[vsnet-grb-info 16267] Swift J0045.2+4151: analysis of XMM-Newton archival data

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17548
SUBJECT: Swift J0045.2+4151: analysis of XMM-Newton archival data
DATE:    15/03/06 15:28:51 GMT
FROM:    Sandro Mereghetti at IASF/CNR  <sandro at iasf-milano.inaf.it>

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), report on 
behalf of the EXTraS collaboration:

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 150301CÂ  (aka Swift 
J0045.2+4151, GCN Circ 17512, 17516, 17536, 17544). The source is detected 
by the EPIC instrument at a 0.2-12 keV flux level of ~10^-14 erg/cm^2/s in 
two observations (2002-01-26 and 2007-01-05), while only upper limits of 
~5x10^-14 erg/cm^2/s can be set from 5 shorter observations performed in 
July 2006. Shallow upper limits of ~10^-12 erg/cm^2/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 10^4 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 
N_H<3x10^21 cm^-2 and photon index 1. 9 (-0.6, +0.8). Fixing the N_H to 
the Galactic value of 10^21 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/cm^2/s, corresponding to ~6x10^35 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).