ﻻ يوجد ملخص باللغة العربية
We have analysed the spectra and the variability of individual X-ray sources in the M-81 field using data from the available ROSAT-PSPC and ROSAT-HRI observations of this nearby spiral galaxy. Here we present the results on the second brightest source in the field (X-9 - Fabbiano, 1988 ApJ 325 544), whose identification and interpretation is still unclear. Our work includes the study of the shape of X-9 from HRI data, the light curve and hardness ratio evolution, and the spectral analysis.
The source X-9 was discovered with the {it Einstein Observatory} in the field of M81, and is located in the dwarf galaxy Holmberg IX. X-9 has a 0.2-4.0 keV luminosity of $sim 5.5times 10^{39}$ ergs~s$^{-1}$, if it is at the same distance as Holmberg
We report variability of the X-ray source, X-7, in NGC 6946, during a 60 ksec Chandra observation when the count rate decreased by a factor of ~1.5 in ~5000 secs. Spectral fitting of the high and low count rate segments of the light curve reveal that
We investigate the long-term spectral variability in the ultra-luminous X-ray source Holmberg IX X--1. By analyzing the data from eight {it Suzaku} and 13 {it XMM-Newton} observations conducted between 2001 and 2015, we perform a detailed spectral mo
The recent discovery by Bachetti et al. (2014) of a pulsar in M82 that can reach luminosities of up to 10^40 ergs s^-1, a factor of ~100 the Eddington luminosity for a 1.4 Msol compact object, poses a challenge for accretion physics. In order to bett
We use archival HST/WFPC2 V and I band images to show that the optical counterpart to the ultra-luminous x-ray source NGC 5204 X-1, reported by Roberts et al., is composed of two sources separated by 0.5. We have also identified a third source as a p