GRB 231214A

The Fermi GBM team reports the detection of a likely LONG GRB

At 20:24:24 UT on 14 Dec 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 231214A (trigger 724278269.684604 / 231214850).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 302.2, Dec = -72.1 (J2000 degrees, equivalent to J2000 20h 08m, -72d 05'), with a statistical uncertainty of 1.0 degrees.

The angle from the Fermi LAT boresight is 50.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231214850/quicklook/glg_skymap_all_bn231214850.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/bn231214850/quicklook/glg_healpix_all_bn231214850.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231214850/quicklook/glg_lc_medres34_bn231214850.gif

R. Brivio (INAF-OAB), P. D'Avanzo (INAF-OAB), S. Dichiara (PSU),
M. Ferro (INAF-OAB), M. J. Moss (GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL), C. Salvaggio (INAF-OAB) and M. A. Williams (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 20:24:28 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 231214A (trigger=1202386).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 305.736, -72.436 which is 
   RA(J2000) = 20h 22m 57s
   Dec(J2000) = -72d 26' 09"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 30 sec.  The peak count rate
was ~8000 counts/sec (15-350 keV), at ~13 sec after the trigger. 

The XRT began observing the field at 20:26:14.5 UT, 106.2 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 305.68573, -72.43256
which is equivalent to:
   RA(J2000)  = 20h 22m 44.58s
   Dec(J2000) = -72d 25' 57.2"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 56 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  39 seconds with the White filter
starting 442 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
0.060. 

Burst Advocate for this burst is R. Brivio (riccardo.brivio AT inaf.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/)

Y.-D. Hu, E. Fernandez-Garcia, I. Perez-Garcia, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, S.-Y. Wu and A. J. Castro-Tirado (IAA-CSIC, Granada), P. J. Meintjes and H. J. van Heerden (UFS, South Africa), A. Martin-Carrillo and L. Hanlon (UCD, Ireland) and C. J. Perez del Pulgar (UMA, Malaga), on behalf of a larger collaboration, report:

Following the detection of GRB 231214A by Swift (Brivio et al. GCNC 35335) and Fermi (Fermi GBM team GCNC 35334), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) automatically observed the GRB location starting on Dec. 14, 20:42 UT (~ 18 min after trigger). No new optical source is detected on the co-added images (11 x 10 s, clear-filter) within the Swift/XRT error region down to 19.1 mag, which is consistent with both reports from UVOT (Brivio et al. GCNC 35335) and MASTER (Lipunov et al. GCNC 35336).

We thank the staff at Boyden Observatory for their excellent support.

P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 842 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 231214A, 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 = 305.68530, -72.43283 which is equivalent
to:

RA (J2000): 20h 22m 44.47s
Dec (J2000): -72d 25' 58.2"

with an uncertainty of 2.2 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.

D. Kocevski (NASA/MSFC), N. Di Lalla (Stanford University), M. Arimoto
(Kanazawa University), and T. Khalil (Johannesburg University) report
on behalf of the Fermi-LAT Collaboration:

On December 14, 2023 Fermi-LAT detected high-energy emission from GRB
231214A, which was also detected by Fermi-GBM (trigger
724278269.684604 / 231214850, GCN 35334
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 ), Swift-BAT and Swift-XRT (GCN
35335
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 , 35341
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 ).

The best LAT on-ground location is found to be
RA, Dec = 306.1, -72.4 (degrees, J2000)
with an error radius of 0.2 deg (90% containment, statistical error
only). This was 51 deg from the LAT boresight at the time of the GBM
trigger: T0 = 20:24:24.69 UT.

