//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7639 SUBJECT: GRB 080426: Swift detection of a possibly short burst DATE: 08/04/26 13:49:12 GMT FROM: David Burrows at PSU/Swift H. Ziaeepour (UCL-MSSL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), C. Guidorzi (INAF-OAB), S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU), N. P. M. Kuin (MSSL), J. Mao (INAF-OAB), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester), S. R. Oates (UCL-MSSL), C. Pagani (PSU), D. M. Palmer (LANL), D. Perez (U Leicester), R. L. C. Starling (U Leicester), G. Tagliaferri (INAF-OAB), T. N. Ukwatta (GSFC/GWU) and P. A. Ward (MSSL-UCL) report on behalf of the Swift Team: At 13:23:22 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 080426 (trigger=310219). Swift slewed to the burst after a brief delay due to Earth limb constraint. The BAT on-board calculated location is RA, Dec 26.574, +69.492 which is RA(J2000) = 01h 46m 18s Dec(J2000) = +69d 29' 30" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of about 2 sec. The peak count rate was ~7500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 13:27:05.2 UT, 222.5 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 26.49931, 69.46856 which is equivalent to: RA(J2000) = 01h 45m 59.83s Dec(J2000) = +69d 28' 06.8" with an uncertainty of 2.8 arcseconds (radius, 90% containment). This location is 126 arcseconds from the BAT onboard position, within the BAT error circle. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 3.65e+21 cm^-2 (Kalberla et al. 2005), so we cannot constrain the redshift at this time using the relation from Grupe et al. (2007). A summary of the promptly downlinked data is given at http://www.swift.ac.uk/sper/310219/. UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)filter starting 226 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. 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 XRT error circle. The list of sources is typically complete to about 18mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.79. Burst Advocate for this burst is H. Ziaeepour (hz AT mssl.ucl.ac.uk). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7640 SUBJECT: GRB 080426, Swift-BAT refined analysis DATE: 08/04/26 18:37:17 GMT FROM: Scott Barthelmy at NASA/GSFC J. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD), D. Palmer (LANL), T. Sakamoto (GSFC/UMBC), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU), H. Ziaeepour (UCL-MSSL) (i.e. the Swift-BAT team): Using the data set from T-119 to T+183 sec from recent telemetry downlinks, we report further analysis of BAT GRB 080426 (trigger #310219) (Ziaeepour, et al., GCN Circ. 7639). The BAT ground-calculated position is RA, Dec = 26.510, 69.469 deg which is RA(J2000) = 01h 46m 02.4s Dec(J2000) = +69d 28' 07.9" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 43%. The mask-weighted light curve shows a single spike starting at T+0 and ending at T+2.0 sec. The lag analysis yields: Lag31 = 88 +/- 9 ms (50-100 to 15-25 keV bands) Lag21 = 74 +/- 6 ms (25-50 to 15-25 keV bands) T90 (15-350 keV) is 1.7 +- 0.4 sec (estimated error including systematics). While the T90 value puts this burst in the middle of the long and Short burst T90-distribution peaks, the lag value puts this burst in the Long burst class. The time-averaged spectrum from T+0.1 to T+2.3 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.98 +- 0.13. The fluence in the 15-150 keV band is 3.7 +- 0.3 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-0.08 sec in the 15-150 keV band is 4.8 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence level. We note that this is an unusual burst. The T90 for the 50-300 keV BATSE range is 1.3 sec which would put it in the short class in that era. However, the long lag and a spectrum that is not hard lead us to believe it is in the long class. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/310219/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7641 SUBJECT: GRB 080426: Enhanced Swift-XRT position DATE: 08/04/26 18:42:21 GMT FROM: Phil Evans at U of Leicester A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 894 s of overlapping XRT Photon Counting mode and UVOT data for GRB 080426, 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 = 26.49890, +69.46823 which is equivalent to: RA (J2000): 01h 45m 59.74s Dec (J2000): +69d 28' 05.6" with an uncertainty of 1.8 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401 http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an extension of this method. This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7642 SUBJECT: GRB080426: Swift/UVOT upper limits DATE: 08/04/26 20:37:54 GMT FROM: Samantha Oates at MSSL S.R. Oates (UCL-MSSL) and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift/UVOT team. The Swift/UVOT began settled observations the field of GRB 080426 (trigger 310219) 226 seconds after the BAT trigger (Ziaeepour, et al., GCN Circ. 7639). No afterglow is detected at the enhanced XRT position (Beardmore, et al., GCN Circ. 7641) in any of the UVOT filters. The 3 sigma upper limits are given below: Filter T_start T_stop Exp. Mag UL (3sig) (s) (s) ------------------------------------------------ white 226 326 98 >20.38 white 446 7457 362 >20.86 v 333 7868 1316 >19.98 b 431 7253 303 >20.01 u 407 7047 333 >19.79 uvw1 382 6843 352 >19.99 uvm2 357 7969 407 >19.94 uvw2 462 7663 510 >20.26 ------------------------------------------------- These upper limits are not corrected for the Galactic extinction in the line of sight, corresponding to a reddening of E(B-V)= 0.798 mag (Schlegel et al., 1998, ApJS, 500, 525). The photometry is based on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383, 627). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7643 SUBJECT: GRB 080426: Swift-XRT refined analysis DATE: 08/04/26 22:03:22 GMT FROM: Andy Beardmore at U Leicester A.P. Beardmore (U. Leicester) and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift-XRT team : The Swift-XRT began observing GRB 080426 (trigger=310219, Ziaeepour et al. GCN Circ. 7639) in Photon Counting mode, 230 s after the BAT trigger. The best XRT position for this burst is the UVOT-enhanced position reported by Beardmore et al. (GCN Circ. 7641). Three orbits of data out to T+13 ks, totalling 5.7 ks of exposure, reveal a light curve which follows a simple power-law decay, with an index of -1.07 +/- 0.08. The spectrum from the first three orbits is well fit by an absorbed power-law model, with a photon index of 2.01 +/- 0.25 and column density of (5.3 +/- 1.3)e21 cm^-2, which is slightly in excess of the average Galactic column density in this direction of 3.7e21 cm^-2. The observed (unabsorbed) 0.3-10 keV flux is 5.1e-12 (9.1e-12) erg cm^-2 s^-1. If the burst continues to decay at the same rate, we predict an XRT count rate of 2.0e-3 count/s at T+24 hours, which corresponds to an observed 0.3-10 keV flux of approximately 1.2e-13 erg cm^-2 s^-1. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7644 SUBJECT: GRB080426: Observations from CAHA DATE: 08/04/26 23:18:44 GMT FROM: Antonio Deugarte at IAA-CSIC A. de Ugarte Postigo (ESO), D. A. Kann (TLS Tautenburg), A.J. Castro-Tirado (IAA-CSIC, Granada), A. Aguirre (CAHA), C. Jordi (U. Barcelona) report on behalf of a larger collaboration: We have observed the XRT error circle (Beardmore et al. GCN 7641) of the possible intermediate GRB 080426 (H. Ziaeepour et al. GCN 7639, J. Cummings et al. GNC 7640) with the 2.2m telescope at Calar Alto Observatory (Almerķa, Spain) at high airmass but good conditions. The observations started at 26 April 19:53:33 UT and were carried out in B, V, R and I bands. In an I-band combined frame comprised of 11x300s with mean epoch 7.50 hours after the burst, we do not detect any source within the XRT error box down to a limiting magnitude of I~22.5. Further analysis is ongoing. This message may be cited.