GRB 060427B

S. Golenetskii, R. Aptekar, E. Mazets, V. Pal'shin, and D. Frederiks
on behalf of the Konus-Wind team,

K. Hurley and T. Cline on behalf of the Ulysses, Mars Odyssey,
and Konus GRB teams,

I. Mitrofanov, A. Kozyrev, M. Litvak, A. Sanin, V. Tret'yakov and
A. Parshukov, on behalf of the HEND-Odyssey GRB team,

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

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

A. von Kienlin, G. Lichti, A. Rau, D. Gotz, and S. Mereghetti,
on behalf of the INTEGRAL GRB team,  report:

A short duration hard spectrum GRB, 060427B, occurred at about 23:51:55
UT.  It was observed by Konus-Wind, Mars Odyssey (GRS and HEND),
INTEGRAL-SPI-ACS, and Swift-BAT.  The burst was outside of the field of
view of Swift-BAT, so it was not imaged.  As the burst arrived almost
along the Odyssey-Earth vector, the resulting annulus was unusually
wide.

The burst light curve shows a single pulse with a duration of ~0.2 sec.
A weak emission is seen in the K-W G2 band (83-360 keV) starting
at ~0.3 sec before the main pulse.

The burst has been triangulated to RA, Dec = 98.472, +21.348 deg (J2000).
The corners of the 3 sigma error box are:
-----------------------
RA, deg   Dec, deg
-----------------------
98.8479  22.7146
98.7014  19.9202
98.0629  19.9948
98.1954  22.8568
--------------------

The area of this error box is 1.7 sq. deg.

Konus-Wind spectral analysis is in progress.  Preliminary analysis
indicates that Epeak was >1 MeV.

V. Lipunov, V.Kornilov, N.Tyurina, A.Belinski, D.Kuvshinov, E.Gorbovskoy,
A.Krylov, N.Shatskiy, G.Borisov, A.Sankovich,  V.Vladimirov, P.Gritsyk, 
S.Korobkin

Sternberg Astronomical Institute, Moscow Union 'Optic'

MASTER  robotic system (http://observ.pereplet.ru) observed
  GRB060427B error box (GRB_TIME is 2006-04-27 23:51:55 UT, IPN 
triangulation, S. Golenetskii et al.
GCN5030
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 ) in survey mode at considerable zenit distances. The weather was 
good.
We start at 28 apr 2006 18:27:10.44 
(18.5 h   after the GRB time) and now we have more than 20 images (each 6 
square degrees) of the large error box.
We note that the error box is very close to galactic plane and we have a 
lot of objects. The reduction is continued.


MASTER team  thanks to Konus team for collaboration. This work is 
supported by RFFI  04-02-16411 grant.
This message can be cited.
Mailto: lipunov@sai.msu.ru

S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, and
T. Cline on behalf of the Konus-Wind team report:

The short hard GRB 060427B localized by IPN (Golenetskii et al.,
GCN 5030
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 ) triggered Konus-Wind at T0=85912.029 s UT (23:51:52.029).

As observed by Konus-Wind it had the fluence 4.95(-3.53,+0.71)x10^-6 
erg/cm2, and the 16-ms peak flux measured from T0-0.012 s
4.30(-3.27, +1.27)x10^-5  erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The spectrum of the burst integrated from T0 to T0+0.128 s is well 
fitted (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 = 0.573 (-0.404,  +0.284)
and Ep = 1746 (-582, +962) keV (chi2 = 24.5/22 dof).

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

Pablo Saz Parkinson (UC Santa Cruz) on behalf of the Milagro
collaboration reports:

We have searched Milagro data for emission at GeV/TeV energies from
GRB 060427B (GCN Circ 5030
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 , K. Hurley et al.), during the burst
duration (0.2 s) reported by the IPN team.
No evidence for prompt GeV/TeV emission was found.
A preliminary analysis, assuming a differential photon spectral
index of -2.4, gives an upper limit on E^2dN/dE at 99% confidence of:

E^2dN/dE at 2 TeV < 4.8 * 10^(-8) erg cm^(-2) (No EBL absorption)

TeV photons are attenuated by pair production with infrared photons in
intergalactic space. We calculate an upper limit assuming a
redshift of 0.5 (a value representative of short/hard bursts) using the
extragalactic infrared background light (EBL) absorption model of
Primack et al. 2005 (AIP Conf. Proc. 745, p. 23).
We find 99% confidence level upper limits on E^2dN/dE of:

E^2dN/dE at 150 GeV < 5.1 * 10^(-6) erg cm^(-2) (Primack et al. EBL model)

The energies quoted represent the approximate median energy of the
events that would be detected assuming a power law spectrum with
differential index -2.4 convolved with the absorption model.
These upper limits are preliminary and will be refined with further
analysis.