GRB 200901A

K. K. Simpson (PSU), S. D. Barthelmy (GSFC), J.D. Gropp (PSU),
N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST),
A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL), B. Sbarufatti (PSU) and
A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 03:47:31 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200901A (trigger=994143).  Swift did not slew immediately
due to an observing constraint. 
The BAT on-board calculated location is 
RA, Dec 61.758, -59.880 which is 
   RA(J2000) = 04h 07m 02s
   Dec(J2000) = -59d 52' 47"
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 50 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

Due to an observing constraint, Swift will not slew until T0+47.5
minutes. There will be no XRT or UVOT data until this time. 

This source lies within the current (Sector 29) field-of-view of TESS camera 3. 

Burst Advocate for this burst is K. K. Simpson (kira.simpson1984 AT gmail.com). 
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/)

D.N. Burrows (PSU), J.A. Kennea (PSU), M. Perri (ASDC), G. Tagliaferri
(INAF-OAB), P.A. Evans (U. Leicester) and J.P. Osborne (U. Leicester)
report on behalf of the Swift-XRT team:

The XRT began observing the field of GRB 200901A at 04:38:21.9 UT,
3050.4 seconds after the BAT trigger. No source was detected in 1.9 ks
of promptly downlinked data, which covered 54% of the BAT error circle.
We are waiting for the full dataset to detect and localise the XRT
counterpart.

P. Veres, R. Hamburg and C. Meegan (all UAH)
report on behalf of the Fermi GBM Team:

"At 03:47:27.62 UT on 1 September 2020, the Fermi Gamma-Ray Burst Monitor
(GBM)
triggered on GRB 200901A (trigger 620624852 / 200901158)
which was also detected by the Swift/BAT (Simpson et al., GCN 28335
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 ).
The GBM on-ground location is consistent with the Swift position.

The event was classified as particle activity by the flight software, but
it is in fact a GRB.

The angle from the Fermi LAT boresight at the GBM trigger time is 151
degrees.

The GBM light curve consists of overlapping pulses
with a duration (T90) of about 10.2 s (50-300 keV).
The time-averaged spectrum from T0-0.9 s to T0+10.4 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.52 +/- 0.09 and
the cutoff energy, parameterized as Epeak, is 410 +/- 150 keV.

The event fluence (10-1000 keV) in this time interval is
(9.4 +/- 0.54)E-6 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.8 s in the 10-1000 keV band
is 11.2 +/- 0.96 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/"

J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E.
Ambrosi  (INAF-IASFPA) , A. Tohuvavohu (U. Toronto), B. Sbarufatti
(PSU) and K. K. Simpson (PSU) report on behalf of the Swift-XRT team:

We have analysed 2.5 ks of XRT data for GRB 200901A (Simpson et al. GCN
Circ. 28335
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 ), from 3.1 ks to 11.1 ks after the	BAT trigger. The data
are entirely in Photon Counting (PC) mode. Using 1707 s of PC mode data
and 4 UVOT images, we find an enhanced XRT position (using the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1 catalogue):
RA, Dec = 61.78319, -59.89084 which is equivalent to:

RA (J2000): 04h 07m 07.97s
Dec(J2000): -59d 53' 27.0"

with an uncertainty of 1.8 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.95 (+0.28, -0.24).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.31 (+0.30, -0.28). The
best-fitting absorption column is  2.2 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 1.5 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 3.0 x 10^-11 (4.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.2 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 1.5 x 10^20 cm^-2
Excess significance: 4.2 sigma
Photon index:	     2.31 (+0.30, -0.28)

If the light curve continues to decay with a power-law decay index of
0.95, the count rate at T+24 hours will be 7.9 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.3 x
10^-13 (3.8 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/00994143.

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

A. A. Breeveld (UCL-MSSL) and K. K. Simpson (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 200901A 3053 s after the BAT trigger 
(Simpson et al., GCN Circ. 28335
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 ).
A possible optical afterglow consistent with the XRT position (Kennea et al., GCN Circ. 28341
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 ) is 
detected in the initial UVOT exposures in the white filter only. It is not clear whether the source 
is fading.
Preliminary detections and 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          3053         3202          147         20.6 +/- 0.3
white             3916         4115          197         20.5 +/- 0.2
v                 4326         4526          197         >19.1
b                 3711         3910          197         >20.4
u                 3211         4987          290         >20.0
w1                4736         4936          197         >19.1
m2                4531         4731          197         >19.1
w2                4121         4321          197         >19.3

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).

T. Sakamoto (AGU), 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),
K. K. Simpson (PSU), M. Stamatikos (OSU),
T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):

Using the data set from T-239 to T+963 sec from the recent telemetry
downlink,
we report further analysis of BAT GRB 200901A (trigger #994143)
(Simpson et al., GCN Circ. 28335
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 ).  The BAT ground-calculated position is
RA, Dec = 61.759, -59.901 deg which is
   RA(J2000)  =  04h 07m 02.3s
   Dec(J2000) = -59d 54' 03.4"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 21%.

The mask-weighted light curve shows several overlapping pulses that start
at ~T-5 s and end at ~T+27 s. The main peak occurs at ~T0.
The burst location went out of the BAT field of view at ~T+514 s.
T90 (15-350 keV) is 20.37 +- 7.55 sec (estimated error including
systematics).

The time-averaged spectrum from T-4.43 to T+26.59 sec is best fit by a
simple
power-law model.  The power law index of the time-averaged spectrum is
1.72 +- 0.11.  The fluence in the 15-150 keV band is 2.9 +- 0.2 x 10^-6
erg/cm2.
The 1-sec peak photon flux measured from T-0.01 sec in the 15-150 keV band
is 7.7 +- 0.6 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/994143/BA/

V. Lipunov, V.Kornilov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, A.Kuznetsov, K.Zhirkov, F.Balakin,
V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, A.Chasovnikov, A.Pozdnyakov, 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 (Irkutsk State University, API),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov, Yu. Sergienko (Blagoveschensk Educational State University)

MASTER-OAFA robotic telescope (Global MASTER-Net http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, v.2010, 30L)
started in alert mode (Lipunov et al. GCN 28334
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 )
Swift GRB 200901A  (Simpson et al. GCN 28335
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 ,  Sakamoto et al. GCN 28344
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 ) 
errorbox observation 25s after notice time (46s after trigger time) at 2020-09-01 03:48:18 UT.

There is OT at XRT (Kennea et al. GNC 28341) and UVOT (Breeveld et al. GCN 28342
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 ) position
first 20 minutes after trigger time.

Data analysis will continue.

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 30cm robotic telescope FRAM-Auger in Malargue (Argentina)
reacted robotically to the Swift/BAT alert of GRB200901A
(Simpson et al., GCNC 28335, Burrows et al., GCNC 28336,
Kennea et al., GCNC 28341, and Breeveld et al., GCNC 28342).

The weather was cloudy but as the clouds moved, we could
select some good images, in particular there is a continuous
set of 14 exposures between 4:00 and 4:17 UT, where the
position could be well identified.

We do not detect any new or strongly variable source at or
around the reported X-ray errorbox at single frames or a
combined 14 x 20s R-band image with the exposure mid-time
21.3 min after the initial trigger. The combined exposure has
a limiting magnitude R(Vega) = 17.8, as calibrated against
the Atlas Catalogue.