arXiv subjects

Terrance J. Gaetz

Publications and source records attributed to Terrance J. Gaetz.

At least 19 recordsLinked to original sources

arXiv2025

Chandra Large Project Observations of the Supernova Remnant N132D: Measuring the Expansion of the Forward Shock

We present results from the Chandra X-ray Observatory Large Project (878 ks in 28 observations) of the Large Magellanic Cloud supernova remnant N132D. We measure the expansion of the forward shock in the bright southern rim to be $0.\!^{\prime\prime}10 \pm 0.\!^{\prime\prime}02$ over the $\sim14.5$ yr baseline, which corresponds to a velocity of $1620\pm400~\mathrm{km\,s^{-1}}$ after accounting for several instrumental effects. We measure an expansion of $0.\!^{\prime\prime}23 \pm 0.\!^{\prime\prime}02$ and a shock velocity of $3840\pm260~\mathrm{km\,s^{-1}}$ for two features in an apparent blowout region in the northeast. The emission-measure-weighted average temperature inferred from X-ray spectral fits to regions in the southern rim is $0.95\pm0.17$ keV, consistent with the electron temperature implied by the shock velocity after accounting for Coulomb equilibration and adiabatic expansion. In contrast, the emission-measure-weighted average temperature for the northeast region is $0.77\pm0.04$ keV, which is significantly lower than the value inferred from the shock velocity. We fit 1-D evolutionary models for the shock in the southern rim and northeast region, using the measured radius and propagation velocity into a constant density and power-law profile circumstellar medium. We find good agreement with the age of $\sim2500$ years derived from optical expansion measurements for explosion energies of $1.5-3.0 \times 10^{51}\,\mathrm{erg}$, ejecta masses of $2-6 \,\mathrm{M_{\odot}}$ and ambient medium densities of $\sim0.33-0.66$ $\mathrm{amu~cm}^{-3}$ in the south and $\sim0.01-0.02$ $\mathrm{amu~cm}^{-3}$ in the northeast assuming a constant density medium. These results are consistent with previous studies that suggested the progenitor of N132D was an energetic supernova that exploded into a pre-existing cavity.

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arXiv2025

XMM-Newton Observations of the High Temperature Plasma in the Large Magellanic Cloud Supernova Remnant N132D

We present an analysis of the archival XMM-Newton observations of the Large Magellanic Cloud (LMC) supernova remnant N132D totaling more than 500ks. We focus on the high temperature plasma ($kt\sim 4.5$keV) that is responsible for the high energy continuum and exciting the Fe K emission. An image analysis shows that the Fe K emission is mainly concentrated in the southern part of the remnant interior to the region defined by the forward shock. This Fe K distribution would be consistent with an asymmetric distribution of the Fe ejecta and/or an asymmetric interaction between the reverse shock and the Fe ejecta. We compare the EPIC-pn and EPIC-MOS spectra in the 3.0 -- 12.0keV bandpass with a model based on RGS data plus a higher temperature component, in collisional ionization equilibrium (CIE), or non-equilibrium (NEI) (both ionizing and recombining). We find that the data are equally well-fitted by the CIE and ionizing models. Assuming the CIE and ionizing spectral models, the Fe in this high temperature component is significantly enhanced with respect to typical LMC abundances. We can place only an upper limit on the neutral Fe K line. We conclude that the Fe~K emission is due to ejecta heated by the reverse shock given the spatial distribution, relatively high temperature, and enhanced abundance. We estimate the progenitor mass based on the Ca/Fe and Ni/Fe mass ratios to be $13\le M_P \le 15 M_\odot$.

