//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29096 SUBJECT: GRB 201221A: Swift detection of a burst DATE: 20/12/21 07:20:48 GMT FROM: David Palmer at LANL K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 07:09:01 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 201221A (trigger=1013852). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 214.477, -45.411 which is RA(J2000) = 14h 17m 55s Dec(J2000) = -45d 24' 38" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 50 sec. The peak count rate was ~800 counts/sec (15-350 keV), at ~10 sec after the trigger. The XRT began observing the field at 07:11:17.8 UT, 136.5 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source located at RA, Dec 214.47885, -45.41606 which is equivalent to: RA(J2000) = 14h 17m 54.92s Dec(J2000) = -45d 24' 57.8" with an uncertainty of 3.8 arcseconds (radius, 90% containment). This location is 18 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. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (9.32 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 5.3 (+4.59/-3.72) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 141 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 0.11. Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 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: 29097 SUBJECT: GRB 201221A: Prompt enhanced Swift-XRT position DATE: 20/12/21 07:36:31 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 201221A, we find an enhanced XRT position of the afterglow: RA, Dec: 214.4805, -45.4166 which is equivalent to: RA (J2000) = 14 17 55.31 Dec (J2000) = -45 24 59.9 with an uncertainty of 2.3 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/1013852. 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: 29098 SUBJECT: Swift GRB 201221A: Global MASTER-Net observations report DATE: 20/12/21 07:56:21 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 201221A ( K. L. Page et al., GCN 29096) errorbox 76 sec after trigger time at 2020-12-21 07:10:17 UT, with upper limit up to 17.6 mag. The observations began at zenith distance = 65 deg. The sun altitude is -23.8 deg. The galactic latitude b = 14 deg., longitude l = 319 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1507781 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 86 | MASTER-OAFA | C | 20 | 17.3 | 126 | MASTER-OAFA | C | 20 | 17.2 | 170 | MASTER-OAFA | C | 30 | 17.5 | 225 | MASTER-OAFA | C | 40 | 17.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29099 SUBJECT: GRB 201221A: FRAM-Auger optical limit DATE: 20/12/21 08:29:10 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov Martin Jelinek, Jan Strobl (ASU CAS Ondrejov, CZ), Martin Masek, Petr Janecek, Sergey Karpov, Jakub Jurysek, Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza (Institute of Physics, Prague, CZ) report: The 30cm robotic telescope FRAM-Auger in Malargue (Argentina) reacted robotically to the Swift/BAT alert of GRB201221A (Page et al., GCNC 29096, Evans et al., GCNC 29097), starting with a series of 20 s R-band images at 07:10:13 UT, i.e. 72 s post trigger. We do not detect any new or strongly variable source at or around the reported gamma-ray errorbox in single frames nor in a combined 20 x 20 s image spanning the period from 1.2 min to 12.1 min after the initial trigger. The combined exposure has a 3-sigma limiting magnitude R(Vega) ~ 17.5. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29100 SUBJECT: GRB 201221A: VLT/X-shooter afterglow discovery and spectroscopic redshift z = 5.7 DATE: 20/12/21 13:16:00 GMT FROM: Daniele B Malesani at DTU Space D. B. Malesani (DTU Space), J.-B. Vielfaure (APC, Paris University), L. Izzo (DARK/NBI), S. D. Vergani (GEPI, Observatoire de Paris), D. Burgarella (AMU, CNRS, CNES, LAM), V. D'Elia (ASI/SSDC), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), J. P. U. Fynbo (DAWN/NBI), A. J. Levan (Radboud Univ.), B. Milvang-Jensen (DAWN/NBI), D. A. Kann (HETH/IAA-CSIC), E. Palazzi (INAF/OAS), G. Pugliese (API, Univ. Amsterdam), N. R. Tanvir (Univ. Leicester), K. Wiersema (Univ. Warwick), report on behalf of the Stargate consortium: We observed the field of GRB 201221A (Page et al., GCN 29096) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Using the acquisition camera, multi-band imaging was secured. Within the XRT error circle (Evans, GCN 29097), no source is detected in an r-band image (taken at mean epoch of 42 min after the GRB) down to limiting magnitude r > 23.5 (AB). However, a source is clearly visible in the z-band image with z = 19.76 +- 0.04 AB (mean time 35 min after the GRB). The corresponding color r-z > 3.7 is exceptionally red. The coordinates of the object are (J2000, 0.3" error): RA = 14:17:55.26 Dec = -45:24:58.0 Spectroscopy of the z-band source was executed covering the wavelength range 3000-25000 AA. Unfortunately due to visibility constraints, only two spectra by 600 s each were secured, plus two extra exposures during twilight which have lower quality. We report on the analysis of the first set only, which has a mean time of 1.65 hr after the GRB. Continuum is well detected in the infrared arm, as well as in the red part of the visible arm. A clear break is detected around 8150 AA, which, if interpreted as the Lyman break, corresponds to z = 5.70. Weak continuum is detected blueward of the break, until it vanishes completely at the corresponding location of the Lyman limit. We thus conclude that z = 5.70 is the redshift of GRB 201221A. Further analysis is undergoing. We acknowledge support from the ESO observing staff at Paranal, in particular Zahed Wahhaj. