//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28337 SUBJECT: GRB 200901B: Swift detection of a burst DATE: 20/09/01 07:25:54 GMT FROM: Boris Sbarufatti at PSU B. Sbarufatti (PSU), P. A. Evans (U Leicester), A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team: At 07:09:26 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 200901B (trigger=994165). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 217.879, -38.716 which is RA(J2000) = 14h 31m 31s Dec(J2000) = -38d 42' 58" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is usual with an image trigger, the available BAT light curve shows no significant structure. The XRT began observing the field at 07:12:16.1 UT, 169.7 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 217.8572, -38.7117 which is equivalent to: RA(J2000) = 14h 31m 25.73s Dec(J2000) = -38d 42' 42.1" with an uncertainty of 5.5 arcseconds (radius, 90% containment). This location is 63 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 1.11e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 175 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18.0 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.09. Burst Advocate for this burst is B. Sbarufatti (bxs60 AT psu.edu). 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/) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28339 SUBJECT: GRB 200901B: Enhanced Swift-XRT position DATE: 20/09/01 14:48:11 GMT FROM: Phil Evans at U of Leicester J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 903 s of XRT Photon Counting mode data and 1 UVOT images for GRB 200901B, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 217.85911, -38.71147 which is equivalent to: RA (J2000): 14h 31m 26.19s Dec (J2000): -38d 42' 41.3" with an uncertainty of 4.2 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). This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28343 SUBJECT: GRB 200901B: Swift/UVOT Detection DATE: 20/09/01 20:17:40 GMT FROM: Alice Breeveld at MSSL-UCL A. A. Breeveld (UCL-MSSL) and B. Sbarufatti (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 200901B 176 s after the BAT trigger (Sbarufatti et al., GCN Circ. 28337). A source consistent with the XRT position (Sbarufatti et al. GCN Circ. 28337)is detected in the initial UVOT exposures in the u filter only, but many exposures are smeared, so the magnitudes may not be reliable. Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag v 482 801 58 >18.1 b 431 750 58 >19.1 u 176 426 245 19.3 ± 0.3 w1 531 851 58 >18.1 m2 506 826 58 >17.9 w2 457 776 58 >18.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.09 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28345 SUBJECT: GRB 200901B: Swift-BAT refined analysis DATE: 20/09/01 23:41:52 GMT FROM: Amy Lien at GSFC M. Stamatikos (OSU), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), B. Sbarufatti (PSU), T. N. Ukwatta (LANL) (i.e. 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 200901B (trigger #994165) (Sbarufatti et al., GCN Circ. 28337). The BAT ground-calculated position is RA, Dec = 217.860, -38.704 deg which is RA(J2000) = 14h 31m 26.5s Dec(J2000) = -38d 42' 15.2" with an uncertainty of 3.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 82%. The mask-weighted light curve shows some weak emission that starts at ~T0 and ends at ~T+900 s. The available event data end at T+963 s, and the burst went out of the BAT FOV soon afterwards (~T+1000 s). T90 (15-350 keV) is 705.94 +- 148.71 sec (estimated error including systematics). The time-averaged spectrum from T+32.14 to T+901.32 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.95 +- 0.63, and Epeak of 46.7 +- 8.6 keV (chi squared 61.80 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 4.3 +- 0.4 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+68.62 sec in the 15-150 keV band is 0.4 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.95 +- 0.13 (chi squared 71.14 for 57 d.o.f.). 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/994165/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28347 SUBJECT: GRB 200901B: Swift-XRT refined Analysis DATE: 20/09/02 07:26:03 GMT FROM: Phil Evans at U of Leicester J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU) and B. Sbarufatti report on behalf of the Swift-XRT team: We have analysed 4.6 ks of XRT data for GRB 200901B (Sbarufatti et al. GCN Circ. 28337), from 11.3 ks to 35.0 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Osborne et al. (GCN Circ. 28339). The light curve can be modelled with a series of power-law decays. The light curve initially rises, with an index alpha=-0.6 (+0.7, -0.9). At T+239 s it breaks to an alpha of 0.54 (+0.08, -0.07) before breaking again at T+950 s to a final decay with index alpha=2.61 (+1.29, -0.12). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.15 (+/-0.05). The best-fitting absorption column is 1.66 (+0.27, -0.26) x 10^21 cm^-2, in excess of the Galactic value of 1.2 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.8 x 10^-11 (6.3 x 10^-11) erg cm^-2 count^-1. A summary of the WT-mode spectrum is thus: Total column: 1.66 (+0.27, -0.26) x 10^21 cm^-2 Galactic foreground: 1.2 x 10^21 cm^-2 Excess significance: 2.9 sigma Photon index: 1.15 (+/-0.05) If the light curve continues to decay with a power-law decay index of 2.61, the count rate at T+24 hours will be 8.7 x 10^-5 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.1 x 10^-15 (5.5 x 10^-15) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00994165. This circular is an official product of the Swift-XRT team.