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arXiv2022

The Proper Motion of the Pulsar J1124-5916 in the Galactic Supernova Remnant G292.0+1.8

We present the first direct measurement of the proper motion of pulsar J1124-5916 in the young, oxygen-rich supernova remnant G292.0+1.8. Using deep Chandra ACIS-I observations from 2006 and 2016, we measure a positional change of $0.^{\prime\prime}21$ $\pm$ $0.^{\prime\prime}05$ over the $\sim$ 10 year baseline, or $\sim$ $0.^{\prime\prime}02$ yr$^{-1}$. At a distance of 6.2 $\pm$ 0.9 kpc, this corresponds to a kick velocity in the plane of the sky of $\mathrm{612\pm 152\,km \, s^{-1}}$. We compare this direct measurement against the velocity inferred from estimates based on the center of mass of the ejecta. Additionally, we use this new proper motion measurement to compare the motion of the neutron star to the center of expansion of the optically emitting ejecta. We derive an age estimate for the supernova remnant of $\gtrsim$ 2000 years. The high measured kick velocity is in line with recent studies of high proper motion neutron stars in other Galactic supernova remnants, and consistent with a hydrodynamic origin to the neutron star kick.

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arXiv2021

First extragalactic measurement of the turbulence driving parameter: ALMA observations of the star-forming region N159E in the Large Magellanic Cloud

Studying the driving modes of turbulence is important for characterizing the impact of turbulence in various astrophysical environments. The driving mode of turbulence is parameterized by $b$, which relates the width of the gas density PDF to the turbulent Mach number; $b\approx 1/3$, $1$, and $0.4$ correspond to driving that is solenoidal, compressive, and a natural mixture of the two, respectively. In this work, we use high-resolution (sub-pc) ALMA $^{12}$CO ($J$ = $2-1$), $^{13}$CO ($J$ = $2-1$), and C$^{18}$O ($J$ = $2-1$) observations of filamentary molecular clouds in the star-forming region N159E (the Papillon Nebula) in the Large Magellanic Cloud (LMC) to provide the first measurement of turbulence driving parameter in an extragalactic region. We use a non-local thermodynamic equilibrium (NLTE) analysis of the CO isotopologues to construct a gas density PDF, which we find to be largely log-normal in shape with some intermittent features indicating deviations from lognormality. We find that the width of the log-normal part of the density PDF is comparable to the supersonic turbulent Mach number, resulting in $b \approx 0.9$. This implies that the driving mode of turbulence in N159E is primarily compressive. We speculate that the compressive turbulence could have been powered by gravo-turbulent fragmentation of the molecular gas, or due to compression powered by H I flows that led to the development of the molecular filaments observed by ALMA in the region. Our analysis can be easily applied to study the nature of turbulence driving in resolved star-forming regions in the local as well as the high-redshift Universe.

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arXiv2021

Spatial and Temporal Variations of the Chandra ACIS Particle-Induced Background and Development of a Spectral-Model Generation Tool

In X-ray observations, estimation of the particle-induced background is important especially for faint and/or diffuse sources. Although software exists to generate total (sky and detector) background data suitable for a given Chandra ACIS observation, no public software exists to model the particle-induced background separately. We aim to understand the spatial and temporal variations of the particle-induced background of Chandra ACIS obtained in the two data modes, VFAINT and FAINT. Observations performed with ACIS in the stowed position shielded from the sky and the Chandra Deep Field South data sets are used. The spectra are modeled with a combination of the instrumental lines of Al, Si, Ni, and Au and continuum components. Similar spatial variations of the spectral shape are found in VFAINT and FAINT data, which are mainly due to inappropriate correction of charge transfer inefficiency for events that convert in the frame-store regions as explained by Bartalucci et al. 2014. Temporal variation of the spectral hardness ratio is found to be $\sim 10\%$ at maximum, which seems to be largely due to solar activity. We model this variation by modifying the spectral hardnesses according to the total count rate. Incorporating these properties, we have developed a tool ``mkacispback'' to generate the particle-induced background spectral model corresponding to an arbitrary celestial observation. As an example application, we use the background spectrum produced by the mkacispback tool in an analysis of the Cosmic X-ray Background in the CDF-S observations. We find an intensity of 3.10 (2.98--$3.21)\times 10^{-12}$ erg s$^{-1}$ cm$^{-2}$ deg$^{-2}$ in the 2--8 keV band, consistent with or lower than previous estimates. The tool mkacispback is available at https://github.com/hiromasasuzuki/mkacispback.