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29101 SUBJECT: GRB 201221B: Fermi GBM Final Real-time Localization DATE: 20/12/21 14:23:08 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM The Fermi GBM team reports the detection of a likely SHORT GRB At 14:11:43 UT on 21 Dec 2020, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 201221B (trigger 630252708.014426 / 201221591). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 110.6, Dec = 32.0 (J2000 degrees, equivalent to J2000 07h 22m, 32d 00'), with a statistical uncertainty of 4.1 degrees. The angle from the Fermi LAT boresight is 14.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn201221591/quicklook/glg_skymap_all_bn201221591.png The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn201221591/quicklook/glg_healpix_all_bn201221591.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn201221591/quicklook/glg_lc_medres34_bn201221591.gif //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29105 SUBJECT: GRB 201221A: Enhanced Swift-XRT position DATE: 20/12/21 18:56:51 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 2103 s of XRT Photon Counting mode data and 5 UVOT images for GRB 201221A, 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 = 214.48016, -45.41620 which is equivalent to: RA (J2000): 14h 17m 55.24s Dec (J2000): -45d 24' 58.3" with an uncertainty of 1.5 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: 29106 SUBJECT: Swift Trigger 1014012: possible GRB 201221C DATE: 20/12/21 19:07:16 GMT FROM: Kim Page at U.of Leicester K. L. Page (U Leicester), J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (PSU), F. E. Marshall (NASA/GSFC), M. J. Moss (GWU) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team: At 18:41:33 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 201221C (trigger=1014012). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 278.205, +34.411 which is RA(J2000) = 18h 32m 49s Dec(J2000) = +34d 24' 39" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is typical for image triggers, there is nothing significant in the real-time light curves. The XRT began observing the field at 18:43:46.4 UT, 132.7 seconds after the BAT trigger. No source was detected in 215 s of promptly downlinked data. We are waiting for the full dataset to detect and localise the XRT counterpart. UVOT took a finding chart exposure of 150 seconds with the White filter starting 136 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 0.07. Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 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: 29107 SUBJECT: GRB 201221C: MASTER optical observtion DATE: 20/12/21 19:41:01 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, V.Kornilov, E.Gorbovskoy, N.Tiurina, P.Balanutsa,A.Kuznetsov,K.Zhirkov, F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, A.Chasovnikov,A.Pozdnyakov, V.Topolev, 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 (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov, Yu. Sergienko (Blagoveschensk Educational State University) MASTER-IAC robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Spain (IAC Teide Observatory) was pointed to the GRB201221.78 133 sec after notice time and 208 sec after trigger time at 2020-12-21 18:45:02 UT. On our 11-th (180s exposure) set , obtained 1451 sec after tigger time at 2020-12-21 19:05:45 UT, we haven`t found optical transient within Swift error-box (ra=278.204 dec=34.4108 r=0.05). The 5-sigma upper limit has been about 13.6mag The message may be cited. The galactic latitude b = 18 deg., longitude l = 63 deg. The observations made on zenith distance = 69 deg.The moon (48 % bright part) is 56 deg. above the horizon. The distance between moon and object is 87 Observations started at twilight. The sun altitude is -11.4 deg. The object can be observed till sunrise at 2020-12-22 07:52:15 The 5-sigma upper limit has been about 14.9mag The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29108 SUBJECT: GRB 201221A: Swift-XRT refined Analysis DATE: 20/12/21 21:57:31 GMT FROM: Phil Evans at U of Leicester A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), D.N. Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester) and K.L. Page report on behalf of the Swift-XRT team: We have analysed 6.2 ks of XRT data for GRB 201221A (Page et al. GCN Circ. 29096), from 143 s to 23.8 ks after the BAT trigger. The data comprise 320 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 29097). The light curve can be modelled with a power-law decay with a decay index of alpha=0.71 (+/-0.04). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.39 (+0.16, -0.15). The best-fitting absorption column is 6.3 (+8.3, -6.3) x 10^22 cm^-2, at a redshift of 5.7, in addition to the Galactic value of 9.3 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 5.0 x 10^-11 (4.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 9.3 x 10^20 cm^-2 Intrinsic column: 6.3 (+8.3, -6.3) x 10^22 cm^-2 at z=5.7 Photon index: 1.39 (+0.16, -0.15) If the light curve continues to decay with a power-law decay index of 0.71, the count rate at T+24 hours will be 0.016 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.0 x 10^-13 (7.4 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/01013852. