GRB 220528A

The Fermi GBM team reports the detection of a likely short GRB.

At 06:12:47.41 UT on 28 May 2022, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 220528A (trigger 675411172 / 220528259).

The on-ground calculated location, using the GBM trigger
data, is RA = 311.2, DEC = 24.3 (J2000 degrees,
equivalent to 20 h 44 m, 24 d 18 '), with a statistical uncertainty
of 4.9 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which we have characterized as a core-plus-tail model, with 90% of
GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg
systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ).

The angle from the Fermi LAT boresight at the GBM trigger time is 68
degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220528259/quicklook/glg_skymap_all_bn220528259.png

The HEALPix FITS file, including the estimated localization systematic, can
be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220528259/quicklook/glg_healpix_all_bn220528259.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220528259/quicklook/glg_lc_medres34_bn220528259.gif

The burst detection reported in GCN 32148
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  "GRB 220528B:
Swift/BAT-GUANO detection... " was misnamed.
The burst is GRB 220528A (see Fermi/GBM discovery and naming in GCN 32147
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 ).
I apologize for the mistake.

J.Mangan (UCD), S. Lesage (UAH) and C.Meegan (UAH) report on behalf of the
Fermi GBM Team:

"At 06:12:47.41 UT on 28 May 2022, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 220528A (trigger 675411172 / 220528259), which
was also
detected by the Swift/BAT-GUANO (Raman et al. 2022, GCN 32148
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  and GCN
32149
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 ).

The Fermi GBM Final Real-time Localization has been reported in GCN 32147
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 .

The GBM light curve consists of a single peak with a duration (T90) of
about 0.58 s (50-300 keV).
The time-averaged spectrum from T0-0.128 s to T0+0.576 s is best fit by a
power law function with an exponential
high-energy cutoff. The power law index is 0.08 +/- 0.17 and the cutoff
energy, parameterized as Epeak, is 467.5 +/- 50.8 keV
The event fluence (10-1000 keV) in this time interval is (1.59 +/-
0.11)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.064 s in the 10-1000 keV band is 4.2 +/- 0.2 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/"

D. Svinkin, D. Frederiks, A. Ridnaia, A. Lysenko,
and T. Cline on behalf of the Konus-Wind team,

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

E. Bozzo and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,

and

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

The short-duration GRB 220528A
(Fermi-GBM detection: Fermi GBM Team, GCN Circ. 32147
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 ;
Mangan et al., GCN Circ. 32155
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 ;
Swift/BAT-GUANO detection: Raman et al., GCN Circ. 32148
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 )
was detected by Fermi (GBM trigger 675411172),
INTEGRAL (SPI-ACS), Konus-Wind, and Swift (BAT)
at about 22367 s UT (06:12:47).
The burst was outside the coded field of view of the BAT.

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   312.961 (20h 51m 51s) +18.856 (+18d 51' 22")
  Corners:
   315.010 (21h 00m 02s) +16.077 (+16d 04' 38")
   315.232 (21h 00m 56s) +16.369 (+16d 22' 08")
   310.761 (20h 43m 03s) +21.508 (+21d 30' 30")
   310.547 (20h 42m 11s) +21.215 (+21d 12' 55")
  ---------------------------------------------
The error box area is 2.3 sq. deg, and its maximum
dimension is 6.8 deg (the minimum one is 21 arcmin).
The Sun distance was 102 deg.

This box may be improved.

The IPN localization is consistent with, but reduces the area of, the
Fermi-GBM final localization (GCN Circ. 32147
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 ).

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB220528_T22370/IPN

The Konus-Wind time history and spectrum will be given in a forthcoming
GCN Circular.

D. Svinkin, D. Frederiks, A.Ridnaia, A.Lysenko,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The short-duration GRB 220528A
(Fermi-GBM detection: Fermi GBM Team, GCN Circ. 32147
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 ;
Mangan et al., GCN Circ. 32155
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 ;
Swift/BAT-GUANO detection: Raman et al., GCN Circ. 32148
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 ;
IPN triangulation: Svinkin at al., GCN Circ. 32156
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 )
triggered Konus-Wind at T0=22370.380 s UT (06:12:50.380).

The burst light curve shows a multipeaked structure,
which starts at T0-0.1 s and has a total duration of ~0.7 s.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB220528_T22370/

As observed by Konus-Wind, the burst
had a fluence of 1.85(-0.03,+0.54)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0+0.034 s,
of 7.88(-1.57,+2.77)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

Since the main fraction of the burst emission was detected
before the trigger, the spectral analysis was performed using
the KW 3-channel light curve data.

Modelling the KW 3-channel time-integrated spectrum
(measured from T0-0.402 s to T0+0.296 s)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep),
yields alpha = -0.06(-0.32,+0.38) and Ep = 542(-78,+118) keV.

All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.