The X-ray Binary Population of the Nearby Dwarf Starburst Galaxy IC 10: Variable and Transient X-ray Sources

Abstract

We have monitored the Cassiopeia dwarf galaxy (IC 10) in a series of 10 Chandra ACIS-S observations to capture its variable and transient X-ray source population, which is expected to be dominated by High Mass X-ray Binaries (HMXBs). We present a sample of 21 X-ray sources that are variable between observations at the 3 sigma level, from a catalog of 110 unique point sources. We find 4 transients (flux variability ratio greater than 10) and a further 8 objects with ratio > 5. The observations span years 2003 - 2010 and reach a limiting luminosity of >10${}^{35}$ erg/s, providing sensitivity to X-ray binaries in IC 10 as well as flare stars in the foreground Milky Way. The nature of the variable sources is investigated from light-curves, X-ray spectra, energy quantiles, and optical counterparts. The purpose of this study is to discover the composition of the X-ray binary population in a young starburst environment. IC 10 provides a sharp contrast in stellar population age (<10 My) when compared to the Magellanic Clouds (40-200 My) where most of the known HMXBs reside. We find 10 strong HMXB candidates, 2 probable background Active Galactic Nuclei, 4 foreground flare-stars or active binaries, and 5 not yet classifiable sources. Complete classification of the sample requires optical spectroscopy for radial velocity analysis and deeper X-ray observations to obtain higher S/N spectra and search for pulsations. A catalog and supporting dataset are provided.

17 pages, 8 figures. Accepted to ApJ

References in corpus (10)

• X-ray Properties of Black-Hole Binaries
• On IC 10 X-1, the Most Massive Known Stellar-Mass Black Hole
• The Orbital Period of the Wolf-Rayet Binary IC 10 X-1; Dynamic Evidence that the Compact Object is a Black Hole
• Molecular Gas in the Low Metallicity, Star Forming Dwarf IC 10
• X-ray binary formation in low-metallicity blue compact dwarf galaxies
• Spectral distribution of Be/X-ray binaries in the Small Magellanic Cloud
• A Deep XMM-Newton Survey of M33: Point Source Catalog, Source Detection and Characterization of Overlapping Fields
• The Chandra ACIS Survey of M33 (ChASeM33): Transient X-ray Sources Discovered in M33
• A Transient Supergiant X-ray Binary in IC10. An Extragalactic SFXT?
• A Flaring X-ray Source with an Halpha-bright Counterpart toward the SMC

Cited by in corpus (7)

• A Multi-epoch X-ray Study of the Spiral Galaxy NGC 7331
• Probing the Stellar Wind of the Wolf-Rayet Star in IC 10 X-1
• Constraints on the number of X-ray Pulsars in IC 10 from a deep XMM-Newton Observation
• Multiwavelength survey of X-ray sources in the Sculptor Dwarf Spheroidal Galaxy
• Monitoring the X-ray Variability of Bright X-ray Sources in M33
• Gravitational slingshots around black holes in a binary
• ZTF IC 10 variable catalog