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arXiv2020

On the X-ray Properties of the Putative Central Compact Object in 1E 0102.2-7219

We have analyzed the archival Chandra X-ray Observatory observations of the compact feature in the Small Magellanic Cloud supernova remnant (SNR) 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, 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 which have significantly enhanced abundances of O, Ne, \& 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 non-equilibrium ionization thermal model with two classes of models that fit the data equally well. One class of models has a temperature of $kT\sim0.79$ keV, an ionization timescale of $\sim3\times10^{11}\,\mathrm{cm}^{-3}\mathrm{s}$, and marginal evidence for enhanced abundances of O and Ne and the other has a temperature of $kT\sim0.91$ keV, an ionization timescale of $\sim7\times10^{10}\,\mathrm{cm}^{-3}\mathrm{s}$, 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.

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arXiv2019

The Expansion of the Forward Shock of 1E 0102.2-7219 in X-rays

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 Spectromete(ACIS) observations from 1999-2016. We estimate an expansion rate of 0.025%\pm0.006%yr^{-1} and a blast-wave velocity of 1.61\pm0.37\times10^3 km s^{-1}. Assuming partial electron-ion equilibration via Coulomb collisions and cooling due to adiabatic expansion, this velocity implies a postshock electron temperature of 0.84\pm0.20 keV which is consistent with the estimate of 0.68\pm0.05 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 \msol) 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 \sim 1700 yr, explosion energies 0.87-2.61\times10^{51} erg, ambient densities 0.85-2.54 amu cm^{-3}, swept-up masses 22-66 \msol, and unshocked-ejecta masses 0.05-0.16 \msol. For the power-law density profile, we find an age of \sim 2600 yr, explosion energies 0.34-1.02\times10^{51} erg, densities 0.22-0.66 amu cm^{-3} at the blast wave, swept-up masses 17-52 \msol, and unshocked-ejecta masses 0.06-0.18 \msol. Assuming the true explosion energy was 0.5-1.5\times10^{51} erg, ejecta masses 2-3.5 \msol are favored for the constant density case and 3-6 \msol 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 \msol, offering a possible explanation for the lack of Fe emission observed in X-rays.

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arXiv2019

Deep Chandra survey of the Small Magellanic Cloud. III. Formation efficiency of High-Mass X-ray binaries

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 127 X-ray sources with detections in our \chandra X-ray Visionary Program (XVP), supplemented by 14 additional (likely and confirmed) HMXBs identified by \cite{2016A&A...586A..81H} that fall within the XVP area, but are not either detected in our survey (9 sources) or matched with any XVP source that has at least one OB counterpart in the OGLE-III catalog (5 sources). Specifically, we examine the number ratio of the HMXBs [N(HMXBs)] to {\it (a)} the number of OB stars, {\it (b)} the local star-formation rate (SFR), and {\it (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 $\sim$40--60\,Myr, and then gradually decreases. The peak formation efficiency N(HMXB)/SFR is (49 $\pm$ 14) $[10^{-5}~{\rm M_{\odot}/yr}]^{-1}$, in good agreement with previous estimates of the average formation efficiency in the broad $\sim$20--60\,Myr age range. The frequency of HMXBs is a factor of 8$\times$ higher than at $\sim$10\,Myr, and 4$\times$ higher than at $\sim$260\,Myr, i.e. at earlier and later epochs, respectively.

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arXiv2017

Supernova Remnants in M33: X-ray Properties as Observed by XMM-Newton

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 8 fields in M33 covering all of the area within the D$_{25}$ contours, and with a typical luminosity of 7.1$\times$10$^{34}$ 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$σ$ 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 timescales, 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 timescales, and small-scale environmental effects appear to cause more significant differences between X-ray luminosity distributions. In addition, we analyze the X-ray detectability of SNRs, and find that in M33 SNRs with higher [SII]/H$α$ ratios, as well as those with smaller galactocentric distances, are more detectable in X-rays.

