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|Title:||Fifteen years of XMM-Newton and Chandra monitoring of Sgr A<SUP>★</SUP>: evidence for a recent increase in the bright flaring rate||Authors:||PONTI, GABRIELE
De Marco, B.
Morris, M. R.
|Issue Date:||2015||Journal:||MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY||Number:||454||Issue:||2||First Page:||1525||Abstract:||We present a study of the X-ray flaring activity of Sgr A<SUP>⋆</SUP> during all the 150 XMM-Newton and Chandra observations pointed at the Milky Way centre over the last 15 years. This includes the latest XMM-Newton and Chandra campaigns devoted to monitoring the closest approach of the very red Brγ emitting object called G2. The entire data set analysed extends from 1999 September through 2014 November. We employed a Bayesian block analysis to investigate any possible variations in the characteristics (frequency, energetics, peak intensity, duration) of the flaring events that Sgr A<SUP>⋆</SUP> has exhibited since their discovery in 2001. We observe that the total bright or very bright flare luminosity of Sgr A<SUP>⋆</SUP> increased between 2013 and 2014 by a factor of 2-3 (̃3.5σ significance). We also observe an increase (̃99.9 per cent significance) from 0.27 ± 0.04 to 2.5 ± 1.0 d<SUP>-1</SUP> of the bright or very bright flaring rate of Sgr A<SUP>⋆</SUP>, starting in late summer 2014, which happens to be about six months after G2's pericentre passage. This might indicate that clustering is a general property of bright flares and that it is associated with a stationary noise process producing flares not uniformly distributed in time (similar to what is observed in other quiescent black holes). If so, the variation in flaring properties would be revealed only now because of the increased monitoring frequency. Alternatively, this may be the first sign of an excess accretion activity induced by the close passage of G2. More observations are necessary to distinguish between these two hypotheses.||Acknowledgments:||The authors wish to thank Jan-Uwe Ness, Ignacio de la Calle and the rest of the XMM–Newton scheduling team for the enormous support that made the new XMM–Newton observations possible. They also wish to thank the anonymous referee for the very useful comments that significantly improved the paper. They thank all the members of the Sgr A ⋆ 's Chandra XVP collaboration ( www.sgra-star.com ) for contributing in collecting X-ray data and for compiling a legacy data set for astronomy. GP thanks Alessandro Ballone for useful discussion and acknowledges Gunther Witzel for useful comments. This research has made use both of data obtained with XMM–Newton , an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA, and of data obtained from the Chandra Data Archive. GP acknowledges support via an EU Marie Curie Intra-European Fellowship under contract no. FP7-PEOPLE-2012-IEF-331095. The Galactic Center XMM–Newton monitoring project is supported by the Bundesministerium für Wirtschaft und Technologie/Deutsches Zentrum für Luft- und Raumfahrt (BMWI/DLR, FKZ 50 OR 1408) and the Max Planck Society. DH acknowledges support from Chandra X-ray Observatory (CXO) Award Numbers GO3-14121X, G04-15091A and GO4-15091C, operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060, and also from NASA Swift grant NNX14AC30G. ND acknowledges support via an EU Marie Curie Intra-European fellowship under contract no. FP-PEOPLE-2013-IEF-627148. MC, AG, RT, SS acknowledge support from CNES.||URI:||http://hdl.handle.net/20.500.12386/29361||URL:||https://academic.oup.com/mnras/article/454/2/1525/1045936||ISSN:||0035-8711||DOI:||10.1093/mnras/stv1537||Bibcode ADS:||2015MNRAS.454.1525P||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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