GRB 210308A

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

The long-duration GRB 210308A
(Swift-BAT detection: D'Elia et al., GCN Circ. 29619
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 ,
Palmer et al., GCN Circ. 29633
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 ;
Fermi-GBM detection: Lesage et al., GCN Circ. 29626
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 )
triggered Konus-Wind at T0=23879.936 s UT (06:37:59.936).

The burst light curve shows a multi-peaked structure
which starts at ~T0-3.8 s and has a total duration of ~8.9 s.
The emission is seen up to ~1 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB210308_T23879/

As observed by Konus-Wind, the burst
had a fluence of 5.00(-0.48,+0.53)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0+1.264 s,
of 3.36(-0.85,+0.87)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 1 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.73(-0.32,+0.38)
and Ep = 150(-19,+25) keV (chi2 = 49/55 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.7
(chi2 = 49/54 dof).

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.

S. Belkin (IKI), N. Pankov (HSE), A. Pozanenko (IKI), E. Klunko (ISTP), 
R. Ya. Inasaridze (AbAO), V. R. Ayvazian (AbAO),  G. V. Kapanadze 
(AbAO), D. G. Datashvili (AbAO) report on behalf of IKI-GRB-FuN:

We observed the field of  GRB 210308A (D'Elia et al., GCN 29619
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 ) with 
AZT-33IK telescope of Sayan observatory (Mondy) starting on  2021-03-08 
(UT) 13:00:45 and AS-32 telescope of Abastumani observatory (AbAO) 
starting on  2021-03-08 (UT) 16:32:07 (both in R-filter). The optical 
afterglow (D'Elia et al., GCN 29619
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 ; Gropp et al., GCN 29630
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 ; see also 
Ogata et al., GCN 29621
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 ; Zhu et al., GCN 29623
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 ; Lipunov et al., GCN 
29627
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 ) is detected in stacked image of AZT-33IK and not detected at AS-32.

Date       UT start   t-T0    Filter  Exp.   OT    Err.  UL(3sigma)
                        (mid, days)     (s)

2021-03-08 13:00:45   0.27626  R      15*120 22.77  0.27 22.8 AZT-33IK
2021-03-08 16:32:07   0.42131  R      25*60  n/d    n/d  21.8 AS-32

The photometry is based on nearby USNO-B1.0 stars
USNO-B1.0_id R2
1274-0090800 15.34
1274-0090824 17.35

D. M. Palmer (LANL), S. D. Barthelmy (GSFC), J. R. Cummings (CPI),
V. D'Elia (SSDC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
  
Using the data set from T-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 210308A (trigger #1036227)
(D'Elia, et al., GCN Circ. 29619
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 ).  The BAT ground-calculated position is
RA, Dec = 67.083, 37.429 deg which is
    RA(J2000)  =  04h 28m 19.9s
    Dec(J2000) = +37d 25' 42.9"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 32%.
  
The mask-weighted light curve shows a double-peaked structure from T-0.5 sec
to T+9 sec.  The first pulse peaks at T+0.2 sec, and the second pulse peaks
at T+3 sec.  T90 (15-350 keV) is 5.3 +- 0.6 sec (estimated error including systematics).
  
The time-averaged spectrum from T-0.04 to T+7.36 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.76 +- 0.28,
and Epeak of 113.6 +- 31.0 keV (chi squared 52.89 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 3.2 +- 0.1 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+2.12 sec in the 15-150 keV band is
13.6 +- 0.7 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.38 +- 0.06 (chi squared 69.63 for 57 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/1036227/BA/

GRB 210308A: Swift/UVOT Detection

J. D. Gropp (PSU) and V. D'Elia (SSDC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210308A
95 s after the BAT trigger (D'Elia et al., GCN Circ. 29619
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 ).
A source consistent with the XRT position
(D'Elia et al., GCN Circ. 29619
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  04:28:17.73 =  67.07389 (deg.)
    Dec (J2000) = +37:26:02.1  =  37.43391 (deg.)
with an estimated uncertainty of 0.46 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

b                       765            1189            38        >18.62
uvm2                864            1115            38        >17.52
u                       338            1164          284        >19.50
v                       667            1090            58        >17.84
uvw1               1120            1140            19        >17.25
uvw2                 815            1231            50        >17.91
white                 126             275           292
18.54+-0.07
white                 618            1213          205        >20.20

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 1.296 in the direction of the burst
(Schlegel et al. 1998).

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-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 210308A ( V. D'Elia et al., GCN 29619
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 ) errorbox  40899 sec after notice time and 40918 sec after trigger time at 2021-03-08 17:59:54 UT, with upper limit up to  13.9 mag. Observations started at twilight.  The observations began at zenith distance = 74 deg. The sun  altitude  is -12.2 deg. 

MASTER-IAC robotic telescope  located in Spain (IAC Teide Observatory) was pointed to the Swift GRB 210308A errorbox  55958 sec after notice time and 55976 sec after trigger time at 2021-03-08 22:10:53 UT, with upper limit up to  18.5 mag. The observations began at zenith distance = 48 deg. The sun  altitude  is -40.8 deg. 

