Advanced CCD Imaging Spectrometer Research Articles

Superluminal Proper Motion in the X-Ray Jet of Centaurus A

The structure of the jet in Cen A is likely better revealed in X-rays than in the radio band, which is usually used to investigate jet proper motions. In this paper, we analyze Chandra Advanced CCD Imaging Spectrometer observations of Cen A from 2000 to 2022 and develop an algorithm for systematically fitting the proper motions of its X-ray jet knots. Most of the knots had an apparent proper motion below the detection limit. However, one knot at a transverse distance of 520 pc had an apparent superluminal proper motion of 2.7 ± 0.4c. This constrains the inclination of the jet to be i < 41° ± 6° and the velocity of this knot to be β > 0.94 ± 0.02. This agrees well with the inclination measured in the inner jet by the Event Horizon Telescope but contradicts previous estimates based on jet and counterjet brightness. It also disagrees with the proper motion of the corresponding radio knot, of 0.8 ± 0.1c, which further indicates that the X-ray and radio bands trace distinct structures in the jet. There are four prominent X-ray jet knots closer to the nucleus, but only one of these is inconsistent with being stationary. A few jet knots also have a significant proper-motion component in the nonradial direction. This component is typically larger closer to the center of the jet. We also detect brightness and morphology variations at a transverse distance of 100 pc from the nucleus.

High-resolution X-ray spectra of the compact binary supersoft X-ray source CAL 87

In this study we present an analysis of the archival X-ray data of the eclipsing supersoft X-ray binary CAL 87 observed with the Chandra Advanced CCD Imaging Spectrometer (ACIS) camera and Low Energy Transmission Grating (LETG) in 2001 August and with XMM-Newton in 2003 April. The high-resolution X-ray spectra are almost unchanged on the two different dates. The average unabsorbed X-ray luminosity during the exposure was 4.64 − 5.46 × 1036 ergs s−1 in 2001 and 4.54 − 4.82 × 1036 ergs s−1 in 2003, with prominent and redshifted emission lines, mostly of nitrogen, oxygen, iron, and argon, contributing to at least 30% of the X-ray flux. The continuum X-ray flux is at least an order of magnitude too low for a hot hydrogen-burning white dwarf (WD). However, the continuum flux is consistent with Thomson-scattering reflecting about 5% of the light of a hydrogen-burning WD with effective temperature of 800 000 K and a mass of ∼1.2 M⊙. It has been noted that a large Thomson-scattering corona explains the X-ray eclipse of CAL 87, in which the size of the eclipsed region is found to be on the order of a solar radius. The emission lines originate in an even more extended region beyond the eclipsed central X-ray source; the emission spectrum is very complex, with unusual line ratios.

The Chandra Source Catalog Release 2 Series

The Chandra Source Catalog (CSC) is a virtual X-ray astrophysics facility that enables both detailed individual source studies and statistical studies of large samples of X-ray sources detected in Advanced CCD Imaging Spectrometer and High Resolution Camera-I imaging observations obtained by the Chandra X-ray Observatory. The catalog provides carefully curated, high-quality, and uniformly calibrated and analyzed tabulated positional, spatial, photometric, spectral, and temporal source properties, as well as science-ready X-ray data products. The latter includes multiple types of source- and field-based FITS format products that can be used as a basis for further research, significantly simplifying follow-up analysis of scientifically meaningful source samples. We discuss in detail the algorithms used for the CSC Release 2 Series, including CSC 2.0, which includes 317,167 unique X-ray sources on the sky identified in observations released publicly through the end of 2014, and CSC 2.1, which adds Chandra data released through the end of 2021 and expands the catalog to 407,806 sources. Besides adding more recent observations, the CSC Release 2 Series includes multiple algorithmic enhancements that provide significant improvements over earlier releases. The compact source sensitivity limit for most observations is ∼5 photons over most of the field of view, which is ∼2× fainter than Release 1, achieved by coadding observations and using an optimized source detection approach. A Bayesian X-ray aperture photometry code produces robust fluxes even in crowded fields and for low-count sources. The current release, CSC 2.1, is tied to the Gaia-CRF3 astrometric reference frame for the best sky positions for catalog sources.

