//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9912 SUBJECT: GRB 090915 Swift-BAT detection of a burst in ground analysis DATE: 09/09/16 03:11:44 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift J. R. Cummings (NASA/GSFC/CRESST) and C. B. Markwardt (NASA/GSFC/CRESST) on behalf of the Swift-BAT team At 15:35:36 Swift-BAT triggered on GRB 090915. This was probably the same event as Fermi-GBM trigger 274721737. No source was found onboard. A weak but significant source was found in ground analysis, 15 degrees from the GBM ground- calculated (2nd version) position as reported at http://gcn.gsfc.nasa.gov/fermi_grbs.html. The GBM position was also in the BAT FOV. The BAT ground-calculated position is RA, Dec = 237.990, +15.480 deg which is RA(J2000) = 15h 51m 57.6s Dec(J2000) = +15d 28' 48" with an uncertainty of 3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 12%. The mask-weighted light curve shows a single weak peak. T90 (15-350 keV) is 8 +- 2 sec (estimated error including systematics). The time-averaged spectrum from T-3 to T+5 sec is best fit by a power law. This fit gives a photon index 1.0 +- 0.2. For this model the total fluence in the 15-150 keV band is 5 +- 2 x 10-7 erg/cm2 and the 1-sec peak flux measured from T+2 sec in the 15-150 keV band is 0.8 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence level. A Swift TOO has been requested and approved. The narrow- field instruments will observe the location approximately 13 hours after the burst. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9914 SUBJECT: GRB 090915: Swift-XRT detection of a fading X-ray counterpart DATE: 09/09/16 11:19:58 GMT FROM: Andy Beardmore at U Leicester A. P. Beardmore, K. L. Page (U. Leicester) and T. Sakamoto (NASA/UMBC) report on behalf of the Swift-XRT team : The Swift-XRT started observing the field of GRB 090915 (Cummings and Markwardt, GCN Circ. 9912) at 2009-09-16 03:59 UT, 12.4 hours after the trigger. In 5ks of photon counting mode data, spanning two orbits, we detect a source which fades from 0.0099 +/- 0.0022 count/s to 0.0033 +/- 0.0016 over a interval of 5.9ks. Using 1678 s of XRT Photon Counting mode data and 1 UVOT image, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) for the source of RA, Dec (J2000) = 238.02021, 15.48775 which is equivalent to : RA (J2000): 15 52 4.85 Dec (J2000): +15 29 15.9 with an uncertainty of 3.3 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) and Evans et al. (2009, MNRAS, 397, 1177). The spectrum of the data from 44.6 ks to 52.8 ks after the trigger can be fit by an absorbed powerlaw with a photon index of 1.20 +0.97/-0.54 and a column density upper limit of 1.4 x 10^21 cm^-2, consistent with the Galactic value of 3.2 x 10^20 cm^-2 in the direction of the burst. The observed 0.3-10 keV flux for this spectrum is 4.9 +3.3/-4.9 x 10^-13 erg cm^-2 s^-1 which corresponds to an unabsorbed 0.3-10 keV flux of 5.1 x 10^-13 erg cm^-2 s^-1. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9918 SUBJECT: GRB 090915: Swift/UVOT detection of an optical afterglow candidate DATE: 09/09/16 22:01:24 GMT FROM: Erik Hoversten at Swift/Penn State E. A. Hoversten (PSU) and T. Sakamoto (NASA/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 090915 44647 s after the BAT trigger (Cummings & Markwardt, GCN Circ. 9912). A faint source is detected with 5.6-sigma confidence in the summed UVOT observations at the position RA, Dec (J2000) = 238.02016,15.48772 which is equivalent to: RA (J2000) = 15:52:04.84 Dec (J2000) = 15:29:15.8 with an estimated uncertainty of 0.8 arcsec (radius, 90% confidence). This position is 0.2 arcsec from the UVOT-enhanced XRT position (Beardmore, et al. GCN Circ. 9914) and the two positions agree within the error bars. It is unclear at this point if the source is fading, but follow-up Swift observations are being planned. The observed magnitudes using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the initial exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag ======================================================================= white 45492 52117 1647 22.15 +/- 0.24 (4.7 sigma) v 46338 52837 1583 21.08 +/- 0.39 (2.8 sigma) u 44647 51275 1647 21.40 +/- 0.43 (2.5 sigma) The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.05 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9920 SUBJECT: GRB 090915: SARA detection of afterglow candidate DATE: 09/09/16 22:34:15 GMT FROM: Adria C. Updike at Clemson U Adria C. Updike, Dieter H. Hartmann (Clemson University), Brian Murphy (Butler University), and Kenneth Rumstay (Valdosta State University) report: We observed the field of GRB 090915 (Cummings & Markwardt GCN 9912, Fermi-GBM trigger 274721737) using the 0.9m SARA telescope located at Kitt Peak National Observatory beginning 44173 seconds after the burst and continuing for about half an hour. Observations were carried out under good weather conditions at high airmass. In 21 minutes of stacked exposures, we marginally detect a source within the XRT error circle (Beardmore, Page, & Sakamoto, GCN 9914) at R ~ 20.5 +/- 0.3 (as compared to field stars using the USNO B1.0 catalog). The object is not found in the DSS catalog. Variability can not be established from these single-epoch observations. It is likely that the above source is the same identified by Hoversten & Sakamoto (GCN 9918). To establish the decay, follow-up observations are encouraged. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9923 SUBJECT: GRB 090915: GROND upper limits DATE: 09/09/17 20:18:51 GMT FROM: Robert Filgas at MPI P. Afonso (MPE Garching), A. Updike (Clemson University), J. Greiner and R. Filgas (MPE Garching) report on behalf of the GROND team: GROND (Greiner et al. 2008, PASP 120, 405), mounted at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile), observed the field of GRB 090915 (Cummings and Markwardt 2009, GCN #9912) simultaneously in the g'r'i'z'JHK bands. With 8 min total integration time in JHK and 7.7 min in g'r'i'z', observations started on September 17, at 00:19 UTC (32.7 h = 117.8 ksec after the burst) and were done at high air mass and under variable sky conditions. Inside the enhanced XRT error circle we do not detect the object reported by Beardmore et al. (GCN #9914), Hoversten and Sakamoto (GCN #9918) and Updike et al. (GCN #9920), down to the following limiting magnitudes (all in the AB system): g' > 23.7 r' > 23.2 i' > 22.7 z' > 21.3 J > 21.1 H > 20.2 K > 19.2 The upper limits were obtained using SDSS and 2MASS catalogs field stars as reference. No correction has been made for the expected extinction corresponding to E(B-V) = 0.05 mag in the direction of the burst (Schlegel et al. 1998). The non-detection of the source suggests this was indeed the afterglow of GRB 090915.