Gamma-ray Burst 231220A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Wed 20 Dec 23 16:10:46 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      45
TRIGGER_NUM:     724781422
GRB_RA:          219.917d {+14h 39m 40s} (J2000),
                 219.271d {+14h 37m 05s} (current),
                 221.371d {+14h 45m 29s} (1950)
GRB_DEC:         +84.950d {+84d 57' 00"} (J2000),
                 +84.847d {+84d 50' 50"} (current),
                 +85.161d {+85d 09' 41"} (1950)
GRB_ERROR:       12.23 [deg radius, statistical plus systematic]
GRB_INTEN:       204 [cnts/sec]
DATA_SIGNIF:     6.40 [sigma]
INTEG_TIME:      2.048 [sec]
GRB_DATE:        20298 TJD;   354 DOY;   23/12/20
GRB_TIME:        58217.40 SOD {16:10:17.40} UT
GRB_PHI:         245.98 [deg]
GRB_THETA:       145.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO:      0.19
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   2%  Cyg X-1
DETECTORS:       0,0,0, 0,0,0, 0,0,1, 0,1,0, 0,0,
SUN_POSTN:       268.37d {+17h 53m 29s}  -23.43d {-23d 25' 36"}
SUN_DIST:        110.00 [deg]   Sun_angle= 3.3 [hr] (West of Sun)
MOON_POSTN:        9.75d {+00h 39m 00s}   +2.97d {+02d 58' 25"}
MOON_DIST:        91.51 [deg]
MOON_ILLUM:      60 [%]
GAL_COORDS:      120.24, 31.60 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      101.09, 69.45 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231220674/quicklook/glg_lc_medres34_bn231220674.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 13.38,-7.37 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Wed 20 Dec 23 16:11:05 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      58
TRIGGER_NUM:     724781422
GRB_RA:           73.650d {+04h 54m 36s} (J2000),
                  74.923d {+04h 59m 42s} (current),
                  71.030d {+04h 44m 07s} (1950)
GRB_DEC:         +82.410d {+82d 24' 36"} (J2000),
                 +82.446d {+82d 26' 46"} (current),
                 +82.325d {+82d 19' 32"} (1950)
GRB_ERROR:       4.31 [deg radius, statistical only]
DATA_SIGNIF:     12.60 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        20298 TJD;   354 DOY;   23/12/20
GRB_TIME:        58217.40 SOD {16:10:17.40} UT
GRB_PHI:         233.00 [deg]
GRB_THETA:       136.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       268.37d {+17h 53m 29s}  -23.43d {-23d 25' 36"}
SUN_DIST:        120.76 [deg]   Sun_angle= -11.1 [hr] (East of Sun)
MOON_POSTN:        9.75d {+00h 39m 01s}   +2.97d {+02d 58' 30"}
MOON_DIST:        83.88 [deg]
MOON_ILLUM:      60 [%]
GAL_COORDS:      130.14, 23.24 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       85.83, 59.21 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231220674/quicklook/glg_lc_medres34_bn231220674.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_724781422.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        Bright hard burst in the GBM.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Wed 20 Dec 23 16:19:26 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     724781422
GRB_RA:           73.370d {+04h 53m 29s} (J2000),
                  74.627d {+04h 58m 30s} (current),
                  70.784d {+04h 43m 08s} (1950)
GRB_DEC:         +82.290d {+82d 17' 24"} (J2000),
                 +82.327d {+82d 19' 36"} (current),
                 +82.204d {+82d 12' 15"} (1950)
GRB_ERROR:       5.04 [deg radius, statistical only]
GRB_DATE:        20298 TJD;   354 DOY;   23/12/20
GRB_TIME:        58217.40 SOD {16:10:17.40} UT
GRB_PHI:         233.00 [deg]
GRB_THETA:       136.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       268.38d {+17h 53m 31s}  -23.43d {-23d 25' 37"}
SUN_DIST:        120.87 [deg]   Sun_angle= -11.1 [hr] (East of Sun)
MOON_POSTN:        9.83d {+00h 39m 18s}   +3.01d {+03d 00' 48"}
MOON_DIST:        83.75 [deg]
MOON_ILLUM:      60 [%]
GAL_COORDS:      130.23, 23.15 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       85.71, 59.10 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231220674/quicklook/glg_lc_medres34_bn231220674.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231220674/quicklook/glg_locplot_all_bn231220674.png
COMMENTS:        Fermi-GBM Final Position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file should be available by the time this FINAL notice is produced.  
COMMENTS:        This notice was generated completely by automated pipeline processing.  
COMMENTS:        Bright hard burst in the GBM.  
COMMENTS:        This is likely a Long GRB.