SAUNAS. I. Searching for Low Surface Brightness X-Ray Emission with Chandra/ACIS

We present Selective Amplification of Ultra Noisy Astronomical Signal (SAUNAS), a pipeline designed for detecting diffuse X-ray emission in the data obtained with the Advanced CCD Imaging Spectrometer (ACIS) of the Chandra X-ray Observatory. SAUNAS queries the available observations in the Chandra archive and performs photometric calibration, point-spread function modeling and deconvolution, point-source removal, adaptive smoothing, and background correction. This pipeline builds on existing and well-tested software including CIAO, VorBin, and LIRA. We characterize the performance of SAUNAS through several quality performance tests and demonstrate the broad applications and capabilities of SAUNAS using two galaxies already known to show X-ray-emitting structures. SAUNAS successfully detects the 30 kpc X-ray superwind of NGC 3079 using Chandra/ACIS data sets, matching the spatial distribution detected with more sensitive XMM-Newton observations. The analysis performed by SAUNAS reveals an extended low surface brightness source in the field of UGC 5101 in the 0.3–1.0 keV and 1.0–2.0 keV bands. This source is potentially a background galaxy cluster or a hot gas plume associated with UGC 5101. SAUNAS demonstrates its ability to recover previously undetected structures in archival data, expanding exploration into the low surface brightness X-ray Universe with Chandra/ACIS.

The Chandra Cygnus OB2 Legacy Survey: Design and X-Ray Point-source Catalog

The Cygnus OB2 association is the largest concentration of young and massive stars within 2 kpc of the Sun, including an estimated ∼65 O-type stars and hundreds of OB stars. The Chandra Cygnus OB2 Legacy Survey is a large imaging program undertaken with the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory. The survey has imaged the central 0.5 deg2 of the Cyg OB2 association with an effective exposure of ∼120 ks and an outer 0.35 deg2 area with an exposure of ∼60 ks. Here we describe the survey design and observations, discuss the data reduction and source detection, and present a catalog of ∼8000 X-ray point sources. The survey design employs a grid of 36 heavily (∼50%) overlapping pointings, a method that overcomes Chandra's low off-axis sensitivity and produces a highly uniform exposure over the inner 0.5 deg2. The full X-ray catalog is described here and is made available online.

Constraints on neutron star superfluidity from the cooling neutron star in Cassiopeia A using all Chandra ACIS-S observations

ABSTRACT Analysis of Chandra observations of the neutron star (NS) in the centre of the Cassiopeia A supernova remnant taken in the subarray (FAINT) mode of the Advanced CCD Imaging Spectrometer (ACIS) detector performed by Posselt and collaborators revealed, after inclusion of the most recent (2020 May) observations, a significant decrease of the source surface temperature from 2006 to 2020. The obtained cooling rate is consistent with those obtained from analysis of the 2000–2019 data taken in the GRADED mode of the ACIS detector, which is potentially more strongly affected by instrumental effects. We performed a joint spectral analysis using all ACIS data to constrain the NS parameters and cooling rate. We constrain the mass of the Cassiopeia A NS at $M=1.55\pm 0.25\, {\rm M}_\odot$, and its radius at R = 13.5 ± 1.5 km. The surface temperature cooling rate is found to be 2.2 ± 0.3 per cent in 10 yr if the absorbing hydrogen column density is allowed to vary and 1.6 ± 0.2 per cent in 10 yr if it is fixed. The observed cooling can be explained by enhanced neutrino emission from the superfluid NS interior due to Cooper pair formation (CPF) process. Based on analysis of all ACIS data, we constrain the maximal critical temperature of triplet neutron pairing within the NS core at (4–9.5) × 108 K. In accordance with previous studies, the required effective strength of the CPF neutrino emission is at least a factor of 2 higher than existing microscopic calculations suggest.

The 3D X-Ray Ejecta Structure of Tycho's Supernova Remnant

We present our velocity measurements of 59 clumpy, metal-rich ejecta knots in the supernova remnant (SNR) of SN 1572 (Tycho). We use our 450 ks Chandra High Energy Transmission Grating Spectrometer observation to measure the Doppler shift of the He-like Si Kα line-center wavelength emitted from these knots to find their line-of-sight (radial) velocities (v r ). We find v r up to ∼5500 km s−1, with roughly consistent speeds between blueshifted and redshifted ejecta knots. We also measure the proper motions (PMs) for our sample based on archival Chandra Advanced CCD Imaging Spectrometer data taken from 2003, 2009, and 2015. We estimate PMs up to 0.″35 yr−1, which corresponds to a transverse velocity of about 5800 km s−1 for the distance of 3.5 kpc to Tycho. Our v r and transverse velocity measurements imply space velocities of ∼1900–6000 km s−1 for the ejecta knots in Tycho. We estimate a new expansion center of R.A.(J2000) = 00h25m18s.725 ± 1.ˢ157 and decl.(J2000) = +64°08′02.″5 ± 11.″2 from our PM measurements, consistent to within ∼13″ of the geometric center. The distribution of space velocities throughout the remnant suggests that the southeast quadrant generally expands faster than the rest of the SNR. We find that blueshifted knots are projected more in the northern shell, while redshifted knots are more in the southern shell. The previously estimated reverse shock position is consistent with most of our estimated ejecta distribution; however, some ejecta show deviations from the 1D picture of the reverse shock.

