GRB 210723A

T. Sbarrato (INAF-OAB), M. G. Bernardini (INAF-OAB),
P. D'Avanzo (INAF-OAB), J. A. Kennea (PSU),
N. J. Klingler (GSFC/UMBC/CRESSTII), N. P. M. Kuin (UCL-MSSL),
S. Laha (GSFC/UMBC/CRESST), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL), M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 14:46:10 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210723A (trigger=1061284).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 121.726, -32.889 which is 
   RA(J2000) = 08h 06m 54s
   Dec(J2000) = -32d 53' 20"
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 50 sec.  The peak count rate
was ~2200 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 14:47:40.4 UT, 89.6 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 121.72157,
-32.88624 which is equivalent to:
   RA(J2000)  = 08h 06m 53.18s
   Dec(J2000) = -32d 53' 10.5"
with an uncertainty of 7.0 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 7.70
x 10^21 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 3.04e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 99 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. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
sub-image. The 8'x8' region for the list of sources generated on-board covers
100% of the XRT error circle. Because of the density of catalogued stars,
further analysis is required to report an upper limit for any afterglow in the
region. No correction has been made for the large, but uncertain, extinction
expected. 

Although the data from this burst are consistent with a classical long
GRB, we note that this source is close to the Galactic plane 
(lat = -0.34 degrees) which raises the possibility that this is
a Galactic transient.  If further analysis determines that to be
the case, we would name the object Swift J0806.9-3253 . 

Burst Advocate for this burst is T. Sbarrato (tullia.sbarrato 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/)

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Using  promptly downlinked XRT event data for GRB 210723A, we find an
enhanced XRT position of the afterglow: RA, Dec: 121.7213, -32.8851
which is equivalent to:
   RA (J2000)  = 08 06 53.12
   Dec (J2000) = -32 53 06.4
with an uncertainty of 1.9 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/1061284.

Position enhancement is is described by Goad et al. (2007, A&A, 476,
1401) and Evans et al. (2009, MNRAS, 397, 1177).

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

V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, 
V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva,
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, O.Ershova 
(Irkutsk State University, API),

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

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




MASTER-OAFA robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 210723A ( T. Sbarrato et al., GCN 30485
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 ) errorbox  29771 sec after notice time and 29801 sec after trigger time at 2021-07-23 23:02:52 UT, with upper limit up to  15.3 mag. Observations started at twilight.  The observations began at zenith distance = 80 deg. The sun  altitude  is -14.6 deg. 

The galactic latitude b = -0 deg., longitude l = 251 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=1668344

We obtain a following upper limits.  

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

   29891 |         MASTER-OAFA |   C |   180 | 15.3 |        
   30091 |         MASTER-OAFA |   C |   180 | 14.7 |        
Filter C is a clear (unfiltred) band. 


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

A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), E. Ambrosi 
(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR),
J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU),
J.P. Osborne (U. Leicester) and T. Sbarrato report on behalf of the
Swift-XRT team:

We have analysed 6.3 ks of XRT data for GRB 210723A (Sbarrato et al.
GCN Circ. 30485
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 ), from 79 s to 57.3 ks after the  BAT trigger. The data
comprise 267 s in Windowed Timing (WT) mode (the first 9 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. Using 3236 s of PC mode data and 6 UVOT images, we find an
enhanced XRT position (using the XRT-UVOT alignment and matching UVOT
field sources to the USNO-B1 catalogue): RA, Dec = 121.72115, -32.88570
which is equivalent to:

RA (J2000): 08h 06m 53.08s
Dec(J2000): -32d 53' 08.5"

with an uncertainty of 2.0 arcsec (radius, 90% confidence).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=2.45 (+/-0.15). At T+154 s  the decay
flattens to an alpha of 1.67 (+/-0.09) before breaking again at T+959 s
to a final decay with index alpha=1.04 (+0.09, -0.23).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.75 (+0.11, -0.10). The
best-fitting absorption column is  1.26 (+0.14, -0.13) x 10^22 cm^-2,
in excess of the Galactic value of 7.7 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.71 (+0.26, -0.25)
and a best-fitting absorption column of 1.6 (+0.4, -0.3) x 10^22 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 6.5 x 10^-11 (1.1 x 10^-10) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.6 (+0.4, -0.3) x 10^22 cm^-2
Galactic foreground: 7.7 x 10^21 cm^-2
Excess significance: 4.1 sigma
Photon index:	     1.71 (+0.26, -0.25)

If the light curve continues to decay with a power-law decay index of
1.04, the count rate at T+24 hours will be 7.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.6 x
10^-13 (7.7 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/01061284.

