//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6375 SUBJECT: GRB 070506: Swift detection of a burst with optical afterglow DATE: 07/05/06 06:05:32 GMT FROM: David Palmer at LANL C. Pagani (PSU), M. M. Chester (PSU), C. Guidorzi (Univ Bicocca&INAF-OAB), S. Immler (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), J. L. Racusin (PSU), T. Sakamoto (NASA/ORAU), M. Stamatikos (NASA/ORAU) and L. Vetere (PSU) report on behalf of the Swift Team: At 05:35:58 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070506 (trigger=278693). Swift slewed to the burst immediately after the end of the 64 second image trigger. The BAT on-board calculated location is RA, Dec 347.217, +10.728 which is RA(J2000) = 23h 08m 52s Dec(J2000) = +10d 43' 42" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a double-peaked structure with a duration of about 6 sec. The peak count rate was ~1700 counts/sec (15-350 keV), at ~6 sec after the trigger. The XRT began observing the field at 05:38:05 UT, 127 seconds after the BAT trigger. Using ground-processed quick-look data, XRT found an uncatalogued X-ray source located at RA, Dec 347.2192, +10.7224 which is RA(J2000) = 23h 08m 52.6s Dec(J2000) = 10d 43' 20.7" with an uncertainty of 9.0 arcseconds (radius, 90% containment). This location is 22 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 2.5e-10 erg/cm2/s (0.2-10 keV). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 459 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 23h 08m 52.39s (= 347.2183d) DEC(J2000) = +10d 43' 20.3" (= 10.7223d) with a 1-sigma error radius of about 0.5 arc sec. This position is 3.0 arcseconds from the center of the XRT error circle. The estimated magnitude is 19.4 with a 1-sigma error of about 0.5 mag. No correction has been made for galactic reddening of E(B-V) = 0.040. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6376 SUBJECT: GRB 070506, Swift-BAT Refined Analysis DATE: 07/05/06 16:38:17 GMT FROM: Michael Stamatikos at GSFC L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team: Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 070506 (trigger #278693) (Pagani, et al., GCN Circ. 6375). The BAT ground-calculated position is RA, Dec = 347.203, 10.711 deg which is RA(J2000) = 23h 8m 48.8s Dec(J2000) = 10d 42' 40.3" with an uncertainty of 2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 96%. The mask-weighted light curve begins to rises at ~T+2 sec, peaks at ~T+6.5 sec, and returns to the background level by ~T+10 sec, with trivial emission above 100 keV. T90 (15-350 keV) is 4.3 +- 0.3 sec (estimated error including systematics). The time-averaged spectrum from T+4.1 to T+9.0 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.72 +- 0.17. The fluence in the 15-150 keV band is 2.1 +- 0.2 x 10^-7 erg/cm^2. The 1-sec peak photon flux measured from T+6.16 sec in the 15-150 keV band is 1.0 +- 0.1 ph/cm^2/sec. All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6377 SUBJECT: GRB070506: Swift XRT refined analysis DATE: 07/05/06 17:16:51 GMT FROM: Claudio Pagani at PSU/Swift-XRT C. Pagani, L. Vetere, J. L. Racusin and J. A. Kennea (PSU) report on behalf of the Swift Team: We have analysed the first two orbits of Swift XRT data from GRB 070506 (trigger number 278693, GCN Circ 6375.), for a total photon counting mode exposure of 2.8ks. The XRT started collecting data in Image mode at 05:38:05 UT, 127 seconds after the BAT trigger, but observations in Photon Counting mode were delayed due to the SAA, starting 432 seconds after the trigger. The refined XRT position from 2.8ks of PC data is RA,DEC(J200) = 347.2179, +10.7217 which is RA(J2000) = 23d 08m 52.30s DEC(J200) = +10d 43' 18.2" with an uncertainty of 5.4 arcsec (radius, 90% containment). This is 5.1 arcsec from the initial X-ray position and 2.4 arcsec from the UVOT optical counterpart (GCN 6375). The XRT light curve created from the first two orbits of PC data reveals a decaying source with hints of flaring activity. A power law fit yields a decay slope of 0.55+/-0.06. The X-ray spectrum of the PC data, modeled with an absorbed power law gives a photon index of 2.5+/-0.5 and a total column density of NH= (1.8+/-1.1)e21 cm**-2, in excess of the Galactic value of 0.4e21 cm**-2. The absorbed (unabsorbed) 0.3-10.0keV flux for this spectrum was 3.0E-12 (5.5E-12) ergs cm^-2 s^-1. Assuming the source continues to decay at the same rate, we predict an XRT count rate of 2.2e-2 count/s at T+24 hours, which corresponds to an observed (unabsorbed) flux of 0.8E-12 (1.5E-12) ergs cm^-2 s^-1. This circular is an official product of the Swift XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6378 SUBJECT: GRB070506: Swift/UVOT Observations DATE: 07/05/07 02:58:56 GMT FROM: Wayne Landsman at GSFC/SSAI W. Landsman (SSAI/GSFC) and C. Pagani (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began taking data in the field of GRB070506 459s after the BAT trigger (Pagani et al., GCN 6375). A fading afterglow is weakly detected in the White, B and V UVOT filters, but not in the U or UV filters. We use the combined white image to obtain an improved position of RA(J2000) = 23h 08m 52.39s Dec(J2000) = +10d 43' 20.8" with a 1-sigma uncertainty radius of about 0.5". This is 0.5" from the UVOT position reported by Pagani et al. (GCN 6375) and 2.9" from the refined XRT position reported by Pagani et al. (GCN 6377). Photometry results are given for the 7 UVOT filters below. Tstart Tstop Exp Mag White 459 558 98 19.7+/-0.18 868 967 98 19.9+/-0.22 7371 7570 196 20.4+/-0.28 V 974 1373 393 19.1+/-0.2 7781 7980 197 >19.3 (3 sigma) B 638 2245 136 19.8+/-0.34 7167 7366 197 >20.4 (3 sigma) U 638 5853 261 >20.1 (3 sigma) UVW1 614 5741 352 >20.4 (3-sigma) UWM2 7984 8142 155 >19.6 (3-sigma) UVW2 840 7775 294 >20.4 (3-sigma) No correction has been made for the expected Galactic reddening of E(B-V)=0.04 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6379 SUBJECT: GRB 070506: VLT redshift DATE: 07/05/07 11:03:32 GMT FROM: Christina Thoene at Niels Bohr Institute,DARK Cosmo Ctr Christina C. Thoene (DARK), Andreas O. Jaunsen (Univ. Oslo), Johan P. U. Fynbo (DARK), Pall Jakobsson (Univ. of Hertfordshire) and Paul M. Vreeswijk (ESO) report: We obtained 2x15min spectra of the OT of GRB 070506 (Pagani et al., GCN 6375 and 6378) on May 6.41 with FORS1/VLT during twilight. The grism used (300V) covers the wavelength range from 3000 to 9000 A. The identification of a strong Lyman-alpha absorption together with SiII, FeII, CIV, AlII, AlIII and ZnII absorption lines leads to a redshift of z=2.31 for GRB 070506. We thank the staff at Paranal for excellent support.