Search for Extended Sources in the Images from Chandra X-Ray Observatory Advanced CCD Imaging Spectrometer

We present a convenient tool (ChaSES) which allows to search for extended structures in Chandra X-ray Observatory Advanced CCD Imaging Spectrometer images. The tool relies on DBSCAN clustering algorithm to detect regions with overdensity of photons compared to the background. Here we describe the design and functionality of the tool which we make publicly available on GitHub. We also provide online extensive examples of its applications to the real data.

Late-time X-ray observations of the transient source Cygnus A-2

ABSTRACT We examine Chandra observations of the powerful Fanaroff–Riley class II (FR II) radio galaxy Cygnus A for an X-ray counterpart to the radio transient Cygnus A-2 that was first detected in 2011. Observations are performed using the High-Resolution Camera (HRC) instrument in order to spatially resolve Cygnus A-2 and the central active galactic nucleus (AGN) at a separation of 0.′′42. Simulated images are generated of the emission region, and radial profiles for the region of interest are extracted. A comparison between the simulations and observations reveals no X-ray detection of Cygnus A-2 to a 0.5–7.0 keV flux upper limit of $1.04 \times 10^{-12}\rm \, erg\, cm^{-2}\, s^{-1}$, or a rest-frame 2–10 keV luminosity of $8.6\times 10^{42}\rm \, erg\, s^{-1}$. We estimate the black hole mass of Cygnus A-2 based on our X-ray flux limit and find it to be consistent with a flaring black hole rather than a steadily accreting source. The HRC observations are additionally compared with archival Advanced CCD Imaging Spectrometer (ACIS) data from 2016 to 2017, and both the overall morphology and the flux limits of the AGN complex agree between the two data sets. This consistency is despite the pile-up effect in ACIS which was previously considered to bias the observed morphology of the AGN. The agreement between the data sets demonstrates the viability of utilizing the archival Chandra data of Cygnus A to analyse its AGN at an unprecedented level of precision.

X-Ray Imaging Observations of the High-mass γ-Ray Binary HESS J0632+057

Abstract The Chandra X-Ray Observatory (CXO) imaged the high-mass γ-ray binary HESS J0632+057 with the Advanced CCD Imaging Spectrometer (ACIS). We analyzed the CXO data together with 967 ks of archival Swift-XRT observations. On arcsecond scales we find a hint of asymmetric extended emission. On arcminute scales, a region of extended emission (“the blob”), located ≈ 5 .′ 5 east of the binary, is seen in both the CXO-ACIS and the Swift-XRT images. The blob does not have a counterpart in the radio, near-IR, IR, or optical images. The ACIS spectrum of the blob fits either an absorbed power-law model with Γ ≃ 2.6, or a thermal plasma model with kT ≃ 3 keV. Since the blob’s N H is significantly higher than that of the binary we conclude that the blob and binary are not directly related. The somewhat larger, very deep XRT image suggests that the binary may be located within a shell (or cavity). The four ACIS spectra taken within the ∼20 day interval near the light-curve minimum suggest that N H varies on timescales of days, possibly due to the inhomogeneous circumbinary environment. The XRT spectra extracted from wider orbital phase intervals support significant changes in N H near the light-curve maximum/minimum, which may be responsible for the substantial systematic residuals seen near 1 keV, and provide tentative evidence for an Fe line at 6.4 keV. We find no significant periodic signal in the ACIS data up to 0.156 Hz.

