//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28499 SUBJECT: GRB 200925B: Swift detection of a burst DATE: 20/09/25 22:00:50 GMT FROM: David Palmer at LANL S. B. Cenko (GSFC), C. Gronwall (PSU), J.D. Gropp (PSU), N. J. Klingler (PSU), H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team: At 21:50:37 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 200925B (trigger=997453). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 246.851, +78.394 which is RA(J2000) = 16h 27m 24s Dec(J2000) = +78d 23' 39" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of about 40 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~5 sec after the trigger. The XRT began observing the field at 21:51:55.3 UT, 78.4 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 246.78990, 78.39033 which is equivalent to: RA(J2000) = 16h 27m 09.58s Dec(J2000) = +78d 23' 25.2" with an uncertainty of 3.9 arcseconds (radius, 90% containment). This location is 46 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 https://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 consistent with the Galactic value of 4.59 x 10^20 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 150 seconds with the White filter starting 81 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 S. B. Cenko (brad.cenko 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/) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28500 SUBJECT: GRB 200925B: Prompt enhanced Swift-XRT position DATE: 20/09/25 23:04:05 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Using promptly downlinked XRT event data for GRB 200925B, we find an enhanced XRT position of the afterglow: RA, Dec: 246.7868, 78.3904 which is equivalent to: RA (J2000) = 16 27 08.83 Dec (J2000) = +78 23 25.5 with an uncertainty of 2.0 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/997453. Position enhancement is is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28501 SUBJECT: GRB 200925B: OSN Afterglow Candidate Discovery DATE: 20/09/25 23:14:27 GMT FROM: Alexander Kann at IAA-CSIC A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D. A. Kann, C. C. Thoene, M. Blazek, J. F. Agui Fernandez (all HETH/IAA-CSIC), and F. Aceituno (IAA-CSIC) report: We observed the location of the Swift GRB 200925B (Cenko et al., GCN #28499) with the 1.5m telescope of the Observatorio Sierra Nevada, in Granada, Spain. We obtained a 300 s image each in the BVRc bands and multiple 100 s images in Ic, beginning 2020-09-25 22:27:07 UT. We detect a source in all filters at RA (J2000) = 16:27:08.50 Dec. (J2000) = +78:23:24.9 with an error of 0".5, within the UVOT-enhanced XRT position (Evans, GCN #28500). We note this source is also clearly detected in the initial Swift UVOT white finding chart, at a significantly brighter magnitude relative to the nearby field star. This strongly suggests the source is fading and is therefore the afterglow of GRB 200925B. At 0.034294 days after the GRB, we measure r' = 19.46 +/- 0.1 (AB magnitude) vs. nearby SDSS field stars. [GCN OPS NOTE: Per the author's request: in the Title the "25A" was changed to "25B", the affiliation of A. de Ugarte Postigo is "*-CSIC" not "*-CSIS", "Thoene" not "Thone", and in the first sentence, the "200906A" should be "200925B".] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28502 SUBJECT: Swift GRB 200925B: Global MASTER-Net OT detection DATE: 20/09/26 00:05:19 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, N.Tyurina, E. Gorbovskoy, V.Kornilov, P.Balanutsa, A.Kuznetsov, F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov, D. Cheryasov (Lomonosov Moscow State University, SAI, Physics Department), O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA), R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias), D. Buckley (South African Astronomical Observatory), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State University) MASTER-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the Swift GRB200925A (trigger No 997453,16h 27m 24.24s , +78d 23m 38.4s, R=0.05) errorbox 14 sec after notice time and 58 sec after trigger time at 2020-09-25 21:51:35 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 53 deg. The sun altitude is -47.0 deg. On our 4-th (40s exposure) set , obtained 229 sec after tigger time at 2020-09-25 21:54:16 UT, we found an optical transient within Swift error-box (ra=246.851 dec=+78.394 r=0.05). T-Tmid Date Time Expt. Ra Dec Mag ---------|---------------------|-------|-----------------|-----------------|----- 229 2020-09-25 21:54:16 40 (246.7866 d, +78.3896 d) 17.9 The OT position in within enhanced XRT position (GCN 28500) and is coincident with OSN afterglow candidate position (A. de Ugarte Postigo et al, GCN 28501) The 5-sigma upper limit has been about 18.4 mag The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28503 SUBJECT: GRB 200925B: Enhanced Swift-XRT position DATE: 20/09/26 04:08:17 GMT FROM: Phil Evans at U of Leicester A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 1704 s of XRT Photon Counting mode data and 1 UVOT images for GRB 200925B, 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 = 246.78522, +78.39052 which is equivalent to: RA (J2000): 16h 27m 8.45s Dec (J2000): +78d 23' 25.9" with an uncertainty of 1.8 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: 28506 SUBJECT: GRB 200925B: Swift-BAT refined analysis DATE: 20/09/26 18:03:43 GMT FROM: Hans Krimm at NSF/NASA-GSFC M. Stamatikos (OSU), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), T. N. Ukwatta (LANL) (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 200925B (trigger #997453) (Cenko, et al., GCN Circ. 28499). The BAT ground-calculated position is RA, Dec = 246.892, 78.393 deg which is RA(J2000) = 16h 27m 34.1s Dec(J2000) = +78d 23' 33.5" with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 50%. The mask-weighted