{
  "bibcode": "2006GCN..4949....1P",
  "body": "Please note: This is courtesy copy of Astronomer's Telegram #789 \nforwarded to the GCN mailing list due to its specific interest to the \nGamma-Ray community.  The URL for this Telegram is\nhttp://www.astronomerstelegram.org/?read=789\nPlease cite the ATEL, rather than the GCN.\n\nSwift-BAT observations of SGR 1900+14\n\nD. Palmer (LANL), T. Sakamoto (GSFC/ORAU), S. Barthelmy (GSFC),\nJ. Cummings (GSFC/ORAU), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),\nC. Markwardt (GSFC/UMD), J. Tueller (GSFC)\nreport on behalf of the Swift BAT team:\n\n\nThe recent re-activation of the Soft Gamma-ray Repeater SGR 1900+14 \n(Vetere et al. GCN# 4922) has been intensively observed by the Swift \nBurst Alert Telescope (BAT) as well as by the Swift UVOT and XRT \ninstruments.  Here we report on the BAT results.\n\nThe first detection by BAT was at 2006-03-25 10:12:04 UTC, and marked \nthe first detection of a burst from this source since 2003 (C. \nKouveliotou, priv. comm.)  The most recent burst was 2006-03-29 \n12:19:51 (as of 2006-04-03 11:00).  A total of 22 bursts or burst \nsequences have been identified by the onboard software (where a burst \nsequence is defined as a set of bursts separated from other detected \nbursts by at least 5 minutes, including gaps due to observational and \ninstrumental effects).\n\nIn the 5 months before this latest round of activity, the upper limit \nto steady-state emission on individual days with good observations of \nthis source is 30 mCrab (3 sigma).  In the 9-month interval \n2004-12-15 to 2005-09-15, the long-term average steady-state emission \nis less than 1.4 mCrab (5 sigma).\n\nThe greatest intensity of activity was during an interval starting \nbefore 2006-03-29 02:38:10 (when the SGR entered the BAT field of \nview) to 02:59:43 (beyond which there is no detected activity through \nthe end of the pointing at 03:13:11).  Within this time period there \nis a considerably more intense interval, 2:53:10 - 2:53:42, which we \nwill call the storm.  Event-by-event data is available for most of \nthis storm period.\n\nThe storm contains both wide and narrow peaks.  The narrow peaks have \ntypical widths of 10-100 ms and peak rates up to 400 counts/ms.  The \nwide peaks have peak rates falling in the narrow range of 400-850 \ncounts/ms and durations of up to 1.5 seconds.  (All rates are ~12-100 \nkeV measured on 1 ms timescales with approximately 2300 cm^2 \neffective area).\n\nThe wide peaks typically show a rapid rise (<10 ms) to near the \nmaximum value, a somewhat steady decline (at rates of ~1 \ncount/ms/ms), sometimes with instances of re-energization, to an \ninflection point typically at a rate around 200-400 counts/ms, \nfollowed by a precipitous drop over the next ~10 ms.\n\nFor spectroscopy, data from the narrow peaks were accumulated into a \nsingle spectrum for analysis, while the wide peaks were analyzed with \ntime-resolved spectra.\n\nThe accumulated spectrum of short peaks is well fitted with an \noptically thin thermal bremsstrahlung spectrum (OTTB), a power-law \ntimes an exponential cutoff model (CPL), and a sum of two blackbodies \nmodel (2BB). A single blackbody model shows a bad fit. kT of OTTB is \n21 keV. In 2BB model, the temperatures are 4.6 keV and 11.2 keV.\n\nThe time-resolved spectra of the bright peaks are well fitted in CPL \nand 2BB. But they show a bad fit in OTTB model, especially at the \nbright part.  However, if we ignore below spectral bins 30 keV, OTTB \nmodel shows an acceptable fit with  temperatures consistent with the \nKonus-Wind, RXTE and BATSE observations (Aptekar et al, ApJS, 137, \n227; Ibrahim et al. ApJ, 558, 237). The temperatures and the \nblackbody radii in 2BB model are consistent with the HETE-2 \nparameters (2001 activity; Olive et al., ApJ, 616, 1148). There \nappears to be an excess above 70 keV during the brightest parts of \nthe peaks.  However, since these spectra reach an intensity of 200 \nCrab, they are dominated by systematics, and the apparent excess may \nbe an artifact of our calibration.\n\nThis behavior is qualitatively consistent with confined fireball \nmodels.  The narrow peaks are optically thin fireballs, and the wide \npeaks are fireballs that are originally optically thick with \ncontracting photospheres that reach transparency at the inflection \npoint.  Quantitative comparison to this model awaits more detailed \ncalculation.\n\nLight curves and lists of burst times for this activity may be viewed \nat http://gcn.gsfc.nasa.gov/gcn/other/SGR1900+14_swift_bat.html\n\n-- \nDavid Palmer  palmer@lanl.gov   (505)665-6863 (voice)   (505)665-4414 (fax)",
  "circularId": 4949,
  "createdOn": 1144103693000,
  "email": "palmer@lanl.gov",
  "subject": "SGR 1900+14: BAT observations",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>"
}