Swift-BAT monitoring for additional bursts from SGR J1745-29 (Trigger 554491)
ATel #5037; N. Gehrels, S. D. Barthelmy (GSFC), W. H. Baumgartner, J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU), C. B. Markwardt (GSFC), A. Maselli (INAF-IASFPA), D. M. Palmer (LANL), T. Sakamoto (AGU), G. Sato (ISAS), M. Stamatikos (OSU), T. N. Ukwatta (MSU), J. A. Kennea, M. C. Stroh, D. N. Burrows (PSU)
on 1 May 2013; 23:34 UT
Credential Certification: Craig B. Markwardt (Craig.Markwardt@nasa.gov)
Subjects: X-ray, Gamma Ray, Gamma-Ray Burst, Neutron Star, Soft Gamma-ray Repeater, Transient, Pulsar
The Swift Burst Alert Telescope (BAT) has continued to monitor the field of trigger 554491, which we designate SGR J1745-29, since the detection of the 32 msec burst at 19:15:25 UT on 25 April 2013 (GCN Circ. 14443, ATEL #5009). The burst location was (RA, Dec) 266.388, -28.982 (17h 45m 33.3s, -28d 59' 55") with an uncertainty of 2.1 arcmin (radius, 90% containment, including systematics) (ATEL #5009). This error circle includes the position of the NuSTAR 3.76 sec pulsar (ATEL #5020), also observed by Chandra (ATEL #5032) and that was found to have a rapidly changing period in the radio by Parkes and GBT (ATEL #5035). XRT was observing the field of the burst at the time of the burst and did not see any enhanced emission.
Short bursts like the one detected by BAT on 25 April are common for SGRs, but uncommon for other types of sources. The NuSTAR-discovered pulsar has a period that falls well within the magnetar period range, suggesting that the pulsar is related to the SGR.
Since the time of the burst, the source location has been in the central part (within 30 degrees of the axis) of the BAT field of view for 75 ksec with no new bursts seen. The 25 April hard X-ray burst was detected with 8.1 sigma significance, well above the 6.5 sigma imaging threshold of BAT. Swift spends substantial amounts of time monitoring the GC region with this source in the BAT field of view, and BAT has not detected any previous SGR-like bursts. The typical exposure time is 3.5 Ms per year.
