GRB 231210B

K. L. Page (U Leicester), J.D. Gropp (PSU), J. A. Kennea (PSU),
D. M. Palmer (LANL), T. M. Parsotan (GSFC/UMBC/CRESSTII) and
M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 21:29:04 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 231210B (trigger=1201696).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 95.772, -48.359 which is 
   RA(J2000) = 06h 23m 05s
   Dec(J2000) = -48d 21' 32"
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 15 sec.  However, since this
GRB occurred while the spacecraft was leaving the SAA, the rate
lightcurve is hard to interpret.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~T+0 sec after the trigger. 

The XRT began observing the field at 21:31:07.8 UT, 123.4 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 95.79386,
-48.37201 which is equivalent to:
   RA(J2000)  = 06h 23m 10.53s
   Dec(J2000) = -48d 22' 19.2"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 70 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. No
spectrum from the promptly downlinked event data is yet available to
determine the column density. 

The initial flux in the 2.5 s image was 4.31e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 462 seconds after the BAT trigger. Due to tracking issues, the 
UVOT image is blurred. However, comparison with DSS shows that there appears
to be a new source coincident with the XRT localization. Further data and 
analysis will be needed to report an accurate localization and magnitude 
of this object. 

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/)

I. Pérez-Fournon, F. Poidevin (IAC and ULL), H. Akoudad-Ekajouan, C. Araujo-Álvarez, C. Arrizabalaga-Díaz-Caneja, F. Barnes-Sánchez, P. Eguiguren-Arrizabalaga, A. Iglesias-López, G.A. Jaimes-Illanes, P. Jiménez-Sánchez, S. Lamolda-Mir, A. Mang-Román, G. Marrero-Ramallo, P.P. Meni-Gallardo, I. Ruiz-Cejudo (ULL), M. Sánchez-Andújar (ULL and IAC), V. Wienzek (ULL), E. Esparza-Borges, and F. Tinaut-Ruano (IAC and ULL)

report observations of GRB 231210B with the LCOGT 40cm telescope at Sutherland Observatory starting on 2023-12-10 22:22:25 UT in the SDSS g', r', and i' filters.

We detect a source in the three filters at the position RA (J2000) = 06h 23m 10.997s,  Dec (J2000) = -48d 22m 19.87s, that is close to the Swift position reported by Page et al. (GCN 35314
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 ) and the optical transient reported by Buckley et al. (GCN 35313
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 ).

We measure the following magnitudes:

  Date      Time        Filter    Exposure (sec)            Mag      Error
---------------------|-----------|---------------------|------------|-------
2023-12-10 22:22:25     g          180                       20.72     0.18 
2023-12-10 22:25:34     r          180                       19.69     0.12
2023-12-10 22:28:42     i          180                       19.62     0.26

A. Saccardi (GEPI, Observatoire de Paris), B. Schneider (MIT), L. Izzo (INAF-Naples & DARK/NBI), D. B. Malesani (DAWN/NBI), C. Peña (Univ. of Utah) report on behalf of the Stargate collaboration:

We observed the field of the Swift GRB 231210B (Page et al., GCN 35314
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 ) using the ESO/VLT/UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 600s each. The observation starting-time is 01:32:26 UT on Dec 11 2023 (~4 hr after the Swift trigger).

In images taken with the acquisition camera, we clearly detect the optical afterglow consistent with the position reported by Buckley et al., GCN 35313
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  and Pérez-Fournon et al., GCN 35316
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 . We measure the following AB magnitudes (calibrated against SkyMapper stars): g' = 21.82 +/- 0.05 mag, r' = 21.23 +/- 0.04 mag, z' = 21.03 +/- 0.07 mag.

We detect a continuum over the entire wavelength range. From the detection of a broad Lya absorption at ~5000 AA and multiple absorption features, which we interpret as being due to NV, SiII, SII, OI, CII, ZnII, FeII, AlII, CIV, SiIV, FeII*, OI*, SiII*, CII*, we infer a common redshift of z = 3.13. We conclude this is the redshift of the burst. We also note the presence of additional absorption features likely due to multiple intervening systems.

We acknowledge the excellent support from the ESO staff in Paranal, in particular Maria Jose Rain, Zahed Wahhaj and Thomas Seifert.

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

Using 1563 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 231210B, 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 = 95.79470, -48.37226 which is equivalent
to:

RA (J2000): 06h 23m 10.73s
Dec (J2000): -48d 22' 20.2"

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.

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

We have analysed 6.4 ks of XRT data for GRB 231210B, from 410 s to 35.6
ks after the  BAT trigger. The data comprise 40 s in Windowed Timing
(WT) mode with the remainder in Photon Counting (PC) mode. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.32 (+0.05, -0.04).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.65 (+0.11, -0.10). The
best-fitting absorption column is  5.3 (+7.7, -5.3) x 10^21 cm^-2, at a
redshift of 3.13, in addition to the Galactic value of 4.1 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 4.0 x
10^-11 (4.3 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 4.1 x 10^20 cm^-2
Intrinsic column:    5.3 (+7.7, -5.3) x 10^21 cm^-2 at z=3.13
Photon index:	     1.65 (+0.11, -0.10)

If the light curve continues to decay with a power-law decay index of
1.32, the count rate at T+24 hours will be 4.5 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.8 x
10^-13 (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/01201696.

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

T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), K. L. Page (U Leicester)
T. Parsotan (GSFC/UMBC), M. Stamatikos (OSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-36 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 231210B (trigger #1201696)
(Page, et al., GCN Circ. 35314
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 ).  The BAT ground-calculated position is
RA, Dec = 95.803, -48.335 deg which is
   RA(J2000)  =  06h 23m 12.7s
   Dec(J2000) = -48d 20' 04.6"
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 17%.
 
The mask-weighted light curve shows a FRED pulse potentially followed by a dimmer spike.
T90 (15-350 keV) is 7.47 +- 0.65 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.23 to T+7.82 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.08 +- 0.19.  The fluence in the 15-150 keV band is 1.4 +- 0.2 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T-0.24 sec in the 15-150 keV band
is 3.9 +- 0.7 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/1201696/BA/

S. de Wet (UCT), P.M. Vreeswijk (Radboud) and P.J. Groot (Radboud/UCT/SAAO) report on behalf of the MeerLICHT consortium:

The 0.6 m wide-field MeerLICHT optical telescope located in Sutherland, South Africa, obtained a repeated series of 60 s exposures in the q,u,g,r,i,z bands of GRB 231210B following the Swift detection (Page et al., GCN 35314
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 ). Observations started at 21:32:26 UT on 2023 November 18 (202 seconds post-trigger) and continued for a further 1.79 hours, following the filter sequence quqgqrqiqz. 

We detect the optical afterglow also detected by MASTER, UVOT, LCOGT, and the VLT (Buckley et al., GCN 35313
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 ; Page et al., GCN 35314
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 ; Pérez-Fournon et al., GCN 35316
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 ; Saccardi et al., GCN 35317
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 ) with the following AB magnitudes:

q = 17.15 +/- 0.02 at 21:32:57 UT
u = 19.67 +/- 0.19 at 21:34:20 UT
g = 18.69 +/- 0.04 at 21:37:17 UT
r = 18.11 +/- 0.03 at 21:40:11 UT
i = 18.15 +/- 0.05 at 21:43:08 UT
z = 18.30 +/- 0.11 at 21:46:05 UT

As a precaution, we note that the absolute photometric calibration may have been adversely affected by condensation in the cryostat window due to high humidity. Our high cadence q-band observations show a power-law decline with a temporal index of -1.2 throughout the observations. 

MeerLICHT is built and run by a consortium consisting of Radboud University, University of Cape Town, the South African Astronomical Observatory, the University of Oxford, the University of Manchester and the University of Amsterdam. 

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 231210B (Page et al., GCN 35314
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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 11 at 00:36:37 UT (i.e. about 3.13 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 (Beardmore et al., GCN 35318
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 ), down the the following 3 sigma upper limits:

r > 21.0 (AB; calibrated against the SkyMapper catalogue)
at a mid time of t-t0 ~ 3.80 h after the GRB trigger;

H > 17.4 (Vega; calibrated against the 2MASS catalogue)
at a mid time of t-t0 ~ 3.56 h after the GRB trigger.

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

We observed short GRB 231210B (Page et al., GCN 35314
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 ) starting at 2023-12-14 10:56UT for 9 hours with the Australia Telescope Compact Array (ATCA), as part of the "PanRadio GRB" Large ATCA follow-up programme C3542 (PI. Anderson).

We do not detect any clear radio counterpart. The rms noise in our observations is 17 and 12 uJy/beam at 5.5 and 9GHz, respectively. At a redshift of 3.13 (Saccardi et al GCN 35317
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 ), our measurements correspond to 3-sigma upper limits of 6.6e30 and 4.7e30 erg/s/Hz at 5.5 and 9GHz, respectively (assuming H0 = 70km/s/Mpc and OmegaM = 0.3)

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.

D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long GRB 231210B (Swift detection: Page et al., GCN 35314
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 )
triggered Konus-Wind (KW) at T0=77347.988 s UT (21:29:07.988).

The burst light curve shows a multi-peaked structure
with a total duration of of ~9 s.
The emission is seen up to ~0.5 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB231210_T77347/

As observed by Konus-Wind, the burst had
a total fluence of (4.02 ± 0.56)x10^-6 erg/cm^2 and
a 64-ms peak energy flux, measured from T0+2.944 s,
of (2.19 ± 0.32)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst (measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 15 MeV range by a power law with exponential
cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.62(-0.37,+0.44) and Ep = 174(-27,+40) keV (chi2 = 65/87 dof).
Fitting this spectrum by a Band function yields the same values of alpha and Ep,
and an upper limit on the high energy photon index beta of -2.5 (chi2 = 65/86 dof).

