-1.0), which is well-known for its enigmatic half-shell morphology both in radio and in X-rays and is associated with the anomalous X-ray pulsar (AXP) 1E 2259+586.
Aims: We want to understand the origin of the X-ray bright feature inside the SNR called the Lobe and the details of the interaction of the SNR shock wave with the ambient interstellar medium (ISM).
Methods: The Lobe and the northeastern part of the SNR were observed with Chandra ACIS-I. We analysed the spectrum of the X-ray emission by dividing the entire observed emission into small regions. The X-ray emission is best reproduced with one-component or two-component non-equilibrium ionisation models depending on the position. In the two-component model, one emission component represents the shocked ISM and the other the shocked ejecta.
Results: We detect enhanced element abundances, in particular for Si and Fe, in and around the Lobe. There is one particular region next to the Lobe with a high Si abundance of 3.3 (2.6-4.0) times the solar value. This is the first, unequivocal detection of ejecta in CTB 109.
Conclusions: The new Chandra data confirm that the Lobe was created by the interaction of the SNR shock and the supernova ejecta with a dense and inhomogeneous medium in the environment of SNR CTB 109. The newly calculated age of the SNR is t ? 1.4 × 10⁴ yr.

ID: 113700
Type: article
Authors: Binder, B.; Williams, B. F.; Eracleous, M.; Gaetz, T. J.; Plucinsky, Paul P.; Skillman, E. D.; Dalcanton, J. J.; Anderson, S. F.; Weisz, D. R.; Kong, A. K. H.
Abstract: We present the source catalog of a new Chandra ACIS-I observation of NGC 300 obtained as part of the Chandra Local Volume Survey. Our 63 ks exposure covers ~88% of the D ₂₅ isophote (R ? 6.3 kpc) and yields a catalog of 95 X-ray point sources detected at high significance to a limiting unabsorbed 0.35-8 keV luminosity of ~10³⁶ erg s^-1. Sources were cross-correlated with a previous XMM-Newton catalog, and we find 75 "X-ray transient candidate" sources that were detected by one observatory, but not the other. We derive an X-ray scale length of 1.7 ± 0.2 kpc and a recent star formation rate of 0.12 M _&sun; yr^-1 in excellent agreement with optical observations. Deep, multi-color imaging from the Hubble Space Telescope, covering ~32% of our Chandra field, was used to search for optical counterparts to the X-ray sources, and we have developed a new source classification scheme to determine which sources are likely X-ray binaries, supernova remnants, and background active galactic nucleus candidates. Finally, we present the X-ray luminosity functions (XLFs) at different X-ray energies, and we find the total NGC 300 X-ray point-source population to be consistent with other late-type galaxies hosting young stellar populations (lsim 50 Myr). We find that XLF of sources associated with older stellar populations has a steeper slope than the XLF of X-ray sources coinciding with young stellar populations, consistent with theoretical predictions.

ID: 109709
Type: article
Authors: Binder, B.; Williams, B. F.; Eracleous, M.; Garcia, Michael R.; Anderson, S. F.; Gaetz, Terrance J.
Abstract: We have obtained a 63 ks Chandra ACIS-I observation of the Wolf-Rayet + black hole binary NGC 300 X-1. We measure rapid low-amplitude variability in the 0.35-8 keV light curve. The power density spectrum has a power-law index γ = 1.02 ± 0.15 consistent with an accreting black hole in a steep power-law state. When compared to previous studies of NGC 300 X-1 performed with XMM-Newton, we find the source at the low end of the previously measured 0.3-10 keV luminosity. The spectrum of NGC 300 X-1 is dominated by a power law (Γ = 2.0

ID: 102308
Type: article
Authors: Binder, B.; Williams, B. F.; Eracleous, M.; Seth, A. C.; Dalcanton, J. J.; Skillman, E. D.; Weisz, D. R.; Anderson, S. F.; Gaetz, T. J.; Plucinsky, Paul P.
Abstract: We present the results of a 100 ks Chandra observation of the NGC 404 nuclear region. The long exposure and excellent spatial resolution of Chandra have enabled us to critically examine the nuclear environment of NGC 404, which is known to host a nuclear star cluster and potentially

ID: 108027
Type: article
Authors: Binder, B.; Williams, B. F.; Kong, A. K. H.; Gaetz, T. J.; Plucinsky, Paul P.; Dalcanton, J. J.; Weisz, D. R.
Abstract: We present the results of a 63 ks Chandra observation of the "supernova impostor" SN 2010da four months after it was first observed on 2010 May 24. We detect an X-ray source at ~7? confidence coincident with the optical location of the outburst. Our imaging analysis has revealed a hard central point source, surrounded by soft diffuse emission extending ~8'' north of the central source. The diffuse emission has a hardness ratio (~-0.4), 0.35-2 keV luminosity (~6 × 10³⁵ erg s^-1), and size (~70 pc) consistent with that of a supernova remnant, although the low number of counts prohibits detailed spectral modeling. The 0.5-6 keV spectrum of the central point source is well described by both a power law with ? ~0 and a blackbody with kT ~ 1.8 keV, with no evidence for intrinsic absorption beyond the Galactic column. We estimate the 0.3-10 keV luminosity to be

ID: 81765
Type: article
Authors: Karovska, Margarita; Gaetz, Terrance J.; Carilli, Christopher L.; Hack, Warren; Raymond, John C.; Lee, Nicholas P.