//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8939 SUBJECT: GRB 090306: Swift detection of a possible burst DATE: 09/03/06 15:21:00 GMT FROM: Scott Barthelmy at NASA/GSFC O. Godet (U Leicester), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), S. Campana (INAF-OAB), P. A. Evans (U Leicester), J. A. Kennea (PSU), R. Margutti (Univ Bicocca&OAB), J. P. Osborne (U Leicester), C. Pagani (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL), M. Perri (ASDC), P. Romano (INAF-IASFPA), B. A. Rowlinson (U Leicester), G. Stratta (ASDC), M. C. Stroh (PSU), G. Tagliaferri (INAF-OAB) and L. Vetere (PSU) report on behalf of the Swift Team: At 13:54:24 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 090306 (trigger=345396). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 16.740, -50.065 which is RA(J2000) = 01h 06m 58s Dec(J2000) = -50d 03' 54" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a short, hard structure with a duration less than a single 64 msec timebin. The peak count rate was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 13:55:57.4 UT, 95.5 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 16.74294, -50.00206 which is equivalent to: RA(J2000) = 01h 06m 58.31s Dec(J2000) = -50d 00' 07.4" with an uncertainty of 4.9 arcseconds (radius, 90% containment). This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 1.37e+20 cm^-2 (Kalberla et al. 2005). At this time we do not have UVOT data. This trigger was the first of a new triggering function within BAT (the so called Subthreshold trigger). While there is a real source in the XRT initial image, this would say the trigger is a real GRB. However because we did not receive the usual BAT Position message (for reasons yet unknown), we caution that we can not say with confidence that this is a real burst. We will not have the full data downlinked until ~17:00 UT. Burst Advocate for this burst is O. Godet (og19 AT star.le.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: 8944 SUBJECT: GRB 090306B: Burst detection from Swift-BAT slew data DATE: 09/03/07 16:50:40 GMT FROM: Antonio Copete at Harvard U A. Copete, J. Grindlay (Harvard) S. Barthelmy, C. Markwardt, N. Gehrels (NASA/GSFC) We report the detection of a bright GRB by the BAT Slew Survey (BATSS) in the slew that started at 23:07:02 and lasted 66 sec. The ground- calculated position is RA, Dec = 231.204, -6.958 deg, which is RA (J2000) = 15h 24m 49s Dec(J2000) = -06d 57' 29" with an uncertainty of 2.87 arcmin (90% confidence, including systematics). The detection was triggered by simultaneous independent detections of 35.6 sigma and 20.2 sigma from imaging in the 15-50 keV and 50-150 keV energy bands, respectively. The burst mask-tagged lightcurve lightcurve in the 15-150 keV band shows a strong and broad emission peak starting at T+21sec, lasting 29 sec, and peaking twice at T+25sec and T+30sec. T90 = 20.4sec and T50 = 8.0sec. The time-averaged spectrum over the 55 sec exposure time of the source is best fit by a power law with an exponential cutoff, with photon index 1.02 and high-energy cut at 133 keV. The fluence in the 15-150 keV band is 3.1 x 10^-6 erg/cm^2, and and the peak 1-sec flux is 2.5 10^-7 erg/cm^2/sec at T+30sec. A follow-up Swift ToO observation for this burst has been scheduled. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8947 SUBJECT: GRB 090306B: Possible XRT afterglow DATE: 09/03/08 13:58:04 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT observed the field of the BAT Slew Survey burst GRB 090306B (Copete et al. GCN Circ. 8944) for 5.8 ks, from T0+67 ks to T0+81 ks. The data were entirely in PC mode. A single, faint source is found in the BATSS error circle, with a position RA,Dec = 231.2083, -6.9682 which is equivalent to: RA (J2000) = 15 24 49.99 Dec (J2000) = -06 58 05.6 with an uncertainty of 4.0 arcsec (radius, 90% confidence). We currently have only 16 counts from this source, at a count rate of 3.5 (+/- 0.9) e-3 counts s-1, and are unable to ascertain whether it is fading. Further observations, to verify the nature of this source, are planned. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8958 SUBJECT: GRB 090306B: GROND Upper Limits DATE: 09/03/09 13:29:06 GMT FROM: Christian Clemens at MPE A. C. Updike (Clemson University), C. Clemens, J. Greiner and P. Afonso (MPE Garching) report on behalf of the GROND team: We observed the field of GRB 090306B (BATSS, Copete et al., GCN #8944) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m ESO/MPI telescope at La Silla Observatory (Chile). Observations started at 04:34 UT on March 8th, about 29.5 hours after the GRB trigger, and lasted 45 min. We do not detect a source within the Swift-XRT error circle reported by Evans (GCN #8947) down to (all in AB system) g' > 23.2, r' > 23.6, i' > 23.3, z' > 23.0, J > 21.7, H > 21.0 and K > 20.1. The given limits are derived based on calibrating the images against GROND zeropoints and 2MASS field stars and are not corrected for the Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.11 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8960 SUBJECT: GRB 090306C: Fermi GBM detection DATE: 09/03/09 14:59:13 GMT FROM: Arne Rau at MPE Arne Rau (MPE) reports on behalf of the Fermi GBM Team: "At 05:52:05.35 UT on 06 March 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090306C (trigger 258011527 / 090306245). The on-ground calculated location, using the GBM trigger data, is RA = 135.0, DEC = +51.7 (J2000 degrees, equivalent to 09 h 00 m, 51 d 36 '), with an uncertainty of 5.5 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which is currently estimated to be 2 to 3 degrees). The angle from the Fermi LAT boresight is 14 degrees. The GBM light curve shows one main peak lasting about 5s followed by a broader tail with a total duration (T90) of about 38.8 s (8-1000 keV). The time-averaged spectrum from T0-4.096 s to T0+6.144 s is adequately fit by a power law function with an exponential high energy cutoff at 107 +/- 16 keV and with index -0.58 +/- 0.29 (chi squared 380 for 381 d.o.f.). The event fluence (8-1000 keV) in this time interval is (9.0 +/- 2.2)E-07 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.024 s in the 8-1000 keV band is 2.4 +/- 0.1 ph/s/cm^2. A Band function fits the spectrum equally well (chi squared 378 for 380 d.o.f.) with Epeak= 87 +/- 25 keV, alpha = -0.32 +/- 0.54 and beta = -2.28 +/-0.43. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8968 SUBJECT: GRB 090306B: INTEGRAL SPI-ACS light curve DATE: 09/03/10 14:23:05 GMT FROM: Volker Beckmann at ISDC V. Beckmann, M. Beck, C. Ferrigno, N. Produit, V. Savchenko (ISDC), J. Borkowski (CAMK/Torun), D. Gotz (CEA/Saclay), S. Mereghetti (INAF/IASF-Milano), A. von Kienlin (MPE) report on behalf of the INTEGRAL SPI-ACS GRB team: GRB 090306B, detected in Swift/BAT slew data (Copete et al. GCN 8944), has been independently detected by the SPI Anti-Coincidence System (ACS) on-board INTEGRAL. The SPI-ACS light curve shows the peak of the burst at 2009-03-06T23:07:21.9 with a maximum count-rate of ~390 counts/50msec. The duration of the GRB is about 14 seconds. The SPI-ACS light curves are available (both as images and data files) at http://isdc.unige.ch/Soft/ibas/ibas_acs_web.cgi The light curves, binned at 50 ms, are derived from 91 independent detectors with different lower energy thresholds (mainly between 50 keV and 150 keV) and an upper threshold at about 100 MeV. The ACS response varies as a function of the GRB incident angle. For these reasons we caution that the count rates cannot be easily translated into physical flux units. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8987 SUBJECT: GRB 090306B: Confirmation of the X-ray afterglow DATE: 09/03/13 13:51:35 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift has performed follow-up observations of the BAT Slew Survey GRB 090306B (Copete et al, GCN Circ. 8944), gathering 4 ks of data in the interval T0+484 ks to T0+555 ks. The X-ray source reported by Evans et al. (GCN Circ 8947) is no longer detected, with a 3-sigma upper limit of 1.9e-3 counts/sec. We thus confirm that it was the afterglow of GRB 090306B. This circular is an official product of the Swift-XRT team.