//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29650 SUBJECT: GRB 210312B: A long GRB detected by INTEGRAL DATE: 21/03/12 22:02:02 GMT FROM: Sandro Mereghetti at IASF-Milano/INAF S.Mereghetti (INAF, IASF-Milano), D.Gotz (CEA, Saclay), C.Ferrigno, E.Bozzo, V.Savchenko (ISDC, Versoix), L.Ducci (IAAT, Germany and ISDC, Versoix) and J.Borkowski (CAMK, Torun) report: a gamma ray burst lasting about 5 s has been detected by IBAS in the IBIS/ISGRI data at 20:52:17 UT of March 12, 2021 The refined coordinates (J2000) are: R.A.= 155.8431 deg DEC.= +76.8714 deg with an uncertainty of 2 arcmin (90% c.l.). The burst had a peak flux of about 1.5 ph/cm2/s (20-200 keV, 1-s integration time) and a fluence in the same energy range of about 2e-7 erg/cm2 A plot of the light curve will be posted at http://ibas.iasf-milano.inaf.it/IBAS_Results.html //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29651 SUBJECT: GRB210312B (Integral alert 9073): Candidate optical afterglow by Ondrejov D50 DATE: 21/03/12 22:05:41 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov M. Jelinek, J. Strobl, S. Trcka, R. Hudec, C. Polasek (ASU CAS Ondrejov) report: We observed the position of the Integral trigger 9073 (GRB 210312.87 or B) with the D50 robotic telescope of the Astronomical Institute Ondrejov, near Prague, Czech Republic. We performed a series of 10s and 20s unfiltered exposures starting 23.8 s after the trigger. In the first images we detect a rapidly fading object not present in the DSS catalogue at 10:23:15.312 +76:52:06.96 J2000. The preliminary magnitude of the object in the earliest images was R~18m. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29652 SUBJECT: GRB 210312B: MASTER OT confirmation DATE: 21/03/12 22:55:02 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, V.Kornilov, E.Gorbovskoy,N.Tiurina,P.Balanutsa,F.Balakin, V.Vladimirov, A.Kuznetsov,K.Zhirkov,D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, A.Chasovnikov,A.Pozdnyakov,V.Topolev, D.Cheryasov(Lomonosov Moscow State University, SAI, Physics Department), D. Buckley (South African Astronomical Observatory), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico FelixAguilar OAFA), R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias), O.A. Gres, N.M. Budnev (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) MASTER Global robotic net (MASTER-Net:http://observ.pereplet.ru Lipunov et al.,2010,Advances in Astronomy,2010,30L) automatically started (Lipunov et al. GCN 29649) Integral GRB 210312B (Mereghetti et al. GCN 29650,Ttrigger=20:52:17UT) optical observations at MASTER-Kislovodsk at 2021-03-12 20:52:58 UT 27s after notice time(41s after trigger time), and at MASTER-Tunka at 2021-03-12 20:52:58UT with mli18.7 at first 10s images. We confirm Jelinek et al. GCN 29651 (Ondrejov) optical counterpart with unfiltered m_OT=18.2 at first image. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29653 SUBJECT: GRB 210312B: GTC photometry DATE: 21/03/13 00:51:28 GMT FROM: Alexander Kann at IAA-CSIC D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), C. C. Thoene, M. Blazek, J. F. Agui Fernandez (all HETH/IAA-CSIC), and R. Scarpa (GTC) report: We observed the afterglow (Jelinek et al., GCN #29651; Lipunov et al., GCN #29652) of INTEGRAL GRB 210312B (Mereghetti et al., GCN #29650) with OSIRIS at the 10.4m Gran Telescopio Canarias (Roque de los Muchachos Observatory, La Palma, Canary Islands, Spain), starting at 2021-03-12 22:57:10.834 UT. We obtained a 60 s finding chart exposure under adverse conditions (2" seeing, bad transparency because of Calima). In the image, the afterglow is clearly detected. Against a nearby PanSTARRS star, we measure r' = 21.52 +/- 0.06 mag at 2.0898 hr after the trigger (0.08708 days). