Discovery of Bright Variable X-Ray Sources in NGC 1569 with Chandra

Abstract

From the analysis of a ~100 ks Chandra observation of the dwarf starburst galaxy NGC 1569, we have found that the X-ray point sources CXOU 043048.1+645050 and CXOU 043048.6+645058 show significant time variability. During this observation, the X-ray flux of CXOU 043048.1+645050 increased by 10 times in only 2 × 104 s. Since the spectrum in its bright phase was fitted with a disk blackbody model with kTin ≈ 0.43 keV and the bolometric luminosity is Lbol ≈ 1038 ergs s-1, this source is an X-ray binary with a stellar mass black hole. Since the spectrum in its faint phase was also fitted with a disk blackbody model, the time variability can be explained by a change of the accretion rate onto the black hole. The other variable source, CXOU 043048.6+645058, had a flat spectrum with a photon index of ~1.6. This source may be an X-ray binary with an X-ray luminosity of several times 1037 ergs s-1. In addition, three other weak sources showed possible time variability. Taking all of the variability into account may suggest an abundant population of compact X-ray sources in NGC 1569.