17 research outputs found
A Hard X-Ray View of Two Distant VHE Blazars: 1ES 1101-232 and 1ES 1553+113
TeV blazars are known as prominent nonthermal emitters across the entire
electromagnetic spectrum with their photon power peaking in the X-ray and TeV
bands. If distant, absorption of gamma-ray photons by the extragalactic
background light (EBL) alters the intrinsic TeV spectral shape, thereby
affecting the overall interpretation. Suzaku observations for two of the more
distant TeV blazars known to date, 1ES 1101-232 and 1ES 1553+113, were carried
out in 2006 May and July, respectively, including a quasi-simultaneous coverage
with the state-of-the-art Cerenkov telescope facilities. We report on the
resulting data sets with emphasis on the X-ray band and set in context to their
historical behavior. During our campaign, we did not detect any significant
X-ray or gamma-ray variability. 1ES 1101-232 was found in a quiescent state
with the lowest X-ray flux ever measured. The combined XIS and HXD PIN data for
1ES 1101-232 and 1ES 1553+113 clearly indicate spectral curvature up to the
highest hard X-ray data point (~30 keV), manifesting as softening with
increasing energy. We describe this spectral shape by either a broken power law
or a log-parabolic fit with equal statistical goodness of fits. The combined
1ES 1553+113 very high energy spectrum (90-500 GeV) did not show any
significant changes with respect to earlier observations. The resulting
contemporaneous broadband spectral energy distributions of both TeV blazars are
discussed in view of implications for intrinsic blazar parameter values, taking
into account the gamma-ray absorption in the EBL.Comment: 9 pages, 10 figure
Upper Bound on the First Star Formation History
Our understanding of the nature of the extragalactic background light (EBL)
has improved with the recent development of gamma-ray observation techniques.
An open subject in the context of the EBL is the reionization epoch, which is
an important probe of the formation history of first stars, the so-called
Population III (Pop III) stars. Although the mechanisms for the formation of
Pop III stars are rather well understood on theoretical grounds, their
formation history is still veiled in mystery because of their faintness. To
shed light into this matter, we study jointly the gamma-ray opacity of distant
objects and the reionization constraints from studies of intergalactic gas. By
combining these studies, we obtain a sensitive upper bound on the Pop III star
formation rate density as at
, where and are the escape fraction of ionizing
photons from galaxies and the clumping factor of the intergalactic hydrogen
gas. This limit is a times tighter constraint compared with previous
studies that take into account gamma-ray opacity constraints only. Even if we
do not include the current gamma-ray constraints, the results do not change.
This is because the detected gamma-ray sources are still at where
the reionization has already finished.Comment: 5 pages, 2 figures, accepted for publication in ApJ
On the Radio and Optical Luminosity Evolution of Quasars
We calculate simultaneously the radio and optical luminosity evolutions of
quasars, and the distribution in radio loudness R defined as the ratio of radio
and optical luminosities, using a flux limited data set containing 636 quasars
with radio and optical fluxes from White et al. We first note that when dealing
with multivariate data it is imperative to first determine the true
correlations among the variables, not those introduced by the observational
selection effects, before obtaining the individual distributions of the
variables. We use the methods developed by Efron and Petrosian which are
designed to obtain unbiased correlations, distributions, and evolution with
redshift from a data set truncated due to observational biases. It is found
that the population of quasars exhibits strong positive correlation between the
radio and optical luminosities. With this correlation, whether intrinsic or
observationally induced accounted for, we find that there is a strong
luminosity evolution with redshift in both wavebands, with significantly higher
radio than optical evolution. We also construct the local radio and optical
luminosity functions and the density evolution. Finally, we consider the
distribution of the radio loudness parameter R obtained from careful treatment
of the selection effects and luminosity evolutions with that obtained from the
raw data without such considerations. We find a significant difference between
the two distributions and no clear sign of bi-modality in the true distribution
for the range of R values considered. Our results indicate therefore, somewhat
surprisingly, that there is no critical switch in the efficiency of the
production of disk outflows/jets between very radio quiet and very radio loud
quasars, but rather a smooth transition. Also, this efficiency seems higher for
the high-redshift and more luminous sources in the considered sample.Comment: 15 pages, 15 figures, accepted to ApJ, updated to in press versio
Prospects for future very high-energy gamma-ray sky survey: impact of secondary gamma rays
