12,064 research outputs found
Hard X-ray emission and Ti line features of Tycho Supernova Remnant
A deep hard X-ray survey of the INTEGRAL satellite first detected the
non-thermal emission up to 90 keV in the Tycho supernova (SN) remnant. Its 3 --
100 keV spectrum is fitted with a thermal bremsstrahlung of keV plus a power-law model of . Based on the
diffusive shock acceleration theory, this non-thermal emission, together with
radio measurements, implies that Tycho remnant may not accelerate protons up to
PeV but hundreds TeV. Only heavier nuclei may be accelerated to the cosmic
ray spectral "knee". In addition, we search for soft gamma-ray lines at 67.9
and 78.4 keV coming from the decay of radioactive Ti in Tycho remnant by
INTEGRAL. A bump feature in the 60-90 keV energy band, potentially associated
with the Ti line emission, is found with a marginal significance level
of 2.6 . The corresponding 3 upper limit on the
Ti line flux amounts to 1.5 10 ph cm s.
Implications on the progenitor of Tycho SN, considered to be the prototype of
type Ia SN, are discussed.Comment: 15 pages, 4 figures, accepted for publication in Ap
Hard X-ray emissions from Cassiopeia A observed by INTEGRAL
Cassiopeia A (Cas A) as the nearby young remnant of a core-collapse supernova
is the best candidate for astrophysical studies in supernova explosion and its
environment. We studied hard X-ray emissions from Cas A using the ten-year data
of INTEGRAL observations, and first detected non-thermal continuum emission
from the source up to 220 keV. The Ti line emissions at 68 and 78 keV
are confirmed by our observations with a mean flux of ph cm s, corresponding to a Ti yield in Cas A of
\ms. The continuum emission from 3 -- 500 keV can
be fitted with a thermal bremsstrahlung of keV plus a
power-law model of . The non-thermal emission from
Cas A is well fitted with a power-law model without a cutoff up to 220 keV.
This radiation characteristic is inconsistent with the diffusive shock
acceleration models with the remnant shock velocity of only 5000km s.
The central compact object in Cas A cannot contribute to the emission above 80
keV significantly. Some possible physical origins of the non-thermal emission
above 80 keV from the remnant shock are discussed. We deduce that the
asymmetrical supernova explosion scenario of Cas A is a promising scenario to
produce high energy synchrotron radiation photons, where a part of ejecta with
the velocity of and opening angle of can account for
the 100-keV emission, consistent with the "jet" observed in Cas A.Comment: 20 pages, 6 figures, 2 tables; accepted for the publication in Ap
Implications of Fermi-LAT observations on the origin of IceCube neutrinos
The IceCube (IC) collaboration recently reported the detection of TeV-PeV
extraterrestrial neutrinos whose origin is yet unknown. By the photon-neutrino
connection in and interactions, we use the \fermi-LAT
observations to constrain the origin of the IC detected neutrinos. We find that
Galactic origins, i.e., the diffuse Galactic neutrinos due to cosmic ray (CR)
propagation in the Milky Way, and the neutrinos from the Galactic point
sources, may not produce the IC neutrino flux, thus these neutrinos should be
of extragalactic origin. Moreover, the extragalactic gamma-ray bursts (GRBs)
may not account for the IC neutrino flux, the jets of active galactic nuclei
may not produce the IC neutrino spectrum, but the starburst galaxies (SBGs) may
be promising sources. As suggested by the consistency between the IC detected
neutrino flux and the Waxman-Bahcall bound, GRBs in SBGs may be the sources of
both the ultrahigh energy, eV, CRs and the ~PeV CRs that
produce the IC detected TeV-PeV neutrinos.Comment: JCAP accepted version; 8 pages, 2 figs; discussion on blazar origin
added; conclusion unchange
High-Energy Gamma-Rays from GRB X-ray Flares
The recent detection of X-ray flares during the afterglow phase of gamma-ray
bursts (GRBs) suggests an inner-engine origin, at radii inside the forward
shock. There must be inverse Compton (IC) emission arising from such flare
photons scattered by forward shock afterglow electrons when they are passing
through the forward shock. We find that this IC emission produces high energy
gamma-ray flares, which may be detected by AGILE, GLAST and ground-based TeV
telescopes. The anisotropic IC scattering between flare photons and forward
shock electrons does not affect the total IC component intensity, but cause a
time delay of the IC component peak relative to the flare peak. The anisotropic
scattering effect may also weaken, to some extent, the suppression effect of
the afterglow intensity induced by the enhanced electron cooling due to flare
photons. We speculate that this IC component may already have been detected by
EGRET from a very strong burst--GRB940217. Future observations by GLAST may
help to distinguish whether X-ray flares originate from late central engine
activity or from external shocks.Comment: 4 pages, Contributed talk presented at "The First GLAST Symposium",
Feb.5-8 2007, Stanford Universit
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