//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8948 SUBJECT: GRB 090308: Swift detection of a burst DATE: 09/03/08 18:21:15 GMT FROM: Scott Barthelmy at NASA/GSFC P. A. Evans (U Leicester), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/USRA/GSFC), R. Margutti (Univ Bicocca&OAB), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester), C. Pagani (PSU), K. L. Page (U Leicester), A. M. Parsons (GSFC), P. Romano (INAF-IASFPA), B. Sbarufatti (INAF-IASFPA), R. L. C. Starling (U Leicester), M. C. Stroh (PSU), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the Swift Team: At 18:01:23 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 090308 (trigger=345777). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 183.526, -48.833 which is RA(J2000) = 12h 14m 06s Dec(J2000) = -48d 49' 57" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). This is an image trigger, but even so the BAT light curve shows a weak peak at T+20 to T+35 sec. The peak count rate was ~350 counts/sec (15-350 keV), at ~25 sec after the trigger. The XRT began observing the field at 18:03:30.4 UT, 126.9 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 183.5017, -48.8169 which is equivalent to: RA(J2000) = 12h 14m 0.41s Dec(J2000) = -48d 49' 00.9" with an uncertainty of 2.2 arcseconds (radius, 90% containment). This location is 81 arcseconds from the BAT onboard position, within the BAT error circle. 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 in excess of the Galactic value (8.54e+20 cm^-2, Kalberla et al. 2005), with an excess column of 1.8 (+1.51/-1.36) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 131 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. Because part of the 2.7'x2.7' sub-image was not received, there is no overlap with the XRT error circle. The 8'x8' region for the list of sources generated on-board covers the entire XRT error circle. No correction has been made for the expected extinction corresponding to E(B-V) of 0.11. Burst Advocate for this burst is P. A. Evans (pae9 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: 8949 SUBJECT: GRB 090308: Swift-BAT refined analysis DATE: 09/03/08 21:02:11 GMT FROM: Scott Barthelmy at NASA/GSFC C. B. Markwardt (GSFC/UMD), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), P. A. Evans (U Leicester), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), D. M. Palmer (LANL), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-60 to T+243 sec from recent telemetry downlinks, we report further analysis of BAT GRB 090308 (trigger #345777) (Evans, et al., GCN Circ. 8948). The BAT ground-calculated position is RA, Dec = 183.545, -48.754 deg, which is RA(J2000) = 12h 14m 10.7s Dec(J2000) = -48d 45' 13.8" with an uncertainty of 3.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 89%. The mask-weighted light curve shows a single peak starting at ~T-10 sec, peaking at ~T+30 sec, and ending at ~T+65 sec. T90 (15-350 keV) is 48 +- 22 sec (estimated error including systematics). The time-averaged spectrum from T+4.0 to T+52.0 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.33 +- 0.37. The fluence in the 15-150 keV band is 2.6 +- 0.6 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+27.50 sec in the 15-150 keV band is 0.1 +- 0.0 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/345777/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8956 SUBJECT: GRB 090308: Swift-XRT refined analysis DATE: 09/03/09 07:33:46 GMT FROM: Phil Evans at U of Leicester P. A. Evans and K.L. Page (U Leicester) report on behalf of the Swift-XRT team: We have analysed 4.4 ks of XRT data for GRB 090308 (Evans et al. GCN Circ. 8948), from 130 s to 12.2 ks after the BAT trigger. The data comprise 55 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. Using 460 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 183.50120, -48.81710 which is equivalent to: RA (J2000): 12 14 0.28 Dec(J2000): -48 49 01.6 with an uncertainty of 1.6 arcsec (radius, 90% confidence). The light curve can be modelled with an initial power-law decay with an index of alpha=2.63 (+0.16, -0.13), followed by a break at T+830 s to an alpha of 1.2 (+0.5, -1.9). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.93 (+0.28, -0.26). The best-fitting absorption column is 2.86 (+1.01, -0.88) x 10^21, in excess of the Galactic value of 8.5 x 10^20 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.5 x 10^-11 (6.8 x 10-11) erg cm^-2 count^-1. If the light curve continues to decay with a power-law decay index of 1.9, the count rate at T+24 hours will be 2.0 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.1 x 10^-15 (1.4 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00345777. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8962 SUBJECT: GRB 090308: Swift/UVOT Upper Limits DATE: 09/03/09 18:31:52 GMT FROM: Frank Marshall at GSFC F.E. Marshall (NASA/GSFC) and P. Evans (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT observed the field of GRB 0900308 starting 132 s after the BAT trigger (Evans et al., GCN Circ. 8948). No optical afterglow is detected in the initial UVOT exposures at the position of the X-ray afterglow (Evans and Page, GCN Circ. 8956). Three-sigma upper limits using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white (FC) 132 282 147 >21.1 white 570 11390 1102 >22.2 v 620 17423 1101 >20.6 b 545 6455 382 >20.8 u 290 6281 639 >20.7 uvw1 669 6077 399 >20.6 uvm2 644 18019 798 >20.8 uvw2 595 12237 1044 >21.2 The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.11 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8963 SUBJECT: GRB 090308B: Fermi GBM detection DATE: 09/03/09 21:42:26 GMT FROM: Adam Goldstein at Fermi-GBM/UAH A. Goldstein (UAH) and A.J. van der Horst (NASA/MSFC/ORAU) report on behalf of the Fermi GBM Team: "At 17:36:24.70 UT on 08 March 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090308B (trigger 258226586 / 090308734). This burst was also independently detected by INTEGRAL SPI-ACS. The on-ground calculated location, using the GBM trigger data, is RA = 22.4, DEC = -58.1 (J2000 degrees, equivalent to 01h 30m, 58d 05'), with an uncertainty of 2.3 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 50 degrees. The GBM light curve consists of two peaks with substructure with a duration (T90) of about 2.11 s (8-1000 keV). The time-averaged spectrum from T0-0.25 s to T0+1.53 s is well fit by a power law function with an exponential high energy cutoff. The power law index is -0.54 +/- 0.11 and the cutoff energy, parameterized as Epeak, is 710.3 +/- 100.0 keV (chi squared 342 for 362 d.o.f.). The event fluence (8-1000 keV) in this time interval is (3.46 +/- 0.13)E-06 erg/cm^2. The 0.128-sec peak photon flux measured starting from T0+0.64 s in the 8-1000 keV band is 14.22 +/- 0.91 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8965 SUBJECT: GRB 090308: Gemini GMOS Observations DATE: 09/03/10 05:31:26 GMT FROM: S. Bradley Cenko at Caltech S. B. Cenko, A. N. Morgan, D. A. Perley, N. R. Butler, and J. S. Bloom (UC Berkeley) report on behalf of a larger collaboration: We have imaged the field of GRB090308 (Evans et al.; GCN 8948) with GMOS mounted on the Gemini South telescope beginning at approximately 1:38 UT on the night of 9 March 2009 (~ 7.6 hours after the burst). Images were taken in the g', r', i', and z' filters for a total of 300 s in each band. We find no significant sources inside the revised XRT error circle (Evans et al.; GCN 8956) to the following limits: g' > 23.8; r' > 24.2; i' > 23.6; z' > 22.5. These limits were calculated using reference stars from the USNO-B1 catalog and applying the filter transformations of Jordi, Grebel, and Ammon (A&A 460, 2009). We do, however, note the presence of an extremely red point source located several arcseconds southwest of the refined XRT position, and immediately outside the X-ray position provided by Butler (AJ 133, 2007; see http://astro.berkeley.edu/~nat/swift/xrt_pos.html). The coordinates of this source are (J2000.0): RA: 12:13:59.89 Dec: -48:49:03.5 This object is detected only in the r', i', and z' filters with approximate magnitudes: r' = 23.6; i' = 21.6; z' = 20.2 (uncorrected for Galactic extinction). While we consider the association unlikely, further observations are required to determine if this is the afterglow of GRB090308. We wish to thank the staff at Gemini Observatory for undertaking these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8966 SUBJECT: GRB 090308: GROND observations DATE: 09/03/10 10:07:05 GMT FROM: Adria C. Updike at Clemson U 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 090308 (Swift trigger 345777; Evans et al., GCN #8948) 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 00:01 UT on March 9th, 6 hours after the GRB trigger for 2 hours, and were followed by a second epoch beginning at 07:44 UT and lasting 30 min. They were carried out at an average seeing of 1.7". The red object just outside the enhanced XRT error circle noted by Cenko et al. (GCN #8965) is detected in both epochs with no sign of fading. Therefore, we conclude this is not the afterglow of GRB 090308. Based on 30 min of our first epoch, we do not detect a source within the Swift-XRT error circle reported by Evans & Page (GCN #8956) down to (all in AB system) g' > 22.7, r' > 22.9, i' > 22.6, z' > 22.3, J > 21.1, H > 20.6 and K > 19.6 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)= 0.114 in the direction of the burst (Schlegel et al. 1998).