Related papers: A Luminous Recurrent Supersoft X-ray Source in NGC…

We analyze 18 sources that were found to show interesting properties of periodicity, very soft spectra and/or large long-term variability in X-rays in our project of classification of sources from the 2XMMi-DR3 catalog but were poorly…

We have re-examined the most luminous X-ray sources in the starburst galaxy NGC 4631, using XMM-Newton, Chandra and ROSAT data. The most interesting source is a highly variable supersoft ULX. We suggest that its bolometric luminosity ~ a…

We report here the results of a full analysis of all the ROSAT PSPC spectral imaging observations and all the ROSAT HRI high resolution imaging observations of the very nearby (D=2.1 Mpc) Sculptor galaxy, NGC 300. Many point sources are…

We present the results of a 63 ks {\it Chandra} observation of the "supernova impostor" SN 2010da four months after it was first observed on 25 May 2010. We detect an X-ray source at $\sim7\sigma$ confidence coincident with the optical…

We have discovered an ultrasoft X-ray transient source, 2XMMi J184725.1-631724, which was detected serendipitously in two XMM-Newton observations in the direction of the center of the galaxy IC 4765-f01-1504 at a redshift of 0.0353. These…

In an XMM-Newton raster observation of the bright local group spiral galaxy M33 we study the population of X-ray sources (X-ray binaries, supernova remnants, super-shells) down to a 0.5-10 keV luminosity of 10^35 erg s^-1 -- more than a…

We present the results of a 30ks XMM-Newton observation of the supergiant fast X-ray transient (SFXT) SAX J1818.6-1703 - the first in-depth soft X-ray study of this source around periastron. INTEGRAL observations shortly before and after…

Another outburst of the recurrent M31 nova M31N 2008-12a was announced in late November 2013. Optical data suggest an unprecedentedly short recurrence time of approximately one year. In this Letter we address the X-ray properties of M31N…

We use a set of conservative criteria to identify luminous supersoft X-ray sources(SSSs) in external galaxies. We test this approach on blackbody models, and then apply it to {\it Chandra} data from 4 galaxies: an elliptical (NGC 4967), 2…

We present the results of ROSAT and XMM-Newton observations of the recurrent ultraluminous X-ray source (ULX) NGC 253 ULX1. This transient is one of the few ULXs that was detected during several outbursts. The luminosity reached 1.4 10^39…

We discuss preliminary results from a joint XMM-Newton and NuSTAR monitoring program on the active galactic nucleus NGC 4593, consisting of 5x20 ks observations, spaced by two days, performed in January 2015. The source is found to be…

We report the results of XMM-Newton and BeppoSAX observations of the radio and X-ray emitting star LS I +61 303, likely associated with the gamma-ray source 2CG 135+01 and recently detected also at TeV energies. The data include a long…

The first supersoft source (SSS) identification with an optical nova in M 31 was based on ROSAT observations. Twenty additional X-ray counterparts (mostly identified as SSS by their hardness ratios) were detected using archival ROSAT,…

We report the detection of an absorbed central X-ray source and its strong, rapid variability in NGC4395, the least luminous Seyfert nucleus known. The X-ray source exhibits a number of flares with factors of 3-4 flux changes during a half…

We present an analysis of recent XMM-Newton and HST archive data of the ultraluminous X-ray source NGC 1313 X-2. Quasi-simultaneous observations taken with XMM-Newton, HST and VLT allow us to study both the X-ray light curve and its…

We observed the accreting white dwarf 1E1339.8+2837 (1E1339) in the globular cluster M3 in Nov. 2003, May 2004 and Jan. 2005, using the Chandra ACIS-S detector. The source was observed in 1992 to possess traits of a supersoft X-ray source…

Short supersoft X-ray source (SSS) states (durations < 100 days) of classical novae (CNe) indicate massive white dwarfs that are candidate progenitors of supernovae type Ia. We carry out a dedicated optical and X-ray monitoring program of…

Recent Chandra ACIS-S observations have detected a point source at the central star of NGC 6543 and confirmed the point source nature of the hard X-ray emission from NGC 7293. The X-ray spectra of both sources peak between 0.5 keV and 1.0…

Classical supersoft X-ray sources (SSSs) are understood as close binary systems in which a massive white dwarf (WD) accretes from its companion at rates sustaining steady hydrogen burning on its surface generating bolometric luminosities of…

A Chandra ACIS-S imaging observation of the nearby galaxy M81 (NGC 3031) reveals 9 luminous soft X-ray sources. The local environments, X-ray spectral properties, and X-ray light curves of the sources are presented and discussed in the…