Variable X-Ray Emission of Comet 46P/Wirtanen

Abstract In this paper, we present an analysis of X-ray and optical/ultraviolet (UV) data from the favorable (Δ ∼ 0.077 au) 2018 apparition of comet 46P/Wirtanen. The comet was observed during three different epochs (before, during, and after perihelion) over a 1.5 month period using the X-Ray Telescope (XRT) and Ultraviolet and Optical Telescope (UVOT) instruments on board the Neil Gehrels Swift Observatory and the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-ray Observatory. We clearly detected the comet’s charge exchange-induced emission during the first two epochs (F x = (11.2 ± 0.8) and (6.9 ± 0.5) × 10−13 erg cm−2 s−1, respectively), while only an upper limit on the flux could be placed for the third epoch (F x &lt; 1.38 × 10−13 erg cm−2 s−1). As such, 46P/Wirtanen is one of the least luminous comets to be detected in X-rays. X-ray emission from the charge exchange between solar wind ions and the neutrals in the coma were analyzed against the water-production rate (Swift/UVOT) and space weather measurements. Further analyses of the emission features show that the solar wind properties inferred from the observed X-ray spectrum are in good agreement with those measured by the Advanced Composition Explorer (ACE) and Solar and Heliospheric Observatory (SOHO) spacecraft, proving the approach is reliable for solar wind diagnostics. It is also found that, despite the variability of the comet’s properties (e.g., the water-production rate used as a neutrals density proxy), cometary X-ray emission is primarily modulated by the solar wind.

A Deep Chandra X-Ray Observatory Study of the Millisecond Pulsar Population in the Globular Cluster Terzan 5

Abstract We present an analysis of 745.8 ks of archival Chandra X-Ray Observatory Advanced CCD Imaging Spectrometer data accumulated between 2000 and 2016 of the millisecond pulsar (MSP) population in the rich Galactic globular cluster Terzan 5. Eight of the 38 MSPs with precise positions are found to have plausible X-ray source matches. Despite the deep exposure, the remaining MSPs are either marginally detected or have no obvious X-ray counterparts, which can be attributed to the typically soft thermal spectra of rotation-powered MSPs, which are strongly attenuated by the high intervening absorbing column (∼1022 cm−2) toward the cluster, and in some instances to severe source crowding/blending. For the “redback” MSP binaries PSR J1748−2446P and PSR J1748−2446ad and the “black widow” binary system PSR J1748−2446O, we find clear evidence for large-amplitude X-ray variability at the orbital period consistent with an intrabinary shock origin. The third redback MSP in the cluster, PSR J1748−2446A, shows order-of-magnitude variations in flux on timescales of years, possibly due to state transitions or intense flaring episodes from a magnetically active secondary star.

A Low Signal Detection of X‐Rays From Uranus

AbstractWithin the solar system, X‐ray emissions have been detected from every planet except the Ice Giants: Uranus and Neptune. We analyze the three archival Chandra X‐ray observations of Uranus (each 24–30 ks duration) to date: a stand‐alone Advanced CCD Imaging Spectrometer (ACIS) observation on August 7, 2002 and two High Resolution Camera (HRC) observations on November 11 and 12, 2017 coordinated with optical observations. For the earlier ACIS observation, the Uranus‐coincident photons were clustered in the 0.6–1.1 keV spectral range, consistent with emission from Jupiter and Saturn. To test the significance of the detected signal, we distributed a grid of ∼10,000 Uranus‐sized regions across the field of view (FoV). The number of Uranus‐coincident X‐ray photons in the 0.5–1.2 keV range exceeded 99.9% of Uranus‐sized regions across the FoV (10.2 standard deviations &gt; FoV mean; probability of chance occurrence ∼10−6–10−7). However, the planetary signal was low with only 5 ± 2.2 X‐ray photons against a FoV mean background of 0.16 photons. Without the possibility of energy filtering, the recent HRC observations had a much brighter background (FoV mean ∼10 photons). Consequently, neither of the new observations provided a second unambiguous Uranus detection, although a 40‐min interval of brightening on November 12, 2017 did produce a signal above 99.9% of the FoV. The observed Uranus X‐ray fluxes of 10−15–10−16 erg/cm2/s are consistent with previous observational limits and modeling predictions. These fluxes exceed expectations from scattered solar emission alone, suggesting either a larger X‐ray albedo than Jupiter/Saturn or the possibility of additional X‐ray production processes at Uranus. Further observations are needed to test this.

