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تسجيل مستخدم جديدThe Ultra-luminous M81 X-9 source: 20 years variability and spectral states
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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 IX (3.4 Mpc). This luminosity is above the Eddington luminosity of a 1~$M_{odot}$ compact accreting object. Past hypotheses on the nature of this Super-Eddington source included a SNR or supershell, an accreting compact object and a background QSO. To shed light on the nature of this source, we have obtained and analyzed archival data, including the {it Einstein} data, 23 ROSAT observations, Beppo-SAX and ASCA pointings. Our analysis reveals that most of the emission of X-9 arises from a point-like highly-variable source, and that lower luminosity extended emission may be associated with it. The spectrum of this source changes between low and high intensity states, in a way reminiscent of the spectra of galactic Black Hole candidates. Our result strongly suggest that X-9 is not a background QSO, but a bonafide `Super-Eddington source in Ho IX, a dwarf companion of M81.
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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 sourc
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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
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Many upcoming surveys, particularly in the radio and optical domains, are designed to probe either the temporal and/or the spatial variability of a range of astronomical objects. In the light of these high resolution surveys, we review the subject of
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