GRB 171022A

M. Palatiello (Univ & INFN Trieste), E. Bissaldi (Poiltecnico & INFN Bari),
M. Axelsson (Stockholm Univ.), M. Yassine (Univ & INFN Trieste),
S. Buson  (NASA/GSFC) and J. Racusin (NASA/GSFC)
report on behalf of the Fermi-LAT team:


On September 22, 2017, Fermi-LAT detected high-energy emission from GRB 171022A,
which was also detected by Fermi-GBM (trigger 530399665) at 21:14:20.77 UTC.

The best LAT on-ground location is found to be

RA, Dec 204.28, 10.98 (degrees, J2000),

with an error radius of 0.16 deg (90% containment, statistical error only).
This position was outside the LAT FoV at the time of the GBM trigger,
and entered the FoV at ~T0+3000s.

The Fermi-LAT data show a significant increase
in the event rate within 12 degrees of the GBM location.
More than 20 photons above 100 MeV are observed between
T0+3000 s and T0+6000 s. The highest-energy photon is a 14 GeV event
which is observed ~4600 seconds after the GBM trigger.

A Swift ToO will not be performed for this GRB due to Sun constraints.

The Fermi-LAT point of contact for this burst is
Michele Palatiello (michele.palatiello@ts.infn.it).


The Fermi-LAT is a pair conversion telescope designed to cover
the energy band from 20 MeV to greater than 300 GeV.
It is the product of an international collaboration between
NASA and DOE in the U.S. and many scientific institutions
across France, Italy, Japan and Sweden.

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

"At 21:14:20.77 UT on 22 October 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 171022A (trigger 530399665 / 171022885).
which was also detected by the Fermi/LAT
(Palatiello et al. 2017, GCN 22045
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 ).
The GBM on-ground location is consistent with the LAT position.

The angle from the Fermi LAT boresight at the GBM trigger time is 99
degrees.

The GBM light curve shows a multi-peaked structure
with a duration (T90) of about 13 s (50-300 keV).
The time-averaged spectrum from T0-0.00 s to T0+15.07 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.49 +/- 0.06 and
the cutoff energy, parameterized as Epeak, is 151 +/- 5 keV.

The event fluence (10-1000 keV) in this time interval is
(8.1 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.23 s in the 10-1000 keV band
is 8.7 +/- 0.3 ph/s/cm^2.

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

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,

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

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

V. Connaughton, M. S. Briggs, C. Meegan, V. Pelassa,
and A. Goldstein, on behalf of the Fermi GBM team, and

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

The long-duration GRB 171022A
(Fermi-LAT detection: Palatiello et al., GCN Circ. 22045
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 ;
Fermi-GBM detection: Hamburg and Meegan, GCN Circ. 22046
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 )
was detected by Fermi (GBM trigger 530399665), Konus-Wind,
INTEGRAL (SPI-ACS), and Mars-Odyssey (HEND)
at about 76461 s UT (21:14:21).

We have triangulated it to a preliminary, 3 sigma error box whose 
coordinates are:
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   215.353 (14h 21m 25s) +12.844 (+12d 50' 37")
  Corners:
   217.045 (14h 28m 11s)  +1.841 ( +1d 50' 29")
   211.510 (14h 06m 02s) +21.802 (+21d 48' 06")
   210.607 (14h 02m 26s) +22.804 (+22d 48' 14")
   216.812 (14h 27m 15s)  +3.167 ( +3d 10' 03")
  ---------------------------------------------
The error box area is 4.1 sq. deg, and its maximum
dimension is 21.9 deg (the minimum one is 12.0 arcmin).
The Sun distance was 16 deg.

This box may be improved.

The Fermi (LAT) on-ground location (RA, Dec, Rerr = 204.28, 10.98, 0.16 
deg) reported in Palatiello et al. is inconsistent with the box, the 
minimum distance between the box and the Fermi (LAT) location is ~11 deg.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB171022_T76456/IPN

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

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

The long GRB 171022A (Fermi-LAT detection: Palatiello et al.,
GCN 22045
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 ; Fermi-GBM detection: Hamburg and Meegan, GCN 22046
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 ;
IPN Triangulation: Hurley et al., GCN 22051
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 )
triggered Konus-Wind at T0=76456.523 s UT (21:14:16.523).

The KW light curve shows a multi-peaked emission complex
with a total duration of ~15 s. A much weaker pulse is also
seen in the softest KW light curve around ~T0+215 s.
The emission is seen up to ~3.5 MeV.

As observed by Konus-Wind, the burst had a fluence of
(7.1 �� 0.7)x10^-6 erg/cm2 and a 64-ms peak energy flux,
measured from T0+3.328, of (2.4 �� 0.2)x10^-6 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+16.640 s)
is best fit in the 20 keV - 15 MeV range by a cutoff power-law
(CPL) function with the following model parameters:
the photon index alpha = -0.51(-0.30,+0.34),
and the peak energy Ep = 144(-13,+17) keV,
chi2 = 93/98 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and an upper limit on beta of -2.7,
chi2 = 93/97 dof.

The spectrum near the peak count rate (measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 15 MeV range by the CPL function
with the following model parameters:
the photon index alpha = -0.40(-0.27,+0.30),
and the peak energy Ep = 146(-12,+14) keV,
chi2 = 111/98 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and an upper limit on beta of -2.8,
chi2 = 110/97 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB171022_T76456/

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.

M. Palatiello (Univ & INFN Trieste), E. Bissaldi (Poiltecnico & INFN Bari),
and E. Moretti (MPI Munich) report on behalf of the Fermi-LAT team:


On October 22nd, 2017, the Fermi-LAT collaboration reported
the detection of GRB 171022A (Palatiello et al., GCN #22045
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 ).

Following the publication of the GRB IPN triangulation
(Hurley et al., GCN #22051
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 ), we performed further analysis to
investigate the discrepancy of the Fermi-LAT localization
with respect to the region defined by the Konus Wind,
Fermi-GBM and INTEGRAL annuli.

The LAT excess reported in Palatiello et al. has a
significance which is only slightly
above the 5 sigma threshold. Moreover, the Fermi-LAT
Point Source Catalog (3FGL, Acero et al. 2015) contains
the source 3FGL J1339.0+1153 in the proximity of the position
of the LAT excess. A likelihood analysis where the normalization
for 3FGL J1339.0+1153 is set as a free parameter of the fit
returns a marginal increase (20 +/- 15 %) in the flux
of that source, tentatively associated with
SDSS J133859.05+115316.7, and results in a non-detection of the
excess which we previously associated with GRB 171022A.
Therefore, we cannot confirm at this stage that
the LAT excess is associated with GRB 171022A.


The Fermi-LAT is a pair conversion telescope designed
to cover the energy band from 20 MeV to greater than 300 GeV.
It is the product of an international collaboration
between NASA and DOE in the U.S. and many scientific
institutions across France, Italy, Japan and Sweden.