//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8723 SUBJECT: GRB 081224: Fermi GBM Detection & LAT Localization DATE: 08/12/25 00:43:55 GMT FROM: Valerie Connaughton at MSFC Colleen Wilson-Hodge (MSFC) and Valerie Connaughton (UAH) on behalf of the Fermi-GBM team, Francesco Longo (INFN Trieste) and Nicola Omodei (INFN Pisa) on behalf of the Fermi LAT team. "On 21:17:55.41 UT of Dec 24 2008 GBM detected a bright GRB. Preliminary analysis of the real-time Fermi GBM data from Trigger number 251846276/ GRB 081224887 / GRB 081224 shows that this is a FRED (Fast Rise Exponential Decay) lasting approximately 50 seconds with a peak of FWHM 15 sec long. It is located to a position of RA=206.2, Dec= 73.3 with statistical uncertainty 1 deg (and an estimated systematic uncertainty of 2-3 deg) which places it at 16 deg to the LAT boresight. The Large Area Telescope (LAT) also provided a tentative onboard localization: RA=213.367, DEC=74.233 (J2000) corresponding to: RA: +14h 13m 28s (J2000), DEC: +74d 13' 60" (J2000) with on board estimated error of 36 arcmin (statistical only). The current estimated onboard systematic error is 1 deg. The estimated LAT position is 2.2 deg from the ground GBM location and may be considered more reliable. Accurate LAT localization and spectral analysis will await the downlink of both LAT and GBM data which could take several hours. We further report that the Fermi Observatory executed a maneuver following this trigger and will track the burst location for the next 5 hours, subject to Earth-angle constraints. We encourage follow up observations. The Fermi LAT point of contact for this burst is Francesco Longo (francesco.longo@ts.infn.it). The Fermi GBM point of contact is Valerie Connaughton (valerie@nasa.gov) The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. This message can be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8725 SUBJECT: GRB 081224: Swift-XRT observation DATE: 08/12/25 10:17:22 GMT FROM: Kim Page at U.of Leicester K.L. Page and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift performed a Target of Opportunity follow-up observation of the Fermi GBM and LAT burst GRB 081224 (Wilson-Hodge et al., GCN Circ. 8723), starting 18 ks after the trigger. There is a faint X-ray source (~6.7x10^-3 count s^-1) within the XRT field of view, detected in the 3.6 ks of data collected so far. Using 1193 s of XRT Photon Counting mode data and 1 UVOT image, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 213.1494, 74.1999, which is equivalent to: RA (J2000): 14 12 35.85 Dec (J2000): +74 11 59.5 with an uncertainty of 3.4 arcsec (radius, 90% confidence). However, we note that the uncertainty on the LAT position (36 arcmin) is larger than the XRT field of view, so Swift has not observed the complete error circle. We also cannot say whether the XRT source is fading at this time. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8726 SUBJECT: GRB081224: LAT retraction DATE: 08/12/25 14:50:33 GMT FROM: Julie McEnery at UMBC/GSFC Julie McEnery (NASA/GSFC) reports on behalf of the LAT collaboration On-ground analysis of GRB 081224 did not confirm the tentative LAT on-board detection reported in GCN 8723. The apparent onboard excess was likely a statistical fluctuation. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8739 SUBJECT: GRB 081224: Suzaku WAM observation of the prompt emission DATE: 08/12/27 03:55:50 GMT FROM: Hidenori Hayasi at Miyazaki U H. Hayashi E. Sonoda, M. Yamauchi, H. Tanaka, R. Hara, N. Ohmori, K. Kono (Univ. of Miyazaki) A. Endo, M. Tashiro, Y. Terada, Y. Urata, K. Onda, N. Kodaka, K. Morigami, T. Sugasahara, W. Iwakiri (Saitama U.), T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo), S. Sugita, K. Yamaoka (Aoyama Gakuin U.), M. Ohno, M. Kokubun, M. Suzuki, T. Takahashi (ISAS/JAXA), Y.E. Nakagawa, T. Tamagawa (RIKEN), Y. Hanabata, T. Uehara, T. Takahashi, Y. Fukazawa, C. Kira (Hiroshima U.), S. Hong (Nihon U.), on behalf of the Suzaku WAM team, report: The long, bright GRB 081224 (Fermi-GBM trigger #251846276; Colleen et al., GCN 8725) triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 2008-12-24 21:17:55.214 UT (=T0). The observed light curve shows a FRED-like peak structure starting at T0-0.2s, ending at T0+19.8s with a duration (T90) of about 10.3 seconds. The fluence in 100 - 1000 keV was 2.87(+0.09, -0.04) erg/cm^2. The 1-s peak flux measured from T0+2s - T0+3s was 16.95(+0.91, -0.55) photons/cm^2/s in the same energy range. Preliminary result shows that the time-averaged spectrum from T0-0.2s to T0+19.8s is well fitted by a power-law with exponential cutoff model dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak) with alpha 0.83(+0.27, -0.28), and Epeak 447(+57, -40) keV (chi^2/d.o.f. = 19/22). All the quoted errors are at statistical 90% confidence level, in which the systematic uncertainties are not included. The light curves for this burst are available at: http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html