Long-term X-ray variability of the symbiotic system RT Cru based on Chandra spectroscopy

ABSTRACT RT Cru belongs to the rare class of hard X-ray emitting symbiotics, whose origin is not yet fully understood. In this work, we have conducted a detailed spectroscopic analysis of X-ray emission from RT Cru based on observations taken by the Chandra Observatory using the Low Energy Transmission Grating (LETG) on the High-Resolution Camera Spectrometer (HRC-S) in 2015 and the High Energy Transmission Grating (HETG) on the Advanced CCD Imaging Spectrometer S-array (ACIS-S) in 2005. Our thermal plasma modelling of the time-averaged HRC-S/LETG spectrum suggests a mean temperature of kT ∼ 1.3 keV, whereas kT ∼ 9.6 keV according to the time-averaged ACIS-S/HETG. The soft thermal plasma emission component (∼1.3 keV) found in the HRC-S is heavily obscured by dense materials (&amp;gt;5 × 1023 cm−2). The aperiodic variability seen in its light curves could be due to changes in either absorbing material covering the hard X-ray source or intrinsic emission mechanism in the inner layers of the accretion disc. To understand the variability, we extracted the spectra in the ‘low/hard’ and ‘high/soft’ spectral states, which indicated higher plasma temperatures in the low/hard states of both the ACIS-S and HRC-S. The source also has a fluorescent iron emission line at 6.4 keV, likely emitted from reflection off an accretion disc or dense absorber, which was twice as bright in the HRC-S epoch compared to the ACIS-S. The soft thermal component identified in the HRC-S might be an indication of a jet that deserves further evaluations using high-resolution imaging observations.

Chandra observations of the planetary nebula IC 4593

ABSTRACT The Advanced CCD Imaging Spectrometer (ACIS-S) camera on board the Chandra X-ray Observatory has been used to discover a hot bubble in the planetary nebula (PN) IC 4593, the most distant PN detected by Chandra so far. The data are used to study the distribution of the X-ray-emitting gas in IC 4593 and to estimate its physical properties. The hot bubble has a radius of ∼2 arcsec and is found to be confined inside the optically bright innermost cavity of IC 4593. The X-ray emission is mostly consistent with that of an optically thin plasma with temperature kT ≈ 0.15 keV (or TX ≈ 1.7 × 106 K), electron density ne ≈ 15 cm−3, and intrinsic X-ray luminosity in the 0.3–1.5 keV energy range LX = 3.4 × 1030 erg s−1. A careful analysis of the distribution of hard (E &amp;gt;0.8 keV) photons in IC 4593 suggests the presence of X-ray emission from a point source likely associated with its central star (CSPN). If this was the case, its estimated X-ray luminosity would be LX, CSPN = 7 × 1029 erg s−1, fulfilling the log(LX, CSPN/Lbol) ≈ −7 relation for self-shocking winds in hot stars. The X-ray detection of the CSPN helps explain the presence of high-ionization species detected in the ultraviolet spectra as predicted by stellar atmosphere models.

An Ejecta Kinematics Study of Kepler’s Supernova Remnant with High-resolution Chandra HETG Spectroscopy

Abstract We report our measurements of the bulk radial velocity from a sample of small, metal-rich ejecta knots in Kepler’s supernova remnant (SNR). We measure the Doppler shift of the He-like Si Kα line-center energy in the spectra of these knots based on our Chandra High-Energy Transmission Grating Spectrometer observation to estimate their radial velocities. We estimate high radial velocities of up to ∼8000 km s−1 for some of these ejecta knots. We also measure proper motions for our sample based on the archival Chandra Advanced CCD Imaging Spectrometer data taken in 2000, 2006, and 2014. Our measured radial velocities and proper motions indicate that some of these ejecta knots are almost freely expanding after ∼400 yr since the explosion. The fastest moving knots show proper motions of up to ∼0.″2 per year. Assuming that these high-velocity ejecta knots are traveling ahead of the forward shock of the SNR, we estimate the distance to Kepler’s SNR d ∼ 4.4–7.5 kpc. We find that the ejecta knots in our sample have an average space velocity of v s ∼ 4600 km s−1 (at a distance of 6 kpc). We note that 8 of the 15 ejecta knots from our sample show a statistically significant (at the 90% confidence level) redshifted spectrum, compared to only two with a blueshifted spectrum. This may suggest an asymmetry in the ejecta distribution in Kepler’s SNR along the line of sight; however, a larger sample size is required to confirm this result.