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arXiv2016

The Effect of Variability on X-Ray Binary Luminosity Functions: Multiple Epoch Observations of NGC 300 with Chandra

We have obtained three epochs of Chandra ACIS-I observations (totaling $\sim$184 ks) of the nearby spiral galaxy NGC~300 to study the logN-logS distributions of its X-ray point source population down to $\sim$2$\times$10$^{-15}$ erg s$^{-1}$ cm$^{-2}$ in the 0.35-8 keV band (equivalent to $\sim$10$^{36}$ erg s$^{-1}$). The individual epoch logN-logS distributions are best described as the sum of a background 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 $\sim$2). The differential power law index of $\sim$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 $\sim$1.7, a bright-end index of $\sim$2.8-4.9, and a break flux of $\sim$8$\times10^{-15}$ erg s$^{-1}$ cm$^{-2}$ ($\sim$4$\times10^{36}$ erg s$^{-1}$), suggesting 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 $\sim$1-3% of the Eddington rate.

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arXiv2015

A Deep XMM-Newton Survey of M33: Point Source Catalog, Source Detection and Characterization of Overlapping Fields

We have obtained a deep 8-field XMM-Newton mosaic of M33 covering the galaxy out to the D$_{25}$ isophote and beyond to a limiting 0.2--4.5 keV unabsorbed flux of 5$\times$10$^{-16}$ erg cm$^{-2}$ s$^{-1}$ (L${>}$4$\times$10$^{34}$ 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. 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. 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 X-ray luminosity function for the sources suggests that only $\sim$15% of the 391 bright sources with L${>}$3.6$\times$10$^{35}$ erg s$^{-1}$ are likely to be associated with M33, and more than a third of these are known supernova remnants. 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 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.

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arXiv2013

Grain Destruction in a Supernova Remnant Shock Wave

Dust grains are sputtered away in the hot gas behind shock fronts in supernova remnants, gradually enriching the gas phase with refractory elements. We have measured emission in C IV $λ$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 micron 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 CIV intensity 10" behind the shock is too high compared to 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.

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arXiv2013

Chandra observation of the Galactic supernova remnant CTB 109 (G109.1-1.0)

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) 1E2259+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 dense and inhomogeneous medium in the environment of SNR CTB 109. The newly calculated age of the SNR is t ~ 1.4 x 10^4 yr.

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arXiv2012

The Chandra Local Volume Survey: The X-ray Point Source Catalog of NGC 300

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 D25 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 ~10^36 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 Msun 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 AGN 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 (<50 Myr). We find 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.

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arXiv2011

A Deep Chandra View of the NGC 404 Central Engine

We present the results of a 100 ks {\it Chandra} observation of the NGC 404 nuclear region. The long exposure and excellent spatial resolution of {\it Chandra} has enabled us to critically examine the nuclear environment of NGC 404, which is known to host a nuclear star cluster and potentially an intermediate-mass black hole (on the order of a few times $10^5$ \Msun). We find two distinct X-ray sources: a hard, central point source coincident with the optical and radio centers of the galaxy, and a soft extended region that is coincident with areas of high H$α$ emission and likely recent star formation. When we fit the 0.3-8 keV spectra of each region separately, we find the hard nuclear point source to be dominated by a power law (\PL = 1.88), while the soft off-nuclear region is best fit by a thermal plasma model ($kT$ = 0.67 keV). We therefore find evidence for both a power law component and hot gas in the nuclear region of NGC 404. We estimate the 2-10 keV luminosity to be 1.3$^{+0.8}_{-0.5}\times10^{37}$ erg s$^{-1}$. A low-level of diffuse X-ray emission is detected out to $\sim$15\as ($\sim$0.2 kpc) from the nucleus. We compare our results to the observed relationships between power law photon index and Eddington ratio for both X-ray binaries and low luminosity active galaxies and find NGC 404 to be consistent with other low luminosity active galaxies. We therefore favor the conclusion that NGC 404 harbors an intermediate-mass black hole accreting at a very low level.

