//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5760 SUBJECT: GRB 061027: Swift detection of a possible burst DATE: 06/10/27 10:48:55 GMT FROM: Scott Barthelmy at NASA/GSFC M. Stamatikos (NASA/ORAU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), S. Campana (INAF-OAB), M. M. Chester (PSU), G. Cusumano (INAF-IASFPA), N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB), K. M. McLean (LANL/UTD), T. Mineo (INAF-IASFPA), P. T. O'Brien (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), S. B. Pandey (UCL-MSSL), P. Romano (Univ. Bicocca & INAF-OAB) and T. Sakamoto (NASA/ORAU) report on behalf of the Swift Team: At 10:15:02 UT, the Swift Burst Alert Telescope (BAT) triggered and located possible GRB 061027 (trigger=235645). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 270.812, -82.228 {18h 03m 15s, -82d 13' 39"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). This is a 64-sec image trigger and as is typical the BAT lightcurve does not show any significant emission. The image peak is barely above the significance threshold for automatic detection, and therefore this may be a statistical fluctuation. The XRT began taking data at 10:17:29 UT, 147 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. Initial down-linked data products also show no evidence for any X-ray source in the image in ~200 s of data. This gives a very rough upper limit of 2E-12 erg/cm2/s for any source in the field of view. We note that only one long burst has had no XRT detection following a prompt slew, out of 119 long GRBs observed by XRT with prompt slews to date. Further analysis awaits the full dowloaded data products. UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 151.7 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. The limiting magnitude of the finding chart image is approximately 19.0. No correction has been made for the expected extinction. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5761 SUBJECT: GRB 061027, Swift refined analysis of a possible burst DATE: 06/10/27 20:02:53 GMT FROM: Scott Barthelmy at NASA/GSFC A. Parsons (GSFC), L. Barbier (GSFC), S.D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), D.N. Burrows (PSU), V. Mangano, T. Mineo, G. Cusumano, B. Sbarufatti (INAF-IASFPA), S.B. Pandey (UCL-MSSL) on behalf of the Swift team: Using the data set from T-239 to T+963 sec from recent telemetry downlinks, we report further analysis of BAT possible GRB 061027 (trigger #235645) (Stamatikos, et al., GCN Circ. 5760). The BAT ground-calculated position is RA,Dec = 270.992, -82.239 deg {18h 3m 58.1s, -82d 14' 19.9"} (J2000) +- 3.7 arcmin, (radius, sys+stat, 90% containment). The partial coding was 68%. The event starts ~100 sec before the trigger and extends to ~T+70 sec. All of the emission is in the 15-50 keV band -- there is nothing above 50 keV. Because this event is very weak, we had to use 10-sec binning for the lightcurve. There appears to be no statistically significant structure in the lightcurve. T90 (15-350 keV) is 150 +- 20 sec (estimated error including systematics). The time-averaged spectrum from T-100 to T+70 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.91 +- 0.48. The fluence in the 15-150 keV band is 4.7 +- 1.5 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+0.00 sec in the 15-150 keV band is 0.08 +- 0.02 ph/cm2/sec. All the quoted errors are at the 90% confidence level. Given the very low flux, the somewhat low detection significance, and the soft spectrum for this event, we can not determine if this is a long soft GRB or some hard x-ray transient from an unknown source. The position in galactic coordinates is l, b = 311, -25, so the source is off the plane but still possibly a galactic transient. We can not rule out the possibility that this event is due to a chance statistical fluctuation in the image and rate domains. XRT observed the field of GRB061027 for 1.5 ks in PC mode starting at 10:17:37 UT (152 seconds after the BAT trigger). No source has been detected within the BAT error circle down to a limiting flux of 3.6e-13 erg cm^-2 s^-1. This is unusually low for a GRB afterglow at this point after a trigger, and suggests that this event may be either an unusual GRB or due to some other source, either transient or noise. UVOT began observing the field around 133 sec after the BAT trigger. No afterglow candidate is found within the BAT error circle. The 3-sigma upper limit of the UVOT filters are given below. Filter T_start T_stop Exposure(s) Mag (3-sig Upper limit) V 133 6777 805 20.41 B 735 6163 206 20.40 U 711 5958 216 20.04 W1 687 5753 235 19.96 M2 663 6839 292 19.95 W2 763 6573 216 20.29 White 152 6367 501 21.10 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5788 SUBJECT: GRB 061027: TAROT La Silla observatory optical observations DATE: 06/11/08 08:24:06 GMT FROM: Alain Klotz at CESR-CNRS Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report: We imaged the field of GRB 061027 detected by SWIFT (trigger 235645) with the TAROT robotic telescope (D=25cm) located at the European Southern Observatory, La Silla observatory, Chile. This trigger was long, had no high-energy emission, it was detected by "image trigger" (Stamatikos et al. GCNC 5760) and UVOT limiting mag. is V=20.4 until two hours after the burst. This is a good high-redshift candidate, so we shot a series of filtered R and I exposures centered on the BAT refined position (Parsons et al. GCNC 5761). The observations started 14.0h after the GRB trigger. The elevation of the field decreased from from 33 degrees above horizon and weather conditions were excellent. We obtained a second set of exposures on 2006 nov. 7 for comparison and to extract fading sources. The date of trigger : t0 = 2006-10-27T10:15:02.304 We co-added series of filtered exposures, and we do not detect any OT: t0+14.0h to t0+18.6h : R > 20.0 and I > 18.9 Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction. N.B. Galactic coordinates are lon=311.3409 lat=-25.2566 and the galactic extinction in R band is 0.1 magnitudes estimated from D. Schlegel et al. 1998ApJ...500..525S. This message may be cited.