A Trio of Massive Black Holes Caught in the Act of Merging*

Abstract We report the discovery of SDSS J0849+1114 as the first known triple Type 2 Seyfert nucleus. It represents three active black holes that are identified from new spatially resolved optical slit spectroscopy using the Dual Imaging Spectrograph on the 3.5 m telescope at the Apache Point Observatory. We also present new complementary observations including the Hubble Space Telescope Wide Field Camera 3 U- and Y-band imaging, Chandra Advanced CCD Imaging Spectrometer S-array X-ray 0.5–8 keV imaging spectroscopy, and NSF Karl G. Jansky Very Large Array radio 9.0 GHz imaging in its most extended A configuration. These comprehensive multiwavelength observations, when combined together, strongly suggest that all three nuclei are active galactic nuclei. While they are now still at kiloparsec-scale separations, where the host-galaxy gravitational potential dominates, the black holes may evolve into a bound triple system in ≲2 Gyr. These triple merger systems may explain the overly massive stellar cores that have been observed in some elliptical galaxies such as M87, which are expected to be unique gravitational wave sources. Similar systems may be more common in the early universe, when galaxy mergers are thought to have been more frequent.

The Soft X-Ray Counterpart of Hanny’s Voorwerp Near IC 2497

Abstract We report the detection in Chandra Advanced CCD Imaging Spectrometer archival data of an elongated soft (&lt;3 keV) X-ray feature to the south of the Compton-thick active galactic nucleus (AGN) galaxy IC 2497, coincident with the emission-line feature known as Hanny’s Voorwerp. The data are consistent with the spatial correspondence between X-ray, optical emission-line, and radio features detected in nearby obscured AGNs (e.g., ESO 428-G014). The X-ray luminosity of the (0.3–3.0 keV) soft feature is ∼1.2 × 1040 erg s−1. We infer an [O iii]/soft-X-ray ratio in the range of ∼200, consistent with the highest values measured in some of the clouds of NGC 4151. Overall, given the uncertainties, Hanny’s Voorwerp appears to be a feature consistent with the ionization cone emission of nearby AGNs. We estimate an X-ray recombination time of ∼2 × 107 yr, longer than the [O iii] recombination time (∼8000 yr). This suggests that extended soft X-ray components may be a better diagnostic of overall long-term activity, while detection of an [O iii] HV would point to a time-limited activity burst.

The Massive Star-forming Regions Omnibus X-ray Catalog, Third Installment

Abstract We offer to the star formation community the third installment of the Massive Star-forming Regions (MSFRs) Omnibus X-ray Catalog (MOXC3), a compilation of X-ray point sources detected in 50 archival Chandra Advanced CCD Imaging Spectrometer observations of 14 Galactic MSFRs and surrounding fields. The MOXC3 MSFRs are NGC 2264, NGC 6193, RCW 108-IR, Aur OB1, DR15, NGC 6231, Berkeley 87, NGC 6357, AFGL 4029, h Per (NGC 869), NGC 281, Onsala 2S, G305, and RCW 49 (Wd 2); they have distances of 0.7–4.2 kpc. Most exhibit clumped or clustered young stellar populations; several contain at least two distinct massive young stellar clusters. The total MOXC3 catalog includes 27,923 X-ray point sources. We take great care to identify even the faintest X-ray point sources across these fields. This allows us to remove this point source light, revealing diffuse X-ray structures that pervade and surround MSFRs, often generated by hot plasmas from massive star feedback. As we found in MOXC1 and MOXC2, diffuse X-ray emission is traceable in all MOXC3 MSFRs; here we perform spectral fitting to investigate the origins of selected diffuse regions. Once again, MOXC3 shows the value of high spatial resolution X-ray studies of MSFRs enabled by Chandra.

The X-Ray-resolved Supernova Remnant S8 in the Dwarf Irregular Galaxy IC 1613

Abstract We conducted an observation of the nearby irregular galaxy IC 1613 with the Chandra X-ray Observatory using the S3 chip of the Advanced CCD Imaging Spectrometer (ACIS) with an effective exposure time of 49.9 ks. The observation primarily targeted the extensive bubble and star formation region in the northeast quadrant of the galaxy. The only known supernova remnant (SNR) in IC 1613, S8, is also the galaxy’s most luminous X-ray source (L X(0.3–8 keV) ∼5–6 × 1036 erg s−1). We resolve the SNR with Chandra and compare its nearly circular X-ray morphology with Hα and radio images. We assign an upper limit on the luminosity of any possible associated compact central object of ≈4 × 1035 erg s−1 (0.3–8 keV band) and conclude that we would detect a Crab-like pulsar but not a Cas A-like object. We infer an age for S8 of ∼3400–5600 yr and compare it to other SNRs in the Local Group. We suggest that S8 is a young composite SNR.