GRB 170222A

S. Ricciarini (U of Florence), A. Yoshida, T. Sakamoto, Y. Kawakubo,
M. Moriyama, Y. Yamada (AGU), K. Yamaoka (Nagoya U),
S. Nakahira (JAXA), I. Takahashi (IPMU), Y. Asaoka, S. Ozawa,
S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), W. Ishizaki (ICRR),
M. L. Cherry (LSU), P. S. Marrocchesi (U of Siena)
and the CALET collaboration:

The short-duration GRB 170222A (Hamburg et al., GCN Circ. 20728
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 ;
Kozlova et al., GCN Circ. 20731
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 ; INTEGRAL-SPI/ACS trigger #7705)
triggered the CALET Gamma-ray Burst Monitor (CGBM) at 05:00:58.48
on 22 February 2017.  The burst signal was only seen by the SGM
instruments.

The light curve of the SGM shows several peaks.  The entire burst
episode starts at T0+0.5 sec, peaks at T0+0.8 sec and ends at T0+2 sec.
The T90 duration measured by the SGM data is 1.2 +- 0.1 sec (40-1000 keV).

The light curve is available at

http://cgbm.calet.jp/cgbm_trigger/flight/1171774567/

The CALET data used in this analysis are provided by the Waseda
CALET Operation Center located at the Waseda University.

A.Kozlova, S. Golenetskii, R. Aptekar, D. Frederiks, P. Oleynik,
M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline
on behalf of the Konus-Wind team, report:

The short-duration GRB 170222A
(IPN triangulation: Hurley et al., GCN 20722
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 ;
Fermi GBM observation: Hamburg et al., GCN 20728
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 )
triggered Konus-Wind at T0=18056.528 s UT (05:00:56.528).

The burst light curve shows a multi-peaked structure
which starts at ~T0-0.1 s and has a total duration of ~1.9 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst had a fluence of
9.10(-2.43,+3.61)x10^-6 erg/cm2, and a 64-ms peak flux,
measured from T0+1.104 s, of 1.23(-0.46,+0.76)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst (measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.72(-0.26,+0.36)
and Ep = 1210(-418,+830) keV (chi2 = 73/88 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.28
(chi2 = 73/87 dof)

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170222_T18056/

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.

A. D'Ai (IASF-PA), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V.
D'Elia (ASDC), S. J. LaPorte (PSU), J.A. Kennea (PSU), B. Sbarufatti
(INAF-OAB/PSU), S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester)
and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the IPN-detected
burst GRB 170222A in a series of observations tiled on the sky and
covering the entire IPN error box. The total exposure time is 5.3 ks,
distributed over 3 tiles; the maximum exposure at a single sky location
was 3.2 ks. The data were collected between T0+33.8 ks and T0+38.9 ks,
and are entirely in Photon Counting (PC) mode.

Three uncatalogued X-ray sources are detected:

Source 1:
   RA (J2000.0):    292.95293 = 19h 31m 48.70s
   Dec (J2000.0):   28.04614  = +28:02:46.1
   Error: 5.0 arcsec
   Count-rate:	 1.01 (+0.21, -0.20) �� 10-2 ct/s

Source 2:
   RA (J2000.0):    292.68930 = 19h 30m 45.43s	
   Dec (J2000.0):    27.96842 = +27:58:06.3
   Error: 5.7 arcsec
   Count-rate: 2.4 (+0.9, -0.7) �� 10-2 ct/s

Source 3:
   RA (J2000.0):    293.02439 = 19h 32m 05.85s	
   Dec (J2000.0):    28.26746 = +28:16:02.9
   Error: 3.1 arcsec
   Count-rate: 8.0 (+2.8, -2.3) ��10-3 ct/s

However, none of these is a credible afterglow candidate.
Source 2 is outside the IPN errorbox, while sources 1 and 3 match
Simbad sources NVSS J193148+280248 and CCDM J19321+2816BC. Sources 2
and 3 are affected by optical loading and might be spurious detections.

The Swift XRT observations did not cover the Fermi GBM error circle
reported by Hamburg et al. (GCN #20728
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 ).

The results of the full analysis of the tiled XRT observations are
available at http://www.swift.ac.uk/xrt_products/TILED_GRB00064.

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

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

"At 05:00:59.08 UT on 22 February 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170222A (trigger 509432464 / 170222209),
which was also reported by IPN (Hurley et al. 2017, GCN 20722
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 ).

The on-ground calculated location, using the GBM trigger
data, is RA = 312.10, DEC = +12.45 (J2000 degrees,
equivalent to 20h 48m, 12d 27'), with an uncertainty
of 3.6 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] ).

Although the GBM localization is not consistent within 3 sigma
of the IPN localization, the GBM localization places this event
in the same part of the sky and is the same event as that reported by IPN.
The angle from the Fermi LAT boresight at the GBM trigger time using
the IPN position is 120 degrees.

The GBM light curve shows a single multi-peaked emission episode
with a duration (T90) of about 1.7 s (50-300 keV).
The time-averaged spectrum from T0-0.64 s to T0+2.43 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.70 +/- 0.08 and
the cutoff energy, parameterized as Epeak, is 862 +/- 118 keV.

The event fluence (10-1000 keV) in this time interval is
(5.31 +/- 0.19)E-06 erg/cm^2. The 0.64-sec peak photon flux measured
starting from T0+1.15 s in the 10-1000 keV band
is 17.4 +/- 1.9 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

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

Swift has initiated a series of observations, tiled on the sky, of the
IPN GRB 170222A. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00064

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. The probability of finding
serendipitous sources, unrelated to the IPN event is high: 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.

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

Swift has initiated a ToO observation of the IPN GRB 170222A. 
Automated analysis of the XRT data will be presented online at
http://www.swift.ac.uk/ToO_GRBs/00020741

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 IPN 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. Hurley, on behalf of the IPN,

I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin,
on behalf of the HEND-Odyssey GRB team,

D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, A. Kozlova,
and T. Cline on behalf of the Konus-Wind team,

V. Connaughton, M. S. Briggs, C. Meegan, V. Pelassa,
and A. Goldstein, 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,

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

and

W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr,
on behalf of the GRS-Odyssey GRB team, report:

The short-duration, hard-spectrum GRB 170222A has been detected by Fermi 
(GBM trigger 509432464), Konus-Wind, INTEGRAL (SPI-ACS), Mars-Odyssey 
(HEND), Swift (BAT), and CALET (GBM), so far, at about 18059 s UT 
(05:00:59).
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:
   292.956 (19h 31m 49s) +28.211 (+28d 12' 40")
  Corners:
   292.896 (19h 31m 35s) +27.812 (+27d 48' 44")
   292.864 (19h 31m 27s) +28.266 (+28d 15' 59")
   293.017 (19h 32m 04s) +28.608 (+28d 36' 28")
   293.048 (19h 32m 12s) +28.156 (+28d 09' 22")
  ---------------------------------------------
The error box area is 254 sq. arcmin, and its maximum
dimension is 0.8 deg (the minimum one is 9.36 arcmin).
The Sun distance was 56 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB170222_T18056/IPN/

A Swift ToO request has been approved.

The time history and spectrum will be given in forthcoming GCN Circulars.