ASCA OBSERVATION OF BRIGHT X-RAY SOURCES IN THE NEARBY SPIRAL GALAXY IC-342

Citation
K. Okada et al., ASCA OBSERVATION OF BRIGHT X-RAY SOURCES IN THE NEARBY SPIRAL GALAXY IC-342, Publications of the Astronomical Society of Japan, 50(1), 1998, pp. 25-30
Citations number
30
Categorie Soggetti
Astronomy & Astrophysics
ISSN journal
00046264
Volume
50
Issue
1
Year of publication
1998
Pages
25 - 30
Database
ISI
SICI code
0004-6264(1998)50:1<25:AOOBXS>2.0.ZU;2-3
Abstract
X-ray observations of the nearby starburst galaxy IC 342 with ASCA led to the detection of three bright X-ray sources, whose positions are c onsistent with those from the Einstein and ROSAT observations. The X-r ay luminosities of the two sources exceed the Eddington limit of a 1.4 M. object by two orders of magnitude for an assumed distance of 4.5 Mp c. The brightest one (source I) among the three exhibited significant time variations on a time scale of a few hours during the ASCA observa tion. Thus, the size of the emission region must be smaller than about 10(14) Cm. The energy spectrum of the source can be represented eithe r by a power-law with an exponential roll-over, or by an optically thi ck accretion disk model with a maximum color temperature of 1.77 keV. Although the large luminosity of source 1 may be explained by a simila r to 100 M. black hole at 4.5 Mpc, the observed energy spectrum is too hard to be accounted for by an optically thick accretion disk around the black hole. If source 1 is a relativistic jet source with strong X -ray beaming, both the large luminosity and the hard X-ray spectrum ca n be explained.