GRB 200425A

M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), M. J. Moss (GWU), D. M. Palmer (LANL),
T. Sbarrato (INAF-OAB) and M. H. Siegel (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 00:16:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200425A (trigger=967774).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 85.241, -13.459 which is 
   RA(J2000) = 05h 40m 58s
   Dec(J2000) = -13d 27' 31"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The immediately-available BAT light curve
data only extends to T+8s, at which time the GRB was still active
with a multi-peaked structure.  The peak count rate up to that time
was ~1000 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 00:17:52.2 UT, 90.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 85.2198, -13.4352 which
is equivalent to:
   RA(J2000)  = 05h 40m 52.76s
   Dec(J2000) = -13d 26' 06.8"
with an uncertainty of 2.9 arcseconds (radius, 90% containment). This
location is 113 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.  We cannot determine whether the source
is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.59
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 93 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 none of
the XRT error circle. 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 0.16. 

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/)

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

Using 3121 s of XRT Photon Counting mode data and 7 UVOT
images for GRB 200425A, 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 = 85.21950, -13.43511 which is equivalent
to:

RA (J2000): 05h 40m 52.68s
Dec (J2000): -13d 26' 06.4"

with an uncertainty of 1.6 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. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), J. D. Gropp (PSU), J.A. Kennea
(PSU), A. Tohuvavohu (U. Toronto), J.P. Osborne (U. Leicester), K.L.
Page (U. Leicester), A.P. Beardmore (U. Leicester), A. Melandri
(INAF-OAB) and M.G. Bernardini report on behalf of the Swift-XRT team:

We have analysed 7.7 ks of XRT data for GRB 200425A (Bernardini et al.
GCN Circ. 27638
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 ), from 78 s to 34.8 ks after the  BAT trigger. The data
comprise 145 s in Windowed Timing (WT) mode (the first 6 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. 27639
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 ).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=2.5 (+1.3, -0.8). At T+105 s  the decay
flattens to an alpha of -1.5 (+0.0, -0.5). The light curve breaks again
at T+125 s to a decay with alpha=2.78 (+0.39, -0.30),  before a final
break at T+268 s s after which the decay index is 1.13 (+/-0.06).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.11 (+0.17, -0.16). The
best-fitting absorption column is  5.8 (+1.0, -0.9) x 10^21 cm^-2, in
excess of the Galactic value of 1.6 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.02 (+0.26, -0.25)
and a best-fitting absorption column of 7.2 (+2.1, -1.8) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.4 x 10^-11 (7.8 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.2 (+2.1, -1.8) x 10^21 cm^-2
Galactic foreground: 1.6 x 10^21 cm^-2
Excess significance: 5.2 sigma
Photon index:	     2.02 (+0.26, -0.25)

If the light curve continues to decay with a power-law decay index of
1.13, the count rate at T+24 hours will be 2.8 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-13 (2.2 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/00967774.

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

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 200425A 94 s after the BAT trigger (Bernardini et al.,
GCN Circ. 27638
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 ). No optical afterglow consistent with the
XRT position (Bernardini et al. GCN Circ. 27638
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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            94          244          147         >20.7
u_FC               253          503          246         >19.9
white               94          728          186         >20.5
v                  585          778           39         >18.6
b                  510          704           39         >19.1
u                  253          679          265         >19.9
w1                 635          827           39         >18.4
m2                 610          802           39         >18.9
w2                 560          753           39         >18.7

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.16 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),

H.Levato 
(Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE),

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 200425A ( M. G. Bernardini et al., GCN 27638
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 ) errorbox  60241 sec after notice time and 60296 sec after trigger time at 2020-04-25 17:01:17 UT, with upper limit up to  19.7 mag. Observations started at twilight.  The observations began at zenith distance = 45 deg. The sun  altitude  is -12.2 deg. 

The galactic latitude b = -21 deg., longitude l = 218 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=1343952

We obtain a following upper limits.  

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

   60386 |         MASTER-SAAO |   C |   180 | 19.2 |        
   60434 |         MASTER-SAAO |   C |   180 | 19.2 |        
   60666 |         MASTER-SAAO |   C |   180 | 19.7 |        
   60713 |         MASTER-SAAO |   C |   180 | 19.7 |        
Filter C is a clear (unfiltred) band. 


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

R. Strausbaugh (U. of the Virgin Islands), A. Cucchiara (U. of the Virgin Islands/College of Marin) report on behalf of a larger collaboration:

We observed Swift GRB 200425A (Bernardini et al., GCN 27638
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 ) with the LCO 1-m Sinistro instrument at the Siding Spring Observatory, Australia site, on April 25, from 08:26 to 09:07 UT (corresponding to 8.17 to 8.85 hours from the GRB trigger time) with the Bessel I and R filters.

We performed a series of 5x240s exposures in R and I. We do not detect any fading sources in the individual frames (or in stacked images) in the Enhanced Swift-XRT position region (Beardmore et al., GCN 27639
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 ).  Using the USNO-B.1 catalog as reference, we obtain the following 3-sigma upper limits:

R > 22.45

I > 21.96

These magnitudes are not corrected for galactic extinction.

R.S. is funded by NSF AST grant #1831682

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC),
M. G. Bernardini (INAF-OAB),  J. R. Cummings (CPI),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (GSFC/UMBC), 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 200425A (trigger #967774)
(Bernardini et al., GCN Circ. 27638
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 ).  The BAT ground-calculated position is
RA, Dec = 85.217, -13.399 deg which is
   RA(J2000)  =  05h 40m 52.2s
   Dec(J2000) = -13d 23' 58.1"
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.

The mask-weighted light curve shows a weak pulse that starts at ~T-10 s,
peaks at ~T+3 s, and ends at ~T+10 s. In addition, there is some weak
emission that starts at ~T-50 s and lasts till ~T+60 s. T90 (15-350 keV)
is 81.0 +- 21.7 sec (estimated error including systematics).

The time-averaged spectrum from T-47.59 to T+58.41 sec is best fit by a
simple
power-law model.  The power law index of the time-averaged spectrum is
1.30 +- 0.21.  The fluence in the 15-150 keV band is 1.2 +- 0.2 x 10^-6
erg/cm2.
The 1-sec peak photon flux measured from T+2.41 sec in the 15-150 keV band
is 0.7 +- 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/967774/BA/