GRB 200907B

M. H. Siegel (PSU) 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 200907B
84 s after the BAT trigger (Beardmore et al., GCN Circ. 28384
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 ).
No optical afterglow consistent with the XRT position
(Evans GCN Circ. 28385
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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            84          233          147         >20.4
u_FC               296          546          246         >19.7
white               84         4892          383         >21.0
v                  625          819           39         >17.7
b                  551         4687          236         >19.4
u                  296         4482          462         >20.4
w1                 675         4277          216         >19.2
m2                 650          670           19         >18.3
w2                 601         5048          186         >19.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.61 in the direction of the burst
(Schlegel et al. 1998).

H. A. Krimm (NSF), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), J. R. Cummings (CPI),
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 200907B (trigger #995004)
(Beardmore et al., GCN Circ. 28384
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 ).  The BAT ground-calculated position is
RA, Dec = 89.019, 6.905 deg which is
   RA(J2000)  =  05h 56m 04.5s
   Dec(J2000) = +06d 54' 17.7"
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 78%.

The mask-weighted light curve shows a multi-peaked structure that
starts at ~T-0.6 and ends at ~T+0.3 s. The main peak occurs
at ~T+0.1 s. T90 (15-350 keV) is 0.83 +- 0.13 sec (estimated error
including systematics).

The time-averaged spectrum from T-0.64 to T+0.28 sec is best fit by
a simple power-law model.  The power law index of the time-averaged
spectrum is 0.68 +- 0.25.  The fluence in the 15-150 keV band
is 1.6 +- 0.2 x 10^-7 erg/cm2. The 1-sec peak photon flux measured
from T-0.68 sec in the 15-150 keV band is 1.5 +- 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/995004/BA/

S. Gupta, V. Sharma and D. Bhattacharya (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (IUCAA/TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data showed a weak detection of a short GRB 200907B, which was also detected by Swift (Beardmore A. et al., GCN #28384
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 ),  Swift-XRT (Evans P. et al., GCN #28385
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 ),  GROWTH-India optical (Kumar H. et al., GCN #28388
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 ), Global MASTER-Net (Lipunov V. et al., GCN #28392
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 ), and  MITSuME Okayama optical (Hosokawa R. et al., GCN #28393
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 ).

The source was clearly detected in the 40-200 keV energy range. The light curve showed a single peak of emission peaking at 2020-09-07 18:51:10.019 UT. The measured peak count rate associated with the burst is 160 +/- 24 cts/s above the background in the combined data of four quadrants, with a total of 259 +/- 3 cts. The local mean background count rate was 515+/- 1 cts/s. Using cumulative rates, we measure a T90 of 1.60 +/- 0.01 s.

It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed a single peak of emission peaking at 2020-09-07 18:51:09.00 UT. The measured peak count rate is 513 +/- 44 cts/s above the background in the combined Veto data of four quadrants, with a total of 560 +/- 5 cts. The local mean background count rate was 1494 +/- 2 cts/s. We measure a T90 of 1.48 +/- 0.06 s from the cumulative Veto light curve.

CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.

M. Capalbi (INAF-IASFPA), M. Perri (ASDC), V. D'Elia (ASDC), D.N.
Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea (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 6.7 ks of XRT data for GRB 200907B (Beardmore et al.
GCN Circ. 28384
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 ), from 83 s to 18.0 ks after the  BAT trigger. The data
comprise 5 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Evans et al. (GCN Circ. 28385
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=2.09 (+/-0.18).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.9 (+0.5, -0.4). The
best-fitting absorption column is  5.7 (+3.0, -1.4) x 10^21 cm^-2,
consistent with the Galactic value of 4.2 x 10^21 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 4.4 x 10^-11 (7.1 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     5.7 (+3.0, -1.4) x 10^21 cm^-2
Galactic foreground: 4.2 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.9 (+0.5, -0.4)

If the light curve continues to decay with a power-law decay index of
2.09, the count rate at T+24 hours will be 1.3 x 10^-6 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.8 x
10^-17 (9.2 x 10^-17) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00995004.

