//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23366 SUBJECT: GRB 181023A: Swift detection of a burst DATE: 18/10/23 02:21:45 GMT FROM: Jamie A. Kennea at PSU/Swift-XRT F. E. Marshall (NASA/GSFC), A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC), J. A. Kennea (PSU), S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC), M. J. Moss (George Washington University) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 02:04:02 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 181023A (trigger=868427). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 248.329, +19.564 which is RA(J2000) = 16h 33m 19s Dec(J2000) = +19d 33' 51" 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 02:07:17.8 UT, 195.7 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 248.32979, 19.57140 which is equivalent to: RA(J2000) = 16h 33m 19.15s Dec(J2000) = +19d 34' 17.0" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 26 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 (6.04 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.4 (+2.82/-2.40) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 199 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 19.6 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 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.05. Burst Advocate for this burst is F. E. Marshall (marshall AT milkyway.gsfc.nasa.gov). 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: 23368 SUBJECT: GRB 181023A: KAIT Optical Upper Limit DATE: 18/10/23 04:24:34 GMT FROM: Weikang Zheng at UC Berkeley Xuhui Han (NAOC), WeiKang Zheng (UC Berkeley) and Alexei V. Filippenko (UC Berkeley) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, responded to Swift GRB 181023A (Marshall et al., GCN 23366) starting at 02:16:07 UT, ~12 minutes after the burst under dusk twilight condition. Observations were performed in the clear (roughly R) filters, and the exposure time was 60s per image. Observations lasted for about 25 minutes before it set beyond KAIT hour agnle limit. We do not detect any optical afterglow candidate within the XRT position error circle (Marshall et al., GCN 23366) neither in single image, nor in the co-add images. The typical limiting magnitude of our single clear image is about 19.0 mag calibrated to the Pan-STARRS1 catalog. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23369 SUBJECT: GRB 181023A: Enhanced Swift-XRT position DATE: 18/10/23 04:59:08 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 1424 s of XRT Photon Counting mode data and 2 UVOT images for GRB 181023A, 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 = 248.32870, +19.57062 which is equivalent to: RA (J2000): 16h 33m 18.89s Dec (J2000): +19d 34' 14.2" with an uncertainty of 1.7 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: 23373 SUBJECT: GRB 181023A: Swift-XRT refined Analysis DATE: 18/10/23 15:40:45 GMT FROM: Phil Evans at U of Leicester A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU), A. Tohuvavohu (PSU), S. J. LaPorte (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester) and F.E. Marshall report on behalf of the Swift-XRT team: We have analysed 10 ks of XRT data for GRB 181023A (Marshall et al. GCN Circ. 23366), from 214 s to 36.1 ks after the BAT trigger. The data comprise 493 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Osborne et al. (GCN Circ. 23369). The late-time light curve (from T0+5.4 ks) can be modelled with a series of power-law decays. The initial decay index is alpha=1.56 (+0.16, -0.18). At T+12.4 ks the decay steepens to an alpha of 3.9 (+2.1, -0.4). The light curve breaks again at T+18.1 ks to a decay with alpha=-1.5 (+0.0, -0.7), before a final break at T+22.9 ks s after which the decay index is 2.9 (+0.9, -0.7). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.79 (+/-0.08). The best-fitting absorption column is 2.3 (+/-0.3) x 10^21 cm^-2, in excess of the Galactic value of 6.0 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.1 x 10^-11 (5.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.3 (+/-0.3) x 10^21 cm^-2 Galactic foreground: 6.0 x 10^20 cm^-2 Excess significance: 9.0 sigma Photon index: 1.79 (+/-0.08) If the light curve continues to decay with a power-law decay index of 2.9, the count rate at T+24 hours will be 4.5 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.8 x 10^-13 (2.4 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00868427. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23376 SUBJECT: GRB 181023A: Swift/UVOT Upper Limits DATE: 18/10/24 00:52:14 GMT FROM: Sam LaPorte at PSU GRB 181023A: Swift/UVOT Upper Limits S. J. LaPorte (PSU) and F. E. Marshall (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 181023A 200 s after the BAT trigger (Marshall et al., GCN Circ. 23366). No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 23369) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 200 350 147 >20.1 white 200 2078 470 >20.8 v 356 2128 194 >19.4 b 455 2054 175 >20.3 u 430 2029 175 >19.6 w1 406 2005 175 >19.6 m2 554 1803 78 >19.2 w2 679 2104 175 >19.2 The magnitudes in the table 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: 23377 SUBJECT: GRB 181023A: Swift-BAT refined analysis DATE: 18/10/24 01:39:15 GMT FROM: Amy Lien at GSFC T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU) (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 181023A (trigger #868427) (Marshall et al., GCN Circ. 23366). The BAT ground-calculated position is RA, Dec = 248.322, 19.581 deg which is RA(J2000) = 16h 33m 17.4s Dec(J2000) = +19d 34' 51.2" with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 53%. The mask-weighted light curve shows a complex structure with some weak overlapping pulses that starts at ~T-30 s and ends at ~T+40 s. Note that the burst entered the BAT FOV at T-48 s, and hence there might be additional emission beforehand. T90 (15-350 keV) is 58.0 +- 8.8 sec (estimated error including systematics). The time-averaged spectrum from T-27.62 to T+36.68 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.74 +- 0.24. The fluence in the 15-150 keV band is 1.3 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+32.18 sec in the 15-150 keV band is 1.0 +- 0.3 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/868427/BA/