GRB 200303A

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

The long-duration GRB200303A
(Swift detection of a burst: Cenko et al., GCN 27297
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 ;
Palmer et al., GCN 27311
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 ;
CALET Gamma-Ray Burst Monitor detection:
Asaoka et al., GCN 27301
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 ;
Fermi GBM observation: Malacaria & Meegan, GCN 27314
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 )
triggered Konus-Wind at T0=9268.336 s UT (02:34:28.336).

The burst light curve shows a multi-peaked structure
which starts at ~T0-4.0 s and has a total duration of~67.1 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst
had a fluence of 3.88(-1.20,+0.80)x10^-5 erg/cm2,
and a 64-ms peak energy flux, measured from T0+32.800 s,
of 2.38(-0.96,+1.15)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+65.792 s)
is best fit in the 20 keV - 3 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.25(-0.21,+0.28),
the high energy photon index beta = -2.17(-7.83,+0.18),
the peak energy Ep = 154(-44,+82) keV,
chi2 = 72/66 dof.

The spectrum near the peak count rate
(measured from T0+24.832 to T0+41.216 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.39(-0.14,+0.20),
the high energy photon index beta = -2.54(-7.46,+0.45),
the peak energy Ep = 183(-53,+54) keV,
chi2 = 80/86 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB200303_T09268/

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

C. Malacaria (NASA-MSFC/USRA) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:


"At 02:34:23.85 UT on 03 March 2020,
the Fermi Gamma-Ray Burst Monitor (GBM) triggered
and located GRB 200303A (trigger 604895668 / 200303107),
which was also detected by the Swift/BAT and Swift/XRT
(Cenko et al. 2020, GCN 27297
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 , Goad et al. 2020, GCN 27300
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 ).
The Fermi GBM Final Real-time Localization (GCN 27294
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 )
is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time
is 106 degrees.

The GBM light curve shows a complex structure
with a duration (T90) of about 82 s (50-300 keV).
The time-averaged spectrum from T0-2.8 s to T0+95.7 s is
best fit by a Band function with Epeak = 151 +/- 18 keV,
alpha = -1.26 +/- 0.05, and beta = -2.14 +/- 0.10.

The event fluence (10-1000 keV) in this time interval is
(3.23 +/- 0.08)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+35.1 s in the 10-1000 keV band
is 9.2 +/- 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/"

P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi  (INAF-IASFPA) , M.
Capalbi (INAF-IASFPA), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU),
D.N. Burrows (PSU) and S.B. Cenko report on behalf of the Swift-XRT
team:

We have analysed 6.6 ks of XRT data for GRB 200303A (Cenko et al. GCN
Circ. 27297
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 ), from 77 s to 41.6 ks after the  BAT trigger. The data
comprise 582 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 Goad et al.
(GCN Circ. 27300
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 ).

The late-time light curve (from T0+4.8 ks) can be modelled with a
power-law decay with a decay index of alpha=1.27 (+0.09, -0.10).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.41 (+/-0.05). The
best-fitting absorption column is  1.10 (+0.05, -0.04) x 10^22 cm^-2,
in excess of the Galactic value of 1.6 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.38 (+0.15, -0.14)
and a best-fitting absorption column of 7.5 (+1.0, -0.9) 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 (8.8 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.5 (+1.0, -0.9) x 10^21 cm^-2
Galactic foreground: 1.6 x 10^20 cm^-2
Excess significance: 13.4 sigma
Photon index:	     2.38 (+0.15, -0.14)

If the light curve continues to decay with a power-law decay index of
1.27, the count rate at T+24 hours will be 0.043 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.6 x
10^-12 (3.8 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00959431.

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

D. M. Palmer (LANL), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC), 
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-240 to T+605 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 200303A (trigger #959431)
(Cenko, et al., GCN Circ. 27297
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 ).  The BAT ground-calculated position is
RA, Dec = 212.695, 51.358 deg which is 
  RA(J2000)  =  14h 10m 46.9s 
  Dec(J2000) = +51d 21' 29.3" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 59%.

The burst entered the BAT field of view around T-100 sec during a spacecraft slew.
The mask-weighted light curve shows a single episode with multiple pulses, 
starting at T-45 sec, peaking at the trigger time and returning to near background
by T+70 sec.  There is extended low-level emission out to nearly T+200 sec.
T90 (15-350 keV) is 94.2 +- 6.4 sec (estimated error including systematics).

