GRB 200307A

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

At 21:26:59 UT on 7 Mar 2020, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 200307A (trigger 605309224.181756 / 200307894).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 84.2, Dec = -46.2 (J2000 degrees, equivalent to J2000 05h 36m, -46d 12'), with a statistical uncertainty of 22.5 degrees.

The angle from the Fermi LAT boresight is 13.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn200307894/quicklook/glg_skymap_all_bn200307894.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/bn200307894/quicklook/glg_healpix_all_bn200307894.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn200307894/quicklook/glg_lc_medres34_bn200307894.gif

Adam Goldstein (USRA), Aaron Tohuvavohu (U Toronto), Jimmy DeLaunay (Penn
State), and Jamie Kennea (Penn State) report on behalf of Fermi/GBM and
Swift/BAT:



The Fermi/GBM Flight-Position notice, distributed at T0+7 seconds, from the
Fermi/GBM detected GRB 200307A (GCN. 27344) triggered the  Swift Mission
Operations Center operated Gamma-ray Urgent Archiver for Novel
Opportunities (GUANO; Tohuvavohu et al. 2020, in prep). Upon trigger by the
Fermi 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 GRB 200307A. All the requested event mode data was delivered to
the ground.



In a ground analysis of the event data, we detect GRB 200307A, determine
the signal in BAT is of astrophysical origin, and can confidently rule out
an origin from inside the contemporaneous BAT field-of-view. At T0, the
Earth's position and size relative to Swift were:



Earth RA: 30.0439

Earth Dec: 5.2549

Earth Radius: 67.139 deg



The Earth, with respect to Swift, occulted over 60% of the Fermi/GBM
localization region and can be ruled out for the GRB localization.



Fermi GBM provides an updated map by removing the Earth-occulted regions
and can be found at the following links:



Skymap image:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn200307894/quicklook/glg_skymap_all_bn200307894.png



HEALPix:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn200307894/quicklook/glg_healpix_all_bn200307894.fit



The 50% confidence region has decreased from 885 square degrees to 290
square degrees and the 90% confidence region has decreased from 2784 square
degrees to 978 square degrees.

A. Ridnaia, D. Svinkin, and K. Hurley, on behalf of the IPN,

A. Goldstein, M. S. Briggs, and C. Wilson-Hodge
on behalf of the Fermi GBM team,

A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo,
and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,

and

S. Barthelmy, J. Cummings, H. Krimm, and D. Palmer,
on behalf of the Swift-BAT team, report:

The short-duration GRB 200307A (The Fermi GBM team,
GCN Circ. 27344
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 ; Goldstein et al., GCN Circ. 27356
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 ) was detected
by Fermi (GBM trigger 605309224), INTEGRAL (SPI-ACS), and
Swift (BAT), at about 77219 s UT (21:26:59).
The burst was outside the coded field of view of the BAT.

We have triangulated this GRB to a GBM-INTEGRAL annulus centered at
RA(2000)=81.577 deg (05h 26m 18s)  Dec(2000)=-38.418 deg (-38d 25' 05"),
whose radius is 32.263 +/- 3.868 deg (3 sigma).

The IPN localization is consistent with, but reduces the area of, the
joint Fermi-GBM/Swift-BAT one (GCN Circ. 27356
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 ).

This localization may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB200307_T77219/IPN/