The galactic latitude b = -7 deg., longitude l = 164 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=1563625

We obtain a following upper limits.  

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

   21950 |             MASTER- |   C |    60 | 18.0 |        
   22210 |             MASTER- |   C |    60 | 15.8 |        
   22945 |             MASTER- |   C |    60 | 12.6 |        
   41008 |         MASTER-SAAO |   C |   180 | 13.9 |        
   56067 |          MASTER-IAC |   C |   180 | 18.5 |        
Filter C is a clear (unfiltred) band. 


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

S. Lesage (UAH), A. von Kienlin (MPE), C. Meegan (UAH), and C. Malacaria
(NASA-MSFC/USRA)
report on behalf of the Fermi GBM Team:

"At 06:37:56.91 UT on 08 March 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 210308A (trigger 636878281 / 210308276)
which was also detected by the Swift/BAT and Swift/XRT
(D'Elia et al. 2021, GCN 29619
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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 26
degrees.

The GBM light curve shows a single-peaked structure
with a duration (T90) of about 5.4 s (50-300 keV).
The time-averaged spectrum from T0-1.7 s to T0+7.5 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.82 +/- 0.04 and
the cutoff energy, parameterized as Epeak, is 142 +/- 5 keV.
A Band function fits the spectrum equally well with
Epeak = 135 +/- 7 keV, alpha = -0.78 +/- 0.05 and beta = -3.0 +/- 0.4.

The event fluence (10-1000 keV) in this time interval is
(6.3 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+2.1 s in the 10-1000 keV band
is 20.0 +/- 0.4 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/"

Z.P. Zhu (NAOC, HUST), S.Y. Fu, X. Liu, D. Xu (NAOC), X. Gao (Urumqi 
No.1 Senior High School), J.Z. Liu (XAO) report:

We observed the field of GRB 210308A (D'Elia et al., GCN 29619
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 ) using 
the NEXT-0.6m optical telescope located at Nanshan, Xinjiang, China. 
Observations started at 14:16:29 UT on 2021-03-08, i.e., 7.67 hr after 
the BAT trigger. We obtained 15x200 s frames in the Sloan r- and i- 
bands, respectively.

The optical afterglow (D'Elia et al., GCN 29619
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 ) of the burst is not 
detected in our stacked images, down to limiting magnitudes of r ~ 21.7 
and i ~ 21.3, calibrated with nearby PS1 stars.

S. Ogata, R. Hosokawa, K. L. Murata, R. Adachi, M. Niwano, F. Ogawa,
N. Nakamura, N. Ito, H. Takamatsu, H. Hara, Y. Yatsu, and N. Kawai
(TokyoTech) report on behalf of the MITSuME collaboration:

We observed the field of GRB 210308A (D'Elia et al.,GCN Circular
#29619) with the optical three color (g', Rc, and Ic) CCD cameras
attached to the MITSuME 50 cm telescope of Okayama Astrophysical
Observatory, Okayama, Japan. The observation with a series of 60 sec
exposures started at 2021-03-08 11:03:59 UT.(4.5 hours after Swift BAT
trigger) We stacked the images with good conditions. We did not detect
the optical afterglow reported previously (D'Elia et al.,GCN Circular
#29619) in all three bands.
We obtained the 5-sigma limits of the stacked images as follows.

T0+[hour] MID-UT T-EXP[sec] 5-sigma limits
------------------------------------------------------------------------------------------------
4.5 11:51:53 4440 g'>17.6, Rc>17.8, Ic>17.8
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time

We used the PS1 catalog for flux calibration.
The magnitudes are expressed in the AB system.
The images were processed in real-time through the MITSuME GPU
reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages
4-24; https://github.com/MNiwano/Eclaire).

V. D'Elia (SSDC), E. Ambrosi (INAF-IASFPA), S. D. Barthelmy (GSFC),
A. D'Ai (INAF-IASFPA), N. J. Klingler (PSU), A. Y. Lien (GSFC/UMBC),
K. L. Page (U Leicester), T. Sakamoto (AGU), M. H. Siegel (PSU) and
A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 06:37:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210308A (trigger=1036227).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 67.088, +37.411 which is 
   RA(J2000)  =  04h 28m 21s
   Dec(J2000) = +37d 24' 39"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a few overlapping peaks
with a duration of about 15 sec.  The peak count rate
was ~6000 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 06:39:21.81 UT, 85.0 seconds after
the BAT trigger. Using promptly downlinked data we find an
uncatalogued X-ray source with a position: RA, Dec 67.076417, 
37.435310 which is equivalent to:
   RA(J2000)  = 04h 28m 18.34s
   Dec(J2000) = +37d 26' 07.11"
with an uncertainty of 4.3 arcseconds (radius, 90% containment). This
location is 94 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 http://www.swift.ac.uk/sper. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 94 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	04:28:17.73 =  67.07388
  DEC(J2000) = +37:26:02.0  =  37.43388
with a 90%-confidence error radius of about 0.63 arc sec. This position is 8.5
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.57 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 1.295. 

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/)