The data from the Fermi-LAT show a significant increase in the event
rate after the GBM trigger that is spatially correlated with the GBM
emission with high significance. The photon flux above 100 MeV in the
time interval 0-3000 s after the GBM trigger is (3.9 +/- 0.8)E-6
ph/cm2/s.
The estimated photon index above 100 MeV is -1.9 +/- 0.2. The
highest-energy photon is a 2.9 GeV event which is observed 414 seconds
after the GBM trigger.
The Fermi-LAT point of contact for this burst is Tamador Khalil
(tamtam2030@gmail.com)

The Fermi-LAT is a pair conversion telescope designed to cover the
energy band from 20 MeV to greater than 300 GeV. It is the product of
an international collaboration between NASA and DOE in the U.S. and
many scientific institutions across France, Italy, Japan and Sweden.

P. K. Navaneeth (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long-duration GRB 231214A which was also detected by Fermi-GBM (Fermi GBM Team, GCN Circ. 35334
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 ), Swift-BAT (Brivio et al., GCN Circ. 35335
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 ), and Fermi-LAT (Kocevski et al., GCN Circ. 35342
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 ).

The source was clearly detected in three of four quadrants of CZT detectors in the 20-200 keV energy range. AstroSat was approaching the South Atlantic Anomaly (SAA) region and hence the background rates were higher. The light curve showed multiple peaks of emission with the strongest peak at 2023-12-14 20:24:41.50 UTC. We limit our analysis to a single quadrant with a relatively stable background. The measured peak count rate associated with the burst is 99 (+28, -12) counts/s above the background in the data of one quadrant (out of four), with a total of 691 (+127, -135) counts. The local mean background count rate was 99 (+2, -2) counts/s. Using cumulative rates, we measure a T90 of 20 (+1, -1) s.

The source was also detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2023-12-14 20:24:29.95 UTC. The measured peak count rate associated with the burst is 245 (+84, -30) counts/s above the background in the combined data of all quadrants, with a total of 2761 (+591, -655) counts. The local mean background count rate was 1761 (+8, -9) counts/s. We measure a T90 of 22 (+3, -2) s from the cumulative Veto light curve.

CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.

CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb

J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC &
INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), A.
Tohuvavohu (U. Toronto), D.N. Burrows (PSU), J. D. Gropp (PSU), A.P.
Beardmore (U. Leicester) and P.A. Evans report on behalf of the
Swift-XRT team:

We have analysed 6.2 ks of XRT data for GRB 231214A, from 407 s to 45.5
ks after the  BAT trigger. The data are entirely in Photon Counting
(PC) mode. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.48 (+/-0.08).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.4 (+/-0.4). The
best-fitting absorption column is  1.2 (+0.4, -0.3) x 10^22 cm^-2, in
excess of the Galactic value of 5.5 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 4.2 x 10^-11 (1.2 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.2 (+0.4, -0.3) x 10^22 cm^-2
Galactic foreground: 5.5 x 10^20 cm^-2
Excess significance: 5.4 sigma
Photon index:	     2.4 (+/-0.4)

If the light curve continues to decay with a power-law decay index of
1.48, the count rate at T+24 hours will be 1.6 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.9 x
10^-14 (1.9 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/01202386.

This circular is an official product of the Swift-XRT team.

M. Ferro, R. Brivio, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) on behalf of the REM team, report:

We observed the field of GRB 231214A (Brivio et al., GCN 35335
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 ) with the REM 60cm robotic telescope located at the ESO Observatory of La Silla (Chile). The observations were carried out in the g,r,i,z, J,H,K bands, starting on 2023 Dec 15 at 00:39:27 UT (i.e. about 4.25 hours after the Swift trigger) and lasted for about 1 hour.
From preliminary analysis, we do not find any source at the enhanced XRT position (Evans et al., GCN 35341
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 ), down the the following 3 sigma upper limits:

r > 20.1 (AB; calibrated against the SkyMapper catalogue)
at a mid time of t-t0 ~ 4.92 h after the GRB trigger;

H > 17.7 (Vega; calibrated against the 2MASS catalogue)
at a mid time of t-t0 ~ 4.68 h after the GRB trigger.

