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Reactivation of Soft Gamma Repeater 1627-41

ATEL # 1548; D. Palmer (LANL), P. Esposito (INAF-IASF Milano), S. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), G. L. Israel (INAF-OA Roma), H. Krimm (GSFC/USRA), T. Sakamoto (GSFC/ORAU), R. Starling (U. of Leicester)
on 29 May 2008; 0:40 UT
Password Certification: David M. Palmer (palmer@lanl.gov)

Subjects: X-ray, Gamma Ray, Soft Gamma-ray Repeaters
Referred to by ATEL #: 1555, 1558, 1564

(The following has also been submitted as GCN #7777, and is being resubmitted as an ATEL to bring it to the attention of the larger astronomical community.)

Swift has detected the resumption of activity of Soft Gamma Repeater SGR 1627-41 after a 9.8-year long quiescent period.  BAT detected the initial burst on 2008-05-28 at 08:21:43 UT, and a larger burst at 09:53:00.  This was followed by a 'forest' of dozens of bursts extending at least to 10:25:54.  The brightest burst seen thus far has a 15-50 keV flux of 550 times the Crab, averaged over a 0.128 second time interval.

Following the BAT detection, Swift observed the source with XRT on 2008 May 28th, starting from 12:58:14 UT.

This SGR was discovered in 1998 June when it emitted over 100 bursts clustered within 6 weeks (Kouveliotou et al. 1998, IAU Circ. 6944, 2; Woods et al. 1999, ApJ 519, L139); no further burst emission has been reported to date.

Preliminary results, based on the first 2 ks XRT observation, found a persistent and relatively constant X-ray source with a count rate of 0.06 +/- 0.01 cts/s at a position RA, Dec = 16 35 51.9, -47 35 23.0 (J2000) with an uncertainty of 4.1 arcsec (radius, 90% confidence level). This position is consistent with the Chandra coordinates of the SGR (Wachter et al. 2004, ApJ 615, 887).

The paucity of detected photons did not allow us to carry out a sensitive search for coherent pulsations (upper limits > 100% pulsed fraction at 3 sigma c.l.).

A single absorbed black body model fits well the spectrum with nH=6.8x10^22 cm^-2  and kT=0.8 keV (Mereghetti et al. 2006, A&A 450, 759). The observed flux is 6.5x10^-12 erg/cm2/s (unabsorbed: 7.3x10^-11). This persistent luminosity is the highest ever recorded from this source (and a factor ~50 higher than the September 2004 XMM-Newton values; Mereghetti et al. 2006).

Analysis of data from this burst is continuing, and will be reported in later circulars.

A plot of the BAT light curve for the forest can be seen at http://gcn.gsfc.nasa.gov/gcn/other/SGR1627-41_timeline_2008.png. The timeline of the previous outbursts can be seen at http://gcn.gsfc.nasa.gov/gcn/other/SGR1627-41_timeline.gif.

We thank the Swift Operations Duty Scientist and Flight Operations Team for performing a rapid ToO.


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