Very high-energy gamma-ray measurements of distant blazars can be well
explained by secondary gamma rays emitted by cascades induced by
ultra-high-energy cosmic rays. The secondary gamma rays will enable one to
detect a large number of blazars with future ground based gamma-ray telescopes
such as Cherenkov Telescope Array (CTA). We show that the secondary emission
process will allow CTA to detect 100, 130, 150, 87, and 8 blazars above 30 GeV,
100 GeV, 300 GeV, 1 TeV, and 10 TeV, respectively, up to assuming the
intergalactic magnetic field (IGMF) strength G and an unbiased all
sky survey with 0.5 hr exposure at each Field of View, where total observing
time is hr. These numbers will be 79, 96, 110, 63, and 6 up to
in the case of G. This large statistics of sources will
be a clear evidence of the secondary gamma-ray scenarios and a new key to
studying the IGMF statistically. We also find that a wider and shallower survey
is favored to detect more and higher redshift sources even if we take into
account secondary gamma rays.Comment: 8 pages, 3 figures, accepted for publication in Astroparticle Physic
Fermi-LAT Detection of a Break in the Gamma-Ray Spectrum of the Supernova Remnant Cassiopeia A
We report on observations of the supernova remnant Cassiopeia A in the energy
range from 100 MeV to 100 GeV using 44 months of observations from the Large
Area Telescope on board the Fermi Gamma-ray Space Telescope. We perform a
detailed spectral analysis of this source and report on a low-energy break in
the spectrum at GeV. By comparing the results with
models for the gamma-ray emission, we find that hadronic emission is preferred
for the GeV energy range.Comment: 18 pages, 5 figures, 2 tables, to be published in Ap
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Bright AGN Source List from the First Three Months of the Fermi Large Area Telescope All-Sky Survey
Recommended from our members
A Multi-Chamber System for Analyzing the Outgassing, Deposition,and Associated Optical Degradation Properties of Materials in a Vacuum
We report on the Camera Materials Test Chamber, a multi-vessel apparatus which analyzes the outgassing consequences of candidate materials for use in the vacuum cryostat of a new telescope camera. The system measures the outgassing products and rates of samples of materials at different temperatures, and collects films of outgassing products to measure the effects on light transmission in six optical bands. The design of the apparatus minimizes potential measurement errors introduced by background contamination
Gravitomagnetism and spinor quantum mechanics
We give a systematic treatment of a spin 1/2 particle in a combined
electromagnetic field and a weak gravitational field that is produced by a
slowly moving matter source. This paper continues previous work on a spin zero
particle, but it is largely self-contained and may serve as an introduction to
spinors in a Riemann space. The analysis is based on the Dirac equation
expressed in generally covariant form and coupled minimally to the
electromagnetic field. The restriction to a slowly moving matter source, such
as the earth, allows us to describe the gravitational field by a
gravitoelectric (Newtonian) potential and a gravitomagnetic (frame-dragging)
vector potential, the existence of which has recently been experimentally
verified. Our main interest is the coupling of the orbital and spin angular
momenta of the particle to the gravitomagnetic field. Specifically we calculate
the gravitational gyromagnetic ratio as gsubg=1 ; this is to be compared with
the electromagnetic gyromagnetic ratio of gsube=2 for a Dirac electron.Comment: 12 pages, 1 figur
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Flux and Photon Spectral Index Distributions of Fermi-LAT Blazars and Contribution to the Extragalactic Gamma-ray Background
We present a determination of the distributions of gamma-ray flux - the so called LogN-LogS relation - and photon spectral index for the 352 blazars detected with a greater than approximately seven sigma detection threshold and located above {+-} 20{sup o} Galactic latitude by the Large Area Telescope of the Fermi Gamma-ray Space Telescope in its first year catalog. Because the flux detection threshold depends on the photon index, the observed raw distributions do not provide the true LogN-LogS counts or the true distribution of the photon index. We use the non-parametric methods developed by Efron and Petrosian to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation among the two variables. We demonstrate the robustness of our procedures using a simulated data set of blazars and then apply these to the real data and find that for the population as a whole the intrinsic flux distribution can be represented by a broken power law of slopes -2.37 {+-} 0.13 and -1.70 {+-} 0.26, and the intrinsic photon index distribution can be represented by a Gaussian with mean 2.41 {+-} 0.13 and 1{sigma} width of 0.25 {+-} 0.03. We also find the intrinsic distributions for the sub-populations of BL Lac and FSRQs type blazars separately. We then calculate the contribution of blazars to the diffuse cosmic gamma-ray background radiation to be 28% {+-} 19%