GRB 220826A

R. Caputo (GSFC), P. A. Evans (U Leicester), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 11:55:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 220826A (trigger=1121751).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 206.431, -44.044 which is 
   RA(J2000) = 13h 45m 44s
   Dec(J2000) = -44d 02' 39"
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 20 sec.  The peak count rate
was ~3500 counts/sec (15-350 keV), at ~7 sec after the trigger. 

The XRT began observing the field at 11:56:42.9 UT, 81.2 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 206.41169, -44.03885 which
is equivalent to:
   RA(J2000)  = 13h 45m 38.81s
   Dec(J2000) = -44d 02' 19.9"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 53 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 (9.05 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.8
(+2.60/-2.30) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 90 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	13:45:38.52 = 206.41049
  DEC(J2000) = -44:02:19.0  = -44.03862
with a 90%-confidence error radius of about 0.62 arc sec. This position is 3.3
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.89 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.110. 

Burst Advocate for this burst is R. Caputo (regina.caputo AT nasa.gov). 
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/)

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

Using 744 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 220826A, 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 = 206.41081, -44.03917 which is equivalent
to:

RA (J2000): 13h 45m 38.59s
Dec (J2000): -44d 02' 21.0"

with an uncertainty of 2.2 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, 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-SAAO robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 220826A ( R. Caputo et al., GCN 32484
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 ) errorbox  19090 sec after notice time and 19104 sec after trigger time at 2022-08-26 17:13:46 UT, with upper limit up to  17.8 mag. Observations started at twilight.  The observations began at zenith distance = 39 deg. The sun  altitude  is -12.5 deg. 

The galactic latitude b = 17 deg., longitude l = 314 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2068190

We obtain a following upper limits.  

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

   19194 |         MASTER-SAAO |   C |   180 | 17.8 |        
Filter C is a clear (unfiltred) band. 


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

I observed the field of GRB 220826A (Caputo et al., GCN Circ. 32484
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 )
using remote telescope T59 (0.51-m f/6.8 reflector + CCD) of
iTelescope.Net in Siding Spring Observatory (Australia) on 2022-08-26.
Three images were obtained from 12:16:07 UTC (1246 sec. after the
trigger) with a Luminance filter (300 seconds exposures, BINx1), but
in the third of them, the object is already below the minimum target
elevation for the telescope.

I clearly detected (SNR ~ 8 in the stacked image) the optical
afterglow with UVOT position and measured its magnitude = 19.3 +/- 0.2
in the stacked image (midtime = 12:23:09 UTC means 1668 sec. after the
trigger), airmass was from 4.041 to 4.463. I compared with Sloan r'
magnitudes of nearby stars from APASS DR9 catalogue (Henden et al.,
2016).

Magnitude was not corrected for Galactic extinction.

Stacked image available here:
https://www.flickr.com/photos/filipp-romanov/52313060415

N. P. M. Kuin (UCL-MSSL) and R. Caputo (GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 220826A
91 s after the BAT trigger (Caputo et al., GCN Circ. 32484
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 ).
A source consistent with the XRT position (Beardmore et al. GCN Circ. 32485
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  13:45:38.51 = 206.41047 (deg.)
    Dec (J2000) = -44:02:19.2  = -44.03866 (deg.)
with an estimated uncertainty of 0.45 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               91          240          147         18.12 +/- 0.05
v                  632          827           39        >18.4
b                  559          753           39        >18.6
u                  303          553          246         18.69 +/- 0.13
w1                 682          702           19        >17.7
m2                 831          851           19        >17.8
w2                 608          802           39        >19.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.110 in the direction of the burst
(Schlegel et al. 1998).

S. de Wet (UCT) and D.B. Malesani (Radboud and DAWN/NBI) report:

Following the detection of GRB 220826A by Swift and its X-ray and optical
counterparts (Caputo et al., GCN 32484
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 ; Kuin et al., GCN 32488
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 ; Romanov
F.P., GCN 32487
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 ), the 1m Lesedi optical telescope located at Sutherland,
South Africa, obtained 600 s exposures in each of the g,r,i and z bands
with the Mookodi low-resolution spectrograph and imager beginning at
17:27:09 UT, approximately 0.23 days post-trigger.

