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  1. OA@INAF
  2. PRODOTTI RICERCA INAF
  3. 1 CONTRIBUTI IN RIVISTE (Journal articles)
  4. 1.01 Articoli in rivista
Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12386/23070
Title: Swift-XRT six-year monitoring of the ultraluminous X-ray source M33 X-8
Authors: LA PAROLA, VALENTINA 
D'AI', ANTONINO 
CUSUMANO, GIANCARLO 
MINEO, TERESA 
Issue Date: 2015
Journal: ASTRONOMY & ASTROPHYSICS 
Number: 580
First Page: A71
Abstract: Context. The long-term evolution of ultraluminous X-ray sources (ULX) with their spectral and luminosity variations in time give important clues on the nature of ULX and on the accretion process that powers them. <BR /> Aims: We report here the results of a Swift-XRT six-year monitoring campaign of the closest example of a persistent ULX, M33 X-8, that extends the monitoring of this source in the soft X-rays to 16 years. The luminosity of this source is a few 10<SUP>39</SUP> erg s<SUP>-1</SUP>, marking the faint end of the ULX luminosity function. <BR /> Methods: We analyzed the set of 15 observations collected during the Swift monitoring. We searched for differences in the spectral parameters at different observing epochs, adopting several models commonly used to fit the X-ray spectra of ULX. <BR /> Results: The source exhibits flux variations of about 30%. No significant spectral variations are observed during the monitoring. The average 0.5-10 keV spectrum can be well described by a thermal model, either in the form of a slim disk, or as a combination of a Comptonized corona and a standard accretion disk.
Acknowledgments: This work has been supported by ASI grant I/011/07/0.
URI: http://hdl.handle.net/20.500.12386/23070
URL: https://www.aanda.org/articles/aa/abs/2015/08/aa25384-14/aa25384-14.html
ISSN: 0004-6361
DOI: 10.1051/0004-6361/201425384
Bibcode ADS: 2015A&A...580A..71L
Fulltext: open
Appears in Collections:1.01 Articoli in rivista

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