GRB 210712A

B. Sbarufatti (PSU), H. A. Krimm (NSF) and K. L. Page (U Leicester)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 09:43:11 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210712A (trigger=1059881).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 97.337, -35.393 which is 
   RA(J2000) = 06h 29m 21s
   Dec(J2000) = -35d 23' 33"
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 20 sec, followed by lower-level 
extended emission.  The peak count rate was ~2600 counts/sec (15-350 keV), 
at ~0 sec after the trigger. 

The XRT began observing the field at 09:44:32.5 UT, 80.6 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 97.3319,
-35.3717 which is equivalent to:
   RA(J2000)  = 06h 29m 19.66s
   Dec(J2000) = -35d 22' 18.0"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). 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 (8.88 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 6.5
(+5.28/-4.30) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 3.52e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 90 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 none of
the XRT error circle. 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 0.076. 

Burst Advocate for this burst is B. Sbarufatti (bxs60 AT psu.edu). 
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/)

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

Using 1702 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 210712A, 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 = 97.33177, -35.37165 which is equivalent
to:

RA (J2000): 06h 29m 19.63s
Dec (J2000): -35d 22' 18.0"

with an uncertainty of 2.1 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.

Y.-D. Hu, E. Fernandez-Garcia, T.-R. Sun, A. J. Castro-Tirado, M. D. Caballero-Garcia, M. A. Castro Tirado (IAA-CSIC), I. Carrasco and C. Perez del Pulgar (Univ. de Malaga), and R. Querel (NIWA), on behalf of a larger collaboration, report:

The 60cm BOOTES-3/YA robotic telescope at NIWA Lauder in Otago (New Zealand) automatically responded to the Swift trigger of GRB 210712A (Sbarufatti et al. GCNC 30447). Images were taken starting at 15:01 UT, but due to poor weather conditions, only images taken after 17:32 UT (~7.8 hrs after trigger) could be used. In the co-added image (30 exposures 60s each), no source is found at the position reported by Swift/XRT (Evans et al. GCNC 30453) down to 19.6 mag which is consistent with the non-detection by Swift/UVOT (Sbarufatti et al. GCNC 30447). Further observations are ongoing.

We thank the staff at NIWA for its excellent support.

M. H. Siegel (PSU) and B. Sbarufatti (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210712A
91 s after the BAT trigger (Sbarufatti et al., GCN Circ. 30447
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 ).
No optical afterglow consistent with the enhanced XRT position
(Evans et al. GCN Circ. 30453
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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 first
finding chart (FC) exposure and subsequent exposures are:

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

white_FC            91          241          147         >19.5
u_FC               304          554          246         >19.6
white               91          604          167         >19.5
b                  560          579           19         >18.0
u                  304          554          246         >19.6
w2                 609          614            4         >17.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.076 in the direction of the burst
(Schlegel et al. 1998).

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

We have analysed 8.5 ks of XRT data for GRB 210712A (Sbarufatti et al.
GCN Circ. 30447
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 ), from 86 s to 44.8 ks after the  BAT trigger. The data
comprise 164 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN Circ. 30453
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 ).

The late-time light curve (from T0+5.4 ks) can be modelled with a
power-law decay with a decay index of alpha=1.06 (+0.10, -0.09).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.52 (+/-0.06). The
best-fitting absorption column is  1.10 (+0.22, -0.21) x 10^21 cm^-2,
consistent with the Galactic value of 8.9 x 10^20 cm^-2 (Willingale et
al. 2013). The PC mode spectrum has a photon index of 1.98 (+0.13,
-0.09) and a best-fitting absorption column consistent with the
Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 3.3 x 10^-11 (4.0 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.9 (+2.9, -0.0) x 10^20 cm^-2
Galactic foreground: 8.9 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.98 (+0.13, -0.09)

If the light curve continues to decay with a power-law decay index of
1.06, the count rate at T+24 hours will be 0.015 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.9 x
10^-13 (5.9 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/01059881.

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

T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU), B. Sbarufatti (PSU),
M. Stamatikos (OSU), (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 210712A (trigger #1059881)
(Sbarufatti, et al., GCN Circ. 30447
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 ).  The BAT ground-calculated position is
RA, Dec = 97.322, -35.376 deg which is 
  RA(J2000)  =  06h 29m 17.3s 
  Dec(J2000) = -35d 22' 32.2" 
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 71%.

The mask-weighted light curve shows a series of peaks.  The first is from roughly
T-40 to T-30.  Then the strongest peak is from T-5 to T+15.  This is followed by a 
string of weaker peaks from T+20 to T+120.  The spacecraft slewed away from 
the burst location by T+700 sec.   T90 (15-350 keV) is 136.41 +- 63.58 sec 
(estimated error including systematics).

The time-averaged spectrum from -39.76 to 174.18 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.00 +- 0.53, 
and Epeak of 51.8 +- 11.6 keV (chi squared 70.95 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 3.0 +- 0.3 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+0.09 sec in the 15-150 keV band is
2.3 +- 0.3 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.85 +- 0.11 (chi squared 80.11 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/1059881/BA/

E. Bissaldi (Politecnico and INFN Bari)
reports on behalf of the Fermi GBM Team:


"At 09:43:10.98 UT on 12 July 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 210712A (trigger 647775795 / 210712405),
which was also detected by the Swift/BAT (Sbarufatti et al. 2021, GCN 30447
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 ).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight
at the GBM trigger time is 36 degrees.

The GBM light curve consists of an emission episode
with a duration (T90) of about 8 s (50-300 keV).
The time-averaged spectrum from T0-0.3 s to T0+6.6 s is
adequately fit by a power law function with an exponential
high-energy cutoff. The power law index is -1.04 +/- 0.13 and
the cutoff energy, parameterized as Epeak, is 230 +/- 50 keV.

The event fluence (10-1000 keV) in this time interval is
(1.51 +/- 0.17)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.1 s in the 10-1000 keV band
is 3.1 +/- 0.2 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/"