We detect the optical afterglow to GRB 220826A in each image at the UVOT
position with the following AB magnitude, calibrated to Skymapper flux
measurements of a nearby star in the field:

r = 21.48 +/- 0.16

Lesedi is built and operated by the South African Astronomical Observatory.

A. Tohuvavohu (U. Toronto), 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) , D.N. Burrows (PSU),
J. D. Gropp (PSU) and R. Caputo report on behalf of the Swift-XRT team:

We have analysed 6.5 ks of XRT data for GRB 220826A (Caputo et al. GCN
Circ. 32484
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 ), from 70 s to 33.8 ks after the  BAT trigger. The data
comprise 37 s in Windowed Timing (WT) mode (the first 9 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 Beardmore
et al. (GCN Circ. 32485
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 ).

The late-time light curve (from T0+5.0 ks) can be modelled with a
power-law decay with a decay index of alpha=1.25 (+/-0.18).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.80 (+0.16, -0.15). The
best-fitting absorption column is  1.6 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 9.1 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 3.9 x 10^-11 (4.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.6 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 9.1 x 10^20 cm^-2
Excess significance: 2.4 sigma
Photon index:	     1.80 (+0.16, -0.15)

If the light curve continues to decay with a power-law decay index of
1.25, the count rate at T+24 hours will be 5.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.0 x
10^-13 (2.4 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/01121751.

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

P. Veres and C. Meegan (both UAH)
report on behalf of the Fermi GBM Team:

"At 11:55:22.98 UT on 26 August 2022, the Fermi Gamma-Ray Burst Monitor
(GBM)
triggered and located GRB 220826A (trigger 220826497 / 683207727)
which was also detected by the Swift/BAT (Caputo et al., GCN 32484
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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 54
degrees.

The GBM light curve shows  two pulses
with a duration (T90) of about 16.6 s (50-300 keV).
The time-averaged spectrum from T0-0.5 s to T0+10.8 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.66 +/- 0.20 and
the cutoff energy, parameterized as Epeak, is 113 +/- 14 keV

The event fluence (10-1000 keV) in this time interval is
(1.50 +/- 0.14)E-6 erg/cm^2. The 1-sec peak photon flux measured
starting from T0 + 5.2 s in the 10-1000 keV band
is 4.3 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 66 +/- 13 keV, alpha = 0.28 +/- 0.58 and beta = -2.14 +/- 0.18.

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/"

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),
R. Caputo (GSFC), 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 220826A (trigger #1121751)
(Caputo et al., GCN Circ. 32484
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 ).  The BAT ground-calculated position is
RA, Dec = 206.421, -44.036 deg which is
   RA(J2000)  =  13h 45m 41.0s
   Dec(J2000) = -44d 02' 10.1"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 92%.

The mask-weighted light curve shows a multi-peaked structure that
starts at ~T0 and ends at ~T+13 s. There are roughly three main
peaks at ~T+1 s, ~T+7 s, and ~T+11 s. respectively.
T90 (15-350 keV) is 11.14 +- 1.02 sec (estimated error including
systematics).

The time-averaged spectrum from T-0.20 to T+13.01 sec is best fit
by a simple power-law model.  The power law index of the time-averaged
spectrum is 1.44 +- 0.10.  The fluence in the 15-150 keV band
is 1.2 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured
from T+6.58 sec in the 15-150 keV band is 2.6 +- 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/1121751/BA/

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 220826A (Swift detection: Caputo et al., GCN 32484
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 ;
Fermi GBM observation: Veres & Meegan, GCN 32495
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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 >10 sigma count rate increase in the interval
from T0-0.525 s to T0+37.747 s where T0 = T0(BAT) = 11:55:21.742 UT.

The KW light curve of this burst is available
at http://www.ioffe.ru/LEA/GRBs/GRB220826A/

Modeling a time-integrated spectrum of the burst
by a power law with exponential cutoff (CPL) model
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -0.48 (-0.22, + 0.25) and Ep = 113(-4,+4) keV.
In the 10 keV -10 MeV band, standard for the KW analysis,
the burst fluence is (2.53 �� 0.29)x10^-6 erg/cm^2
and the 2.944 s peak energy flux is (2.86 �� 0.18)x10^-7 erg/cm^2/s.

All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.