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29109 SUBJECT: GRB 201221A: Swift/UVOT Upper Limits DATE: 20/12/21 22:06:23 GMT FROM: Alice Breeveld at MSSL-UCL A. A. Breeveld (UCL-MSSL) and K. L. Page (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 201221A 141 s after the BAT trigger (Page et al., GCN Circ. 29096). No optical afterglow consistent with the optical position (Malesani et al. GCN Circ. 29100) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 141 291 147 >20.0 u_FC 300 549 246 >19.1 white 141 951 257 >20.2 v 629 4762 236 >18.8 b 555 748 39 >18.3 u 300 5271 357 >19.5 w1 679 5172 236 >19.4 m2 654 4967 236 >19.2 w2 605 4557 235 >19.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.11 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29110 SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 201221A DATE: 20/12/21 22:28:27 GMT FROM: Peter Veres at UAH P. Veres (UAH) reports on behalf of the Fermi-GBM Team: "At 07:09:01 UT on 21 December, 2020 Swift detected GRB 201221A (Page et al. GCN 29096). There was no Fermi-GBM onboard trigger around the event. An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified a long counterpart with high significance. This was not included in the public list (https://gcn.gsfc.nasa.gov/gcn/fermi_gbm_subthresh_archive.html), because the search reports only short candidates. The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals identified a transient most significantly on the 8.192 s timescale, with a log likelihood ratio of 52 and a location consistent with the event. The GBM light curve consists of a single peak. The time-averaged spectrum from T0-10 s to T0+47 s is best fit by a power law function with an exponential high-energy cutoff (T0 is the Swift trigger time). The power law index is -1.17 +/- 0.21 and the cutoff energy, parameterized as Epeak, is 129 +/- 28 keV. The event fluence (10-1000 keV) in this time interval is (3.30 +/- 0.27)E-04 erg/cm^2. Using the redshift z=5.7 reported by Malesani et al (GCN 29100), we derive an isotropic equivalent energy in the 1-10,000 keV range of (2.02 +/- 0.16)E+55 erg. This analysis is preliminary. [1] Goldstein et al. 2019 arXiv:1903.12597 " //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29111 SUBJECT: correction to GCN 29110 - Fermi GBM Sub-Threshold Detection of GRB 201221A DATE: 20/12/21 23:14:59 GMT FROM: Peter Veres at UAH P. Veres (UAH) reports: In GCN 29110 we reported the sub-threshold detection of GRB 201221A. The reported fluence value contained an error. The corrected paragraph reads: " The event fluence (10-1000 keV) in the T0-10 s to T0+47 s time interval (T0 is the Swift trigger time) is (3.6 +/- 0.4)E-06 erg/cm^2. Using the redshift z=5.7 reported by Malesani et al (GCN 29100), we derive an isotropic equivalent energy in the 1-10,000 keV range of (2.2 +/- 0.2)E+53 erg. " We apologize for the confusion this may have caused. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29112 SUBJECT: GRB 201221D: Swift detection of a bright short burst DATE: 20/12/21 23:16:01 GMT FROM: David Palmer at LANL K. L. Page (U Leicester), S. D. Barthelmy (GSFC), J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), B. Sbarufatti (PSU), M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team: At 23:06:34 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 201221D (trigger=1014037). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 171.049, +42.144 which is RA(J2000) = 11h 24m 12s Dec(J2000) = +42d 08' 39" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of about 0.3 sec. The peak count rate was ~9000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 23:08:01.7 UT, 87.4 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 171.05873, 42.14332 which is equivalent to: RA(J2000) = 11h 24m 14.10s Dec(J2000) = +42d 08' 36.0" with an uncertainty of 5.7 arcseconds (radius, 90% containment). This location is 26 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. No spectrum from the promptly downlinked event data is yet available to determine the column density. UVOT took a finding chart exposure of 150 seconds with the White filter starting 92 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 0.02. Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 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: 29113 SUBJECT: GRB 201221D: Prompt enhanced Swift-XRT position DATE: 20/12/21 23:32:42 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 201221D, we find an enhanced XRT position of the afterglow: RA, Dec: 171.0587, 42.1438 which is equivalent to: RA (J2000) = 11 24 14.09 Dec (J2000) = +42 08 37.5 with an uncertainty of 4.2 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/1014037. 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: 29114 SUBJECT: GRB 201221E: Fermi GBM Final Real-time Localization DATE: 20/12/21 23:50:46 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM The Fermi GBM team reports the detection of a likely LONG GRB At 23:28:47 UT on 21 Dec 2020, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 201221E (trigger 630286132.63327 / 201221978). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 158.1, Dec = -39.9 (J2000 degrees, equivalent to J2000 10h 32m, -39d 53'), with a statistical uncertainty of 5.2 degrees. The angle from the Fermi LAT boresight is 90.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn201221978/quicklook/glg_skymap_all_bn201221978.png The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn201221978/quicklook/glg_healpix_all_bn201221978.