////////////////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21011 SUBJECT: Swift Trigger 748858: a possible GRB DATE: 17/04/19 08:07:46 GMT FROM: Kim Page at U.of Leicester M. H. Siegel (PSU), C. Gronwall (PSU), A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team: At 07:43:33 UT, the Swift Burst Alert Telescope (BAT) triggered and located a possible GRB (trigger=748858). Swift slewed immediately to the source. The BAT on-board calculated location is RA, Dec 199.853, +15.471 which is RA(J2000) = 13h 19m 25s Dec(J2000) = +15d 28' 16" 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 07:45:58.1 UT, 145.1 seconds after the BAT trigger. No source was detected in 844 s of promptly downlinked data. We are waiting for the full dataset to detect and localise any XRT counterpart. UVOT took a finding chart exposure of 150 seconds with the White filter starting 146 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 25% of the BAT 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 BAT 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 0.03. Given the relatively low significance of the image detection (7.1 sigma) and the lack of detection in the initial XRT data, we cannot confirm that this is a true astrophysical event. A final determination of the nature of this trigger will require the full downlinked dataset. Burst Advocate for this burst is M. H. Siegel (siegel AT swift.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/too.html.) ////////////////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21012 SUBJECT: Swift Trigger 748858: Zadko observatory - Gingin optical observations DATE: 17/04/19 13:33:13 GMT FROM: Alain Klotz at IRAP-CNRS-OMP A. Klotz, D. Turpin (IRAP-CNRS-OMP), D. Macpherson (UWA/ICRAR), D. Coward (UWA), M. Boer, (UNS-CNRS-OCA), Gendre B. (UVI - Etelman Obs.), A. Williams (PO-UWA), R. Martin (PO-UWA) report: We imaged the field of the trigger 748858 detected by SWIFT with the Zadko robotic telescope (D=100cm) located at the observatory - Gingin, Australia. The observations started 4.25h after the GRB trigger. The elevation of the field increased from 18 degrees above horizon and weather conditions were good. We co-added a two series of exposures: t0+4.25h to t0+4.40h : Rlim = 20.1 t0+4.65h to t0+5.22h : Rlim = 20.3 No source exhibit a variation flux compatible with a GRB afterglow. All sources detected by Zadko are presents in the DR9 SDSS-III image. Magnitudes were estimated with the nearby NOMAD1 stars and are not corrected for galactic dust extinction. ////////////////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21014 SUBJECT: Swift Trigger 748858: MASTER-OAFA early optical observations DATE: 17/04/19 13:58:58 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs R.Podesta, C.Lopez, F. Podesta Observatorio Astronomico Felix Aguilar (OAFA) , National University of San Juan, Argentina H. Levato, C. Saffe Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE), San Juan, Argentina V. Lipunov, E. Gorbovskoy, V.Kornilov, D.Kuvshinov, N.Tyurina, A.V.Krylov, I.Gorbunov, P.Balanutsa, A.Kuznetsov, V.V.Chazov, D. Vlasenko Lomonosov Moscow State University, Sternberg Astronomical Institut of MSU K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk, O. Ershova Irkutsk State University V.Yurkov, Yu.Sergienko Blagoveschensk Educational State University, Blagoveschensk A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory D.Buckley, S. Potter, A.Kniazev, M.Kotze South African Astronomical Observatory R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in OAFA was pointed to the possible grb's Swift Trigger 748858 17 sec after notice time and 93 sec after trigger time at 2017-04-19 07:45:09 UT. On our first (20s exposure) set we haven`t found optical transient within SWIFT error-box (ra=199.85 dec=15.4703 r=0.05) (M. H. Siegel et al. GCN 21011). The 5-sigma upper limit has been about 18.7 mag Maximal limit of coadded images starting at 2017-04-19 07:45:09 (93 s after trigger time, 5000s exposure) is 19.7 mag. The observations made on zenit distance = 71 degrees, galaxy latitude b = 76 degree. The moon (51 % bright part) is 47 degrees above the horizon. The distance between moon and object is 104 The sun altitude is -41.8 