GRB 201008A

F. Kunzweiler, B. Biltzinger, F. Berlato, J. Burgess & J. Greiner (all MPE Garching) report:

The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger
623846261 at 10:37:36 on 08 Oct. 2020 were automatically fitted for spectrum
and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427;
Berlato et al. 2019, ApJ 873, 60).

The best-fit position (1 sigma statistical errors) is:
RA(2000.0) = 167.1+/-4.3 deg
Decl.(2000.0) = 42.1+/-3.9 deg
We estimate an additional systematic error of 2 deg.

Further details are available at:
https://grb.mpe.mpg.de/grb/GRB201008443/

The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB201008443/healpix

The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB201008443/json

James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), Jamie Kennea (PSU),
Peter Veres (UAH) report:

Swift/BAT did not trigger on GRB 201008A (T0: 2020-10-08 10:37:36 UTC,
Fermi/GBM Team TRIGGER 623846261).

The Fermi/GBM notice, distributed in near real-time triggered the Swift
Mission Operations Center operated Gamma-ray Urgent Archiver for Novel
Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).

Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert
Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150]
seconds around the time of the burst. All the requested event mode data was
delivered to the ground.

The burst is detected in BAT with a T90 duration of ~2.5 seconds.

With a maximum likelihood analysis (DeLaunay et al. 2020, in prep.) on

the event-mode data we detect a location for the burst with a square

root of the test statistic, sqrt(TS), of 13.22. The sqrt(TS) behaves

similarly to SNR.

Using the normal BAT imaging technique, we find the location of the GRB
with an SNR of 4.2.

Since this is a low significance detection near the edge of the coded field
of view there is a chance that this localization may be incorrect.

The BAT ground-calculated position is

RA, Dec = 161.744, 46.101 deg which is

   RA(J2000)  = 10h 46m 58.56s

   Dec(J2000) =  46d 06��� 03.6���

with an uncertainty of 5 arcmin, (radius, sys+stat, 90% containment).

The partial coding was 3.5%.

This position is consistent with the Fermi GBM localization (
https://gcn.gsfc.nasa.gov/other/623846261.fermi) and BALROG localization
(GCN 28577
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 ).

XRT and UVOT follow-up has been triggered. Results of follow-up
observations will be reported in future circulars.

GUANO is a fully autonomous, extremely low latency, spacecraft commanding
pipeline designed for targeted recovery of BAT event mode data around the
times of compelling astrophysical events to enable more sensitive GRB
searches.

A live reporting of Swift/BAT event data recovered by GUANO can be found
at: https://www.swift.psu.edu/guano/

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

Swift has initiated a ToO observation of the Fermi/GBM GRB 201008A. 
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021034

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. These are
not necessarily related to the Fermi/GBM event. Any X-ray source
considered to be a probable afterglow candidate will be reported via a 
GCN Circular after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

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

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

Swift-XRT has performed follow-up observations of the Fermi/GBM and
Swift/BAT-GUANO detected burst GRB 201008A (DeLaunay et al. GCN Circ.
28583
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 ), collecting 4.5 ks of Photon Counting (PC) mode data between
T0+46.9 ks and T0+60.1 ks. 

Two uncatalogued X-ray sources have been detected consistent with being
within 296 arcsec of the BAT/GUANO position, however none of them is
above the RASS limit or shows definitive signs of fading. Therefore, at
the present time we cannot identify which, if any, is the afterglow.
Details of these sources are given below:

Source 1:
  RA (J2000.0):  161.7543  =  10:47:1.02
  Dec (J2000.0): +46.1475  =  +46:08:51.1
  Error: 5.1 arcsec (radius, 90% conf.)
  Count-rate: (1.79 [+1.09, -0.80])e-3 ct s^-1	 
  Distance: 169 arcsec from BAT position.
  NB, this position is consistent with SDSS J104701.20+460848.8,
  a likely quasar in the SDSS Quasar Catalogue. If this association
  and ID is accurate, this source is unlikely to be related to the GRB.


Source 4:
  RA (J2000.0):  161.8588  =  10:47:26.10
  Dec (J2000.0): +46.1019  =  +46:06:06.9
  Error: 4.8 arcsec (radius, 90% conf.)
  Count-rate: (4.1 [+1.3, -1.1])e-3 ct s^-1   
  Distance: 286 arcsec from BAT position.
  Flux: (1.68 [+0.52, -0.44])e-10 erg cm^-2 s^-1 (observed, 0.3-10 keV)


Two uncatalogued sources were also detected too far from the GRB
position to be likely afterglow candidates.

The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
https://www.swift.ac.uk/ToO_GRBs/00021034.

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

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

Swift-XRT has conducted further observations of the field of the
Fermi/GBM and Swift-BAT/GUANO detected burst GRB 201008A (DeLaunay et
al. GCN Circ. 28583
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 ). The observations now extend from T0+47.0 ks to
T0+650.8 ks. 

Of the sources reported by Page et al. (GCN Circ. 28587
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 ), "Source 4" is
fading with 3-sigma significance, and is therefore likely the GRB
afterglow.  The position of this source is RA, Dec=161.8588, +46.1019
which is equivalent to:

RA (J2000): 10:47:26.10
Dec(J2000): +46:06:06.9

with an uncertainty of 4.8 arcsec (radius, 90% confidence).  This
position is 4.8 arcmin from the BAT/GUANO position.  The source is
fading with alpha >0.8.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00021034.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021034.

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

E. Bissaldi (Politecnico and INFN Bari) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:


"At 10:37:36.71 UT on 8 October 2020, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 201008A (trigger 623846261 / 201008443),
which was also detected by the Swift/BAT-GUANO (DeLaunay et al. 2020, GCN 28583
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 ).
The Fermi GBM Final Real-time Localization is consistent with the Swift position.

The angle from the Fermi LAT boresight
at the GBM trigger time is 60 degrees.

The GBM light curve consists of a multi-peaked emission episode
with a duration (T90) of about 2 s (50-300 keV).
The time-averaged spectrum from T0-0.26 s to T0+2.11 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.80 +/- 0.13 and
the cutoff energy, parameterized as Epeak, is 166 +/- 21 keV.

The event fluence (10-1000 keV) in this time interval is
(1.17 +/- 0.09)E-06 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+1.28 s in the 10-1000 keV band
is 7.3 +/- 1.3 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/"