//////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4985 SUBJECT: GRB(?) 060421: Swift detection of a burst DATE: 06/04/21 01:15:46 GMT FROM: Scott Barthelmy at NASA/GSFC M. R. Goad (U Leicester), L. M. Barbier (NASA/GSFC), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), P. J. Brown (PSU), D. N. Burrows (PSU), J. R. Cummings (NASA/ORAU), N. Gehrels (NASA/GSFC), S. T. Holland (GSFC/USRA), J. A. Kennea (PSU) and D. M. Palmer (LANL) report on behalf of the Swift Team: At 00:39:23 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060421 (trigger=206257). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 343.630,+62.727 {22h 54m 31s, +62d 43' 37"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a multi-peak structure starting at about T-5sec and lasting to at least T+20 sec (a duration of about 25 sec). The peak count rate was ~6000 counts/sec (15-350 keV), at ~3 sec after the trigger. This source is coincident with the Cepheus OB3 molecular cloud association in our Galaxy. Therefore it is possible that this burst (galactic long,lat = 109.99, +2.83) was from a galactic source. The XRT began taking data at 00:40:50 UT, 88 seconds after the BAT trigger. The XRT on-board centroid algorithm did not find a source in the image and no prompt position is available. Analysis of down-linked image data reveals no obvious X-ray point source in the field. We are waiting for the full down-linked dataset to detect and determine a position for the source, and to determine the nature of this source. UVOT took a finding chart exposure of 400 seconds with the V filter starting 85 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of the BAT error circle. The typical 3-sigma upper limit has been about 18.5 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the BAT error circle. The limiting magnitude is expected to be about 17.7. No correction has been made for the large, but uncertain extinction expected. Results from analysis of downlinked data will not be available until approximately 09:00UT. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4986 SUBJECT: Possible GRB060421: BART limits DATE: 06/04/21 07:45:54 GMT FROM: Martin Jelinek at Inst.Astrophys.Andalucia,Granada Jan Strobl, Martin Topinka, Martin Nekola and René Hudec (ASU Ondrejov, Czech Republic), Petr Kubánek (ISDC Versoix, Swtzerland and ASU Ondrejov) and Martin Jelínek (IAA Granada) report Robotic telescope BART located in Ondrejov observatory in Czech Republic, followed the Swift trigger 206257 (Goad et al, GCN 4985). The observation in fully automatic mode (under control of RTS2), started 33.7s after the Swift trigger time. We did not find any new optical source. Particularly we set the following limits: Tmean Exp limit 44s 20s B>14.2 98.0s 20s V>15.2 152s 20s i>15.3 206s 20s z>14.3 184s 8x45s R>15.3 The magnitudes are calibrated against USNO-A2.0. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4987 SUBJECT: GRB(?)060421 : XRT position DATE: 06/04/21 09:05:47 GMT FROM: Michael Goad at U Leicester Mike Goad, Kim Page (U Leicester) report on behalf of the Swift XRT team : From a ground analysis of 436 seconds of PC mode data starting 98 seconds after the BAT trigger (trigger no. 206257) we detect a fading source at position RA 22 54 32.4, Dec +62 43 49.0 (J2000), with an estimated uncertainty of 4.1 arcseconds (90% containment). This circular is an official product of the Swift XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4988 SUBJECT: GRB(?)060421:MASTER optical limit DATE: 06/04/21 11:50:19 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, V.Kornilov, N.Tyurina, A.Belinski, D.Kuvshinov, E.Gorbovskoy, A.Krylov, G.Borisov, A.Sankovich, V.Vladimirov, P.Gritsyk, S.Korobkin Sternberg Astronomical Institute, Moscow Union 'Optic' MASTER robotic system (http://observ.pereplet.ru) responded to GRB060421 (GRB_TIME is 2006-04-21 00:39:23.33, M. R. Goad et al. GCN4985). Unfortunaly 2 minutes before notice time roof closed roboticaly due to meteo alert "cloudy". The first image was at 2006-04-21 00:48:45 UT, 562 s after the GRB time. The unfiltered image is calibrated relative to USNO A2.0 (0.8 R + 0.2 B). The robot not find OT-candidate in error box brighter then 16.8 (s/n=3) at Swift XRT position (Mike Goad, Kim Page GCN4987). This work is supported by RFFI 04-02-16411 grant. This message can be cited. Mailto: lipunov@sai.msu.ru //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4992 SUBJECT: GRB 060421: Swift-XRT refined analysis DATE: 06/04/21 15:32:18 GMT FROM: Kim Page at U.of Leicester M.R. Goad, K.L. Page (U Leicester) and D.N. Burrows (PSU) report on behalf of the Swift-XRT team: We have analysed the first 14 ks of Photon Counting (PC) mode data, starting 97 seconds after the BAT trigger time, determining a refined position of RA (J2000): 22 54 32.63 Dec(J2000): +62 43 50.07 with an estimated uncertainty of 3.8 arcsec (90% containment). This is 1.7 arcsec from the initial XRT position given