Bibcode
Ponti, G.; De Marco, B.; Morris, M. R.; Merloni, A.; Muñoz-Darias, T.; Clavel, M.; Haggard, D.; Zhang, S.; Nandra, K.; Gillessen, S.; Mori, K.; Neilsen, J.; Rea, N.; Degenaar, N.; Terrier, R.; Goldwurm, A.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 454, Issue 2, p.1525-1544
Fecha de publicación:
12
2015
Número de citas
76
Número de citas referidas
67
Descripción
We present a study of the X-ray flaring activity of Sgr
A⋆ 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⋆ has exhibited since their discovery in 2001.
We observe that the total bright or very bright flare luminosity of Sgr
A⋆ 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-1 of the bright or very bright flaring rate of
Sgr A⋆, 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.
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