GRB 211207A

E. Ambrosi (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR),
S. Dichiara (PSU), J.D. Gropp (PSU), J. A. Kennea (PSU),
S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), T. M. Parsotan (GSFC/UMBC/CRESSTII) and
B. Sbarufatti (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 20:52:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 211207A (trigger=1088376).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 149.625, -24.352 which is 
   RA(J2000) = 09h 58m 30s
   Dec(J2000) = -24d 21' 05"
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 4 sec.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 20:54:17.2 UT, 80.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 149.62449, -24.35970 which is
equivalent to:
   RA(J2000)  = 09h 58m 29.88s
   Dec(J2000) = -24d 21' 34.9"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 27 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (4.94 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.1
(+3.50/-2.89) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 84 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	09:58:29.78 = 149.62408
  DEC(J2000) = -24:21:31.1  = -24.35863
with a 90%-confidence error radius of about 0.62 arc sec. This position is 3.5
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.45 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.050. 

Burst Advocate for this burst is E. Ambrosi (elena.ambrosi 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/)

V. Lipunov, V.Kornilov, E.Gorbovskoy, K.Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, 
D. Vlasenko, G.Antipov, D.Zimnukhov, V.Senik, T.Pogrosheva, E.Minkina,
A.Chasovnikov, V.Topolev, V.Grinshpun, 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
(Irkutsk State University, API),

A. Tlatov, D. Dormidontov 
(Kislovodsk Solar Station of the Pulkovo Observatory),

A. Gabovich, V.Yurkov 
(Blagoveschensk Educational State University)


MASTER-Kislovodsk robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Swift GRB 211207A ( E. Ambrosi et al., GCN 31182
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 ) errorbox  4112 sec after notice time and 4128 sec after trigger time at 2021-12-07 22:01:45 UT, with upper limit up to  15.3 mag. The observations began at zenith distance = 87 deg. The sun  altitude  is -66.2 deg. 

The galactic latitude b = 24 deg., longitude l = 261 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=1807266

We obtain a following upper limits.  

Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

    4219 |   MASTER-Kislovodsk |   C |   180 | 14.6 |        
    4219 |   MASTER-Kislovodsk |   C |   180 | 14.3 |        
    4419 |   MASTER-Kislovodsk |   C |   180 | 14.5 |        
    4419 |   MASTER-Kislovodsk |   C |   180 | 14.2 |        
    4619 |   MASTER-Kislovodsk |   C |   180 | 14.8 |        
    4619 |   MASTER-Kislovodsk |   C |   180 | 14.4 |        
    4819 |   MASTER-Kislovodsk |   C |   180 | 15.3 |        
    4819 |   MASTER-Kislovodsk |   C |   180 | 14.7 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

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

Using 1514 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 211207A, 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 = 149.62381, -24.35968 which is equivalent
to:

RA (J2000): 09h 58m 29.71s
Dec (J2000): -24d 21' 34.8"

with an uncertainty of 2.3 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.

P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M.G. Bernardini (INAF-OAB), M. Capalbi (INAF-IASFPA), B.
Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU) and E. Ambrosi
report on behalf of the Swift-XRT team:

We have analysed 6.3 ks of XRT data for GRB 211207A (Ambrosi et al. GCN
Circ. 31182
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 ), from 87 s to 39.7 ks after the  BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Osborne et al. (GCN Circ. 31184
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.92 (+0.08, -0.07).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.08 (+0.29, -0.27). The
best-fitting absorption column is  1.7 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 4.9 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 3.3 x 10^-11 (4.6 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.7 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 4.9 x 10^20 cm^-2
Excess significance: 2.7 sigma
Photon index:	     2.08 (+0.29, -0.27)

If the light curve continues to decay with a power-law decay index of
0.92, the count rate at T+24 hours will be 1.9 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.3 x
10^-14 (8.7 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01088376.

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

B. Schneider (CEA Paris-Saclay), L. Izzo (DARK/NBI), D. B. Malesani (Univ. Radboud and DAWN/NBI), J. P. U. Fynbo (DAWN/NBI), K. Wiersema (Univ. Lancaster), V. D���Elia (ASI/SSDC, INAF/OAR), K. E. Heintz (Univ. Iceland and DAWN/NBI), report on behalf of the Stargate collaboration:

We observed the afterglow of GRB 211207A (Ambrosi et al., GCN 31182
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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 1200 s each. The observation mid time was 2021 Dec 8.288 UT (10.04 hr after the GRB).

In a 60 s image taken with the acquisition camera on Dec 8.249 UT, we detect the optical afterglow, for which we measure an AB magnitude r = 22.16 +/- 0.05 mag (calibrated against two nearby stars from the Pan-STARRS catalog).

We clearly detect continuum over the wavelength range 3400 - 18000 AA. A trough is visible around 3960 AA, which we identify as due to H I. From detection of multiple absorption features, which we interpret as due to Si II, O I, C II, Fe II, Si IV, C IV, Al II, Mg II, we infer a redshift z = 2.272. An emission line is also detected at 16390 AA, which we interpret as due to [O III] from the GRB host galaxy.

We acknowledge excellent support from the ESO observing staff in Paranal, in particular Joe Anderson, Zahed Wahhaj and Rob van Holstein.

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), T. Parsotan (GSFC/UMBC),

M. Stamatikos (OSU), (i.e. the Swift-BAT team):



Using the data set from T-240 to T+962 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 211207A (trigger #1088376)
(Ambrosi et al., GCN 31182
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 ).  The BAT ground-calculated position is RA, Dec
= 149.601, -24.360 deg which is

   RA(J2000)  =  09h 58m 24.1s

   Dec(J2000) = -24d 21' 37.3"

with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment). The
partial coding was 62%.



The BAT light curve showed a complex structure with a duration of about 4
sec. T90 (15-350 keV) is 3.73 +- 0.87 sec (estimated error including
systematics).



The time-averaged spectrum from T-1.30 to T+2.97 sec is best fit by a
simple power-law model.  The power law index of the time-averaged spectrum
is 1.72 +- 0.30.  The fluence in the 15-150 keV band is 1.9 +- 0.4 x 10^-07
erg/cm2. The 1-sec peak photon flux measured from T-0.15 sec in the 15-150
keV band is 0.9 +- 0.2 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/1088376/BA/

M. H. Siegel (PSU) and Ambrosi (INAF-IASFPA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 211207A
85 s after the BAT trigger (Ambrosi et al., GCN Circ. 31182
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 ).
A source consistent with the XRT position
(Osborne et al. GCN Circ. 31184
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  09:58:29.79 = 149.62412 (deg.)
    Dec (J2000) = -24:21:31.3  = -24.35869 (deg.)
with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: 

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

white               85          234          147         17.52 +/- 0.04
v                  627         1595          117        >18.5
b                  553          743           36         19.08 +/- 0.31
u                  297          546          246         18.15 +/- 0.09
w1                 677         1470           97        >18.7
m2                 652         1272           39        >18.7
w2                 776         1570           78        >19.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.050 in the direction of the burst
(Schlegel et al. 1998).

C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team:

Swift-BAT detected GRB 211207A at 20:52:56 UT (GCN 31182
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 ). 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 no counterparts.

The GBM targeted search [1], the most sensitive, coherent search for
GRB-like signals identified a transient most significantly on the 2.048 s
timescale, with a false alarm rate of 3.2e-05 Hz and a location consistent with
the Swift-BAT event, using the standard search protocol with a S/N of 8.
The GBM targeted search event was found with the highest
significance with a "soft" spectrum (Band function with
Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB.

[1] Goldstein et al. 2019 arXiv:1903.12597
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