by Goad & Page in GCN 4987 and 16.2 arcsec from the on-board BAT position quoted in GCN 4985 (Goad et al.) The X-ray source was initially quite faint, with a peak count rate of only ~1 count s^-1. The light-curve shows a flat decay of alpha = 0.49 +/- 0.29, breaking to a steeper slope of alpha = 1.54 +/- 0.36, approximately 1500 seconds after the burst. Because of the faintness of the afterglow, only 3 seconds of data were obtained in Windowed Timing mode before switching into PC. The first orbit of PC data (97-717 seconds post-trigger) can be modelled with a simple power-law of Gamma = 1.54 +/- 0.34, with the Galactic absorbing column of 1e22 cm^-2. The observed (unabsorbed) flux over 0.3-10 keV for this time period is 3.78e-11 (5.64e-11) erg cm^-2 s^-1. Assuming the current rate of decay continues, the estimated count rate at 24 hours is 4.2e-3 count s^-1, corresponding to an observed (unabsorbed) flux of 4.55e-14 (6.38e-14) erg cm^-2 s^-1. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4993 SUBJECT: GRB 060421: Swift-BAT Refined Analysis DATE: 06/04/21 15:34:38 GMT FROM: Louis M Barbier at NASA/GSFC/Swift E. Fenimore (LANL), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/ORAU), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (ISAS), J. Tueller (GSFC), on behalf of the Swift-BAT team: Using the data set from T-120 to T+78 sec from the recent telemetry downlink, we report further analysis of BAT GRB 060421 (trigger #206257) (Goad, et al., GCN 4985). The BAT ground-calculated position is (RA,Dec) = 343.627, 62.730 deg {22h 54m 30.4s, 62d 43' 47.0"} (J2000) +- 0.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 82%. The mask-weighted light curve shows one strong peak followed by several smaller peaks extending out to 10 seconds after the trigger. T90 (15-350 keV) is 11 +- 1 sec (estimated error including systematics). The time-averaged spectrum from T-3.8 to T+10.9 is well fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.53 +- 0.07. The fluence in the 15-150 keV band is 1.2 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+2.28 sec in the 15-150 keV band is 3.0 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. Based on the shape of the light curve and the hard spectrum, we believe that this is a GRB, however, we can not rule out a hard x-tray transient nature of this event. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4994 SUBJECT: GRB060421: Swift/UVOT observations DATE: 06/04/21 17:04:13 GMT FROM: Peter Brown at PSU P. J. Brown (PSU), M. R. Goad (U Leicester), S. T. Holland (GSFC/USRA), & P. O'Brien (U Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began taking settled exposures of the field of GRB0604213 at 2006-04-21 00:40:48, 84 s after the BAT trigger (Goad et al., GCN 4985). Within the revised XRT error circle (Goad, Page, & Burrows GCN 4992) we detect a V=19.0 +/- 0.2 source at 22:54:32.18, +62:43:49.5 (+/- 1") which is coincident with 2MASS 22543217+6243493 and also visible in the DSS. This source does not vary over ~5 hours of observations and is not considered an afterglow candidate. We do not detect this or any other sources in summed images from any of the other filters down to the following three-sigma upper limits. Filter T_range(s) Exp(s) 3sig_UL V 84-17355 1700 19.0 B 562-23873 1116 20.6 U 538-23145 2035 20.5 UVW1 514-22233 2204 20.2 UVM2 490-18091 2074 20.4 UVW2 578-16442 1318 20.2 These upper limits are uncorrected for extinction. The Galactic latitude is +2.83 degrees and the Schlegel et al. (1998) reddening in this direction is E(B-V)=1.28 mag. As noted in GCN 4985 the Cepheus OB3 molecular cloud association in our Galaxy is near this line of sight. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4999 SUBJECT: GRB 060421: TTT Observations DATE: 06/04/24 02:50:10 GMT FROM: Chelsea Louise MacLeod at UNC-Chapel Hill/PROMPT C. MacLeod, J. Harvey, A. Trotter, M. Nysewander, A. LaCluyze, D. Reichart, A. Crain, K. Ivarsen, A. Foster, J. Haislip, J. Kirschbrown, and J. Carpenter report on behalf of the UNC team of the FUN GRB Collaboration: Skynet observed the localization of GRB 060421 (Goad et al., GCN 4985; Goad & Page, GCN 4987; Goad, Page & Burrows, GCN 4992) with 14.5-inch TTT in Colorado beginning 2.2 hours after the burst in variable conditions: Filter Start (UT) Stop (UT) Exposures Total (min) Red* 02:49:45 03:12:03 6 x 160s 16.0 Green** 03:13:48 03:34:41 6 x 160s 16.0 Blue 03:35:51 03:54:51 5 x 160s 13.3 Red* 03:57:17 04:15:58 5 x 160s 13.3 Green** 04:19:00 05:00:41 11 x 160s 29.3 Blue 05:02:14 05:42:19 11 x 160s 29.3 Red* 05:44:56 06:28:07 11 x 160s 30.7 + 1 x 80s Green** 06:29:39 07:12:54 11 x 160s 29.3 Blue 07:14:37 07:55:35 11 x 160s 29.3 Red* 07:57:16 09:20:36 19 x 160s 50.7 Green** 09:22:42 10:45:43 21 x 160s 56.0 Blue 10:48:00 11:06:50 5 x 160s 13.3 * Approximates R band ** Approximates V band No new source is found to V > 18.3 mag (3 sigma; calibrated to five NOMAD stars) at 4.0 hours after the burst.