skip to main content

Title: TRANSIENT X-RAY SOURCE POPULATION IN THE MAGELLANIC-TYPE GALAXY NGC 55

We present the spectral and temporal properties of 15 candidate transient X-ray sources detected in archival XMM-Newton and Chandra observations of the nearby Magellanic-type, SB(s)m galaxy NGC 55. Based on an X-ray color classification scheme, the majority of the sources may be identified as X-ray binaries (XRBs), and six sources are soft, including a likely supernova remnant. We perform a detailed spectral and variability analysis of the data for two bright candidate XRBs. Both sources displayed strong short-term X-ray variability, and their X-ray spectra and hardness ratios are consistent with those of XRBs. These results, combined with their high X-ray luminosities (∼10{sup 38} erg s{sup −1}), strongly suggest that they are black hole (BH) binaries. Seven less luminous sources have spectral properties consistent with those of neutron star or BH XRBs in both normal and high-rate accretion modes, but one of them is the likely counterpart to a background galaxy (because of positional coincidence). From our spectral analysis, we find that the six soft sources are candidate super soft sources (SSSs) with dominant emission in the soft (0.3–2 keV) X-ray band. Archival Hubble Space Telescope optical images for seven sources are available, and the data suggest that most of themmore » are likely to be high-mass XRBs. Our analysis has revealed the heterogeneous nature of the transient population in NGC 55 (six high-mass XRBs, one low-mass XRBs, six SSSs, one active galactic nucleus), helping establish the similarity of the X-ray properties of this galaxy to those of other Magellanic-type galaxies.« less
Authors:
;  [1]
  1. Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China)
Publication Date:
OSTI Identifier:
22518508
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 821; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; COLOR; COSMIC X-RAY SOURCES; IMAGES; KEV RANGE; LUMINOSITY; MAGELLANIC CLOUDS; MASS; NEUTRON STARS; SPACE; SUPERNOVA REMNANTS; TELESCOPES; TRANSIENTS; X-RAY GALAXIES; X-RAY SPECTRA