GRB 210226A

A. P. Beardmore (U Leicester), N. J. Klingler (PSU),
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 04:43:57 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210226A (trigger=1034721).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 124.138, +57.577 which is 
   RA(J2000) = 08h 16m 33s
   Dec(J2000) = +57d 34' 38"
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 30 sec.  The peak count rate
was ~3400 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 04:45:35.3 UT, 98.1 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 124.1144, 57.5839 which
is equivalent to:
   RA(J2000)  = 08h 16m 27.46s
   Dec(J2000) = +57d 35' 02.2"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 51 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 (5.24 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.2
(+1.84/-1.67) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 101 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. The typical 3-sigma upper limit has been about 19.6 mag. 
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
0.048. 

Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk). 
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/)

Martin Jelinek, Jan Strobl, Rene Hudec and Cyril Polasek (ASU CAS Ondrejov,
CZ), report:

The 0.2 m Small Binocular Telescope (BART/SBT) of Ondrejov observatory in
Czech republic reacted robotically to the alert of GRB 210226A (Beardmore
et al, GCNC 29568), obtaining a series of 12 s unfiltered images starting
at 04:54:55.8 UT, i.e. 659 s post trigger.

We do not detect any new source within the XRT errorbox neither in single
images (3-sigma limit r'(AB) > ~14.0) nor in a combined 30 x 12 s frame
(mean exp time 1033 s post trigger, 3-sigma limit r'(AB) > ~15.8) as
calibrated against the Atlas catalog (Tonry et al. ApJ 867, 105, 2018).

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

Using 1421 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 210226A, 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 = 124.11528, +57.58394 which is equivalent
to:

RA (J2000): 08h 16m 27.67s
Dec (J2000): +57d 35' 02.2"

with an uncertainty of 1.5 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.

I observed the field of GRB 210226A (Beardmore et al., GCN Circ.
29568
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 ) with remote telescope (0.61-m f/6.5 Corrected Dall-Kirkham +
CCD) of Burke-Gaffney Observatory (Halifax, Canada). Image (clear:
without filter) with 180 seconds exposure time was obtained on
2021-02-26. Start time of exposure: 08:00:36 UT (3 h. 16 m. 39 s.
after trigger). I did not detect any optical transients (magnitude
limit of about 18.0). Image available here:
http://www.ap.smu.ca/~bgo/sm/id.php?app=0&id=13614

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 210226A ( A. P. Beardmore et al., GCN 29568
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 ) errorbox  42015 sec after notice time and 42682 sec after trigger time at 2021-02-26 16:35:20 UT, with upper limit up to  17.3 mag. Observations started at twilight.  The observations began at zenith distance = 30 deg. The sun  altitude  is -13.1 deg. 

The galactic latitude b = 34 deg., longitude l = 160 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=1556267

We obtain a following upper limits.  

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

   42773 |      MASTER-Tavrida |   C |   180 | 17.3 |        
Filter C is a clear (unfiltred) band. 


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

M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC &
INAF-OAR), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), D.N.
Burrows (PSU), P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester)
and A.P. Beardmore report on behalf of the Swift-XRT team:

We have analysed 6.2 ks of XRT data for GRB 210226A (Beardmore et al.
GCN Circ. 29568
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 ), from 101 s to 39.3 ks after the  BAT trigger. The
data comprise 12 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Goad et al. (GCN Circ. 29571
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 ).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=1.0 (+0.3, -0.4). At T+423 s  the decay
flattens to an alpha of -0.3 (+0.4, -1.1) before breaking again at
T+1011 s to a final decay with index alpha=1.14 (+0.09, -0.08).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.96 (+0.18, -0.17). The
best-fitting absorption column is  1.9 (+/-0.6) x 10^21 cm^-2, in
excess of the Galactic value of 5.2 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 3.6 x 10^-11 (4.7 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.9 (+/-0.6) x 10^21 cm^-2
Galactic foreground: 5.2 x 10^20 cm^-2
Excess significance: 4.0 sigma
Photon index:	     1.96 (+0.18, -0.17)

If the light curve continues to decay with a power-law decay index of
1.14, the count rate at T+24 hours will be 4.5 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.6 x
10^-13 (2.1 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/01034721.

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

WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on

behalf of the KAIT GRB team:


The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at

Lick Observatory, responded to Swift GRB 210226A (Beardmore et al.,

GCN 29568
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 ) starting at 04:56:15 UT, 738s after the burst.

