//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29619 SUBJECT: GRB 210308A: Swift detection of a burst with an optical counterpart DATE: 21/03/08 06:49:21 GMT FROM: Scott Barthelmy at NASA/GSFC V. D'Elia (SSDC), E. Ambrosi (INAF-IASFPA), S. D. Barthelmy (GSFC), A. D'Ai (INAF-IASFPA), N. J. Klingler (PSU), A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester), T. Sakamoto (AGU), M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team: At 06:37:56 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210308A (trigger=1036227). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 67.088, +37.411 which is RA(J2000) = 04h 28m 21s Dec(J2000) = +37d 24' 39" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a few overlapping peaks with a duration of about 15 sec. The peak count rate was ~6000 counts/sec (15-350 keV), at ~3 sec after the trigger. The XRT began observing the field at 06:39:21.81 UT, 85.0 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with a position: RA, Dec 67.076417, 37.435310 which is equivalent to: RA(J2000) = 04h 28m 18.34s Dec(J2000) = +37d 26' 07.11" with an uncertainty of 4.3 arcseconds (radius, 90% containment). This location is 94 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. UVOT took a finding chart exposure of 150 seconds with the White filter starting 94 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 04:28:17.73 = 67.07388 DEC(J2000) = +37:26:02.0 = 37.43388 with a 90%-confidence error radius of about 0.63 arc sec. This position is 8.5 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.57 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 1.295. Burst Advocate for this burst is V. D'Elia (valerio.delia AT ssdc.asi.it). 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: 29621 SUBJECT: GRB 210308A: MITSuME Okayama optical upper limits DATE: 21/03/08 13:51:21 GMT FROM: Ryohei Hosokawa at Tokyo Institute of Technology S. Ogata, R. Hosokawa, K. L. Murata, R. Adachi, M. Niwano, F. Ogawa, N. Nakamura, N. Ito, H. Takamatsu, H. Hara, Y. Yatsu, and N. Kawai (TokyoTech) report on behalf of the MITSuME collaboration: We observed the field of GRB 210308A (D'Elia et al.,GCN Circular #29619) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Okayama Astrophysical Observatory, Okayama, Japan. The observation with a series of 60 sec exposures started at 2021-03-08 11:03:59 UT.(4.5 hours after Swift BAT trigger) We stacked the images with good conditions. We did not detect the optical afterglow reported previously (D'Elia et al.,GCN Circular #29619) in all three bands. We obtained the 5-sigma limits of the stacked images as follows. T0+[hour] MID-UT T-EXP[sec] 5-sigma limits ------------------------------------------------------------------------------------------------ 4.5 11:51:53 4440 g'>17.6, Rc>17.8, Ic>17.8 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used the PS1 catalog for flux calibration. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29623 SUBJECT: GRB 210308A: Nanshan/NEXT optical upper limits DATE: 21/03/08 16:27:50 GMT FROM: Dong Xu at NAOC/CAS Z.P. Zhu (NAOC, HUST), S.Y. Fu, X. Liu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report: We observed the field of GRB 210308A (D'Elia et al., GCN 29619) using the NEXT-0.6m optical telescope located at Nanshan, Xinjiang, China. Observations started at 14:16:29 UT on 2021-03-08, i.e., 7.67 hr after the BAT trigger. We obtained 15x200 s frames in the Sloan r- and i- bands, respectively. The optical afterglow (D'Elia et al., GCN 29619) of the burst is not detected in our stacked images, down to limiting magnitudes of r ~ 21.7 and i ~ 21.3, calibrated with nearby PS1 stars. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29626 SUBJECT: GRB 210308A: Fermi GBM detection DATE: 21/03/08 20:27:21 GMT FROM: Stephen Lesage at Fermi-GBM Team S. Lesage (UAH), A. von Kienlin (MPE), C. Meegan (UAH), and C. Malacaria (NASA-MSFC/USRA) report on behalf of the Fermi GBM Team: "At 06:37:56.91 UT on 08 March 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 210308A (trigger 636878281 / 210308276) which was also detected by the Swift/BAT and Swift/XRT (D'Elia et al. 2021, GCN 29619). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 26 degrees. The GBM light curve shows a single-peaked structure with a duration (T90) of about 5.4 s (50-300 keV). The time-averaged spectrum from T0-1.7 s to T0+7.5 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.82 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 142 +/- 5 keV. A Band function fits the spectrum equally well with Epeak = 135 +/- 7 keV, alpha = -0.78 +/- 0.05 and beta = -3.0 +/- 0.4. The event fluence (10-1000 keV) in this time interval is (6.3 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+2.1 s in the 10-1000 keV band is 20.0 +/- 0.4 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29627 SUBJECT: Swift GRB 210308A: Global MASTER-Net observations report DATE: 21/03/08 22:18:11 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, 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), 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), O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State University) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 210308A ( V. D'Elia et al., GCN 29619) errorbox 40899 sec after notice time and 40918 sec after trigger time at 2021-03-08 17:59:54 UT, with upper limit up to 13.9 mag. Observations started at twilight. The observations began at zenith distance = 74 deg. The sun altitude is -12.2 deg. MASTER-IAC robotic telescope located in Spain (IAC Teide Observatory) was pointed to the Swift GRB 210308A errorbox 55958 sec after notice time and 55976 sec after trigger time at 2021-03-08 22:10:53 UT, with upper limit up to 18.5 mag. The observations began at zenith distance = 48 deg. The sun altitude is -40.8 deg. The galactic latitude b = -7 deg., longitude l = 164 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1563625 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 21950 | MASTER- | C | 60 | 18.0 | 22210 | MASTER- | C | 60 | 15.8 | 22945 | MASTER- | C | 60 | 12.6 | 41008 | MASTER-SAAO | C | 180 | 13.9 | 56067 | MASTER-IAC | C | 180 | 18.