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

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

We observed the field of GRB 200907B (Beardmore et al., GCN 28384
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 ;
Evans et al., GCN 28385
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 ,28391
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 ) 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
2020-09���07 18:52:16UT. We did not find any new point sources within
the enhanced Swift/XRT error circle (Evans et al., GCN 28391
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 ) in the
60 sec exposure images and the stacked images. We obtained the 5-sigma
limits of the stacked images as follows.

T0+[sec] MID-UT T-EXP[sec] 5-sigma limits
------------------------------------------------------------------------------------------------
65 2020-09-07T19:19:48 2100 g'>17.1, Rc>17.9, Ic>17.3
------------------------------------------------------------------------------------------------
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., accepted
for publication in PASJ, https://arxiv.org/abs/2008.11486
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 ;
https://github.com/MNiwano/Eclaire).

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 200907B ( A. P. Beardmore et al., GCN 28384
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 ) errorbox  22142 sec after notice time and 22169 sec after trigger time at 2020-09-08 01:00:40 UT, with upper limit up to  17.6 mag. The observations began at zenith distance = 59 deg. The sun  altitude  is -23.0 deg. 

MASTER-SAAO robotic telescope  located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 200907B errorbox  22375 sec after notice time and 22402 sec after trigger time at 2020-09-08 01:04:33 UT, with upper limit up to  15.9 mag. The observations began at zenith distance = 73 deg. The sun  altitude  is -46.6 deg. 

The galactic latitude b = -8 deg., longitude l = 201 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=1435309

We obtain a following upper limits.  

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

   22260 |      MASTER-Tavrida |   C |   180 | 17.3 |        
   22461 |      MASTER-Tavrida |   C |   180 | 17.6 |        
   22493 |         MASTER-SAAO |   C |   180 | 15.9 |        
Filter C is a clear (unfiltred) band. 


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

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

Using 742 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 200907B, 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 = 89.02906, +6.90625 which is equivalent
to:

RA (J2000): 05h 56m 6.97s
Dec (J2000): +06d 54' 22.5"

with an uncertainty of 1.8 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.

H. Kumar (IITB), P. Dorje (IIA), V. Bhalerao(IITB), G. C. Anupama(IIA), S.
Barway(IIA), report on behalf of the GROWTH-India collaboration:

We apologize for the confusion caused in GRB name. GROWTH-India Telescope
followed-up GRB 200907B, not GRB 200907A.


Here is the corrected GCN:-

We observed GRB 200907B reported by Swift-BAT (A.P. Beardmore et al., GCN
#28384
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 , P.A. Evans et al., GCN #28385
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 ) with 0.7m GROWTH-India telescope.
The field was observed in the SDSS r filter starting at
2020-09-07T20:59:05.36 UT i.e. ~2.1 hrs after the event detection by
Swift-BAT. We didn���t find any new source in stacked image of 7*500 sec
exposure, within an uncertainty region of 2.2 arcsec around RA(J2000) =
05:56:06.93, Dec(J2000)= +06:54:22.8 (GCN 28385
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 ) up to

r > 20.83 mag (5-sigma) (calibrated against PanSTARRs PS1 data
release, Flewelling
et al., 2018).



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).

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Using  promptly downlinked XRT event data for GRB 200907B, we find an
enhanced XRT position of the afterglow: RA, Dec: 89.0289, 6.9063 which
is equivalent to:
   RA (J2000)  = 05 56 06.93
   Dec (J2000) = +06 54 22.8
with an uncertainty of 2.2 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/995004.

Position enhancement is is described by Goad et al. (2007, A&A, 476,
1401) and Evans et al. (2009, MNRAS, 397, 1177).

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

A. P. Beardmore (U Leicester), S. D. Barthelmy (GSFC),
J. A. Kennea (PSU), N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
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 18:51:11 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200907B (trigger=995004).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 89.013, +6.911 which is 
   RA(J2000) = 05h 56m 03s
   Dec(J2000) = +06d 54' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 1 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 18:52:31.3 UT, 80.1 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 89.02837, 6.90752 which is equivalent
to:
   RA(J2000)  = 05h 56m 06.81s
   Dec(J2000) = +06d 54' 27.1"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 56 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 4.23
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 83 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
0.61. 

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/)