degree. The object observed till 2017-04-19 09:29:17 The message may be cited. ////////////////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21017 SUBJECT: Swift trigger 748858: Swift BAT, XRT, and UVOT refined analysis DATE: 17/04/19 22:30:06 GMT FROM: Amy Lien at GSFC T. Sakamoto (AGU), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), D. N. Burrows (PSU), N. Gehrels (GSFC), H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) on behalf of the Swift team: Using the data set from the recent telemetry downlink, we report further analysis of the Swift/BAT trigger #748858 (Siegel et al., GCN Circ. 21011). The BAT data analysis is performed using data from T-239 to T+963 sec. The BAT ground-calculated position is RA, Dec = 199.804, 15.442 deg which is RA(J2000) = 13h 19m 13.0s Dec(J2000) = +15d 26' 31.1" with an uncertainty of 2.7 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%. The BAT mask-weighted light curve shows a very weak pulse that starts at ~T0 and ends at ~T+65 s. T90 (15-350 keV) is 61 +- 15 sec (estimated error including systematics). The time-averaged spectrum from T-2.00 to T+65.00 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.19 +- 0.58. The fluence in the 15-150 keV band is 1.8 +- 0.7 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+7 sec in the 15-150 keV band is 0.2 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence level. Results from the BAT data analysis are consistent with those of a long GRB. Also, the image significance of 7.4 sigma suggests that the detection is likely to be real. However, because there is no confirmed XRT and UVOT detections of a fading counterpart, we cannot rule out the possibility that the BAT signal is from some other origin. In 3.8 ks of XRT Photon Couning data covering T+158 s to T+16.8 ks we detect a single source inside the BAT error circle: RA (J2000): 13h 19m 24.41s = 199.8517d Dec (J2000): +15d 30’ 00.4” = 15.5001d Pos. error: 7.9" (radius, 90% confidence) Peak rate: 4.45e-3 (+1.43e-3, -1.20e-3) ct/sec The source is much fainter than expected for early time XRT observations of a long GRB and shows no evidence of fading, so we cannot rule out the possibility that it is an unrelated object or a non-GRB source. The Swift/UVOT began settled observations of the field 150s after the BAT trigger. No optical afterglow consistent with the BAT or XRT positions was detected in the initial UVOT exposures down to a limit of 21.0 in the white filter and 20.0 in the u filter. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/748858/BA/ ////////////////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21026 SUBJECT: Swift Trigger 748858: RATIR Optical and NIR Observations DATE: 17/04/20 23:58:05 GMT FROM: Nat Butler at Az State U Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report: We observed the field of Swift Trigger 748858 (Siegel, et al., GCN 21011) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir from 2017/04 19.32 to 2017/04 19.49 UTC (2.4 minutes to 4.10 hours after the BAT trigger), obtaining a total of 2.49 hours exposure in the r and i bands and 1.04 hours exposure in the Z, Y, J, and H bands. We observed the field for a second time for image subtraction purposes from 2017/04 20.15 to 2017/04 20.48 UTC (19.84 to 27.89 hours after the BAT trigger), obtaining a total of 4.74 hours exposure in the r and i bands and 2.09 hours exposure in the Z, Y, J, and H bands. We do not detect a fading source within either the GCN 21011 BAT error circle or the BAT error circle from Sakamoto et al. (GCN 21017), although our observations miss 4% of the southern portion of the GCN 21017 error region. For a source within the BAT error regions, in comparison with the SDSS DR9 and 2MASS catalogs, we obtain the following (3-sigma) upper limits for our observations on 4/19: r > 24.41 i > 23.95 Z > 22.59 Y > 22.44 J > 22.03 H > 21.79 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. We note that an optical source is cleanly detected at a position consistent with the XRT candidate position (GCN 21017). It has r~i~19.5 mag and is also present in DSS and SDSS. This source does not vary in flux between our epochs and is thus not likely to be the GRB afterglow. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. ////////////////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21027 SUBJECT: Swift Trigger 748858: TAROT La Silla observatory optical observations DATE: 17/04/21 00:57:47 GMT FROM: Alain Klotz at IRAP-CNRS-OMP Klotz A., Turpin D., Atteia J.L. (CNRS-OMP-IRAP), Boer, M., Laugier, R. (CNRS-ARTEMIS), Gendre B. (UVI - Etelman Obs.) report: We imaged the field of the trigger 748858 detected by SWIFT with the TAROT robotic telescope (D=25cm) located at the European Southern Observatory, La Silla observatory, Chile. The observations started 91.6s after the GRB trigger (14.7s after the notice). The elevation of the field decreased from 22 degrees above horizon and weather conditions were good. The first image is trailed with a duration of 60.0s (see the description in Klotz et al., 2006, A&A 451, L39). We do not detect any OT in the BAT error box from Siegel et al. (GCN 21011) and by Sakamoto et al. (GCN 21017) with a limiting magnitude of: t0+92s to t0+152s : Rlim = 18.0 The second image is 30.0s exposure in tracking mode: t0+165s to t0+195s : Rlim = 18.2 We co-added a series of exposures: t0+165s to t0+455s : Rlim = 19.2 t0+465s to t0+1356s : Rlim = 19.3 Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction. ////////////////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21029 SUBJECT: Swift Trigger 748858: AbAO and TSHAO optical observations DATE: 17/04/21 20:16:17 GMT FROM: Alexei Pozanenko at IKI, Moscow E. Mazaeva (IKI), A. Pozanenko (IKI), R. Inasaridze (AbAO), I. Reva (Fesenkov Astrophysical Institute), A. Kusakin (Fesenkov Astrophysical Institute), A. Volnova (IKI), V. Ayvazian (AbAO), O. Kvaratskhelia (AbAO), G. Inasaridze (AbAO), I. Molotov (KIAM), report on behalf of larger GRB follow-up collaboration: We observed the field of the SWIFT trigger 748858 (Siegel, et al., GCN 21011) with AS-32 (0.7m) telescope of Abastumani Observatory and with Zeiss-1000 1-m telescope of Tien Shan Astronomical Observatory. In each observation we fully cover both BAT error circles, initial (Siegel et al., GCN 21011) and ground-calculated error circle (Sakamoto et al., GCN 21017). Within ground-calculated error circle we do not find any new source in comparison with SDSS catalog. Within XRT error circle of the source reported in GCN 21017 (Sakamoto et al.) we find the source which is already mentioned by (Butler et al., GCN 21026). The source coincides with the star of J131924.35+153001.6 and has the brightness of R =19.53 +/- 0.04 according to SDSS DR9 and Lupton gri -> R transformations. Limiting magnitudes as well as the brightness of the star J131924.35+153001.6 for each observation are presented below. Date UT start t-T0 Filter Exp. XRT Err UpLim (3 sigma) (mid, days) (s) 2017-04-19 17:03:29 0.39918 CR 33*60 19.35 0.06 22.2 2017-04-19 17:37:14 0.42414 R 21*180 19.47 0.05 22.0 Photometry is based on nearby SDSS DR9 stars (Lupton transformations) J131940.43+152853.2 15.63 J131934.46+152944.3 15.44 J131930.90+152831.0 16.02 J131927.38+153041.9 16.17 J131911.74+152820.9 15.72 J131859.43+153017.2 16.72 J131859.61+152435.2 16.63 ////////////////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21057 SUBJECT: Swift Trigger 748858: 15 GHz upper limits from AMI DATE: 17/05/02 17:26:09 GMT FROM: Kunal Mooley at Oxford U K. P. Mooley (Hintze Fellow, Oxford), T. D. Staley, R. P. Fender (Oxford), G. E. Anderson (Curtin), T. Cantwell (Manchester), D. Titterington, S. H. Carey, J. Hickish, Y. C. Perrott, N. Razavi-Ghods, P. Scott (Cambridge), K. Grainge, A. Scaife (Manchester) The AMI Large Array responded robotically to Swift trigger 748858 (a possible GRB; Siegel et al., GCN 21011) as part of the 4pisky program, and subsequent follow up observations were obtained up to 10 days post-burst. Our observations at 15 GHz on 2016 Apr 19.79 and Apr 21.09 (UT) do not reveal any radio source in the BAT error circle (Sakamoto et al., GCN 21017), with 3sigma upper limits of 195 uJy and 120 uJy respectively. We thank the AMI staff for scheduling these observations. The AMI-GRB database is a log of all GRB follow up observations with the AMI, and is available at http://4pisky.org/ami-grb/. //////////////////////////////////////////////////////////////////////////////////