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn201221978/quicklook/glg_lc_medres34_bn201221978.gif //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29116 SUBJECT: GRB 201221A: Swift-BAT refined analysis DATE: 20/12/22 01:05:18 GMT FROM: Amy Lien at GSFC S. D. Barthelmy (GSFC), J. R. Cummings (CPI), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-240 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 201221A (trigger #1013852) (Page et al., GCN Circ. 29096). The BAT ground-calculated position is RA, Dec = 214.488, -45.406 deg which is RA(J2000) = 14h 17m 57.1s Dec(J2000) = -45d 24' 20.8" with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 42%. The mask-weighted light curve shows a weak pulse that starts at ~T-7 s and ends at ~T+40 s. T90 (15-350 keV) is 44.5 +- 6.2 sec (estimated error including systematics). The time-averaged spectrum from T-7.63 to T+41.72 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.40 +- 0.15. The fluence in the 15-150 keV band is 1.9 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+4.16 sec in the 15-150 keV band is 1.0 +- 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/1013852/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29117 SUBJECT: GRB 201221D: candidate optical counterpart from the NOT DATE: 20/12/22 01:34:37 GMT FROM: Daniele B Malesani at DTU Space D. B. Malesani (DTU Space) and E. Knudstrup (NOT and Aarhus Univ.) report on behalf of a larger collaboration: We observed the field of GRB 201221D (Page et al., GCN 29112) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC imaging camera. Observations were carried out using the SDSS r (3x300 s) and z (5x200 s) filters. The data were taken as soon as the target rised, so at quite high airmass (2.9 to 2.3), yielding a seeing of ~1.5". Inside or close to the XRT werror circle (current uncertainty 4.2": https://www.swift.ac.uk/xrt_positions/), a very faint object is detected in the stack of the r-band images. Calibrating against nearby stars from the Pan-STARRS catalog, we measure r = 23.1 +- 0.3 (AB), at a mean epoch 2020 Dec 22.032 UT (1.67 hr after the GRB). Its coordinates are: RA = 11:24:14.02 Dec = +42:08:39.97 No object is visible at this location in the Pan-STARRS r-band image, which has however a limiting magnitude (r ~ 23.3 AB) comparable to our measurement. Given the lack of variability and the still relatively large XRT error circle size, we cannot confirm at the present time whether this object is associated with GRB 201221D. Further observations are planned. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29118 SUBJECT: GRB 201221D: Nanshan/NEXT early optical upper limit DATE: 20/12/22 01:38:32 GMT FROM: Dong Xu at NAOC/CAS D. Xu (NAOC), Z.P. Zhu (NAOC, HUST), S.Y. Fu, X. Liu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report: We observed the field of GRB 201221D (Page et al., GCN 29112) using the NEXT-0.6m optical telescope located at Nanshan, Xinjiang, China. Observations automatically started at 23:07:39 UT on 2020-12-21, i.e., 65 s after the BAT trigger. We obtained 3x40s, 4x60s and 12x90s frames in the Sloan r-filter. No optical source is detected in our stacked image at the XRT enhanced position (Evans et al., GCN 29113), down to a upper limit of r~21.3, calibrated with the nearby PanSTARRS field. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29119 SUBJECT: GRB 201221D: Enhanced Swift-XRT position DATE: 20/12/22 01:46:49 GMT FROM: Phil Evans at U of Leicester P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 651 s of XRT Photon Counting mode data and 1 UVOT images for GRB 201221D, 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 = 171.05914, +42.14319 which is equivalent to: RA (J2000): 11h 24m 14.19s Dec (J2000): +42d 08' 35.5" with an uncertainty of 3.9 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: 29121 SUBJECT: Fermi GRB 201221E: Global MASTER-Net observations report DATE: 20/12/22 05:30:33 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 201221E ( Fermi GBM team, GCN 29114) errorbox 19065 sec after notice time and 20298 sec after trigger time at 2020-12-22 05:07:05 UT, with upper limit up to 18.7 mag. The observations began at zenith distance = 49 deg. The sun altitude is -35.0 deg. The galactic latitude b = 16 deg., longitude l = 276 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1508233 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 20328 | 2020-12-22 05:07:05 | MASTER-OAFA | (10h 39m 23.18s , -41d 10m 51.0s) | C | 60 | 18.6 | 20407 | 2020-12-22 05:08:25 | MASTER-OAFA | (10h 50m 13.21s , -41d 11m 40.1s) | C | 60 | 18.5 | 20487 | 2020-12-22 05:09:44 | MASTER-OAFA | (10h 26m 46.41s , -35d 13m 03.7s) | C | 60 | 18.6 | 20566 | 2020-12-22 05:11:04 | MASTER-OAFA | (10h 36m 45.15s , -35d 12m 44.4s) | C | 60 | 18.7 | 20646 | 2020-12-22 05:12:23 | MASTER-OAFA | (10h 28m 41.13s , -41d 11m 05.1s) | C | 60 | 18.5 | 20934 | 2020-12-22 05:17:11 | MASTER-OAFA | (10h 51m 32.55s , -39d 10m 36.3s) | C | 60 | 18.7 | 21013 | 2020-12-22 05:18:30 | MASTER-OAFA | (10h 16m 14.44s , -43d 12m 07.6s) | C | 60 | 18.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29122 SUBJECT: Swift GRB 201221D: Global MASTER-Net observations report DATE: 20/12/22 08:54:08 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 201221D ( K. L. Page et al., GCN 29112) errorbox 33444 sec after notice time and 33517 sec after trigger time at 2020-12-22 08:25:12 UT, with upper limit up to 17.5 mag. Observations started at twilight. The observations began at zenith distance = 75 deg. The sun altitude is -12.3 deg. The galactic latitude b = 67 deg., longitude l = 167 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1508187 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 33608 | MASTER-OAFA | C | 180 | 17.