GCN Circular #35407
The Fermi GBM team reports the detection of a likely LONG GRB
At 16:10:17 UT on 20 Dec 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 231220A (trigger 724781422.403544 / 231220674).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 73.4, Dec = 82.3 (J2000 degrees, equivalent to J2000 04h 53m, 82d 17'), with a statistical uncertainty of 5.0 degrees.
The angle from the Fermi LAT boresight is 136.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231220674/quicklook/glg_skymap_all_bn231220674.png
The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231220674/quicklook/glg_healpix_all_bn231220674.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231220674/quicklook/glg_lc_medres34_bn231220674.gif

GCN Circular #35408
V. Lipunov, V.Kornilov, E. Gorbovskoy, K. Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, V.Senik, D. Vlasenko, G.Antipov, D.Zimnukhov, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov, D. Cheryasov, Ya.Kechin, Yu.Tselik, A. Sosnovskij (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. Gress, N.M. Budnev, O.Ershova (Irkutsk State University, API),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
V. Yurkov, A. Gabovich (Blagoveschensk Educational State University)
MASTER-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB231220.67 (trigger No 724781422,04h 53m 28.80s , +82d 17m 24.0s, R=5.04) errorbox 47 sec after notice time and 81 sec after trigger time at 2023-12-20 16:11:39 UT, with upper limit up to 19.6 mag. The observations began at zenith distance = 31 deg. The sun altitude is -60.6 deg.
MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB231220.67 errorbox 111 sec after notice time and 146 sec after trigger time at 2023-12-20 16:12:43 UT, with upper limit up to 19.6 mag. The observations began at zenith distance = 44 deg. The sun altitude is -27.3 deg.
The galactic latitude b = 23 deg., longitude l = 130 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2338295
We obtain a following upper limits.

