J/MNRAS/454/1525 XMM-Newton and Chandra monitoring of Sgr A* (Ponti+, 2015)
Fifteen years of XMM-Newton and Chandra monitoring of Sgr A*: evidence for
a recent increase in the bright flaring rate.
Ponti G., De Marco B., Morris M.R., Merloni A., Munoz-Darias T., Clavel M.,
Haggard D., Zhang S., Nandra K., Gillessen S., Mori K., Neilsen J., Rea N.,
Degenaar N., Terrier R., Goldwurm A.
<Mon. Not. R. Astron. Soc., 454, 1525-1544 (2015)>
=2015MNRAS.454.1525P 2015MNRAS.454.1525P (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; X-ray sources ; Ephemerides
Keywords: accretion, accretion discs - black hole physics -
methods: data analysis - Galaxy: centre - X-rays: binaries -
X-rays: individual: Sgr A*
Abstract:
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 percent
significance) from 0.27±0.04 to 2.5±1.0/d 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.
Description:
As of 2014 November 11 the XMM-Newton archive contains 37 public
observations that can be used for our analysis of Sgr A*. In addition,
we consider four new observations aimed at monitoring the interaction
between the G2 object and Sgr A*, performed in fall 2014 (see Table A4).
A total of 41 XMM-Newton data sets are considered in this work.
All the 46 Chandra observations accumulated between 1999 and 2011 and
analysed here are obtained with the ACIS-I camera without any gratings
on (see Table A1). From 2012 onwards, data from the ACIS-S camera were
also employed. The 2012 Chandra "X-ray Visionary Project" (XVP) is
composed of 38 High-Energy Transmission Grating (HETG) observations
with the ACIS-S camera at the focus (Nowak et al. 2012ApJ...759...95N 2012ApJ...759...95N;
Neilsen et al. 2013ApJ...774...42N 2013ApJ...774...42N; 2015ApJ...799..199N 2015ApJ...799..199N; Wang et al.
2013Sci...341..981W 2013Sci...341..981W; see Table A2). The first two observations of the
2013 monitoring campaign were performed with the ACIS-I instrument, while
the ACIS-S camera was employed in all the remaining observations, after
the outburst of SGR J1745-2900 on 2013 April 25. Three observations
between 2013 May and July were performed with the HETG on, while all
the remaining ones do not employ any gratings (see Table A2).
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
17 45 40.04 -29 00 28.2 Sgr A* = NAME Sagittarius A
----------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 125 58 List of all Chandra observations on Sgr A*
performed between 1999 and 2011
tablea2.dat 125 62 List of all Chandra observations on Sgr A*
performed in 2012
tablea3.dat 125 40 List of all Chandra observations on Sgr A*
performed in 2013 and 2014
tablea4.dat 125 53 List of all XMM-Newton observations with Sgr A*
in the field of view, considered in this work
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
B/xmm : XMM-Newton Observation Log
(XMM-Newton Science Operation Center, 2012)
J/ApJ/589/225 : Chandra X-ray sources toward Galactic Center (Muno+, 2003)
J/ApJS/181/110 : Galactic center X-ray sources (Muno+, 2009)
Byte-by-byte Description of file: tablea[1234].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- ObsID Observation identifier
12- 13 A2 --- Mode [I SH S] Instrument set-up
(not in tablea4.dat) (1)
15- 19 F5.1 ks TExp ? Total exposure time (not in tablea4.dat)
21- 26 F6.2 ks Exp Cleaned exposure time
28- 46 A19 --- Obs.date Observation date/time (YYYY-MM-DDThh:mm:ss)
48- 51 F4.1 ks Time1 ? Start time (only in tablea4.dat)
53- 57 F5.1 ks Time2 ? End time (only in tablea4.dat)
59- 60 I2 --- Nb [1/10] Number of different blocks detected
in our Bayesian block analysis
62- 64 F3.1 --- Nf [0/4] Number of flaring blocks
65 A1 --- n_Nf [a] Note on Nf (only in tablea4.dat) (2)
67- 68 I2 --- Nblock [1/10]? Block number
70- 79 F10.4 d MJD1 ? Modified Julian Date, block start time
81- 90 F10.4 d MJD2 ? Modified Julian Date, block stop time
92- 98 F7.1 s Dur ? Duration
100-105 F6.4 ph/s CR ? Mean observed count rate
107-112 F6.4 ph/s e_CR ? 1σ uncertainty in CR
114-118 F5.1 10-13J/m2 Fl ? Fluence after subtraction of the average
contribution of the non-flaring blocks
(10-10erg/cm2)
120-125 F6.1 10-13J/m2 TFl ? Total flare fluence (10-10erg/cm2)
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Note (1): Instrument set-up as follows:
I = The observation was taken with the ACIS-I;
SH = The observation was taken with the ACIS-S with HETG;
S = The observation was taken with ACIS-S with no gratings and 1/8 subarray.
Note (2): Note as follows:
a = Eclipses of CXOGC J174540.0-290031 are detected during these observations.
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 10-Jan-2018