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29124 SUBJECT: GRB 201221D: Swift-XRT refined Analysis DATE: 20/12/22 09:36:27 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), J. D. Gropp (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), J.P. Osborne (U. Leicester) and K.L. Page report on behalf of the Swift-XRT team: We have analysed 6.7 ks of XRT data for GRB 201221D (Page et al. GCN Circ. 29112), from 96 s to 23.5 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 29113). The source is fading with alpha >0.4. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01014037. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29125 SUBJECT: GRB 201221D: FRAM-ORM optical limit DATE: 20/12/22 10:25:06 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov Martin Jelinek and Jan Strobl (ASU CAS Ondrejov, CZ), Sergey Karpov, Martin Masek, Petr Janecek, Jakub Jurysek, Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza (Institute of Physics, Prague, CZ) report: The 25cm robotic telescope FRAM-ORM at La Palma (Spain) reacted robotically to the Swift alert of GRB201221D (Page et al., GCNC 29112 and Evans et al. GCNC 29113, GCNC 29119 and 29124), obtaining a series of 20s unfiltered images starting at 23:07:11.9 UT, i.e. 37.6s post trigger. We do not detect any new or strongly variable source neither in single images (detection limit R>~16.9) nor in a combined 40x20s frame (mean exp time 560s post trigger, with a limit R>~18.5). While we analysed the entire 25'x25' field of view centred at the XRT localization, we did pay a special attention to the location of the candidate afterglow mentioned by Malesani & Knudstrup (GCNC 29117) with a negative outcome. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29128 SUBJECT: GRB 201221D: Lowell Discovery Telescope afterglow observations DATE: 20/12/22 12:59:55 GMT FROM: Simone Dichiara at UMCP/NASA/GSFC S.Dichiara (UMD, NASA-GSFC), E. Troja (UMD, NASA-GSFC), S.B. Cenko (NASA-GSFC), B. O'Connor (GWU, UMD), P. Gatkine (Caltech), J.M. Durbak (UMD), A. Kutyrev (UMD, NASA-GSFC), S. Veilleux (UMD), report on behalf of a larger collaboration: We observed the short GRB 201221D (Page et al., GCN 29112) using the Large Monolithic Imager (LMI) on the 4.3m Lowell Discovery Telescope (LDT) at Happy Jack, AZ. Observations started on December 22, at 09:13:28 UT (about 10.11 hours after the Swift trigger) with SDSS r, i and z filters. Observations were taken at an airmass of about 1.3 and seeing of about 0.8". At the position of the optical candidate counterpart (Malesani et al., GCN 29117) we detect a source in all bands with r~23.9 AB mag and i~23.7 AB mag. This is fainter than the value reported by Malesani et al. (r~23.1 at 1 hr) and may suggest that the source faded between the two epochs. However, we note that at the same position a weak source is visible in archival Pan-STARRS images, which we suggest as the putative GRB host galaxy. Our observations could be dominated by the galaxy's contribution, and further observations to determine variability are planned. We thank the staff of the Lowell Discovery Telescope for assistance with these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29129 SUBJECT: GRB 201221D: Swift/UVOT Upper Limits DATE: 20/12/22 13:27:07 GMT FROM: Alice Breeveld at MSSL-UCL A. A. Breeveld (UCL-MSSL) and K. L. Page (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 201221D 92 s after the BAT trigger (Page et al., GCN Circ. 29112). No optical afterglow consistent with the NOT or XRT position (Malesani et al. GCN Circ. 29117; Evans et al. GCN Circ. 29119) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 92 242 147 >20.3 u_FC 305 554 246 >19.3 white 4047 4247 197 >21.0 v 634 4657 216 >19.2 u 305 5110 282 >19.4 w1 684 5068 216 >19.7 m2 4663 4863 197 >19.5 w2 4253 4453 197 >19.9 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29130 SUBJECT: Konus-Wind detection of GRB 201221D (short) DATE: 20/12/22 13:33:30 GMT FROM: Dmitry Frederiks at Ioffe Institute D. Frederiks, S. Golenetskii, R.Aptekar, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The short GRB 201221D (Swift detection: Page et al., GCN 29112) triggered Konus-Wind (KW) at T0=83197.636 s UT (23:06:37.636). The burst light curve shows a single pulse with the total duration of ~1.9 s (20-1500 keV). 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/GRB201221_T83197/ As observed by Konus-Wind, the burst had a fluence of (5.3 ± 1.1)x10^-7 erg/cm^2 and a 16-ms peak energy flux, measured from T0-0.016 s, of (6.6 ± 1.3)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The spectrum of the burst (measured from T0 to T0+0.128 s) is best fit in the 20 keV - 1.5 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.95(-0.52,+0.64) and Ep = 148(-37,+86) keV (chi2 = 19/20 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.1 (chi2 =19/19 dof). All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29132 SUBJECT: Short GRB201221D: High Redshift from OSIRIS/GTC DATE: 20/12/22 14:49:53 GMT FROM: Alexander Kann at IAA-CSIC A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D. A. Kann (HETH/IAA-CSIC), L. Izzo (DARK/NBI), C.C. Thoene, M. Blazek, J. F. Agui Fernandez (all HETH/IAA-CSIC) and G. Lombardi (GRANTECAN, IAC) report: We obtained spectroscopy of the optical counterpart (Malesani et al., GCN #29117) of the short GRB 201221D (Page et al., GCN #29112) with OSIRIS at the 10.4m Gran Telescopio Canarias (Roque de los Muchachos Observatory, La Palma, Spain), starting at 1:52 UT (2.757 hr after the burst). The observation consisted of 4 x 1200 s exposures with the R1000B grism, covering the range between 3700 and 7800 Angstrom. The spectrum shows a weak continuum over the full spectral range. There is a prominent emission feature that we identify as the [OII] 3727/3729 doublet at a redshift of 1.046. This line happens to lie in the atmospheric A band, and therefore must be quite strong to be detectable. There are also low significance absorption featuress coincident with FeII and MgII at a similar redshift (z = 1.045). We identify this as the redshift of GRB 201221D. We note this is a high redshift for a short GRB, and it represents one of the few short GRB spectra to show afterglow absorption features. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29133 SUBJECT: GRB 201221D: Archival PS1 Imaging of the Putative Host Galaxy DATE: 20/12/22 15:34:10 GMT FROM: Charles Kilpatrick at UC Santa Cruz C. D. Kilpatrick (Northwestern), D. B. Malesani (DTU Space), and W. Fong (Northwestern), report: “We analyzed stacked images from the PS1 Data Release 1 image archive (Flewelling et al., 2016, arXiv:1612.05243) of the location of the short-duration GRB 201221D (Page et al., GCN 29112). We detected a single source centered at: RA (J2000): 11:24:14.01 Dec (J2000): +42:08:39.69 in PS1 g-band, 4.6 arcseconds from the latest enhanced XRT position of GRB 201221D (Evans et al., GCN 29119). We note that this places the centroid of the candidate host galaxy just outside the enhanced XRT error circle reported by GCN 29119, which has a radius of 3.9 arcsec (90% confidence), although consistent with the real-time XRT error circle at https://www.swift.ac.uk/xrt_positions/01014037/ . Performing forced aperture photometry on this position with an aperture fixed to the FWHM size in all PS1 bands (approximately 1.1 arcseconds), we found that this source has a brightness: g = 23.2 +/- 0.2 mag r > 23.2 mag i > 23.3 mag z > 22.2 mag y = 22.6+/-0.2 mag All magnitudes are given in AB. We note that this source is coincident with emission identified in Malesani & Knudstrup (GCN 29117) who find a source with r = 23.1+/-0.3 mag (AB) in NOT follow up imaging. Similarly, Dichiara et al. (GCN 29128) find r=23.9 mag and i=23.7 mag (AB), all of which are consistent with our limiting magnitudes. Based on this photometry, it is fully plausible that the reported optical candidate (GCN 29117, GCN 29128) is dominated by the host galaxy. However, the detection of absorption features in the spectrum (de Ugarte Postigo et al., GCN 29132), coupled with the possible r-band fading between NOT and DCT observations (reported in GCN 29128) may indicate the presence of an optical afterglow on top of the host emission. Image subtraction will be required to test for fading, and further, deep optical observations are encouraged. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29138 SUBJECT: Swift Trigger 1014012 (possible GRB 201221C) is likely not an astrophysical event DATE: 20/12/22 17:42:53 GMT FROM: Amy Lien at GSFC S. D. Barthelmy (GSFC), A. Y. Lien (GSFC/UMBC) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: Using the full data set from recent downlinks, we report further ground data analysis for Swift trigger 1014012 (Page et al. GCN Circ. 29106). The BAT analysis uses data from T-239 to T+963 sec. The BAT image significance has now decreased to 5.2 sigma (15-350 keV). Also, the mask-weighted light curve does not show anything significant. There is no good evidence for an X-ray source in 4.7 ks data, to a 3 sigma upper limit of 2.3x10^-3 count s^-1 (corresponding to an observed flux of 1x10^-13 erg cm^-2 s^-1, assuming a typical power-law spectrum). We therefore conclude that this event is likely due to noise, and is not an astrophysical event. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29139 SUBJECT: GRB 201221D: Swift-BAT refined analysis DATE: 20/12/22 17:44:15 GMT FROM: Amy Lien at GSFC H. A. Krimm (NSF), S. D. Barthelmy (GSFC), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 201221D (trigger #1014037) (Page et al., GCN Circ. 29112). The BAT ground-calculated position is RA, Dec = 171.055, 42.152 deg which is RA(J2000) = 11h 24m 13.2s Dec(J2000) = +42d 09' 08.4" with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 23%. The mask-weighted light curve shows a single-peaked structure that starts at ~T-0.06 s, peaks at ~T+0.02 s, and ends at ~T+0.2 s. T90 (15-350 keV) is 0.16 +- 0.04 sec (estimated error including systematics). The time-averaged spectrum from T-0.06 to T+0.17 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.56 +- 0.13. The fluence in the 15-150 keV band is 3.9 +- 0.4 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-0.44 sec in the 15-150 keV band is 5.6 +- 0.5 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/1014037/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29140 SUBJECT: GRB 201221D: Fermi GBM detection DATE: 20/12/22 18:52:47 GMT FROM: Rachel Hamburg at UAH R. Hamburg (UAH), C. Malacaria (NASA-MSFC/USRA), and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 23:06:34.33 UT on 21 December 2020, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 201221D (trigger 630284799 / 201221963) which was also detected by the Swift/BAT and Swift/XRT (Page et al. 2020, GCN 29112) and Konus-Wind (Frederiks et al. 2020, GCN 29130). This trigger was initially classified as a particle event by the flight software, but is in fact a GRB. The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 