The time-averaged spectrum from T-36.55 to T+193.26 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.39 +- 0.17, 
and Epeak of 131.4 +- 75.1 keV (chi squared 46.32 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.3 +- 0.0 x 10^-5 erg/cm2
and the 1-sec peak flux measured from T+0.34 sec in the 15-150 keV band is
5.0 +- 0.3 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.65 +- 0.04 (chi squared 53.75 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/959431/BA/

D. Xu (NAOC), L. Izzo (DARK/NBI),  D. B. Malesani (DTU Space), A.A. Djupvik (NOT), T. Pursimo (NOT) report on behalf of a larger collaboration:
We observed GRB 200303A (Fermi GBM team, GCN 27294
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 , Cenko et al., GCN 27297
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 , Asaoka et al., GCN 27301
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 ) with the Nordic Optical Telescope (NOT) equipped with StanCAM, covering 100% of the afterglow region as provided by the Swift-XRT (Cenko et al. 27297). We obtained 3x300 s exposures with the Bessel R filter starting at 03:36:18 UT on March 3 (median time 1.161 hr after the GRB trigger) and 5x200 s exposures with the z-SDSS filter starting at 03:53:59 UT (median time 1.483 hr). We do not detect any optical afterglow candidate down to a limit of R > 23.0 mag (AB) and z > 21.5 mag (AB), calibrated against PS1 catalog. 
With the above upper limits, the optical to X-ray spectral index is then beta_OX < -0.09 (Fnu propto nu^-beta) computed assuming the R-Bessel value and X-rays data from Swift-XRT. This suggests a ������dark'' nature for GRB 200303A

A. A. Breeveld (UCL-MSSL) and S. B. Cenko (GSFC) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of
GRB 200303A 96 s after the BAT trigger (Cenko et al., GCN Circ. 27297
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 ).
No optical afterglow consistent with the XRT position
(Goad et al. GCN Circ. 27300
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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            96          246          147         >20.7
u_FC               308          558          246         >20.4
white               96         5034          550         >21.5
v                 1219         1238           19         >18.4
b                 1144         1163           19         >19.4
u                  308          558          246         >20.4

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).

Martin Jelinek, Jan Strobl (ASU CAS Ondrejov, CZ), Martin Masek, Petr
Janecek, Sergey Karpov, Jakub Jurysek, Jan Ebr, Ronan Cunniffe, Petr
Travnicek and Michael Prouza (Institute of Physics, Prague, CZ)

report:

The 25cm robotic telescope FRAM-ORM at La Palma (Spain) reacted robotically
to the GBM/Swift/CALET alert of GRB200303A (Cenko et al, GCNC 27297, Goad
et al. GCNC 27300, Asaoka et al. GCNC 27301 and Fermi GBM team GCNC 27294),
obtaining a series of 20s unfiltered images starting at 02:35:38.75UT, i.e.
41.3s post trigger.

We do not detect any new source in comparison to USNO-B2.0 catalog neither
in single images (3-sigma limit R>~17.9) nor in a combined 20x20s frame
(mean exp time 289s post trigger, 3-sigma limit R>~19.5) similarly to de
Ugarte et al. (GCNC 27303) and Mong et al. (GCNC 27304)

Y.-L. Mong (1); K. Ackley (1); D. K. Galloway (1); D. Steeghs (2); V. 
Dhillon (3); P. O'Brien (4); G. Ramsay (5); D. Pollacco (2); E. Thrane 
(1); S. Poshyachinda (6); R. Kotak (7); L. Nuttall (8); E. Pall\'e (9); 
K. Ulaczyk (2); J. Lyman (2); R. Cutter (2); A. Levan (2); T. Marsh (2); 
R. West (2); E. Stanway (2); B. Gompertz (2); K. Wiersema (2); T. 
Killestein (2); A. Casey (1); M. Brown (1); B. Muller (1); M. Dyer (3); 
J. Mullaney (3); E. Daw (3); S. Littlefair (3); J. Maund (3); L. 
Makrygianni (3); U. Burhanudin (3); R. Starling (4); R. Eyles (4); S. 
Tooke (4); S. Aukkaravittayapun (6); U. Sawangwit (6); S. Awiphan (6); 
D. Mkrtichian (6); P. Irawati (6); S. Mattila (7); T. Heikkil\"a (7); E. 
Rol (1)

((1) Monash University, (2) Warwick University, (3) University of 
Sheffield, (4) University of Leicester, (5) Armagh Observatory & 
Planetarium, (6) National Astronomical Research Institute of Thailand, 
(7) University of Turku, (8) University of Portsmouth, (9) Instituto de 
Astrofisica de Canarias)

report on behalf of the GOTO collaboration:

We carried out observations with the Gravitational-wave Optical 
Transient Observer (GOTO), in response to GRB 2000303A (Cenko et al. 
2020; GCN #27297
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 ; Fermi GBM; GCN #27294
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 ).