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

      92 | 2023-12-20 16:11:39 |        MASTER-Tunka | (04h 50m 37.99s , +82d 29m 18.3s) |   C |    20 | 18.9 |        
     117 | 2023-12-20 16:11:39 |        MASTER-Tunka | (04h 50m 37.99s , +82d 29m 18.3s) |   C |    70 | 19.6 |  Coadd 
     177 | 2023-12-20 16:11:39 |        MASTER-Tunka | (04h 50m 38.02s , +82d 29m 18.3s) |   C |   190 | 19.5 |  Coadd 
     116 | 2023-12-20 16:12:03 |        MASTER-Tunka | (04h 50m 37.58s , +82d 29m 18.9s) |   C |    20 | 19.0 |        
     145 | 2023-12-20 16:12:27 |        MASTER-Tunka | (04h 50m 37.01s , +82d 29m 20.5s) |   C |    30 | 19.2 |        
     161 | 2023-12-20 16:12:43 |   MASTER-Kislovodsk | (05h 23m 52.17s , +82d 05m 38.2s) |   C |    30 | 18.4 |        
     206 | 2023-12-20 16:12:43 |   MASTER-Kislovodsk | (05h 23m 52.18s , +82d 05m 38.2s) |   C |   120 | 19.4 |  Coadd 
     391 | 2023-12-20 16:12:43 |   MASTER-Kislovodsk | (05h 23m 52.15s , +82d 05m 38.2s) |   C |   490 | 19.4 |  Coadd 
     179 | 2023-12-20 16:13:00 |        MASTER-Tunka | (04h 50m 36.68s , +82d 29m 21.6s) |   C |    30 | 19.2 |        
     224 | 2023-12-20 16:13:00 |        MASTER-Tunka | (04h 50m 36.71s , +82d 29m 21.6s) |   C |   120 | 19.1 |  Coadd 
     216 | 2023-12-20 16:13:33 |   MASTER-Kislovodsk | (05h 23m 55.20s , +82d 06m 40.5s) |   C |    40 | 18.8 |        
     218 | 2023-12-20 16:13:34 |        MASTER-Tunka | (04h 50m 35.94s , +82d 29m 23.3s) |   C |    40 | 18.3 |        
     266 | 2023-12-20 16:14:18 |        MASTER-Tunka | (04h 50m 35.30s , +82d 29m 25.3s) |   C |    50 | 18.4 |        
     283 | 2023-12-20 16:14:35 |   MASTER-Kislovodsk | (05h 23m 57.88s , +82d 05m 45.2s) |   C |    50 | 19.0 |        
     326 | 2023-12-20 16:15:13 |        MASTER-Tunka | (04h 50m 34.17s , +82d 29m 28.2s) |   C |    60 | 18.5 |        
     386 | 2023-12-20 16:15:13 |        MASTER-Tunka | (04h 50m 34.19s , +82d 29m 28.2s) |   C |   180 | 12.4 |  Coadd 
     360 | 2023-12-20 16:15:47 |   MASTER-Kislovodsk | (05h 23m 49.33s , +82d 04m 49.1s) |   C |    60 | 19.0 |        
     515 | 2023-12-20 16:15:47 |   MASTER-Kislovodsk | (05h 23m 49.29s , +82d 04m 49.1s) |   C |   370 | 19.6 |  Coadd 
     390 | 2023-12-20 16:16:16 |        MASTER-Tunka | (04h 50m 33.23s , +82d 29m 30.4s) |   C |    60 | 18.5 |        
     599 | 2023-12-20 16:19:46 |        MASTER-Tunka | (04h 49m 16.45s , +82d 24m 30.5s) |   C |    60 | 18.6 |        
     663 | 2023-12-20 16:20:50 |        MASTER-Tunka | (04h 49m 15.45s , +82d 24m 32.6s) |   C |    60 | 18.8 |        
     723 | 2023-12-20 16:20:50 |        MASTER-Tunka | (04h 49m 15.47s , +82d 24m 32.5s) |   C |   180 | 19.3 |  Coadd 
     727 | 2023-12-20 16:21:54 |        MASTER-Tunka | (04h 49m 14.41s , +82d 24m 34.9s) |   C |    60 | 18.8 |        
     777 | 2023-12-20 16:22:04 |   MASTER-Kislovodsk | (05h 22m 17.38s , +81d 58m 31.2s) |   C |   140 | 19.2 |        
     791 | 2023-12-20 16:22:58 |        MASTER-Tunka | (04h 49m 13.31s , +82d 24m 37.6s) |   C |    60 | 18.8 |        
     953 | 2023-12-20 16:24:45 |   MASTER-Kislovodsk | (05h 22m 25.64s , +81d 59m 51.5s) |   C |   170 | 19.3 |        
    1149 | 2023-12-20 16:27:56 |   MASTER-Kislovodsk | (05h 22m 17.42s , +81d 59m 23.7s) |   C |   180 | 19.4 |        
    1291 | 2023-12-20 16:31:18 |   MASTER-Kislovodsk | (04h 54m 53.65s , +82d 03m 55.3s) |   C |    60 | 15.0 |        
    2595 | 2023-12-20 16:53:02 |   MASTER-Kislovodsk | (04h 36m 40.50s , +82d 37m 42.1s) |   C |    60 | 18.4 |        
    2675 | 2023-12-20 16:54:22 |   MASTER-Kislovodsk | (06h 40m 35.82s , +82d 35m 35.2s) |   C |    60 | 18.5 |        
    2757 | 2023-12-20 16:55:44 |   MASTER-Kislovodsk | (06h 17m 17.19s , +84d 28m 19.6s) |   C |    60 | 18.6 |        
    2839 | 2023-12-20 16:57:05 |   MASTER-Kislovodsk | (05h 42m 20.32s , +78d 51m 06.7s) |   C |    60 | 18.8 |        
    2921 | 2023-12-20 16:58:28 |   MASTER-Kislovodsk | (05h 42m 52.38s , +78d 51m 07.7s) |   C |    60 | 14.8 |        
    3001 | 2023-12-20 16:59:48 |   MASTER-Kislovodsk | (05h 44m 09.29s , +78d 51m 11.1s) |   C |    60 | 14.8 |        
    3082 | 2023-12-20 17:01:09 |   MASTER-Kislovodsk | (03h 38m 32.79s , +80d 46m 42.5s) |   C |    60 | 18.5 |        
    3163 | 2023-12-20 17:02:29 |   MASTER-Kislovodsk | (03h 28m 26.96s , +84d 34m 57.7s) |   C |    60 | 18.6 |        
    3244 | 2023-12-20 17:03:51 |   MASTER-Kislovodsk | (05h 26m 07.87s , +86d 21m 38.1s) |   C |    60 | 18.7 |        
    3324 | 2023-12-20 17:05:11 |   MASTER-Kislovodsk | (07h 02m 56.70s , +78d 48m 04.5s) |   C |    60 | 18.6 |        
    3406 | 2023-12-20 17:06:32 |   MASTER-Kislovodsk | (04h 51m 59.60s , +76d 58m 32.8s) |   C |    60 | 18.6 |        
    4959 | 2023-12-20 17:32:26 |   MASTER-Kislovodsk | (05h 16m 05.81s , +80d 44m 30.6s) |   C |    60 | 18.7 |        
    5040 | 2023-12-20 17:33:47 |   MASTER-Kislovodsk | (04h 36m 36.25s , +82d 40m 42.7s) |   C |    60 | 18.5 |

Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
View this GCN Circular online at https://gcn.nasa.gov/circulars/35408.

GCN Circular #35409
Samuele Ronchini (PSU), James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT did not localize GRB 231220A onboard (T0: 2023-12-20T16:10:17.4 UTC, Fermi/GBM GCN 35407).
The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).=20
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), detects the burst in a 4.096 s analysis time bin with a sqrt(TS) of 28.32, starting at T0 - 1.02 s. An arcminute localization is found with DeltaLLHOut of 48.29 and a DeltaLLHPeak of 49.13.
See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.
The BAT position is RA, Dec =3D 27.321, 77.897 deg which is
```
   RA(J2000)   01h 49m 17.04s
   Dec(J2000)  +77d 53' 49.2"
```
with an estimated uncertainty of 5 arcmin radius.
XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars.
GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/
GCN Circular #35410
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the GUANO GRB 231220A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021638
Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the GUANO event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.
GCN Circular #35411
C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), R. Brivio (INAF-OAB) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the GUANO-detected burst GRB 231220A, collecting 3.6 ks of Photon Counting (PC) mode data between T0+27.0 ks and T0+39.5 ks.=20
No candidate counterpart was detected, with an upper limit of=20 2.2=C3=9710-3 ct s-1 at the best BAT position (GCN 35409).=20
One uncatalogued X-ray source was flagged as spurious=20 after manual inspection.=20
The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021638.
This circular is an official product of the Swift-XRT team.
GCN Circular #35477
N. Klingler (UMBC/NASA-GSFC/CRESST II) reports on behalf of the Swift-UVOT team:
Swift-UVOT has performed follow-up observations of the Swift-BAT/GUANO-detected and Fermi-GBM-detected GRB 231220A, collecting 2.6 ks of data between T0+35.2 ks and T0+47.8 ks. No candidate counterpart was detected. The 3 sigma limiting (AB) magnitude in the White filter near the center of the BAT/GUANO localization (GCN 35409) is >23.20.

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