89 degrees. The GBM light curve shows a single-peaked structure with a duration (T90) of about 0.14 s (50-300 keV). The time-averaged spectrum from T0-0.064 s to T0+0.192 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.20 +/- 0.16 and the cutoff energy, parameterized as Epeak, is 108 +/- 5 keV. A Band function fits the spectrum equally well with Epeak = 98 +/- 8 keV, alpha = 0.01 +/- 0.24 and beta = -3.3 +/- 0.5. The event fluence (10-1000 keV) in this time interval is (1.076 +/- 0.046)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.00 s in the 10-1000 keV band is 41 +/- 2 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: 29141 SUBJECT: GRB 201221D: LCOGT upper limits DATE: 20/12/22 19:18:16 GMT FROM: Igor Andreoni at Caltech Igor Andreoni (Caltech), Michael M. Coughlin (UMN) on behalf of the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration We used the Sinistro camera on the 1-m LCO Global Telescope Network (LCOGT, Brown et al., 2013) to observe the afterglow of short-duration GRB 201221D (Page et al., GCN #29112). Two sets of 300s exposures were acquired in g-r-i bands between 2020-12-22T07:57 and 2020-12-22T08:47 UTC. The observations were performed under proposal IDs TOM2020A-008 (PI Andreoni) and NOAO2020B-005 (PI Coughlin). We do not identify any source within 3.9 arcsec of the enhanced Swift-XRT position (Evans et al., GCN #29119). Photometric upper limits, calibrated against Pan-STARRS DR1 magnitudes (Chambers et al., 2016), were measured to be g > 22.8, r > 22.2, and i > 21.5 mag (5-sigma) after image stacking. The candidate optical counterpart (transient or host galaxy: Malesani et al., GCN #29117; Dichiara et al., GCN #29128; de Ugarte Postigo et al., GCN #29132; Kilpatrick et al., GCN #29133) is too faint to be detectable in our observations, which did not show any significant brightening, as expected. We thank the TOM Community Development Program and the TOM Toolkit Workshop organizers for the generous LCOGT time allocation. GROWTH is a worldwide collaboration comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, TTU, USyd, Australia, and SDSU, USA. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29142 SUBJECT: GRB 201221D: MMT MMIRS detection of marginally extended source DATE: 20/12/22 22:39:03 GMT FROM: Jillian Rastinejad at Northwestern Univ. J. Rastinejad, K. Paterson, C. D. Kilpatrick, W. Fong (Northwestern) report: We observed the location of the Swift GRB 201221D (Page et al., GCN 29112) with the MMT and Magellan Infrared Spectrograph (MMIRS) mounted on the MMT 6.5-meter telescope on Mount Hopkins, Arizona. We obtained 25x60-sec imaging in J-band at a mid-time of 2020 December 22.36 UT (0.40 days post-burst). Within the vicinity of the XRT position (Evans et al., GCN 29113; Evans et al., GCN 29119), we detect a marginally extended source, consistent with the location of emission detected in previously reported optical follow up and archival imaging (Malesani et al., GCN 29117; Dichiara et al., GCN 29128; de Ugarte Postigo et al., GCN 29132; Kilpatrick et al., GCN 29133). After calibrating our stacked image to isolated stars detected in the 2MASS photometric catalog (Cutri et al., 2003, NASA/IPAC), we applied a 3 arcsecond aperture and measure a magnitude of J = 21.8 +/- 0.2 mag (AB and not corrected for Milky Way extinction). Further observations are planned to assess any variability of the source. We thank Ryan Howie and Joannah Hinz at the MMT for the rapid scheduling and execution of these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29144 SUBJECT: GRB 201221D: SMA submm observation DATE: 20/12/23 02:49:57 GMT FROM: Yuji Urata at Nat. Central U. Huang, K. (CYCU), Urata, Y. (NCU) and Petitpas, G (SAO). report: We observed the field of the GRB201221D (Page et al., GCN #29112) at 228 GHz using the Submillimeter Array (SMA). The observation was started at 2020 December 11:27 UT (12.3 h after the burst). There was no source at the candidate of optical afterglow (Malesani et al., GCN #29117; Dichiara et al., GCN #29128; de Ugarte Postigo et al., GCN #29132; Kilpatrick et al., GCN #29133; Rastinejad et al. GCN #29142). The preliminary limit of the observation is ~0.2 mJy (rms). We thank Ramprasad Rao, Mark Gurwell and staff of SMA for the scheduling and execution of observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29147 SUBJECT: GRB 201221B: Insight-HXMT/HE detection DATE: 20/12/23 11:32:53 GMT FROM: Ce Cai at IHEP C. Cai, S. Xiao, Y. F. Du, Y. G. Zheng, Q. Luo, Q. B. Yi, Y. Huang, C. K. Li, G. Li, X. B. Li, J. Y. Liao, S. L. Xiong, C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, A. M. Zhang, Y. F. Zhang, X. F. Lu, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, M. Wu, Y. P. Xu, S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team: At 2020-12-21T14:11:43.00 (T0), Insight-HXMT/HE detected GRB 201221B (trigger ID: HEB201221591) in a routine search of the data, which also triggered Fermi/GBM (GCN #29101). The Insight-HXMT/HE light curve mainly consists of a single pulse with a duration (T90) of 0.03 s measured from T0-0.00 s. The 1-ms peak rate, measured from T0-0.005 s, is 9739 cnts/sec. The total counts from this burst is 193 counts. URL_LC: http://twiki.ihep.ac.cn/pub/HXMT/GRBList/HEB201221591_lc.jpg All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 80-800 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29148 SUBJECT: GRB 201221D: 3.6m DOT optical observations DATE: 20/12/23 12:27:46 GMT FROM: Rahul Gupta at ARIES, India Dimple (ARIES), A. Panchal (ARIES), A. Gangopadhyay (ARIES), A. Ghosh (ARIES), R. Gupta (ARIES), A. Kumar (ARIES), K. Misra (ARIES), and S. B. Pandey (ARIES) report: We carried out the follow-up observations of GRB 201221D (Page et al., GCN 29112) with Aries Devasthal Faint Object Spectrograph and Camera (ADFOSC) mounted on the 3.6m Devasthal Optical Telescope (DOT) at Devasthal observatory of Aryabhatta Research Institute of observational sciencES (ARIES), India. The observations were started on 2020-12-22 at 23:10:00 UT. We observed a series of 4 images with the exposure time of 900 seconds each in r-band. At the position reported by Malesani et al., (GCN 29117), we detect an uncatalogued source in r-band with a magnitude of 23.46 +- 0.09 (AB mag), calibrated with the nearby PanSTARRS field. However, we remark that this is an extended source and may contain significant host galaxy contribution. For further verification, host galaxy subtraction is highly encouraged. The magnitude is not corrected for the Galactic extinction in the direction of the burst. This circular may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29149 SUBJECT: GRB 201221A: REM early-time afterglow detection DATE: 20/12/23 14:46:01 GMT FROM: Paolo D'Avanzo at INAF-OAB P. D'Avanzo, S. Covino, D. Fugazza, A. Melandri (INAF-OAB), D. B. Malesani (DTU space) on behalf of the REM team, report: We observed the field of GRB 201221A (Page et al., GCN Circ. 29096) with the REM 60cm robotic telescope located at the ESO premise of La Silla (Chile). The observations were performed starting on 2020 December 21 at 07:10:33 UT (i.e. 92 seconds after the burst) and were carried in the g, r, i, z bands simultaneously. From preliminary photometry, we estimate the following magnitudes and 3sigma upper limits for the afterglow reported by Malesani et al. (GCN Circ. 29100): g > 17.9 r > 17.8 i > 17.7 z = 15.8 +/- 0.3 (AB; calibrated against the APASS catalogues), at a mean time of 97 seconds after the GRB t0. By combining our z-band magnitude with the one reported by Malesani et al., we infer an afterglow temporal decay (f propto t^(alpha)) of alpha ~ -1.2 between 97 seconds and 2100 seconds after the GRB t0. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29150 SUBJECT: GRB 201221A: Konus-Wind detection and joint Konus-Wind + Swift-BAT spectral analysis DATE: 20/12/23 15:51:43 GMT FROM: Dmitry Frederiks at Ioffe Institute D. Frederiks, S. Golenetskii, R.Aptekar, A. Kozlova, A.Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, T. Cline, on behalf of the Konus-Wind team, and A. Lien (GSFC/UMBC), report: The long GRB 201221A (Swift-BAT trigger #1013852, T0 = T0(BAT)= 07:09:01.4258 UT: Page et al., GCN 29096; Breadmore et al., GCN 29108; Fermi GBM Sub-Threshold Detection: Veres, GCN 29110, 29111) was detected by Konus-Wind (KW) in the waiting mode. A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band reveals a ~11 sigma count rate increase over background in the interval from ~T0(BAT)-10 s to ~T0(BAT)+20 s. The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB201221A/ To derive the broad-band spectral parameters of this burst, we performed a joint spectral analysis of the Swift/BAT data (15-150 keV) and the Konus-Wind 3-channel spectral data, which cover the energy range from ~20 keV to ~1.5 MeV. The time-averaged spectrum, measured from T0(BAT)-9.6 s to T0(BAT)+19.8 s, is best fit in the 15 keV - 1.5 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.95 (-0.22,+0.31), the high energy photon index beta = -2.39 (-0.89,+0.38), and the peak energy Ep = 194 (-63,+81) keV, chi2 = 65/58 dof. In the 15-1500 keV band, the total burst fluence S is 4.3(-0.4, + 0.7)x10^-6 erg/cm^2, and the 2.944 s peak energy flux Fp is 2.0 (-0.2, + 0.3)x10^-7 erg/cm^2. In the 10-10000 keV band, standard for the KW analysis, S = 5.3(-1.0, + 2.3)x10^-6 erg/cm^2 and Fp = 2.4 (-0.4, + 1.0)x10^-7 erg/cm^2. Assuming the redshift z=5.70 (Malesani et al., GCN 29100) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the isotropic energy release E_iso to 3.0(-0.5,+1.3)x10^53 erg, the isotropic luminosity L_iso to 9.0(-1.6,+3.9)x10^52 erg/s, and the rest-frame peak energy of the time-integrated spectrum Ep,z to 1300(-420,+540) keV. With these values, GRB 201221A is within 90% prediction bands for both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (part I: Tsvetkova et al., ApJ 850 161, 2017; part II: Tsvetkova et al., ApJ, accepted), see http://www.ioffe.ru/LEA/GRBs/GRB201221A/GRB201221A_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29311 SUBJECT: GRB 201221D: near-infrared observation with LBT DATE: 21/01/17 15:18:45 GMT FROM: Andrea Rossi at INAF A. Rossi (INAF-OAS) reports on behalf of the CIBO collaboration: We observed the location of the optical afterglow (Malesani et al., GCN 29117) of the short GRB 201221D (Page et al., GCN 29112) simultaneously in the J and Ks bands with the LUCI near-infrared imager and spectrograph mounted on the Large Binocular Telescope (LBT, Mt Graham, AZ, USA). Observations were obtained on 2020-12-24 at the UT midtime 11:40:00, i.e. ~2.5 days after the burst trigger, for a total of 20 min of exposure in each band. Inspection of the combined J and K-band images reveals a faint, extended source in both filters, for which we preliminary measure J=21.7+-0.3 (Vega system), calibrated against 2MASS field stars. We acknowledge the excellent support from the LBTO and LBT-INAF staff, particularly A. Cardwell, F. Cusano, and D. Paris, in obtaining these observations.