GRB 220813A

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

The long GRB 220813A (Swift detection: Bernardini et al., GCN 32465
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 )
was detected by Konus-Wind (KW) in the waiting mode.

A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band
reveals a >6 sigma count rate increase in the interval
from T0-8.841 s to T0+5.879 s where T0 = T0(BAT) = 19:23:03.577 UT.

The KW light curve of this burst is available
at http://www.ioffe.ru/LEA/GRBs/GRB220813A/

Modeling a time-integrated spectrum of the burst (from T0-8.841 s to T0+8.823 s)
by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -0.81 (-0.12, + 0.12) and Ep = 242(-17,+23) keV.
In the 10 keV -10 MeV band, standard for the KW analysis,
the burst fluence is (1.41 �� 0.14)x10^-6 erg/cm^2
and the 2.944 s peak energy flux is (1.30 �� 0.13)x10^-7 erg/cm^2/s.

Assuming the likely host galaxy redshift z=0.82 (Fausey et al., GCN 32471
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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 ~2.7x10^51 erg,
the isotropic peak luminosity L_iso to ~8.0x10^50 erg/s,
and the rest-frame peak energy of the spectrum Ep,z to ~440 keV.
With the obtained estimates, GRB 220813A is a hard-spectrum / low-luminosity outlier
in both 'Amati' and 'Yonetoku' relations 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/GRB220813A/GRB220813A_rest_frame.pdf

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.

H. Fausey (GWU), Z.P. Zhu (NAOC, HUST), P. D'Avanzo (INAF-OAB), D. B. 
Malesani (Radboud Univ. and DAWN/NBI), L. Izzo (DARK/NBI), D. A. Kann 
(IAA-CSIC), D. Xu (NAOC) report on behalf of the Stargate collaboration:

We observed the field of GRB 220813A (Bernardini et al., GCN 32465
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 ) 
using the ESO VLT/UT3 equipped with the X-shooter acquisition camera. 
Observations started at 08:06:45 UT on 2022-08-14 (i.e., ~12.73 hr after 
the BAT trigger) and consisted of 3x60 s, 4x60 s, 3x60 s exposures in 
the Sloan g-/r-/z- bands, respectively.

The previously reported optical afterglow (Bernardini et al., GCN 32465
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 ; 
Kuin & Bernardini, GCN 32470
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 ) is marginally detected in the stacked 
r-band image with r ~  21.8 mag (AB), and is not detected in g-band and 
z-band with upper limits of g > 22.1 and z > 19.9, respectively (both AB).

In addition, we note that from Legacy Survey there exists a source at 
coordinates R.A. (J2000) = 05:26:07.5 and Dec.(J2000) = -33:00:59.2, 
being consistent with the Swift/UVOT position, which has photometric 
magnitudes of g ~ 24.99, r ~ 24.28 and z ~ 23.76 as well as photometric 
redshift of z ~ 0.82, which is the likely host galaxy of GRB 220813A.

We thank the great support of the ESO VLT staff, in particular Steffen 
Mieske and Michael Abdul-Masih.

N. P. M. Kuin (UCL-MSSL) and M. G. Bernardini (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 220813A
100 s after the BAT trigger (Bernardini et al., GCN Circ. 32465
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 ).
A source consistent with the XRT position (Osborne et al.,
GCN Circ. 32466
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 ) is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  05:26:07.60 =  81.53166 (deg.)
    Dec (J2000) = -33:00:59.0  = -33.01638 (deg.)
with an estimated uncertainty of 0.52 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              100          250          147         19.67 +/- 0.11
v                  589         1581          117        >18.3
b                  515         1506           97        >19.6
u                  258         1652          360        >20.6
w1                 638         1630          117        >19.6
m2                 613         1605          117        >20.1
w2                 564         1556          117        >20.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.022 in the direction of the burst
(Schlegel et al. 1998).

J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), P.A. Evans (U.
Leicester), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), T.
Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU) and
M.G. Bernardini report on behalf of the Swift-XRT team:

We have analysed 8.4 ks of XRT data for GRB 220813A (Bernardini et al.
GCN Circ. 32465
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 ), from 80 s to 30.0 ks after the  BAT trigger. The data
comprise 149 s in Windowed Timing (WT) mode (the first 8 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Osborne et
al. (GCN Circ. 32466
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 ).

The late-time light curve (from T0+4.9 ks) can be modelled with a
power-law decay with a decay index of alpha=0.98 (+0.15, -0.14).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.53 (+/-0.13). The
best-fitting absorption column is  1.37 (+0.29, -0.27) x 10^21 cm^-2,
in excess of the Galactic value of 2.3 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.00 (+/-0.13) and a
best-fitting absorption column of 4.9 (+2.9, -2.6) x 10^20 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.2 x 10^-11 (3.6 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.9 (+2.9, -2.6) x 10^20 cm^-2
Galactic foreground: 2.3 x 10^20 cm^-2
Excess significance: 1.7 sigma
Photon index:	     2.00 (+/-0.13)

If the light curve continues to decay with a power-law decay index of
0.98, the count rate at T+24 hours will be 9.7 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.1 x
10^-13 (3.5 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/01120270.

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

V. Lipunov, V.Kornilov, E.Gorbovskoy, K.Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, D. Vlasenko, 
G.Antipov, D.Zimnukhov, V.Senik, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov,  D.Cheryasov, Ya.Kechin
(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),

L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez 
(INAOE, Guillermo Haro Astrophysics Observatory),

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

A. Gabovich, V.Yurkov 
(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 220813A ( M. G. Bernardini et al., GCN 32465
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 ) errorbox  40368 sec after notice time and 40414 sec after trigger time at 2022-08-14 06:36:37 UT, with upper limit up to  17.0 mag. The observations began at zenith distance = 72 deg. The sun  altitude  is -58.5 deg. 

The galactic latitude b = -31 deg., longitude l = 237 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2055501

We obtain a following upper limits.  

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

   40504 |         MASTER-OAFA |   C |   180 | 17.0 |        
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 4997 s of XRT Photon Counting mode data and 11 UVOT
images for GRB 220813A, 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 = 81.53144, -33.01688 which is equivalent
to:

RA (J2000): 05h 26m 7.55s
Dec (J2000): -33d 01' 00.8"

with an uncertainty of 2.0 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.

M. G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB),
M. Ferro (INAF-OAB), J.D. Gropp (PSU), A. Melandri (INAF-OAB),
K. L. Page (U Leicester), D. M. Palmer (LANL),
T. M. Parsotan (GSFC/UMBC/CRESSTII), T. Sbarrato (INAF-OAB) and
M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 19:23:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 220813A (trigger=1120270).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 81.501, -32.985 which is 
   RA(J2000) = 05h 26m 00s
   Dec(J2000) = -32d 59' 06"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peak
structure with a duration of about 30 sec.  The peak count rate
was ~1200 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 19:24:34.2 UT, 90.6 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 81.53235,
-33.01546 which is equivalent to:
   RA(J2000)  = 05h 26m 07.76s
   Dec(J2000) = -33d 00' 55.7"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 144 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 (2.32 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.7
(+3.14/-2.65) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 100 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	05:26:07.57 =  81.53155
  DEC(J2000) = -33:00:58.9  = -33.01636
with a 90%-confidence error radius of about 0.67 arc sec. This position is 4.7
arc sec. from the center of the XRT error circle. The estimated magnitude is
19.61 with a 1-sigma error of about  0.17. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.022. 

Burst Advocate for this burst is M. G. Bernardini (grazia.bernardini AT brera.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/)