//////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3296 SUBJECT: Swift Detection of GRB050421 DATE: 05/04/21 05:52:28 GMT FROM: Louis M Barbier at NASA/GSFC/Swift L. Barbier (GSFC), D. Palmer (LANL), D. Burrows (PSU), A. Blustin (MSSL), C. Markwardt (GSFC/UMd), N. Gehrels (GSFC), P. Roming (PSU) At 04:11:52 UT, the Swift Burst Alert Telescope (BAT) triggered and located on-board GRB050421 (trigger # 115135). The BAT on-board calculated location is RA, Dec 307.241, +73.665 (20:28:58, 73:39:54) (J2000) with an uncertainty of 4 arcmin (radius, 3-sigma, including estimated systematic uncertainty). The BAT light curve showed a weak, multipeak structure with a duration of about 10 seconds. The peak count rate was measured by BAT to be 1000 counts/sec in the 15 - 350 keV band. The Swift spacecraft slewed promptly onto the BAT position and observations by the Swift X-Ray Telescope (XRT) began at 04:13:42 UT with the XRT in the auto state. An uncatalogued X-ray source was detected at the following position: RA, Dec 307.2542, +73.6528 (20:29:01, 73:39:10) (J2000) with an uncertainty of 5 arcsec (radius). This is 46 arcsec from the BAT position reported above. The Swift Ultra-Violet/Optical Telescope (UVOT) began observations 112 seconds after the burst at 04:13:44 UT. Information on UVOT observations will be published in the next GCN. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3297 SUBJECT: GRB 050421: Optical observations at the INT DATE: 05/04/21 07:43:55 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia A. de Ugarte Postigo (IAA-CSIC), J. Furnes, R. Corradi (ING, La Palma), M. Jelinek, J. Gorosabel and A. J. Castro-Tirado (IAA-CSIC Granada), report: "Following the detection by SWIFT/BAT of GRB 050421 (Barbier et al. GCN Circ. 3296), we started observations at the 2.5m Isaac Newton Telescope at Observatorio del Roque de los Muchachos in La Palma. The first 120-s image (in the Sloan i-band filter), started on Apr 21.1858 UT (i.e. 15.7 min after the event). We do not see any object within the reported SWIFT/XRT position. Further analysis of additional i-band images is in progress." This message can be quoted. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3298 SUBJECT: GRB 050421: BOOTES-2 simultaneous optical observations DATE: 05/04/21 07:57:42 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia M. Jelinek, A. J. Castro-Tirado, J. Gorosabel, A. de Ugarte Postigo (IAA-CSIC Granada), P. Kubanek, R. Hudec (Astronomical Institute of the Academy of Sciences, Ondrejov), T. J. Mateo Sanguino (Universidad de Huelva), T. Soria, R. Fernández (EELM-CSIC, Málaga) and J. Fabregat (Universidad de Valencia) report: "The BOOTES-2 very wide field camera, located at the Estación Experimental de La Mayora (EELM-CSIC) in Málaga, observed the region of the sky containing the SWIFT/BAT error box for GRB 050421 (Barbier et al. GCN 3296) as part of its routine observing schedule. A 30 s exposure started at 04:12:00 UT (8 s after the onset of the 10 s long burst), with the previous frame starting at 04:11:00 UT. A limiting (unfiltered) magnitude of 9.0 is derived for any prompt optical flash arising from this event." This message can be quoted. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3299 SUBJECT: GRB050421: P60 Observations DATE: 05/04/21 09:54:40 GMT FROM: S. Bradley Cenko at Caltech S. Bradley Cenko and Derek B. Fox (Caltech) report on behalf of the Caltech-NRAO-GRB collaboration: We have imaged the field of GRB050421 (GCN #3296) with the automated Palomar 60-inch telescope. Observations consisted of 17 x 120 s images in the Kron R band, taken at a mean epoch of 08:50 UT (~ 4.6 hours after the burst). We find no sources in the XRT error circle reported in GCN #3296. Our 3.0-sigma limiting magnitude, estimated by comparison with several stars from the Guide Star Catalog, is approximately R < 22.0. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3300 SUBJECT: GRB 050421: NIR observations DATE: 05/04/21 10:08:29 GMT FROM: Daniele Malesani at SISSA-ISAS,Trieste,Italy D. Fugazza (INAF-OABr), L.A. Antonelli, V. Testa (INAF-OAR), L. Di Fabrizio, G. Tessicini (INAF-TNG), and D. Malesani (SISSA), report on behalf of a larger collaboration: We imaged the field of GRB 050421 (Barbier et al., GCN 3296) with the Italian 3.6m TNG. Observations were carried out under moderate observing conditions (seeing ~0.8"), just before the dawn. Exposures were acquired in the K filter, for a total integration time of 20 min, starting on Apr 21.2313 UT (mean time Apr 21.2453 UT, 1.7 h after the GRB). We find no sources within the XRT error circle, down to a limiting magnitude K = 18.6 (3 sigma). This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3301 SUBJECT: GRB 050421: early Swift XRT analysis results DATE: 05/04/21 10:59:17 GMT FROM: David Burrows at PSU/Swift O. Godet, M. Goad, K. Page, J. Osborne (U. Leicester), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC) report on behalf of the Swift XRT team: We have analyzed the Swift XRT data from the first orbit observation of GRB 050421. The refined coordinates are: RA(J2000) = 20h 29m 01.75s Dec(J2000) = +73d 39' 17.4" This position is 40 arcseconds from the BAT position given in GCN 3296 (Barbier et al 2005). We estimate a total uncertainty of 5 arcseconds radius (90% containment). We note that this refined position is 8.1 arcseconds from the XRT position reported in GCN 3296. Optical observers should re-check their images for sources in the new error circle. Our 0.2-10 keV light curve covers the interval 116-591 sec after the BAT trigger. It is well-fit with a broken powerlaw with initial slope of 0.9 +1.1/-1.6 breaking to a steeper slope of 3.3 +0.6/-0.3 after 147 +/-10 sec. All errors are 90% confidence. A single power law decline is not a good fit to the data. A preliminary spectral fit to the WT mode data gives a power law photon index of 1.23 +0.37/-0.34 (error at 90% confidence level) in the 0.3-10 keV band, assuming Galactic absorption (1.44 E21 cm^-2) and a possible excess in the absorption of 6 +4/-3 E21 cm^-2. The unabsorbed 0.3-10 keV flux is 8.5E-10 erg cm^-2 s^-1 in the interval 116-171 sec after the BAT trigger. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3302 SUBJECT: GRB050421 DATE: 05/04/21 12:48:00 GMT FROM: Guy Pooley at MRAO, Cambridge, UK The field of GRB050421 (GCN 3296, using the updated position in GCN 3301) was observed with the Ryle Telescope in Cambridge at 15 GHz from 08:37 to 12:12 UT on 2005 Apr 21 (4h25m to 8h after the trigger). The angular resolution is 25". A formal measure of the flux density at the position in GCN 3301 is 0.59 mJy with an rms noise 0.27 mJy, and is therefore not a convincing detection. This message is quotable. Guy Pooley, Astrophysics, Cavendish Laboratory //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3303 SUBJECT: GRB 050421: NIR observations re-examination DATE: 05/04/21 13:01:48 GMT FROM: Daniele Malesani at SISSA-ISAS,Trieste,Italy V. Testa, L.A. Antonelli (INAF-OAR), D. Fugazza (INAF-OABr), L. Di Fabrizio, G. Tessicini (INAF-TNG), and D. Malesani (SISSA), report on behalf of a larger collaboration: After the revision of the XRT position (Godet et al., GCN 3301) of the X-ray afterglow of GRB 050421 (Barbier et al., GCN 3296), we re-examined our TNG K-band images (Fugazza et al., GCN 3300). We find no sources within the revised XRT error box down to the 3-sigma limit K > 18.6. This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3304 SUBJECT: GRB 050421: ROTSE-III Optical Limits DATE: 05/04/21 15:24:42 GMT FROM: Eli Rykoff at U of Michigan/ROTSE E.S. Rykoff (U Mich), S.A. Yost (U Mich), H. Swan (U Mich) report on behalf of the ROTSE collaboration: ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB 050421 (Swift trigger 115135), producing images beginning 9.7 s after the GCN notice time. An automated response took the first image at 04:12:58.8 UT, 67.2 s after the burst, under good conditions. These observations were affected by the bright moon. We took 10 5-sec, and 350 20-sec eposures. These unfiltered images are calibrated relative to USNO A2.0 (R). Comparison to the DSS (second epoch) reveals no new sources within the 3-sigma BAT error circle including the 3-sigma XRT error circle (GCN 3301). Individual images have limiting magnitudes ranging from 16.49-17.34. In particular, we set a limit of magnitude 16.49 in a single 5 s exposure, starting 67.1 s after the burst. Coadding images into sets of 10 reveals no new sources down to limits of 17.8 (t0+61.7s - t0+130.7s) and 18.4 (t0+144s - t0+431s) //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3305 SUBJECT: GRB 050421: Swift-BAT refined analysis DATE: 05/04/21 15:44:53 GMT FROM: Louis M Barbier at NASA/GSFC/Swift T. Sakamoto (GSFC/NRC), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), T. Mitani (ISAS), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), M. Suzuki (Saitama), J. Tueller (GSFC), on behalf of the Swift/BAT team: At 04:11:52 UT Swift-BAT detected GRB 050421 (trigger=115135) (GCN Circ 3296, Barbier et al.). The refined BAT ground position is (RA,Dec) = 307.306, +73.665, [deg; J2000] +- 3.4 arcmin, (95% containment). The partial coding was 91%. The light curve has a FRED structure with a rise in < 1 second and a decay in ~10 seconds. T90 (15-350 keV) is (10.3 +- 2) seconds (estimated error including systematics). The photon index of the time-averaged spectrum is 1.7 +-0.4. The fluence in the 15-350 keV band is (1.8 +- 0.7 ) x 10^-7 erg/cm2. The 1-s peak photon flux measured from T0+1.4 seconds in the 15-350 keV band and is (0.5 +- 0.1) ph/cm2/s. All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3306 SUBJECT: GRB 050421: IR Observations DATE: 05/04/21 15:58:46 GMT FROM: Josh Bloom at Harvard/CFA J. S. Bloom (UCB) reports on behalf of a larger collaboration: "We observed the field of GRB 050421 (GCN 3296, GCN 3301) with the PAIRITEL 1.3m on Mt. Hopkins over several epochs. In a 502 sec exposure beginning on 2005-04-21 11:23:45 UT, we find a faint source in J,H,Ks, consistent with XRT position, located at: RA 20:29:00.94 DEC +73:39.19.2 (J2000; uncertainty ~ 0.5 arcsec) We have not checked the variability of this source so its identification as the afterglow cannot be confirmed at this time. We note that there is also a JHKs source just outside the XRT 5 arcsec error radius at (end figures): 02.01, 22.3." This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3307 SUBJECT: GRB 050421: Swift-UVOT observation DATE: 05/04/21 17:36:02 GMT FROM: Alexander Blustin at MSSL-UCL A. Blustin (MSSL), L. Barbier (GSFC), K. McGowan (MSSL), P. Roming (PSU), M. De Pasquale (MSSL), S. T. Holland (GSFC), N. Gehrels (GSFC), K. Mason (MSSL), J. Nousek (PSU), on behalf of the Swift UVOT team Starting with the data taken ~245s after the BAT trigger (Barbier et al., GCN 3296) we have co-added the early time data of GRB 050421 in each of the Ultra-Violet/Optical Telescope (UVOT) V, B and U bands. The co-added images are made up of 9 x 10s exposures. No source is detected within the revised XRT error circle (Godet et al., GCN 3301) in any of the bands; we estimate the five sigma magnitude upper limits from the co-added images to be: Filter Upper limit V 17.5 B 19.1 U 18.8 The magnitudes are based on preliminary zero-points, measured in orbit, and will require refinement with further calibration. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3308 SUBJECT: GRB050421: Radio Observations DATE: 05/04/21 17:49:52 GMT FROM: Alicia Soderberg at Caltech A. M. Soderberg (Caltech) and D. A. Frail (NRAO) report on behalf of the Caltech-NRAO-Carnegie GRB Collaboration: "We observed the field centered on the BAT position of the Swift burst GRB 050421 (GCN#3296) using the VLA at a frequency of 8.46 GHz on Apr 21.62 UT (t ~ 0.4 days after the burst). We do not detect any radio sources within the XRT error circle (GCN#3301). We place a 2-sigma detection limit of 34 uJy on the field." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3309 SUBJECT: GRB050421: Radio Observations DATE: 05/04/21 18:43:58 GMT FROM: Alicia Soderberg at Caltech A. M. Soderberg (Caltech) and D. A. Frail (NRAO) report on behalf of the Caltech-NRAO-Carnegie GRB Collaboration: "We observed the field centered on the BAT position of the Swift burst GRB 050421 (GCN#3296) using the VLA at a frequency of 8.46 GHz on Apr 21.62 UT (t ~ 0.4 days after the burst). We do not detect any radio sources within the XRT error circle (GCN#3301). We place a 2-sigma detection limit of 34 uJy on the field." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3310 SUBJECT: GRB 050421: Further Analysis of IR imaging DATE: 05/04/21 19:00:29 GMT FROM: Josh Bloom at Harvard/CFA C. Blake and J. S. Bloom report on behalf of a larger collaboration: "Following further analysis of ~2000 seconds of J,H,Ks observations of the field of GRB 050421 (GCN 3296, GCN 3301) with the PAIRITEL 1.3m on Mt. Hopkins we cannot confirm variability in the source reported in GCN 3306. Furthermore, analysis of our full J,H,Ks data set from UT April 21 does not reveal any sources detected at >3 sigma within the XRT error-circle." This message may be cited.