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29630 SUBJECT: GRB 210308A: Swift/UVOT Detection DATE: 21/03/09 01:16:01 GMT FROM: Sam LaPorte at PSU GRB 210308A: Swift/UVOT Detection J. D. Gropp (PSU) and V. D'Elia (SSDC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 210308A 95 s after the BAT trigger (D'Elia et al., GCN Circ. 29619). A source consistent with the XRT position (D'Elia et al., GCN Circ. 29619) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 04:28:17.73 = 67.07389 (deg.) Dec (J2000) = +37:26:02.1 = 37.43391 (deg.) with an estimated uncertainty of 0.46 arc sec. (radius, 90% confidence). 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 b 765 1189 38 >18.62 uvm2 864 1115 38 >17.52 u 338 1164 284 >19.50 v 667 1090 58 >17.84 uvw1 1120 1140 19 >17.25 uvw2 815 1231 50 >17.91 white 126 275 292 18.54+-0.07 white 618 1213 205 >20.20 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 1.296 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29633 SUBJECT: GRB 210308A: Swift-BAT refined analysis DATE: 21/03/09 03:09:52 GMT FROM: Takanori Sakamoto at AGU D. M. Palmer (LANL), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), V. D'Elia (SSDC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-60 to T+243 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210308A (trigger #1036227) (D'Elia, et al., GCN Circ. 29619). The BAT ground-calculated position is RA, Dec = 67.083, 37.429 deg which is RA(J2000) = 04h 28m 19.9s Dec(J2000) = +37d 25' 42.9" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 32%. The mask-weighted light curve shows a double-peaked structure from T-0.5 sec to T+9 sec. The first pulse peaks at T+0.2 sec, and the second pulse peaks at T+3 sec. T90 (15-350 keV) is 5.3 +- 0.6 sec (estimated error including systematics). The time-averaged spectrum from T-0.04 to T+7.36 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.76 +- 0.28, and Epeak of 113.6 +- 31.0 keV (chi squared 52.89 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 3.2 +- 0.1 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+2.12 sec in the 15-150 keV band is 13.6 +- 0.7 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.38 +- 0.06 (chi squared 69.63 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/1036227/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29634 SUBJECT: GRB 210308A: Mondy and AbAO optical observations DATE: 21/03/09 06:13:56 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Belkin (IKI), N. Pankov (HSE), A. Pozanenko (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO), V. R. Ayvazian (AbAO), G. V. Kapanadze (AbAO), D. G. Datashvili (AbAO) report on behalf of IKI-GRB-FuN: We observed the field of GRB 210308A (D'Elia et al., GCN 29619) with AZT-33IK telescope of Sayan observatory (Mondy) starting on 2021-03-08 (UT) 13:00:45 and AS-32 telescope of Abastumani observatory (AbAO) starting on 2021-03-08 (UT) 16:32:07 (both in R-filter). The optical afterglow (D'Elia et al., GCN 29619; Gropp et al., GCN 29630; see also Ogata et al., GCN 29621; Zhu et al., GCN 29623; Lipunov et al., GCN 29627) is detected in stacked image of AZT-33IK and not detected at AS-32. Date UT start t-T0 Filter Exp. OT Err. UL(3sigma) (mid, days) (s) 2021-03-08 13:00:45 0.27626 R 15*120 22.77 0.27 22.8 AZT-33IK 2021-03-08 16:32:07 0.42131 R 25*60 n/d n/d 21.8 AS-32 The photometry is based on nearby USNO-B1.0 stars USNO-B1.0_id R2 1274-0090800 15.34 1274-0090824 17.35 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29643 SUBJECT: Konus-Wind detection of GRB 210308A DATE: 21/03/10 12:11:00 GMT FROM: Dmitry Svinkin at Ioffe Institute D. Svinkin, S. Golenetskii, D. Frederiks, M. Ulanov, A. Tsvetkova, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 210308A (Swift-BAT detection: D'Elia et al., GCN Circ. 29619, Palmer et al., GCN Circ. 29633; Fermi-GBM detection: Lesage et al., GCN Circ. 29626) triggered Konus-Wind at T0=23879.936 s UT (06:37:59.936). The burst light curve shows a multi-peaked structure which starts at ~T0-3.8 s and has a total duration of ~8.9 s. The emission is seen up to ~1 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB210308_T23879/ As observed by Konus-Wind, the burst had a fluence of 5.00(-0.48,+0.53)x10^-6 erg/cm2, and a 64-ms peak flux, measured from T0+1.264 s, of 3.36(-0.85,+0.87)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 1 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.73(-0.32,+0.38) and Ep = 150(-19,+25) keV (chi2 = 49/55 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.7 (chi2 = 49/54 dof). All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.