Observations were performed with an automatic sequence in the

clear (roughly R), V, and I filters, and the exposure time was 20s

per image. We do not detect any optical afterglow candidate within

the enhanced XRT position error circle (Goad et al., GCN 29571
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 ),

neither in single image, nor in the co-add images. The typical

limiting magnitude of our single clear image is about 19.0 mag

calibrated to the USNOB1.0 catalog. Our result is consistent with

the optical upper limit reported by other groups (Jelinek et al.,

GCN 29570
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 ; Romanov, GCN 29572
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 ; Lipunov et al., GCN 29574
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 ).

J. Wood (NASA/MSFC) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 04:43:56.56 UT on 26 February 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 210226A (trigger 636007441 / 210226197)
which was also detected by the Swift/BAT and Swift/XRT (A.P. Beardmore et al. 2019, GCN 29568
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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 58.6 degrees.

The GBM light curve consists of a single peak
with a duration (T90) of about 26 s (50-300 keV).
The time-averaged spectrum from T0-6 s to T0+18 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -1.2 +/- 0.1 and
the cutoff energy, parameterized as Epeak, is 170 +/- 29 keV

The event fluence (10-1000 keV) in this time interval is
(2.7 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.2 s in the 10-1000 keV band
is 4.1 +/- 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/"

S. D. Barthelmy (GSFC), J. R. Cummings (CPI),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 210226A (trigger #1034721)
(Beardmore, et al., GCN Circ. 29568
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 ).  The BAT ground-calculated position is
RA, Dec = 124.153, 57.585 deg which is
   RA(J2000)  =  08h 16m 36.7s
   Dec(J2000) = +57d 35' 06.9"
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 47%.

The BAT light curve showed a complex structure with a duration of about ~30 sec.
T90 (15-350 keV) is 20.80 +- 1.68 sec (estimated error including systematics).

The time-averaged spectrum from T-1.92 to T+20.95 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.44 +- 0.15.  The fluence in the 15-150 keV band is 1.2 +- 0.1 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+0.02 sec in the 15-150 keV band
is 2.8 +- 0.3 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/1034721/BA/

N. P. M. Kuin (UCL-MSSL) and A. P. Beardmore (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210226A
102 s after the BAT trigger (Beardmore et al., GCN Circ. 29568
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 ).
No optical afterglow consistent with the XRT position
(Beardmore et al. GCN Circ. 29568
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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           102          251          147         >20.9
u_FC               314          563          246         >20.4
white              102         1192          353         >21.4
v                  643         1236           72         >19.1
b                  569         1167           58         >19.9
u                  314         5121          463         >20.5
w1                 692         4935          236         >20.4
m2                4530         4730          197         >20.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.049 in the direction of the burst
(Schlegel et al. 1998).

H. Kumar(IITB), K. Sharma (IITB), U. Stanzin (IAO), A. Dutta(IIA), V.
Bhalerao(IITB), G. C. Anupama(IIA), S. Barway(IIA) report on behalf of the
GIT team:

We observed GRB 210226A detected by Swift-BAT (A. P. Beardmore et al., GCN
29568
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 ) with 0.7m GROWTH-India Telescope (GIT). We obtained 10 exposures of
300 sec each in the r' filter. We did not detect any new source in our
stacked image within the 1.5 arcsec circle around R.A.= 08h 16m 27.67s,
DEC.=+57d 35' 02.2". The obtained upper limit follows as:

-------------------------------------------------------------------

 JD (mid) | T_mid-T0(hrs) | Exposure (sec) | Filter | Lim_mag (5-sigma) |

-------------------------------------------------------------------

2459272.1074 | 9.84 | 3000 (stacked) | r' | > 20.34 |

-------------------------------------------------------------------

The magnitudes are calibrated against PanSTARRS (Flewelling et al., 2018)
and not corrected for galactic extinction.

The GROWTH India Telescope (GIT) is a 70-cm telescope with a 0.7 degree
field of view, set up by the Indian Institute of Astrophysics and the
Indian Institute of Technology Bombay with support from the Indo-US Science
and Technology Forum (IUSSTF) and the Science and Engineering Research
Board (SERB) of the Department of Science and Technology (DST), Government
of India (https://sites.google.com/view/growthindia/). It is located at the
Indian Astronomical Observatory (Hanle), operated by the Indian Institute
of Astrophysics (IIA).