light curve shows two peaks, the first beginning ~T-2 sec, peaking at T+5 sec, and decaying by T+12 sec. The second, weaker, peak runs from T+16 to T+22 sec. T90 (15-350 keV) is 18.25 +- 0.97 sec (estimated error including systematics). The time-averaged spectrum from T+0.20 to T+19.59 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.01 +- 0.14. The fluence in the 15-150 keV band is 1.0 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+4.38 sec in the 15-150 keV band is 3.0 +- 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/997453/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28507 SUBJECT: GRB 200925B: Swift/UVOT Detection DATE: 20/09/26 20:14:25 GMT FROM: Samantha Oates at MSSL S. R. Oates (U.Birmingham) and S. B. Cenko (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 200925B 82 s after the BAT trigger (Cenko et al., GCN Circ. 28499). A source consistent with the XRT position (Beardmore et al. GCN Circ. 28503) and the optical position reported by the OSN (de Ugarte Postigo et al., GCN Circ. 28501) and MASTER (Lipunov et al., GCN Circ. 28502) is detected in the initial UVOT exposures. 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 (FC) 82 232 147 19.80 +/- 0.20 white 574 1714 264 20.77 +/- 0.37 v 623 1763 136 >18.9 b 549 1689 117 >19.6 u (FC) 294 544 246 >19.7 u 294 1663 343 >19.9 w1 672 1813 136 >19.0 m2 1249 1441 39 >17.7 w2 599 1739 117 >18.9 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). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28508 SUBJECT: GRB 200925B: Swift-XRT refined Analysis DATE: 20/09/26 22:00:05 GMT FROM: Phil Evans at U of Leicester B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAB), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB) and S.B. Cenko report on behalf of the Swift-XRT team: We have analysed 5.1 ks of XRT data for GRB 200925B (Cenko et al. GCN Circ. 28499), from 87 s to 47.2 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 28500). The late-time light curve (from T0+29.2 ks) is consistent with a constant source of mean count rate 1.3e-01 ct/sec. A power-law fit gives an index of 1.0 (+/-1.2). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.12 (+0.19, -0.18). The best-fitting absorption column is 7.5 (+4.4, -2.9) x 10^20 cm^-2, consistent with the Galactic value of 4.6 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 3.1 x 10^-11 (3.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 7.5 (+4.4, -2.9) x 10^20 cm^-2 Galactic foreground: 4.6 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 2.12 (+0.19, -0.18) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00997453. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28511 SUBJECT: GRB 200925B NUTTelA-TAO / BSTI Early Measurements (Preliminary) DATE: 20/09/27 05:14:22 GMT FROM: Bruce Grossan at LBNL/UCB SSL B. Grossan (UCB, NU) , Z. Maksut (NU), A. Kim (NU), M. Krugov (FAI), G. F. Smoot (HKUST, UCB, NU), E. Linder (UCB, NU), report on behalf of the Energetic Cosmos Laboratory: The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at GRB200925B on receipt of an automated GCN / BAT position alert. We report measurements made with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32,14) instrument ***during commissioning phase*** and we note cautions with these measurements below. Calibration with bright Pan-STARRS catalog I stars on our images, for our standard SDSS filters and 45 s co-added images yields, *without color corrections*, the following photometric values for the OT consistent with the position given in Evans et al. (GCN 28503): # tc-t0(s) g'(mag) r'(mag) i'(mag) -- --------- ----------- ----------- ------------ 1 67.5 UL18.27 UL18.07 UL17.32 2 136.5 UL18.15 18.62 17.94** 3 181.5 UL18.21 17.99 17.47 4 226.5 UL18.25 18.09 17.63 5 271.5 UL18.27 18.17 17.48 6 316.5 UL18.31 18.26 17.70 7 361.5 UL18.14 18.60 17.83 8 406.5 UL18.17 18.55 17.87* UL = 5 sigma upper limit ** = very large certainty, close to limit ; poor by-eye confirmation and aperture centering * = large uncertainty ; poor by-eye confirmation and aperture centering Other uncertainties are estimated at ~ 0.1 mag tc-t0 = trigger time minus image center time. The measurements suggest that the early emission peaked ~180 s after trigger. We caution the reader that the BSTI instrument is in commissioning phase, with known imperfections, and we have not extensively tested our results, e.g. against other simultaneous measurements, or near our detection limits. Please also note that the times are approximate. We anticipate additional analysis in 15-30 days posted at http://ecl.nu.edu.kz/gamma-ray-burst/grb200925b. Some earlier images may have usable data. ---------------------------------- UCB = University of California, Berkeley, USA NU = Nazarbayev University, Nur-Sultan, Kazakhstan HKUST = Hong Kong University of Science and Technology FAI = Fesenkov Astrophysical Institute, Kazakhstan The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28512 SUBJECT: GRB 200925B: Swift-XRT refined analysis update DATE: 20/09/27 11:32:20 GMT FROM: Andy Beardmore at U Leicester A.P. Beardmore (U. Leicester) and S. B. Cenko (GSFC) report on behalf of the Swift-XRT team: An additional 4.9 ks of Swift-XRT Photon Counting mode data have been collected on GRB 200925B (Cenko et al. GCN Circ. 28499, Sbarufatti et al. GCN Circ. 28508), bringing the total XRT exposure to 10 ks, from 87 s to 86.3 ks after the BAT trigger. The late time X-ray light curve from T0+29.2 ks to 86.3 ks is now decaying with a power-law decay slope of 1.1 +/- 0.4. If the light curve continues to decay at the same rate than the predicted count rate at T0+3 days will be 3.4e-03 count/sec, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.05 x 10^-13 (1.28 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/00997453. This circular is an official product of the Swift-XRT team.