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

H. A. Krimm (NSF), S. D. Barthelmy (GSFC),

S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),

C. B. Markwardt (GSFC), D. M. Palmer (LANL),

T. Sakamoto (AGU), T. Sbarrato (INAF-OAB),

M. Stamatikos (OSU), T. N. Ukwatta (LANL)

(i.e. the Swift-BAT team):



Using the data set from T-239 to T+861 sec from the recent telemetry
downlink,

we report further analysis of BAT GRB 210723A (trigger #1061284)

(Sbarrato et al., GCN Circ. 30485
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 ).  The BAT ground-calculated position is

RA, Dec = 121.723, -32.893 deg which is

   RA(J2000)  =  08h 06m 53.4s

   Dec(J2000) = -32d 53' 35.8"

with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).

The partial coding was 77%.



The mask-weighted light curve shows a single-pulse structure that

starts at ~T-5 s, peaks at ~T0, and ends at ~T+65 s. T90 (15-350 keV)

is 48.54 +- 3.50 sec (estimated error including systematics).



The time-averaged spectrum from T-4.59 to T+66.64 sec is best fit

by a power law with an exponential cutoff.  This fit gives a photon

index 0.85 +- 0.29, and Epeak of 88.2 +- 15.3 keV (chi squared 54.48

for 52 d.o.f.).  For this model the total fluence in the 15-150 keV band

is 5.3 +- 0.2 x 10^-6 erg/cm2 and the 1-sec peak flux measured from

T+2.68 sec in the 15-150 keV band is 3.1 +- 0.3 ph/cm2/sec.

A fit to a simple power law gives a photon index of 1.60 +- 0.06 (chi

squared 75.55 for 53 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/1061284/BA/

S. Lesage (UAH), B. Hristov (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

At 14:46:07 UT on 23 July 2021, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 210723A (trigger 648744372/210723615).
which was also detected by Swift BAT (T. Sbarrato et al. 2021, GCN 30485
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 )
The Fermi GBM on-ground location is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 94 degrees.

The GBM light curve consists of a single emission episode with a duration
(T90)
of about 43 s (10-1000 keV). The time-averaged spectrum
from T0+1.5 to T0+36.4 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.67 +/- 0.07 and the cutoff energy,
parameterized as Epeak, is 113 +/- 5 keV.

The event fluence (10-1000 keV) in this time interval is
(7.6 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1 s in the 10-1000 keV band is 4.7 +/- 0.3 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/"

Y. Asaoka (ICRR),
A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU),
Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN),
S. Torii, Y. Akaike, K. Kobayashi (Waseda U),
Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC),
M. L. Cherry (LSU), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:

The long GRB 210723A (Swift detection: Sbarrato et al., GCN Circ. 30485
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 ,
Krimm and Barthelmy, GCN Circ. 30495
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 ; Fermi GBM Observation:
Lesage et al., GCN Circ. 30499
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 ;
https://gcn.gsfc.nasa.gov/other/210723A.gcn3) triggered the CALET Gamma-ray
Burst Monitor (CGBM) at 14:46:05.572 UTC on 23 July 2021
(http://cgbm.calet.jp/cgbm_trigger/flight/1311086521/index.html).
The burst signal was seen only by the SGM detector.

The burst light curve shows a single-pulse structure which starts
at T+0.9 sec, peaks at T+12.6 sec,and ends at T+22.0 sec.
The T90 and T50 durations measured by the SGM data are 17.2 +- 3.2 sec and
10.6 +- 3.2 sec (40-1000 keV), respectively.

The ground processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1311086521/

The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at the Waseda University.

GRB 210723A: Swift/UVOT Upper Limits

S. J. LaPorte (PSU) and Sbarrato (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210723A
99 s after the BAT trigger (Sbarrato et al., GCN Circ. 30485
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 ).
No optical afterglow consistent with the XRT position
(Evans GCN Circ. 30486
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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            99          249          147         >20.6
u_FC               312          562          246         >19.2
white               99         1364          369         >20.6
v                  641         1241           78         >18.2
b                  567         1339           78         >19.3
u                  312         1315          304         >19.4
w1                 691         1290           58         >19.0
m2                 666         1266           78         >18.8
w2                 617         1217           78         >19.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.962 in the direction of the burst
(Schlegel et al. 1998).