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29655 SUBJECT: GRB 210312B: Redshift from OSIRIS/GTC DATE: 21/03/13 13:13:31 GMT FROM: Alexander Kann at IAA-CSIC D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), C. C. Thoene, M. Blazek, J. F. Agui Fernandez (all HETH/IAA-CSIC), and R. Scarpa (GTC) report: We observed the afterglow (Jelinek et al., GCN #29651; Lipunov et al., GCN #29652) of INTEGRAL GRB 210312B (Mereghetti et al., GCN #29650) with OSIRIS at the 10.4m Gran Telescopio Canarias (Roque de los Muchachos Observatory, La Palma, Canary Islands, Spain), starting at 2021-03-12 22:57:10.834 UT under adverse conditions (2" seeing, bad transparency because of Calima). Following the finding chart exposure (Kann et al., GCN #29653), we obtained 2 x 900 s spectroscopic exposures with the R1000B grism, covering the spectral range from 3700 to 7800 AA, before the telescope was shut down due to worsening observing conditions. We detect a faint trace in both images. We resumed observations after an improvement in weather conditions at 2021-03-13 01:41:40.281 UT, obtaining two further finding charts and 4 x 900 s spectra with the same grism. Using the same comparison star as Kann et al., GCN #29653, we find the afterglow has faded to r' = 22.36 +/- 0.03 mag (AB) at 4.8316 hrs after the GRB trigger. Combining the first spectral exposure and the latter, for a total exposure of 5 x 900 s, a trace is clearly detected redwards of 4300 AA, as well as several absorption lines. We identify these as FeII, MgII, and MgI, at a mean redshift of z = 1.069. At this redshift, we also detect OII in emission, which allows us to identify this as the redshift of the GRB. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29716 SUBJECT: GRB 210312B: OSN Afterglow Observations DATE: 21/03/24 19:45:39 GMT FROM: Alexander Kann at IAA-CSIC D. A. Kann (HETH/IAA-CSIC), M. Jelinek (ASU CAS Ondrejov), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), C. C. Thoene, M. Blazek, J. F. Agui Fernandez (all HETH/IAA-CSIC), A. Sota, and R. M. Eloy (both IAA-CSIC) report: We observed the optical afterglow of GRB 210312B (INTEGRAL detection: Mereghetti et al., GCN #29650) with both the 1.5m T150 and the 0.9m T90 telescopes of the Observatorio de Sierra Nevada (OSN), Granada, Spain. We obtained 5 x 90 s exposures in B, V, Rc, and 6 x 90 s in Ic, followed by 21 x 180 s exposures in Rc with the T150 telescope, and 18 x 180 s in Rc with the T90 telescope in parallel, starting at 2021-03-12 22:51:28.19 UT. The afterglow is detected in multiple combined images from T150, and in the complete combined T90 image. We furthermore obtained 10 x 500 s Rc images in the second night with the T150. The afterglow is detected in the combined image. From three stacked images observed from 0.09577 to 0.14106 days after the GRB, we detect a potential plateau phase, measuring Rc ~ 21.69 mag (AB mag, vs. a nearby Pan-STARRS star converted to Rc following the Lupton transformations, then transformed back to AB mag; errors range from 0.04 to 0.11 mag). Then at 1.0850 days, we find the afterglow has significantly decayed to Rc = 23.04 +/- 0.07 mag (AB). Using photometry from our GTC observations (Kann et al., GCNs #29653, #29655) as well as earlier photometry from the Ondrejov D50, we find a broken power-law decay with a late slope of alpha ~ 2.2. The second-day OSN detection is in excess of the extrapolated decay, indicating that the host galaxy may contribute already, or that another rebrightening has taken place. [GCN OPS NOTE(01apr21): The typo in the SUBJECT line "230312B" was changed to 210312B.]