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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

Referred to by ATel #: 7185, 7187

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).