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 3σ 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 −1 , 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.

A Multi-epoch X-Ray Study of the Spiral Galaxy NGC 7331

“…A total of 13 variables, among 48 sources with multiple detections, are denoted as a "v" in Table 2. We also check if there is any transient in our sample by following the criterion of defining a transient in Laycock et al (2017). They define a transient as the source with a maximum to minimum flux ratio > 10 and a flux variability > 3.…”

Constraints on the number of X‐ray pulsars in IC 10 from a deep XMM‐Newton observation

“…That IC 10 hosts a significant HMXB population seems probable based on the work of Wang et al (), and Laycock et al (, ); therefore the lack of detected pulsars implies a true absence, perhaps because they have not had time to form. Whether our dataset has the sensitivity to make this claim can be examined as follows.…”

“…Furthermore, the integrated spectrum of these objects follows a “High Mass X‐ray binary (HMXB)‐like” hard power law. Monitoring over several years with Chandra has revealed a sample of 110 unique point sources, 21 of which are variable (Laycock et al ) and up to 16 are associated with blue supergiants (with an overlap of five objects between those subgroups) (Laycock et al ). Perhaps the single strongest candidate for a pulsar hosting system is IC 10 X‐2, a large amplitude X‐ray transient paired with an extremely luminous blue supergiant (Kwan et al ; Laycock et al ).…”

“…We have conducted a complete study of the properties of these sources, including their light curves and spectra, and searched for pulsations. We have combined the 2012 XMM‐Newton data with a catalog of IC 10 sources from the Chandra X‐ray archive (Laycock et al ) and the previous XMM‐Newton observation of the galaxy (Wang et al ). The results from this study will help better understand the accretion process in compact binaries, the mass transfer from WR stars to their companions, as well as tidal interactions and gravitational wave emission from a young starburst environment, which is expected to be heavily populated by NS and BH binaries born in roughly the last 10 million years.…”

Approximating Photo-z PDFs for Large Surveys

“…One parametrization that has not previously been investigated in the context of photometric redshifts is that of quantiles, though they have appeared elsewhere in the astronomy literature (Sun et al 2015;Pizzocaro et al 2016;Laycock et al 2017). The quantiles are defined in terms of the cumulative distribution function (CDF), which is the antiderivative of the PDF.…”