679 research outputs found
New X-ray bound on density of primordial black holes
We set a new upper limit on the abundance of primordial black holes (PBH)
based on existing X-ray data. PBH interactions with interstellar medium should
result in significant fluxes of X-ray photons, which would contribute to the
observed number density of compact X-ray objects in galaxies. The data
constrain PBH number density in the mass range from a few to . PBH density needed to account for the origin of black holes
detected by LIGO is marginally allowed.Comment: 12 pages, 2 figures, accepted for publication in JCA
An LDPCC decoding algorithm based on Bowman-Levin approximation --Comparison with BP and CCCP--
Belief propagation (BP) and the concave convex procedure (CCCP) are both
methods that utilize the Bethe free energy as a cost function and solve
information processing tasks. We have developed a new algorithm that also uses
the Bethe free energy, but changes the roles of the master variables and the
slave variables. This is called the Bowman-Levin (BL) approximation in the
domain of statistical physics. When we applied the BL algorithm to decode the
Gallager ensemble of short-length regular low-density parity check codes
(LDPCC) over an additive white Gaussian noise (AWGN) channel, its average
performance was somewhat better than that of either BP or CCCP. This implies
that the BL algorithm can also be successfully applied to other problems to
which BP or CCCP has already been applied.Comment: 2005 IEEE International Symposium on Information Theor
Prospects for Very High Energy Blazar Survey by the Next Generation Cherenkov Telescopes
The prospects for future blazar surveys by next-generation very high energy
(VHE) gamma-ray telescopes, such as Advanced Gamma-ray Imaging System (AGIS)
and Cherenkov Telescope Array (CTA), are investigated using the latest model of
blazar luminosity function and its evolution which is in good agreement with
the flux and redshift distribution of observed blazars as well as the
extragalactic gamma-ray background. We extend and improve the template of
spectral energy distributions (SEDs) based on the blazar SED sequence paradigm,
to make it reliable also in the VHE bands (above 100 GeV) by comparing with the
existing VHE blazar data. Assuming the planned CTA sensitivities, a blind
survey using a total survey time of ~100 hrs could detect ~3 VHE blazars, with
larger expected numbers for wider/shallower surveys. We also discuss
following-up of Fermi blazars. Detectability of VHE blazars in the plane of
Fermi flux and redshift is presented, which would be useful for future survey
planning. Prospects and strategies are discussed to constrain the extragalactic
background light (EBL) by using the absorption feature of brightest blazar
spectra, as well as cut-offs in the redshift distribution. We will be able to
get useful constraints on EBL by VHE blazars at different redshifts ranging
0.3-1 TeV corresponding to z=0.10-0.36.Comment: 11 pages, 11 figures, accepted for publication in PAS
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