666 research outputs found
Neutrinos from Gamma Ray Bursts
The observed fluxes of cosmic rays and gamma rays are used to infer the
maximum allowed high-energy neutrino flux allowed for Gamma Ray Bursts (GRBs),
following Mannheim, Protheroe, and Rachen (2000). It is shown that if GRBs
produce the ultrahigh-energy cosmic rays, they should contribute (a) at least
10% of the extragalactic gamma ray background between 3 MeV and 30 GeV,
contrary to their observed energy flux which is only a minute fraction of this
flux, and (b) a cumulative neutrino flux a factor of 20 below the AMANDA
(Neutrino 2000) limit on isotropic neutrinos. This could have two implications,
either GRBs do not produce the ultrahigh energy cosmic rays or that the GRBs
are strongly beamed and emit most of their power at energies well above 100 GeV
implausibly increasing the energy requirements, but consistent with the
marginal detections of a few low-redshift GRBs by MILAGRITO, HEGRA-AIROBICC,
and the Tibet-Array. All crucial measurements to test the models will be
available in the next few years. These are measurements of (i) high-energy
neutrinos with AMANDA-ICECUBE or an enlarged ANTARES/NESTOR ocean detector,
(ii) GRB redshifts from HETE-2 follow-up studies, and (iii) GRB spectra above
10 GeV with low-threshold imaging air Cherenkov telescopes such as MAGIC and
the space telescopes AGILE and GLAST.Comment: 8 pages, 1 figure, to appear in the Proc. of the Heidelberg
International Symposium on High Energy Gamma-Ray Astronomy, Heidelberg, June
26-30, 2000, ed. by H.J. Voelk and F. Aharonian, AIP Conf. Pro
Gamma-rays from pulsar wind nebulae in starburst galaxies
Recently, gamma-ray emission at TeV energies has been detected from the
starburst galaxies NGC253 (Acero et al., 2009) and M82 (Acciari et al., 2009.
It has been claimed that pion production due to cosmic rays accelerated in
supernova remnants interacting with the interstellar gas is responsible for the
observed gamma rays. Here, we show that the gamma-ray pulsar wind nebulae left
behind by the supernovae contribute to the TeV luminosity in a major way. A
single pulsar wind nebula produces about ten times the total luminosity of the
Sun at energies above 1 TeV during a lifetime of 10^5 years. A large number of
3x10^4 pulsar wind nebulae expected in a typical starburst galaxy at a distance
of 4 Mpc can readily produce the observed TeV gamma rays.Comment: 5 pages, 2 figures, accepted for publication in Astropart. Phy
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