We made a series of 3 x 60 s exposures using our wide L-band filter 
(400-700 nm) covering the Swift XRT position (Cenko et al. 2020; GCN 
#27297
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 ), starting at 6.4 minutes after the Swift BAT trigger with 
midtime 02:52:17 UT on 03 March 2020.

Using a difference imaging analysis with recent survey observations of 
the same pointings as reference, we identify no viable afterglow 
candidate. Our mean 5-sigma detection limit was g=19.6 mag based on PS1 
catalogue calibrators.

GOTO is operated at the La Palma observing facilities of the University 
of Warwick on behalf of a consortium including the University of 
Warwick, Monash University, Armagh Observatory, the University of 
Leicester, the University of Sheffield, the National Astronomical 
Research Institute of Thailand (NARIT) and the Instituto de Astrofisica 
de Canarias (IAC) (https://goto-observatory.org)

A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D. A. Kann, C. Thoene,
J. F. Agui Fernandez, M. Blazek (all HETH/IAA-CSIC), R. Pedro Hedrosa (CAHA) 
report:

We observed the field of GRB 200303A (Cenko et al. GCN 27297
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 ) with CAFOS, 
on the 2.2 m telescope, at Calar Alto observatory (Almeria, Spain). Observations 
consisted of 5x360s in R-band with mean epoch 03:48:02 UT (1.249 hr after the 
burst).

Our initial analysis does not reveal any object within the refined error box (Goad 
et al. GCN 27300
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 ) down to a 3-sigma limit of R(AB) > 24.0 mag, with photometry 
performed against SDSS field stars.

Y. Asaoka (Waseda U),
A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU),
Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN),
S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U),
N. Cannady (GSFC/UMBC), M. L. Cherry (LSU),
S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena),
and the CALET collaboration:

The long GRB 200303A (Fermi GBM Final Real-time Localization: Fermi GBM
Team, GCN Circ. 27294
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 ; Swift detection: Cenko et al., GCN Circ. 27297
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 ;
https://gcn.gsfc.nasa.gov/other/200303A.gcn3)
triggered the CALET Gamma-ray Burst Monitor (CGBM) at 02:34:20.728 UTC
on 3 March 2020. The burst signal was seen by all CGBM detectors.

The burst light curve shows a multi-peaked structure which starts at
T+2.3 sec, peaks at T+39.4 sec, and ends at T+88.8 sec.
The T90 and T50 durations measured by the SGM data are 68.9 +- 12.8 sec
and 28.9 +- 3.3 sec (40-1000 keV), respectively.

The ground processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1267237773/

The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at the Waseda University.

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

Using 822 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 200303A, 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 = 212.71895, +51.35930 which is equivalent
to:

RA (J2000): 14h 10m 52.55s
Dec (J2000): +51d 21' 33.5"

with an uncertainty of 1.7 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.

S. B. Cenko (GSFC), S. D. Barthelmy (GSFC), C. Gronwall (PSU),
J.D. Gropp (PSU), N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), M. J. Moss (GWU),
K. L. Page (U Leicester), D. M. Palmer (LANL) and
A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 02:34:57 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200303A (trigger=959431).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 212.698, +51.360, which is 
   RA(J2000)  =  14h 10m 47s
   Dec(J2000) = +51d 21' 35"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a multi-peak
structure with a duration of about 60 sec.  The peak count rate
was ~3500 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 02:36:25.1 UT, 87.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 212.7173, 51.3583 which is equivalent to:
   RA(J2000)  = 14h 10m 52.15s
   Dec(J2000) = +51d 21' 29.9"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 43 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 8.77e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 96 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
0.02. 

This source lies within the current (Sector 22) field-of-view of TESS camera 3. 

Burst Advocate for this burst is S. B. Cenko (brad.cenko 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/)

The Fermi GBM team reports the detection of a likely LONG GRB

At 02:34:23 UT on 3 Mar 2020, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 200303A (trigger 604895668.847358 / 200303107).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 207.4, Dec = 50.8 (J2000 degrees, equivalent to J2000 13h 49m, 50d 47'), with a statistical uncertainty of 3.8 degrees.

The angle from the Fermi LAT boresight is 108.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn200303107/quicklook/glg_skymap_all_bn200303107.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn200303107/quicklook/glg_healpix_all_bn200303107.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn200303107/quicklook/glg_lc_medres34_bn200303107.gif