GRB 150510A

S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik,
M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration, hard-spectrum, intense GRB 150510A
(Fermi-LAT detection: Vianello & Racusin, GCN 17805
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 ;
Racusin et al., GCN 17806
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 ;
Fermi-GBM detection: Burns & Meegan GCN 17807
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 )
triggered Konus-Wind at T0=11988.505 s UT (03:19:48.505).

The KW light curve shows a FRED-like structure with
a duration of ~62 s.
The emission is visible up to ~15 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150510_T11988/

As observed by Konus-Wind, the burst had a fluence
of 1.9(-0.1,+0.1)x10^-4 erg/cm2, and a 64-ms peak flux,
measured from T0+0.064 s, of 4.0(-0.3,+0.3)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum (measured from T0 to T0+39.168 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 = -0.99 (-0.04,+0.05),
the high energy photon index beta = -2.81 (-1.10,+0.37),
the peak energy Ep = 1253 (-129,+134) keV,
chi2 = 106/95 dof.

The spectrum near the peak count rate
(measured from T0 to T0+6.400 s)
is best fit in the 20 keV - 15 MeV range
by the cutoff power law with the following model parameters:
the photon index alpha = -0.74(-0.05,+0.05),
and the peak energy Ep = 1320(-85,+93) keV,
chi2 = 100/87 dof.
Fitting this spectrum with the Band model yields the same
values of alpha and Ep with an upper limit on the high-energy
photon index beta of -2.9

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

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

"At 03:19:53.74 UT on 10 May 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 150510A (trigger 452920796 / 150510139),
which was also detected by the Fermi LAT (Vianello et al. 2015,
GCN 17805
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 ). The GBM on-ground location is marginally consistent
with the LAT position.

The angle of the burst direction to the Fermi LAT boresight was
55 degrees. The trigger resulted in an Autonomous Repoint Request
(ARR) that was accepted and the spacecraft slewed to the GBM
in-flight location.

The GBM light curve shows a FRED profile
with a duration (T90) of about 52 s (50-300 keV).
The time-averaged spectrum from T0+0.256 s to T0+52.480 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.04 +/- 0.01 and
the cutoff energy, parameterized as Epeak, is 1651 +/- 58 keV.

The event fluence (10-1000 keV) in this time interval is
(9.32 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.064 s in the 10-1000 keV band
is 32.0 +/- 0.3 ph/s/cm^2.

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

J. L. Racusin (NASA/GSFC), M. Axelsson (KTH), M. Yassine (LUPM), D. Kocevski (NASA/GSFC) 
report on behalf of the Fermi-LAT team:

Additional data on GRB 150510A has been downlinked from Fermi and processed, and we report 
an improved LAT localization of 

R.A., Dec = 16.16,  4.79 (J2000)

with an error radius of 0.36 deg (90% containment, statistical error only).  This was 55 deg from the 
LAT boresight at the time of the trigger.  The GRB position was within the LAT FoV from ~500 s prior 
to the trigger to ~T0+600 s, when an autonomous repoint request to the initial GBM flight position 
caused the spacecraft to slew away.

There are 13 photons with energies >100 MeV within a 12 degree radius around the GRB position. 
The highest energy photon is detected at T0+170 s with an energy of 1.5 GeV.  The burst is also 
detected in the LAT Low Energy (LLE) data with energies >30 MeV with a significance of 9 sigma 
above background with a duration of ~20 s, coinciding with the time of the GBM emission.

The GRB localization is within the Swift Sun avoidance constraint, and will not emerge until May 25, 
therefore a Swift TOO is not being requested.

The Fermi-LAT point of contact for this burst is Judith Racusin (judith.racusin@nasa.gov).

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.

G. Vianello (Stanford), J. Racusin (GSFC)

report on behalf of the Fermi-LAT team:

At  03:19:53.74 on May 10, 2015, Fermi-LAT detected high-energy emission
from GRB 150510A, which was also detected by Fermi-GBM (trigger 452920796/
150510139).

The best LAT on-ground location is found to be

RA, Dec = 15.138,  4.985 (J2000)

with an error radius of 1.3 deg (90% containment, statistical error
only). This was 55 deg from the LAT boresight at the time of the trigger.

Our localization has an unusually large error because so far we have
received only 60 s worth of data after the trigger. Further contacts with
the spacecraft are scheduled for the next hours. We will release another
circular if the new data will allow us to refine the localization.

Our current localization is based on 5 photons between 100 and 300 MeV,
detected within 60 seconds from the trigger time.

Due to the large localization error, a Swift ToO has not been requested.

The Fermi-LAT point of contact for this burst is Judith Racusin (
judith.racusin@nasa.gov).

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.