//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 20286 SUBJECT: GRB 161218B: Fermi GBM detection DATE: 16/12/18 18:19:00 GMT FROM: Rachel Hamburg at UAH R. Hamburg (UAH), C. Meegan (UAH), and H. Yu (MPE) report on behalf of the Fermi GBM Team: "At 08:32:40.65 UT on 18 December 2016, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 161218B (trigger 503742764 / 161218356). The on-ground calculated location, using the GBM trigger data, is RA = 358.64, DEC = -16.95, with an uncertainty of 1.00 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a core-plus-tail model, with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ). The trigger resulted in an Autonomous Repoint Request (ARR) by the GBM Flight Software owing to the high peak flux of the GRB. This ARR was accepted and the spacecraft slewed to the GBM in-flight location. The initial angle from the Fermi LAT boresight to the GBM ground location is 80 degrees. The GBM light curve consists of multiple peaks with a duration (T90) of about 26 s (50-300 keV). The time-averaged spectrum from T0-2.0 s to T0+32.8 s is best fit by a Band function with Epeak = 214.80 +/- 2.51 keV, alpha = -0.51 +/- 0.01, and beta = -3.06 +/- 0.10. The event fluence (10-1000 keV) in this time interval is (8.91 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.7 s in the 10-1000 keV band is 74.1 +/- 0.6 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 20288 SUBJECT: GRB 161218B: POLAR observation DATE: 16/12/18 19:04:42 GMT FROM: Yuanhao Wang at IHEP/CAS Y. H. Wang (IHEP), Z. H. Li (IHEP), S. L. Xiong (IHEP) report for the POLAR collaboration: At 2016-12-18T08:32:41.341 UT (T0), during a routine on-ground  search of data, POLAR detected the GRB 161218B, which was also detected by the Fermi/GBM (trigger 503742764/161218356). The POLAR light curve consists of multiple peaks, with a duration (T90) of 26.28 s measured from T0+1.0 s . The 1s peak rate measured from T0+1.25 s is 9849 cnts/s, The total counts is about 29340 cnts.The above measurements are in the energy range of about 80-500 keV. The preliminary estimation of minimum detectable polarization(MDP) is 36.8%[3-sigma, statistical only]. Follow-up observations are strongly encouraged. LC_URL: http://polar.ihep.ac.cn/grb/2016/GRB161218B/lc/POLAR_lc_grb161218356.png Using the best location from the Fermi/GBM, which is (J2000): RA: 358.640 [deg] Dec: -16.950 [deg] Err: 1.00 [deg] the incident angle in POLAR coordinate at T0 is: theta:  77.7612  [deg] phi:   252.239  [deg] The analysis results presented above are preliminary. POLAR is a dedicated Gamma-Ray Burst polarimeter (50-500 keV) on-board the Chinese space laboratory Tiangong-2 launched on Sep 15, 2016. More information about POLAR can be found at http://polar.ihep.ac.cn/en/, http://isdc.unige.ch/polar/ and http://polar.psi.ch/html/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 20303 SUBJECT: IPN Triangulation of GRB 161218B (long/very bright) DATE: 16/12/20 09:25:37 GMT FROM: Dmitry Svinkin at Ioffe Institute D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, A. Kozlova, and T. Cline on behalf of the Konus-Wind team, K. Hurley, on behalf of the IPN, S. Barthelmy, J. Cummings, N. Gehrels, H. Krimm, and D. Palmer, on behalf of the Swift-BAT team, A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team, and V. Connaughton, M. S. Briggs, C. Meegan, V. Pelassa, and A. Goldstein, on behalf of the Fermi GBM team, report: The long-duration, very bright GRB 161218B has been detected by Fermi (GBM; Hamburg et al., GCN Circ. 20286), Konus-Wind, INTEGRAL (SPI-ACS), Swift (BAT), and POLAR (Wang et al., GCN Circ. 20288), so far, at about 30760 s UT (08:32:40). The burst was outside the coded field of view of the BAT. We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 0.888 (00h 03m 33s) -14.700 (-14d 42' 00") Corners: 2.344 (00h 09m 23s) -18.473 (-18d 28' 23") 3.138 (00h 12m 33s) -17.987 (-17d 59' 13") 359.466 (23h 57m 52s) -10.927 (-10d 55' 37") 358.690 (23h 54m 46s) -11.401 (-11d 24' 03") --------------------------------------------- The error box area is 7.05 sq. deg, and its maximum dimension is 8.0 deg (the minimum one is 53.5 arcmin). The Sun distance was 87 deg. This box may be improved. A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB161218_T30761/IPN The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 20304 SUBJECT: Konus-Wind observation of GRB 161218B DATE: 16/12/20 10:06:29 GMT FROM: Dmitry Frederiks at Ioffe Institute D. Frederiks, S. Golenetskii, R.Aptekar, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline, on behalf of the Konus-Wind team, report: The long GRB 161218B (Fermi-GBM detection: Hamburg et al., GCN 20286; POLAR observation: Wang et al., GCN 20288; IPN triangulation: Svinkin et al., GCN 20303) triggered Konus-Wind at T0=30761.134 s UT (08:32:41.134). The light curve starts with a bright, short pulse followed by a weaker emission; the total duration of the burst is ~30 s. The emission is seen up to ~10 MeV. As observed by Konus-Wind, the burst had a fluence of (8.6 ± 0.4)x10^-5 erg/cm2 and a 64-ms peak energy flux, measured from T0+1.344, of (2.7 ± 0.2)x10^-5 erg/cm2 (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+34.560 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.42 (-0.08,+0.08), the high energy photon index beta = -3.37 (-0.80,+0.31), the peak energy Ep = 203 (-8,+8) keV, chi2 = 106/97 dof. The spectrum near the peak count rate (measured from T0+0.256 to T0+1.536 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.08 (-0.18,+0.21), the high energy photon index beta = -2.71 (-0.24,+0.18), the peak energy Ep = 203 (-15,+16) keV, chi2 = 69/68 dof. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB161218_T30761/ All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 20324 SUBJECT: GRB 161218B: Astrosat CZTI detection DATE: 16/12/21 18:20:09 GMT FROM: Vedant Kumar at Astrosat/CZTI/IUCAA V. Kumar, D. Bhattacharya and V. Bhalerao (IUCAA), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data showed clear detection of a long duration and bright GRB161218B (Fermi-GBM detection: Hamburg et al., GCN 20286) in the 40-200 keV energy range. The light curve shows multiple peak structure with at least 4 clear peaks and main peak at 08:32:42.0 UT followed by a weaker emission, 1.35 secs after the Fermi- GBM trigger(consistent with GCN 20286). The measured peak count rate is 738.478 counts/sec above the background in combined data of four quadrants, with a total of 6025.78 counts. The local mean background count rate was 328.52 counts/sec. Using cumulative rates, we measure a T90 of 29.0 sec. CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.