An XMM-Newton and Chandra study of the starburst galaxy IC 10

Abstract

We present an X‐ray study of our nearest starburst galaxy IC 10, based on XMM–Newton and Chandra observations. A list of 73 XMM–Newton and 28 Chandra detections of point‐like X‐ray sources in the field is provided; a substantial fraction of them are likely stellar objects in the Milky Way due to the low Galactic latitude location of IC 10. The brightest source in the IC 10 field, X‐1, has a mean 0.3–8.0 keV luminosity of ∼1.2 × 1038 erg s−1 and shows a large variation by a factor of up to ∼6 on time‐scales of ∼104 s during the XMM–Newton observation. The X‐ray spectra of the source indicate the presence of a multicolour blackbody accretion disc with an inner disc temperature Tin≈ 1.1 keV. These results are consistent with the interpretation of the source as a stellar mass black hole (BH), probably accreting from a Wolf–Rayet (W–R) star companion. We infer the mass of this BH to be ∼4 M⊙ if it is not spinning, or a factor of up to ∼6 higher if there is significant spinning. We also detect an apparent diffuse soft X‐ray emission component of IC 10. An effective method is devised to remove the X‐ray CCD‐readout streaks of X‐1 that strongly affect the study of the diffuse component in the XMM–Newton and Chandra observations. We find that the diffuse X‐ray morphology is oriented along the optical body of the galaxy and is chiefly associated with starburst regions. The diffuse component can be characterized by an optically thin thermal plasma with a mean temperature of ∼4 × 106 K and a 0.5–2 keV luminosity of ∼8 × 1037 erg s−1, representing only a small fraction of the expected mechanical energy inputs from massive stars in the galaxy. There is evidence that the hot gas is driving outflows from the starburst regions; therefore, the bulk of the energy inputs may be released in a galactic wind.

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

“…Analysis in the X-ray quantile diagram reveals a split between soft thermal sources and harder power-law like spectra that cluster along the model grid contour consistent with the average column density towards IC 10. While this separation is not a complete diagnostic of source classes, it supports to a large extent the hypothesis of Wang et al (2005) that IC 10 hosts numerous HMXBs. Our variability study, better positions, and the increased spectral S/N ratios made possible by analyzing a cumulative 225 ksec of Chandra exposure (vs the previous 30 ksec) have provided a richer and more detailed view of this population.…”

“…A pair of very deep ACIS-S3 observations (2×45 ksec) made in November 2006 provide a reference dataset for improved source positions and spectral information. The original Wang et al (2005) Chandra (ACIS-S3, 1/2 subarray) observation of 30 ksec made in 2003 was included in our analysis to provide additional time baseline for the variability study and to make use of their published source identifications. The complete listing of 10 observation identifiers (ObsIDs) comprising the dataset is summarized in Table 1.…”

“…Positional matching to the catalog of Wang et al (2005) was performed using our and their 95% error radii in quadrature; the resulting IDs are provided in 11 http://heasarc.gsfc.nasa.gov/cgi−bin/Tools/w3pimms/w3pimms.pl Table 2. To facilitate observations at other wavelengths, and cross-correlation with other databases we provide our complete point-source catalog as supplemental data in the online journal.…”

“…Class is a candidate source classification based on the X-ray and optical properties: T = Transient (Ratio > 10), TC = Transient Candidate, V = Variable, X = X-ray binary, S = Stellar Corona, A=AGN, U = unclassified. Column W 05 is the source identifier from Wang et al (2005) where the suffix C and X denote Chandra and XMM-Newton respectively. A full version of this table containing all 110 unique sources, their celestial coordinates, and error bars for all columns is provided in the online journal.…”

“…Important large samples have been constructed by mining the Chandra archive, (for example Fabbiano 2006;Brorby et al 2014;Prestwich et al 2013) and by concerted multi-year efforts to intensively observe nearby galaxies (e.g., Tüllmann et al 2011;Binder et al 2015;Williams et al 2015;Li et al 2010). An X-ray study of point sources in IC 10 was conducted by Wang et al (2005) using single epoch data from XMM-Newton and Chandra. Among their important findings was a population of point sources significantly above the expected background density and spatially concentrated within the optical outline of the galaxy.…”