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http://hdl.handle.net/20.500.12386/23162
Titolo: | Missing hard states and regular outbursts: the puzzling case of the black hole candidate 4U 1630-472 | Autori: | CAPITANIO, FIAMMA CAMPANA, RICCARDO DE CESARE, GIOVANNI Ferrigno, C. |
Data pubblicazione: | 2015 | Rivista: | MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY | Numero: | 450 | Fascicolo: | 4 | Da pagina:: | 3840 | Abstract: | 4U 1630-472 is a recurrent X-ray transient classified as a black hole candidate from its spectral and timing properties. One of the peculiarities of this source is the presence of regular outbursts with a recurrence period between 600 and 730 d that has been observed since the discovery of the source in 1969. We report on a comparative study of the spectral and timing behaviour of three consecutive outbursts that occurred in 2006, 2008 and 2010. We have analysed all the data collected by INTEGRAL and the Rossi X-ray Timing Explorer (RXTE) during these three years of activity. We show that, in spite of having a similar spectral and timing behaviour in the energy range between 3 and 30 keV, these three outbursts show pronounced differences above 30 keV. In fact, the 2010 outburst extends at high energies without any detectable cut-off until 150-200 keV, while the two previous outbursts that occurred in 2006 and 2008 are not detected at all above 30 keV. Thus, in spite of a very similar accretion disc evolution, these three outbursts exhibit totally different characteristics of the Compton electron corona, showing a softening in their evolution rarely observed before in a low-mass X-ray binary hosting a black hole. We argue the possibility that the unknown perturbation that causes the outbursts to be equally spaced in time could be at the origin of this particular behaviour. Finally, we describe several possible scenarios that could explain the regularity of the outbursts, identifying the most plausible, such as a third body orbiting around the binary system. | Acknowledgments: | The authors would like to thank Roberto Ricci and Marcello Giroletti for checking the radio data. RC and the other authors thank T. M. Belloni for his help with the timing analysis software. FC also thanks Carla Maceroni, Agnieszka Janiuk, Massimo Cocchi, Agata Rozanska and Melania Del Santo for useful scientific discussions. Special thanks go to Valeria Mangano for scientific discussions and careful editing of the text. The RXTE data were obtained through the High Energy Astrophysics Science Archive Research Center (HEASARC) online service. The INTEGRAL data were obtained through the INTEGRAL Science Data Center (ISDC) online service. The Swift /BAT light curve is part of the SWIFT /BAT transient monitor results provided by the Swift /BAT team. | URI: | http://hdl.handle.net/20.500.12386/23162 | URL: | https://academic.oup.com/mnras/article/450/4/3840/989613 | ISSN: | 0035-8711 | DOI: | 10.1093/mnras/stv687 | Bibcode ADS: | 2015MNRAS.450.3840C | Fulltext: | open |
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