S. Bala (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 20:24:24.68 UT on 14 December 2023, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 231214A (trigger 724278269 / 231214850),
which was also detected by the Swift/BAT (Brivio et al. 2023, GCN 35335
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 ),
Fermi-LAT (Kocevski et al. 2023, GCN 35342
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 ) and AstroSat CZTI (Navaneeth et al. 
GCN 35348
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 ). The Fermi GBM Final Real-time Localization (GCN 35334
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 ) is consistent
with the Swift position. 

The angle from the Fermi LAT boresight at the GBM trigger time is 50.0 degrees.

The GBM light curve consists of two distinct peaks
with a duration (T90) of about 21 s (50-300 keV).
The time-averaged spectrum from T0-0.5 s to T0+26.1 s is
best fit by a Band function with Epeak = 142.5 +/- 5 keV,
alpha = -0.46 +/- 0.05, and beta = -2.5 +/- 0.1.

The event fluence (10-1000 keV) in this time interval is
(2.25 +/- 0.05)E-5 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+16.12 s in the 10-1000 keV band
is 22.24 +/- 1.77 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/"

A. A. Breeveld (UCL-MSSL) and Brivio (INAF-OAB) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 231214A (Fermi GBM Team, GCN Circ. 35334
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 ; Kocevski et al., GCN Circ. 35342
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 ; Navaneeth et al., GCN Circ. 35348
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 ), 442 s after the BAT trigger (Brivio et al., GCN Circ. 35335
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 ).
No optical afterglow consistent with the XRT position (Evans et al., GCN Circ. 35341
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 ) 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 initial exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white              442         4733          382         >20.7
v                  4944          4998           54         >18.1
b                  4329         4528          197         >19.6
u                  4123         4322          197         >19.3
w2                4739         4939          197         >19.5

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.060 in the direction of the burst (Schlegel et al. 1998).

M. Stamatikos (OSU), S. D. Barthelmy (GSFC), R. Brivio (INAF-OAB),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), M. Moss (GSFC), D. M. Palmer (LANL),
T. Parsotan (GSFC/UMBC), T. Sakamoto (AGU)
(i.e. the Swift-BAT team):
 Using the data set from T-35 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 231214A (trigger #1202386)
(Brivio, et al., GCN Circ. 35335
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 ).  The BAT ground-calculated position is
RA, Dec = 305.666, -72.432 deg which is
   RA(J2000)  =  20h 22m 39.7s
   Dec(J2000) = -72d 25' 54.3"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 39%.
 The mask-weighted light curve shows two bright overlapping peaks.  The first
peak starts from T-5 s, peaks at T+1 s and ends at T+10 s.  The second peak
starts from T+10 s, peaks at T+12 s and ends at T+25 s.
T90 (15-350 keV) is 27.8 +- 7.3 sec (estimated error including systematics).
 The time-averaged spectrum from T-5.37 to T+49.42 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.87 +- 0.23,
and Epeak of 167 +- 94 keV (chi squared 60.53 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 9.6 +- 0.3 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+12.57 sec in the 15-150 keV band is
11.3 +- 0.6 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.25 +- 0.05 (chi squared 69.34 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/1202386/BA/

A. Gulati (USyd), G. E. Anderson (Curtin), J. K. Leung (UofT/HUJI), S. D. Ryder (Macquarie), A. J. van der Horst (GWU), S. Chastain (UNM), and L. Rhodes (Oxford) on behalf of the ATCA PanRadio GRB collaboration

We observed long GRB 231214A (Fermi GBM Collaboration, GCN 35334
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 ; R. Brivio et al., GCN 35335
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 ) as part of the The Australia Telescope Compact Array (ATCA) "PanRadio GRB" Large Project C3542 (PI: G. Anderson) at 5.5, 9, 16.7, 21.2, 33 and 35 GHz on 2023-12-16 and at 5.5 and 9 GHz on 2023-12-21 UT. 

No radio sources were detected near the Swift/XRT enhanced position (J. P. Osborne et al., GCN 35350
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 )in either observation epoch. The 3-sigma upper limits for the 9 GHz observations are 73 and 81 uJy respectively.

We thank the CSIRO Space and Astronomy staff for supporting these observations.
We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO.