//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15505 SUBJECT: GRB 131120A: Swift detection of a burst DATE: 13/11/20 14:47:45 GMT FROM: David Palmer at LANL A. Maselli (INAF-IASFPA), S. T. Holland (STScI), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sakamoto (AGU), B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 14:37:56 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 131120A (trigger=578227). Swift could not slew to the burst due to a Sun constraint. The BAT on-board calculated location is RA, Dec 278.921, -11.997 which is RA(J2000) = 18h 35m 41s Dec(J2000) = -11d 59' 49" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is usual for image triggers, the immediately-available BAT lightcurve does not show strong variation. Due to a Sun observing constraint, Swift cannot slew to the BAT position until 15:39 UT on 2014 February 13. There will thus be no XRT or UVOT data for this trigger before this time. Burst Advocate for this burst is A. Maselli (maselli AT ifc.inaf.it). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15508 SUBJECT: GRB 131120A, Swift-BAT refined analysis DATE: 13/11/22 01:12:54 GMT FROM: Takanori Sakamoto at AGU A. Y. Lien (NASA/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU) (i.e. the Swift-BAT team): Using the data set from T-250 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 131120A (trigger #578227) (Maselli, et al., GCN Circ. 15505). The BAT ground-calculated position is RA, Dec = 278.937, -12.026 deg which is RA(J2000) = 18h 35m 44.8s Dec(J2000) = -12d 01' 34.8" with an uncertainty of 3.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 50%. The mask-weighted light curve shows two weak peaks at T-20 sec and T+50 sec. The emission starts at T-100 sec, and ends at T+80 sec. T90 (15-350 keV) is 131 +- 20 sec (estimated error including systematics). The time-averaged spectrum from T-71.1 to T+64.3 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.94 +- 0.50. The fluence in the 15-150 keV band is 5.7 +- 1.5 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+49.40 sec in the 15-150 keV band is 0.5 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/578227/BA/ We note that the fluence ratio in a simple power-law fit between the 25-50 keV band and the 50-100 keV band is 1.92. This fluence ratio is larger than 1.32 which can be achieved in the Band function of alpha=-1.0, beta=-2.5, and Epeak=30 keV. Thus, preliminary analysis shows that Epeak of the burst is very likely around or below 30 keV. Therefore the burst can be classified as an X-ray flash (e.g. Sakamoto et al. 2008, ApJ, 679, 570).