GRB 210930A

V. D'Elia (SSDC & INAF-OAR), E. Ambrosi (INAF-IASFPA),
S. Laha (GSFC/UMBC/CRESST), A. Y. Lien (U Tampa),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), M. H. Siegel (PSU)
and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels
Swift Observatory Team:

At 02:46:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210930A (trigger=1075565).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 197.435, +48.623 which is 
   RA(J2000) = 13h 09m 44s
   Dec(J2000) = +48d 37' 22"
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 15 sec.  The peak count rate
was ~800 counts/sec (15-350 keV), at ~8 sec after the trigger. 

The XRT began observing the field at 02:49:12.3 UT, 140.1 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 197.40185, 48.62853 which
is equivalent to:
   RA(J2000)  = 13h 09m 36.44s
   Dec(J2000) = +48d 37' 42.7"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 81 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (9.55 x
10^19 cm^-2, Willingale et al. 2013), with an excess column of 6.4
(+3.87/-3.20) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 143 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 0.010. 

Burst Advocate for this burst is V. D'Elia (valerio.delia AT ssdc.asi.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/)

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

Using 1714 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 210930A, 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 = 197.40188, +48.62856 which is equivalent
to:

RA (J2000): 13h 09m 36.45s
Dec (J2000): +48d 37' 42.8"

with an uncertainty of 2.4 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.

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-Tavrida robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the Swift GRB 210930A ( V. D'Elia et al., GCN 30897
Loading...
 
 ) errorbox  48786 sec after notice time and 48953 sec after trigger time at 2021-09-30 16:22:45 UT, with upper limit up to  17.2 mag. Observations started at twilight.  The observations began at zenith distance = 59 deg. The sun  altitude  is -11.0 deg. 

The galactic latitude b = 68 deg., longitude l = 114 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=1737711

We obtain a following upper limits.  

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

   32055 |             MASTER- |   C |     1 | 14.1 |        
   32055 |             MASTER- |   C |     1 | 15.1 |        
   36978 |             MASTER- |   C |   180 | 20.0 |        
   49043 |      MASTER-Tavrida |   C |   180 | 17.2 |        
Filter C is a clear (unfiltred) band. 


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

A. D'Ai (INAF-IASFPA), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU),
D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), P.A. Evans (U. Leicester), A. Melandri (INAF-OAB), T.
Sbarrato (INAF-OAB) and V. D'Elia report on behalf of the Swift-XRT
team:

We have analysed 6.3 ks of XRT data for GRB 210930A (D'Elia et al. GCN
Circ. 30897
Loading...
 
 ), from 143 s to 52.5 ks after the  BAT trigger. The data
comprise 63 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Osborne et al. (GCN Circ. 30900
Loading...
 
 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.71 (+0.09, -0.08).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 4.04 (+0.30, -0.27). The
best-fitting absorption column is  1.46 (+0.18, -0.16) x 10^22 cm^-2,
in excess of the Galactic value of 9.6 x 10^19 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.2 (+0.4, -0.3) and
a best-fitting absorption column of 6.1 (+2.4, -2.0) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.7 x 10^-11 (7.5 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.1 (+2.4, -2.0) x 10^21 cm^-2
Galactic foreground: 9.6 x 10^19 cm^-2
Excess significance: 5.0 sigma
Photon index:	     2.2 (+0.4, -0.3)

If the light curve continues to decay with a power-law decay index of
0.71, the count rate at T+24 hours will be 6.7 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.5 x
10^-13 (5.0 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/01075565.

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

A. Belles (PSU) and V. D'Elia (SSDC & INAF-OAR)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210930A
144 s after the BAT trigger (D'Elia et al., GCN Circ. 30897
Loading...
 
 ).
No optical afterglow consistent with the XRT position
(Osborne et al. GCN Circ. 30900
Loading...
 
 )
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           144          293          147         >19.9
u_FC               302          551          246         >19.6
white              144         1722          411         >20.6
v                  631         1773          136         >18.7
b                  559         1873          134         >19.6
u                  302         1848          363         >19.7
w1                 681         1824          136         >19.5
m2                 655         1450           39         >18.7
w2                 607         1747          117         >20.4

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.010 in the direction of the burst
(Schlegel et al. 1998).

Y.-D. Hu, T.-R. Sun, E. Fernandez-Garcia, A. J. Castro-Tirado, M. D. Caballero-Garcia, R. Sanchez-Ramirez, M. A. Castro Tirado (IAA-CSIC) and I. Vico (CAHA) on behalf of a larger collaboration, report:

Following the detection of GRB 210930A by Swift (V. D'Elia et al. GCNC 30897), we triggered the 2.2m CAHA telescope (+ CAFOS) at the Calar Alto Observatory (Almeria, Spain). Images were gathered after the twilight starting on Sep. 30 18:56:50 UT (i.e. 16.2 hour post trigger) in Sloan-gri bands with 90 s exposure each. On the co-added r-band image (6x90s), no optical transient down to 22.6 mag is detected at the X-ray afterglow candidate position reported by Swift/XRT (V. D'Elia et al. GCNC 30897, J.P. Osborne et al. GCNC 30900). This non-detection is consistent with the report from A. Belles et al. (GCNC 30903) and V. Lipunov et al.(GCNC 30901).

We thank the staff at Calar Alto observatory for their excellent support.

H. A. Krimm (NSF), S. D. Barthelmy (GSFC),
V. D'Elia (SSDC & INAF-OAR), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Parsotan (GSFC/UMBC),
T. Sakamoto (AGU), 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 210930A (trigger #1075565)
(D'Elia et al., GCN Circ. 30897
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 197.415, 48.630 deg which is
   RA(J2000)  =  13h 09m 39.5s
   Dec(J2000) = +48d 37' 47.1"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.

The mask-weighted light curve shows a single-pulse structure that
starts at ~T+6 s, peaks at ~T+9 s, and ends at ~T+20 s.
T90 (15-350 keV) is 11.81 +- 1.94 sec (estimated error including
systematics).

The time-averaged spectrum from T+5.84 to T+19.24 sec is best fit
by a simple power-law model.  The power law index of the time-averaged
spectrum is 1.58 +- 0.19.  The fluence in the 15-150 keV band is
4.0 +- 0.5 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from
T+8.40 sec in the 15-150 keV band is 0.7 +- 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/1075565/BA/