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arXiv2010

The Chandra ACIS Survey of M33: X-ray, Optical and Radio Properties of the Supernova Remnants

M33 contains a large number of emission nebulae identified as supernova remnants (SNRs) based on the high [S II]:Ha ratios characteristic of shocked gas. Using Chandra data from the ChASeM33 survey with a 0.35-2 keV sensitivity of about 2 x 10**34 ergs/s, we have detected 82 of 137 SNR candidates, yielding confirmation of (or at least strongly support for) their SNR identifications. This provides the largest sample of remnants detected at optical and X-ray wavelengths in any galaxy, including the Milky Way. A spectral analysis of the seven X-ray brightest SNRs reveals that two, G98-31 and G98-35, have spectra that appear to indicate enrichment by ejecta from core-collapse supernova explosions. In general, the X-ray detected SNRs have soft X-ray spectra compared to the vast majority of sources detected along the line of sight to M33. It is unlikely that there are any other undiscovered thermally dominated X-ray SNRs with luminosities in excess of about 4 x 10**35 ergs/s in the portions of M33 covered by the ChASeM33 survey. We have used a combination of new and archival optical and radio observations to attempt to better understand why some objects are detected as X-ray sources and others are not. We have also developed a morphological classification scheme for the optically-identified SNRs, and discuss the efficacy of this scheme as a predictor of X-ray detectability. Finally, we have compared the SNRs found in M33 to those that have been observed in the Galaxy and the Magellanic Clouds. There are no close analogs of Cas A, Kepler's SNR, Tycho's SNR or the Crab Nebula in the regions of M33 surveyed, but we have found an X-ray source with a power law spectrum coincident with a small-diameter radio source that may be the first pulsar-wind nebula recognized in M33.

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arXiv2008

The Chandra ACIS Survey of M33 (ChASeM33): Transient X-ray Sources Discovered in M33

The Chandra ACIS Survey of M33 (ChASeM33) has acquired 7 fields of ACIS data covering M33 with 200 ks of exposure in each field. A catalog from the first 10 months of data, along with archival Chandra observations dating back to the year 2000, is currently available. We have searched these data for transient sources that are measured to have a 0.35-8.0 keV unabsorbed luminosity of at least 4$\times10^{35}$ erg s$^{-1}$ in one epoch and are not detected in another epoch. This set of the survey data has yielded seven such sources, including one previously-known supersoft source. We analyzed XMM-Newton data from the archive distributed over the years 2000 to 2003 to search for recurrent outbursts and to get a spectrum for the supersoft transient. We find only one recurrent transient in our sample. The X-ray spectra, light curves, and optical counterpart candidates of two of the other sources suggest that they are high-mass X-ray binaries. Archival Spitzer photometry and high X-ray absorption suggest that one of the sources is a highly variable background active galactic nucleus. The other three sources are more difficult to classify. The bright transient population of M33 appears to contain a large fraction of high-mass X-ray binaries compared with the transient populations of M31 and the Galaxy, reflecting the later morphology of M33.

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arXiv2007

Chandra ACIS Survey of M33 (ChASeM33): A First Look

We present an overview of the Chandra ACIS Survey of M33 (ChASeM33): A Deep Survey of the Nearest Face-on Spiral Galaxy. The 1.4 Ms survey covers the galaxy out to $R \approx 18\arcmin (\approx 4$ kpc). These data provide the most intensive, high spatial resolution assessment of the X-ray source populations available for the confused inner regions of M33. Mosaic images of the ChASeM33 observations show several hundred individual X-ray sources as well as soft diffuse emission from the hot interstellar medium. Bright, extended emission surrounds the nucleus and is also seen from the giant \hii regions NGC 604 and IC 131. Fainter extended emission and numerous individual sources appear to trace the inner spiral structure. The initial source catalog, arising from $\sim$~2/3 of the expected survey data, includes 394 sources significant at the $3σ$ confidence level or greater, down to a limiting luminosity (absorbed) of $\sim$1.6\ergs{35} (0.35 -- 8.0 keV). The hardness ratios of the sources separate those with soft, thermal spectra such as supernova remnants from those with hard, non-thermal spectra such as X-ray binaries and background active galactic nuclei. Emission extended beyond the Chandra point spread function is evident in 23 of the 394 sources. Cross-correlation of the ChASeM33 sources against previous catalogs of X-ray sources in M33 results in matches for the vast majority of the brighter sources and shows 28 ChASeM33 sources within 10\arcsec of supernova remnants identified by prior optical and radio searches. This brings the total number of such associations to 31 out of 100 known supernova remnants in M33.

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