Swift J0045.2+4151: analysis of XMM-Newton archival data
ATel #7181; A. Belfiore (INAF/IASF Milano), A. Tiengo (IUSS Pavia), G. L. Israel (INAF/OA Roma), A. M. Read (U. Leicester), R. Salvaterra, D. Salvetti (INAF/IASF Milano), G. Novara (IUSS Pavia), S. Mereghetti, M. Marelli (INAF/IASF Milano), G. Rodriguez (INAF/OA Roma), G. Lisini (IUSS Pavia), S. R. Rosen (U. Leicester), A. De Luca (INAF/IASF Milano)
on 6 Mar 2015; 15:49 UT
Credential Certification: Sandro Mereghetti (sandro@mi.iasf.cnr.it)
Subjects: X-ray, Gamma-Ray Burst, Soft Gamma-ray Repeater, Transient
Based on the preliminary results of the EXTraS project (DeLuca et al.
2015, arXiv:1503.01497), we report on the analysis of XMM-Newton archival
data of 3XMM J004514.7+415035 (aka [PFH2005] 622, Pietsch et al. 2005, ApJ
434, 483), the candidate X-ray counterpart of GRB 150301C (aka Swift
J0045.2+4151, GCN Circ 17512, 17516, ATEL#7166, ATEL#7176). The source is detected
by the EPIC instrument at a 0.2-12 keV flux level of ~10-14 erg/cm2/s in
two observations (2002-01-26 and 2007-01-05), while only upper limits of
~5x10-14 erg/cm2/s can be set from 5 shorter observations performed in
July 2006. Shallow upper limits of ~10-12 erg/cm2/s can be derived from
three non-detections during slew observations on 2005-07-03, 2007-01-06,
and 2010-01-31.
The EPIC light curves of the two observations show no evidence for
variability. The search for coherent pulsations in the PN data, between
0.15 and 104 s, gives negative results. The blind search for transients
does not report any significant candidates within the BAT error circle of
GRB 150301C in any of the seven XMM-Newton observations.
We extracted the EPIC spectra of 3XMM J004514.7+415035 and, after
verifying that there are no significant spectral differences between the
two observations, we fit them simultaneously with an absorbed power-law
model. The best-fit parameters (errors at the 90% confidence level) are
NH<3x1021 cm-2 and photon index 1.9 (-0.6, +0.8). Fixing the NH to
the Galactic value of 1021 cm-2, as appropriate for sources in the M31
disk, the photon index can be constrained in the 1.6-2.2 range (C-stat=142
for 143 degrees of freedom) and the unabsorbed flux in the 0.1-10 keV
range is (1.3 +/- 0.3)x10-14 erg/cm2/s, corresponding to ~6x1035 erg/s
at the M31 distance.
We note that the properties of 3XMM J004514.7+41503 are consistent with
those of an active magnetar, like, e.g., SGR1806-20, at the distance of
M31. Considering that the duration, fluence and spectrum of the burst
detected by BAT are compatible with an intermediate flare from a magnetar
in M31, 3XMM J004514.7+41503 might be considered as a magnetar candidate
in the Andromeda galaxy.
Plots of the long term flux evolution, the background-subtracted and
exposure-corrected light curves, and the power density spectra with pulsed
fraction upper limits can be found on the EXTraS website: http://www.extras-fp7.eu/index.php/home/90-extras/news/158-gcn-atel-1
EXTraS ("Exploring the X-ray Transient and variable Sky") is a project
aimed at the systematic exploitation of the XMM/EPIC database, to search
for, and characterize variability (both periodic and aperiodic), to search
for new transients and to provide a phenomenological classification of
variable sources. All EXTraS results, products and tools will be released
to the community at the end of the project. EXTraS is carried out by a
collaboration including INAF (Italy), IUSS (Italy), CNR/IMATI (Italy),
University of Leicester (UK), MPE (Germany) and ECAP (Germany) and has
been funded within the EU-FP7 framework (grant agreement n. 607452).