Assuming the redshift z=3.13 (Saccardi et al., GCN 35317
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 )
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 burst isotropic energy release E_iso to (8.8 ± 1.3)x10^52 erg,
the isotropic peak luminosity L_iso to (2.0 ± 0.3)x10^53 erg/s,
the rest-frame peak energy of the spectrum Ep,z to ~720 keV.
With the obtained estimates, GRB 231210B is inside 90% prediction band for
the 'Amati' relation and inside 68% prediction band for the 'Yonetoku' relation
derived for the sample of >300 long KW GRBs with known redshifts
(Tsvetkova et al., 2017; Tsvetkova et al., 2021), see
http://www.ioffe.ru/LEA/GRBs/GRB231210_T77347/GRB231210B_rest_frame.pdf

All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.

K. Siellez, B. Emptage, K. Hill, J.-P. Beaulieu (Institute of Astrophysics in Paris / UTas), A. Cole, T. Plunkett report: 

a new optical transient for the GRB 231210B observed with the Harlingten 50cm Telescope starting on 2023-12-11 17:14:35 UT in Sloan r' and g' filters. 

We detect an optical transient at the position RA (J2000) = 06h 23m 05.924s, Dec (J2000) = -48d 19' 11.65", which is not included in the Swift XRT position (Page et al., GCN 35314
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 ), but is within the BAT enhanced ground-calculated position (Sakamoto et al., GCN 35322
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 ). It has a different position than the optical afterglows already published (GCN 35316
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 , GCN 35323
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 ). 

The observations leading to the measurements of the magnitude were made as followed:

  Date     Time             Filter        Exposure (sec)            
-------------------------|-----------|-----------------------------------
2023-12-11 17:14:35.536        r               180                       
2023-12-11 17:17:44.365        r               180                       
2023-12-11 17:20:53.192        r               180      
2023-12-11 17:24:02:021        r               180      
2023-12-11 17:27:10.853        r               180   

On 2023-12-11 we stacked 5 pictures of 180s exposure time for a total of 900s exposure time, with r' filter. We obtain a magnitude of 19.2 +/- 0.1 in r'. 



  Date     Time             Filter        Exposure (sec)            
-------------------------|-----------|-----------------------------------
2023-12-12 11:49:41.012        g'               180                       
2023-12-12 11:52:49.835        g'               180                       
2023-12-12 11:55:58.661        g'               180      
2023-12-12 11:59:07.480        g'               180      
2023-12-12 12:05:25.121        g'               180   

On 2023-12-12 we stacked 5 pictures of 180s exposure time for a total of 900s exposure time, with g' filter. We obtain a magnitude of 20.3 +/- 0.1 in g'. 

On 2023-12-17 we stacked 5 pictures of 180s exposure time for a total of 900s exposure time, with r' filter. We obtain a magnitude of 20.1 +/- 0.1 in r'. 

More data were taken on the days in between and will be released soon.  We encourage the follow up of this optical transient in all wavelengths. 



We acknowledge the traditional custodians of the land upon which we built our telescope: the Palawa / Pakana and Gadigal people. The team wants to thank Caisey Harlingten for his donation and support, the late Dr. John Greenhill who created and pushed forward the development of this optical observatory, as well as Dr. Tony Sprent and Dr. Keith Bolton, who keep supporting and developing the telescopes. 

A. J. Castro-Tirado, Y.-D. Hu, E. Fernandez-Garcia, M.D. Caballero-Garcia, R. Sanchez-Ramirez, I. Perez-Garcia, S.-Y. Wu, S. Guziy  (IAA-CSIC Granada), C. Perez del Pulgar, A. Castellon, A. Reina (Univ. de Malaga), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), report:

Following the detection of GRB 231210B by Swift (Page et al., GCNC 35314) and Konus-Wind (Frederiks et al. GCNC 35359), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) pointed to the burst position on Dec. 21 at 01:32 UT (i.e. ~10.2 days after trigger). Images were gathered in different optical bands. In the co-added r-band image (8 x 300 s, SDSS-r filter), the optical afterglow reported by MASTER (Lipunov et al. GCNC 35313), UVOT (Page et al., GCNC 35314), LCOGT (Pérez-Fournon et al. GCNC 35316), VLT (Saccardi et al. GCNC 35317) and MeerLICHT (de Wet et al. GCNC 35323) is not detected within the enhanced Swift/XRT position (Beardmore et al. GCNC 35318) down to 21.0 mag, which is consistent with the REM results (Ferro et al. GCNC 35333).

Regarding the source reported at the Greenhill Observatory (Siellez et al. GCNC 35406), we cannot clearly identify it since it is blended with a nearby and brighter star 0.4" away. In any case, we notice that this object is present on the DESI catalog and it is far from the enhanced Swift/XRT position and therefore unrelated to GRB 231210B.

BOOTES-7 is the last observatory completing the BOOTES Global Network of robotic telescopes in all the continents (Castro-Tirado 2023, Nat. Astron. 7, 1136), 25 years after the first astronomical station was deployed in south Spain.

We thank the staff at San Pedro de Atacama Celestial Explorations observatory for their excellent support.