//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23129 SUBJECT: GRB 180812A: Swift detection of a burst DATE: 18/08/12 08:37:38 GMT FROM: Scott Barthelmy at NASA/GSFC A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), A. D'Ai (INAF-IASFPA), V. D'Elia (ASDC), C. Gronwall (PSU), K. L. Page (U Leicester) and E. Troja (NASA/GSFC/UMCP) report on behalf of the Neil Gehrels Swift Observatory Team: At 08:22:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180812A (trigger=852903). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 245.886, +74.670, which is RA(J2000) = 16h 23m 33s Dec(J2000) = +74d 40' 11" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows several peaks with a total duration of about 25 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 08:24:17.6 UT, 107.5 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 245.8360, 74.6647 which is equivalent to: RA(J2000) = 16h 23m 20.64s Dec(J2000) = +74d 39' 53.0" with an uncertainty of 2.7 arcseconds (radius, 90% containment). This location is 51 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. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (4.37 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.8 (+4.29/-3.49) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 112 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 0.04. Burst Advocate for this burst is A. Y. Lien (amy.y.lien AT 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: 23130 SUBJECT: GRB 180812A: BOOTES-5/JGT optical afterglow detection DATE: 18/08/12 09:52:43 GMT FROM: Irene Carrasco at Inst.De Astrofisica de Andalucia I. Carrasco (Univ. de Malaga), Y. Hu, E. Fernandez-Garcia, J. C. Tello and A. J. Castro-Tirado (IAA-CSIC), D. Hiriart and W. H. Lee (UNAM), S. Jeong and I. H. Park (SKKU), M. D. Caballero-Garcia (ASU-CAS, CZ) and R. Cunniffe (Inst. of Physics, CZ) on behalf of a larger collaboration, report: The 60cm BOOTES-5/JGT robotic telescope at Observatorio Astronomico Nacional in San Pedro Martir (Mexico) automatically responded in 22s (and 52s after the GRB onset) to the Swift trigger of GRB 180812A (Lien et al., GCNC 23129). The first image (10s exposure, r-band) was obtained at 08:23:25 UT. At the position of the Swift X-ray afterglow, a variable optical source with r about 17 mag is detected, which is fading in brightness in the late images. Therefore we propose this source to be the optical afterglow to GRB 180812A. Spectroscopic observations are encouraged. We thank the staff at Observatorio Astronomico Nacional in San Pedro Martir for its excellent support. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23131 SUBJECT: GRB 180812A: Enhanced Swift-XRT position DATE: 18/08/12 12:30:57 GMT FROM: Phil Evans at U of Leicester M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 2046 s of XRT Photon Counting mode data and 2 UVOT images for GRB 180812A, 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 = 245.83465, +74.66472 which is equivalent to: RA (J2000): 16h 23m 20.32s Dec (J2000): +74d 39' 53.0" 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: 23132 SUBJECT: GRB 180812A: COATLI Detection and Light Curve DATE: 18/08/12 12:52:06 GMT FROM: Alan M. Watson at Instituto de Astronomia UNAM Alan M. Watson (UNAM), Eleonora Troja (GSFC), Nat Butler (ASU), Rosa L. Becerra (UNAM), William H. Lee (UNAM), Carlos Román-Zúñiga (UNAM), and Alexander Kutyrev (GSFC) report: We observed the field of GRB 180812A (Lien et al., GCN 23129) with the COATLI 50-cm telescope and interim imager at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir (http://coatli.astroscu.unam.mx) from 2018-08-12 08:13.5 to 11:53:16.7 (from 11.6 seconds after the alert or 43.1 seconds after the trigger to 3.5 hours after the trigger), obtaining a total of 2.46 hours of exposure in the w filter. We detect the optical counterpart reported by Carrasco et al. (GCN Circ. 23130). We see it rise from w = 17.4 to w = 17.2 at 160 seconds after burst, and then fade rapidly. We note that simultaneous observations with UVOT in the white filter do not detect anything to a limit of about 19.8 (Lien et al., GCN 23129). Our w filter is much redder than the UVOT white filter, which suggests that this might be an intrinsically red afterglow or be attenuated by intergalactic absorption in the blue. These magnitudes are calibrated against the USNO-B1 catalog (adjusted to an approximate AB system) and are not corrected for Galactic extinction in the direction of the GRB. We thank the COATLI technical team (Fernando Ángeles, Oscar Chapa, Salvador Cuevas, Alejandro Farah, Jorge Fuentes, Rosalía Langarica, Fernando Quirós, and Carlos Tejada) and the staff of the Observatorio Astronómico Nacional. [GCN OPS NOTE(12aug18): The GRB name in the Subject-line and the first pagragraph has been changed from "180612A" to "180812A".] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23134 SUBJECT: GRB 180812A: Swift-XRT refined Analysis DATE: 18/08/12 17:18:20 GMT FROM: Phil Evans at U of Leicester P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), S. J. LaPorte (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and A.Y. Lien report on behalf of the Swift-XRT team: We have analysed 8.2 ks of XRT data for GRB 180812A (Lien et al. GCN Circ. 23129), from 114 s to 24.0 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN Circ. 23131). The light curve can be modelled with a power-law decay with a decay index of alpha=1.08 (+/-0.05). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.74 (+0.16, -0.14). The best-fitting absorption column is 6.8 (+4.3, -2.4) x 10^20 cm^-2, consistent with the Galactic value of 4.4 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 3.8 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 6.8 (+4.3, -2.4) x 10^20 cm^-2 Galactic foreground: 4.4 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.74 (+0.16, -0.14) If the light curve continues to decay with a power-law decay index of 1.08, the count rate at T+24 hours will be 2.7 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.0 x 10^-13 (1.1 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/00852903. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23135 SUBJECT: GRB 180812A: Fermi GBM detection DATE: 18/08/12 20:52:06 GMT FROM: Rachel Hamburg at UAH A. von Kienlin (MPE), R. Hamburg (UAH), and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 08:22:30.31 UT on 12 August 2018, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 180812A (trigger 555754955 / 180812349), which was also detected by the Swift BAT and XRT instruments (Lien et al. 2008, GCN 23129). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 46 degrees. The GBM light curve shows several peaks with a duration (T90) of about 38 s (50-300 keV). The time-averaged spectrum from T0-2.0 s to T0+34.8 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -0.56 +/- 0.36 and the cutoff energy, parameterized as Epeak, is 110 +/- 25 keV. The event fluence (10-1000 keV) in this time interval is (1.2 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+15.7 s in the 10-1000 keV band is 2.5 +/- 0.2 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: 23136 SUBJECT: GRB 180812A: Swift-BAT refined analysis DATE: 18/08/12 21:19:33 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), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 180812A (trigger #852903) (Lien et al., GCN Circ. 23129). The BAT ground-calculated position is RA, Dec = 245.839, 74.674 deg which is RA(J2000) = 16h 23m 21.3s Dec(J2000) = +74d 40' 27.0" with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 26%. The mask-weighted light curve shows a multi-peaked structure that starts at ~T0 and ends at ~T+17 s. T90 (15-350 keV) is 16.51 +- 0.92 sec (estimated error including systematics). The time-averaged spectrum from T-0.30 to T+16.63 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.22 +- 0.27. The fluence in the 15-150 keV band is 8.0 +- 1.4 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+15.62 sec in the 15-150 keV band is 1.9 +- 0.4 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/852903/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23138 SUBJECT: GRB 180812A: Swift/UVOT Detection DATE: 18/08/13 18:24:45 GMT FROM: Sam LaPorte at PSU GRB 180812A: Swift/UVOT Detection S. J. LaPorte (PSU) and A. Y. Lien (GSFC/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 180812A 112 s after the BAT trigger (Lien et al., GCN Circ. 23129). A fading source consistent with the XRT position (Goad et al. GCN Circ. 23131) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 16:23:20.45 = 245.83522 (deg.) Dec (J2000) = 74:39:52.9 = 74.66471 (deg.) with an estimated uncertainty of 0.50 arc sec. (radius, 90% confidence), consistent with detections reported by BOOTES-5/JGT (Carrasco et al. GCN Circ. 23130) and COATLI (Watson et al. GCN Circ. 23132). 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 white 140 289 431 19.81 +/- 0.17 white 1551 2092 77 >20.85 v 600 6610 372 >18.9 b 526 5994 352 >20.0 u 270 5789 598 >19.8 w1 650 6857 211 >19.5 m2 6616 6815 197 >20.2 w2 6206 6406 197 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998).