GRB 170409A

F. Longo (University and INFN, Trieste), J. L. Racusin (NASA/GSFC), and 
D. Kocesvki (NASA/MSFC)report on behalf of the Fermi-LAT team:

At 02:41:59.49 on April 9, 2017, Fermi-LAT detected high-energy emission 
from GRB 170904A, which was also detected by Fermi-GBM (trigger 
513398525/170409112). 

The best LAT on-ground location is found to be:

RA, Dec = 347.53, -7.16 (degrees, J2000)

with an error radius of 0.15 deg (90% containment, statistical error only). This 
was 82 deg from the LAT boresight at the time of the trigger and triggered an 
autonomous repoint of the spacecraft.

The data from the Fermi-LAT show a significant increase in the event rate that 
is spatially and temporally consistent with the GBM emission. More than 14 
photons above 100 MeV and 2 photons above 1 GeV are observed within 1000 
seconds.  The highest-energy photon is a 10 GeV event which is observed 442 
seconds after the GBM trigger.

A Swift ToO has been requested for this burst.

The Fermi-LAT point of contact for this burst is Francesco Longo 
(francesco.longo@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.

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

"At 02:42:00.49 UT on 09 April 2017 , the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170409A (trigger 513398525/170409113)
which was also detected by the Fermi LAT (Longo et al. 2017, GCN 21004
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 ).
The GBM on-ground location is consistent with the LAT position.

The trigger resulted in an Autonomous Repoint Request (ARR)
by the GBM Flight Software owing to the high peak flux
of the GRB. This ARR was accepted and the spacecraft slewed to the GBM
in-flight location. The initial angle from the Fermi LAT boresight to
the LAT location is 82 degrees.

The GBM light curve shows multiple peaks
with a duration (T90) of about 68 s (50-300 keV).
The time-averaged spectrum from T0+26.880 s to T0+97.537 s is
best fit by a Band function with Epeak = 1150 +/- 20 keV,
alpha = -0.82 +/- 0.01, and beta = -2.84 +/- 0.06.

The event fluence (10-1000 keV) in this time interval is
(2.956 +/- 0.009)E-04 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+38.0164 s in the 10-1000 keV band
is 61.8 +/- 0.6 ph/s/cm^2.

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

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, very bright GRB 170409A (Fermi-LAT detection: Longo et al.,
GCN 21004
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 ; Fermi-GBM detection: Burns et al., GCN 21005
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 )
triggered Konus-Wind at T0=9741.024 s UT (02:42:21.024)

The burst light curve shows multiple partially overlapped
emission peaks in the interval from ~T0-29 s to ~T0+95 s.
A possible precursor is seen as a weak count rate excess in
the same KW detector at ~T0-143 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst had a fluence of
(5.7 �� 0.2)x10^-4 erg/cm2 and a 64-ms peak energy flux,
measured from T0+12.982, of (1.00 �� 0.06)x10^-4 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+91.648 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.76 (-0.05,+0.05),
the high energy photon index beta = -2.23 (-0.11,+0.09),
the peak energy Ep = 808 (-65,+69) keV,
chi2 = 111/95 dof.

The spectrum near the peak count rate (measured from T0+12.288 s
to T0+13.056 s) is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.60 (-0.06,+0.07),
the high energy photon index beta = -3.52 (-6.48,+0.65),
the peak energy Ep = 1671 (-180,+192) keV,
chi2 = 99/77 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170409_T09741/

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

Klotz A., Turpin D., Atteia J.L. (CNRS-OMP-IRAP),
Boer, M., Laugier, R. (CNRS-ARTEMIS),
Gendre B. (UVI - Etelman Obs.)
Peyrot A., Teng J.P. (Les Makes Observatory, France),
Thierry P. (Auragne Observatory, France),
Klotz A.N.O. (Guitalens Observatory, France)
report:

We imaged the field of GRB 170409A detected by Fermi LAT and GBM
(trigger 513398525/170409112) with the TAROT robotic telescope (D=18cm)
located at the Reunion observatory, France.

The GRB is located at 34 degrees from the sun and is
observable only in the dawn light in the morning.

The observations started 0.95 day after the GRB trigger.
We stacked 13 images of 120s and examined a field of view of 0.2
degree (radius) around the position provided by
Longo et al. (GCNC 21004). We do not see any new source
at the limiting magnitude of:

t0+0.95d to t0+0.96h : Rlim=17.0 +/- 0.2

Magnitudes were estimated with the nearby NOMAD1 stars
and are not corrected for galactic dust extinction.