//////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3155 SUBJECT: GRB 050331: Swift XRT Position DATE: 05/03/31 18:23:59 GMT FROM: David Burrows at PSU/Swift L. Angelini (GSFC), J. L. Racusin, S. Hunsberger, D. N. Burrows, J. E. Hill, J. A. Kennea, D. C. Morris, D. Grupe, J. A. Nousek (PSU), J. P. Osborne, K. L. Page, M. R. Goad, A. P. Beardmore, O. Godet, A. F. Abbey, A. A. Wells (U. Leicester), S. Campana, A. Moretti, C. Pagani, P. Romano, G. Tagliaferri, G. Chincarini (INAF-OAB), G. Cusumano, V. La Parola, V. Mangano, T. Mineo (INAF-IASF/Palermo), P. Giommi, M. Capalbi, M. Perri, F. Tamburelli (ASDC), F. Marshall, N. White, N. Gehrels (GSFC), P. Roming, P. Meszaros (PSU), P. Schady (MSSL), report on behalf of the Swift XRT team: The Swift spacecraft executed a prompt slew to GRB050331 (discovered by the Swift BAT). The XRT found a bright source located at the following position: RA(J2000) = 09:22:57, Dec(J2000) = -41:26:18 We estimate an uncertainty of about 6 arcseconds. This source is located 1.5 arcminutes from the BAT position. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3156 SUBJECT: Swift-BAT detection of GRB 050331 DATE: 05/03/31 18:40:05 GMT FROM: David Palmer at LANL D. Palmer (LANL), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cannizzo (GSFC/UMBC), J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markward (GSFC/UMD), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), A. Smale (NASA HQ) M. Suzuki (Saitama), J. Tueller (GSFC) on behalf of the Swift team: At 17:11:53 UT Swift-BAT triggered on a burst GRB 050331, and automatically slewed. A few of the standard GCN/Swift Notices were delayed, because this burst occurred during a regular Malindi telemetry downlink session. The BAT-derived position is RA,Dec=140.771,-41.430 (J2000). We note this is 91 arcsec from the XRT Position GCN Notice. The lightcurve has some low-significance peaks for the first ~15 sec, then two peaks at T+15 and T+18 sec (of 1 and 2 sec duration, resp.) with a total burst duration of ~20 sec. The peak count rate is ~1000 cnts/sec. -- //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3157 SUBJECT: GRB 050331: Swift UVOT Source DATE: 05/03/31 19:03:26 GMT FROM: Pete Roming at PSU M. Still (GSFC/USRA), W. Landsman (GSFC), A. Morgan, C. James (MSSL), S. Hunsberger (PSU), A. Breeveld (MSSL), P. Roming (PSU), K. Mason, P. Schady (MSSL), M. Ivanushkina (PSU), T. Poole (MSSL), C. Gronwall (PSU), A. Blustin (MSSL), P. Brown (PSU), S. Rosen, K. McGowan, M. De Pasquale (MSSL), P. Boyd (GSFC/UMBC), S. T. Holland (GSFC/USRA), M. Carter, H. Huckle (MSSL), P. Broos (PSU), T. Kennedy, P. Smith, B. Hancock (MSSL), S. Koch (PSU), S. Zane (MSSL), D. Hinshaw (GSFC/SPSYS), J. Nousek (PSU), N. Gehrels (GSFC), on behalf of the Swift UVOT team. The Swift Ultra-Violet/Optical Telescope (UVOT) began settled observations of the field of GRB 050331 (Angelini et al; GCN 3155) at 17:14:09 UT, 135s after the BAT trigger. The first data taken after spacecraft settling was a 100s V image, sent directly to the ground through the TDRSS system, with pixel binning of 8x8 to reduce telemetry. Binned pixel sizes are 4x4 arcsec and the field of view is 5.3x5.3 arcmin. An extremely bright source, consistent with the XRT position, is found in the image. A magnitude can not be determined at this time due to saturation of the detector (13.0 mag). //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3158 SUBJECT: Swift-BAT detection of GRB 050331b DATE: 05/03/31 19:52:38 GMT FROM: Craig Markwardt at NASA/GSFC/UMD C. B. Markwardt (GSFC/UMD), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cannizzo (GSFC/UMBC), J. Cummings (GSFC/NRC), M. DePasquale (MSSL), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), H. Krimm (GSFC/USRA), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), A. Smale (NASA HQ), M. Suzuki (Saitama), J. Tueller (GSFC) on behalf of the Swift team: At 18:44:04 UT Swift-BAT triggered on GRB 050331b, trigger 112981, a second burst within ninety minutes. The BAT-derived position is RA,Dec= 143.840,-42.678 (J2000). We note this is 81 arcsec from the XRT Position GCN Notice. The lightcurve has a series of low-significance peaks covering a total burst duration of ~30 sec. The light curve also shows a slow rise from T+60 to T+160 s in the lowest energy bands. We believe that this slow variation is due to Vela X-1, which is within 10 degrees of the GRB position. While similar in duration to GRB 050331a, the light curve of GRB 050331b is significantly different in appearance. The peak count rate is ~1000 cnts/sec. NOTE: This is the second verified burst of the day. The earlier burst, now called GRB 050331a, trigger 112977, was located 2.6 degrees away from this burst (trigger 112981). The wide angular separation, and dissimilar light curves make it highly unlikely that these two bursts are a gravitationally lensed pair. The two bursts GRB 050331a and GRB 050331b are two distinct bursts. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3159 SUBJECT: GRB050331: No Afterglow Detected DATE: 05/03/31 20:47:13 GMT FROM: Aaron Price at AAVSO B. Monard and A. Price report on behalf of the AAVSO International High Energy Network on optical observations of the field of GRB050331 (GCN#3156 Palmer et al.). A field centered on the coordinates of the XRT position in GCN #3155 (Burrows et al.) was observed at midpoint time of 19:03 UT and compared with the DSS/POSS red plate. The CCD was unfiltered but with a red zeropoint response. No new source was identified down to a limiting magnitude (SNR=3) of 20. Full details on the report is below along with a link to the FITS image: Report filed on March 31 22:08 UT Name: Berto Monard email: bmonard@mweb.co.za Site: Bronberg Observatory / CBA Pretoria Location: -25 º 54' 48", 28º 26' 44"E Elevation: 1590m Scope: LX200 31cm ScopeFocalRatio: f/3.7 CCDVendor: SBIG, ST-7XME CCDPixelScale: about 1.8 arcsec /pixel CCDFOV: 21 arcmin (E/W) x 14 arcmin (N/S) Object: GRB 050331 ObsDate: 050331 ObsMidPointTime: 19 03 UT Exposure per frame: 28 sec NumberOfFrames: 35 stacked Filters: none Processing: dark/flat Seeing: fair (about 3.5 arcsec) LimitingMag: about 21CR for stack Sky: open / no moon / object near zenith afterglowmag: none down to magnitude 20CR Report: the observed star field was set to be centered on 09 22 57 -41 25 48. The obtained deep image was compared visually to a DSS-2 red image over the entire error box of 4 arcmin. No new object was found to an estimated limit of 20 CR and no further observations are planned. FITS image is located at http://www.aavso.org/tmp/grb050331.fits ///////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3160 SUBJECT: Retraction of three Swift GRB triggers DATE: 05/03/31 21:17:08 GMT FROM: David Burrows at PSU/Swift N. Gehrels (GSFC), J. A. Nousek (PSU), S. Barthelmy (GSFC), D. N. Burrows, P. Roming (PSU), report on behalf of the Swift team: The Swift team reported three GRBs earlier today, but has now determined that all of these triggers (BAT triggers 112977, 112981, and 112982; GCN Circulars #3155, 3156, 3157, 3158) were due to Vela X-1. The positions were assigned incorrectly due to attitude errors on the spacecraft. All of these triggers are being retracted. Swift has not found a true GRB yet today.