181 research outputs found
Combining the Swift/BAT and the INTEGRAL/ISGRI observations
Current surveys of Active Galactic Nuclei (AGN) find only a very small
fraction of AGN contributing to the Cosmic X-ray Background (CXB) at energies
above 15 keV. Roughly 99% of the CXB is so far unresolved. In this work we
address the question of the unresolved component of the CXB with the combined
surveys of INTEGRAL and Swift. These two currently flying X-ray missions
perform independent surveys at energies above 15 keV. Our approach is to
perform the independent surveys and merge them in order to enhance the exposure
time and reduce the systematic uncertainties. We do this with resampling
techniques. As a result we obtain a new survey over a wide sky area of 6200
deg2 that is a factor ~4 more sensitive than the survey of Swift or INTEGRAL
alone. Our sample comprises more than 100 AGN. We use the extragalactic source
sample to resolve the CXB by more than a factor 2 compared to current parent
surveys.Comment: 4 pages, 1 figure. To appear on World Scientific Vol.7 "Proceedings
of the 13th ICATPP Conference on Astroparticle, Particle, Space Physics and
Detectors for Physics Applications
Deeply x-raying the high-energy sky
All-sky explorations by Fermi-LAT have revolutionized our view of the
gamma-ray sky. While its ongoing all-sky survey counts thousands of sources,
essential issues related to the nature of unassociated sources call for
sensitive all-sky surveys at hard X-ray energies that allow for their
identification. We present the results of the association of the Fermi-LAT
second source catalog to hard X-ray detected sources.Comment: 5 pages, 4 figures, submitted JPC
Identifying the 3FHL catalog: I. Results of the KOSMOS optical spectroscopy campaign
We present the results of the optical spectroscopy follow-up of a sample of
28 unclassified blazars from the Third Fermi-LAT Catalog of High-Energy Sources
(3FHL). All the spectra were taken with the 4m Mayall telescope at Kitt Peak.
With this follow-up program we are able to classify 27 out of 28 objects as BL
Lacs, while the remaining one is a flat spectrum radio quasar. We determine a
redshift (z) for three of these objects and a lower limit on z for other four
sources: the farthest object for which we obtain a redshift has z>0.836. These
results are part of a more extended campaign of optical spectroscopy follow-up
of 3FHL blazars, aimed to obtain a complete sample of blazars at >10 GeV which
will then be used to extend our knowledge on blazar emission mechanisms and on
the extragalactic background light.Comment: 12 pages, 6 figures. Accepted for publication on the Astronomical
Journal Supplement Series. The spectra analyzed in this work are available at
the following link:
https://clemson.app.box.com/s/uu1hk6g4qy0ow9j4nst4nifm3mmrs19
The deep look onto the hard X-ray sky: The Swift - INTEGRAL X-ray (SIX) survey
The super-massive black-holes in the centers of Active Galactic Nuclei (AGNs)
are surrounded by obscuring matter that can block the nuclear radiation.
Depending on the amount of blocked radiation, the flux from the AGN can be too
faint to be detected by currently flying hard X-ray (above 15 keV) missions. At
these energies only ~1% of the intensity of the Cosmic X-ray Background (CXB)
can be resolved into point-like sources that are AGNs. In this work we address
the question of the undetected sources contributing to the CXB with a very
sensitive and new hard X-ray survey: the SIX survey that is obtained with the
new approach of combining the Swift/BAT and INTEGRAL/IBIS X-ray observations.
We merge the observations of both missions. This enhances the exposure time and
reduces systematic uncertainties. As a result we obtain a new survey over a
wide sky area of 6200 deg^2 that is more sensitive than the surveys of
Swift/BAT or INTEGRAL/IBIS alone. Our sample comprises 113 sources: 86 AGNs
(Seyfert-like and blazars), 5 galaxies, 2 clusters of galaxies, 3 Galactic
sources, 3 previously detected unidentified X-ray sources, and 14 unidentified
sources. The scientific outcome from the study of the sample has been properly
addressed to study the evolution of AGNs at redshift below 0.4. We do not find
any evolution using the 1/V_max method. Our sample of faint sources are
suitable targets for the new generation hard X-ray telescopes with focusing
techniques.Comment: ApJS accepte
Gamma-ray Emission from Galaxies Hosting Molecular Outflows
Many star-forming galaxies and those hosting active galactic nuclei (AGN)
show evidence of massive outflows of material in a variety of phases including
ionized, neutral atomic, and molecular. Molecular outflows in particular have
been the focus of recent interest as they may be responsible for removing gas
from the galaxy, thereby suppressing star formation. As material is ejected
from the cores of galaxies, interactions of the outflowing material with the
interstellar medium can accelerate cosmic rays and produce high-energy gamma
rays. In this work, we search for gamma-ray emission from a sample of local
galaxies known to host molecular outflows using data collected by the {\fermi}
Large Area Telescope. We employ a stacking technique in order to search for and
characterize the average gamma-ray emission properties of the sample. Gamma-ray
emission is detected from the galaxies in our sample at the
level with a power-law photon index of in the 1-800 GeV
energy range. The emission is found to correlate with tracers of star formation
activity, namely the m infrared luminosity. We also find that
the observed signal can be predominantly attributed to \ion{H}{ii} galaxies
hosting energy-driven outflows. While we do not find evidence suggesting that
the outflows are accelerating charged particles directly, galaxies with
molecular outflows may produce more gamma rays than galaxies without outflows.
In particular, the set consisting of gamma-ray-detected galaxies with molecular
outflows are nearly perfect calorimeters and may be future targets for searches
of high-energy neutrinos.Comment: 20 pages, 9 figures, 3 tables. Accepted to The Astrophysical Journa
Disentangling the Hadronic Components in NGC 1068
The recent detection of high-energy neutrinos by IceCube in the direction of
the nearby Seyfert/starburst galaxy NGC 1068 implies that radio-quiet active
galactic nuclei can accelerate cosmic-ray ions. Dedicated multi-messenger
analyses suggest that the interaction of these high-energy ions { with ambient
gas or photons} happens in a region of the galaxy that is highly opaque for
GeV-TeV gamma rays. Otherwise, the GeV-TeV emission would violate existing
constraints provided by {\it Fermi}-LAT and MAGIC. The conditions of high
optical depth are realized near the central super-massive black hole (SMBH). At
the same time, the GeV emission detected by the {\it Fermi}-Large Area
Telescope (LAT) is likely related to the galaxy's sustained star-formation
activity. In this work, we derive a 20\,MeV - 1\,TeV spectrum of NGC 1068 using
14\,yrs of {\it Fermi}-LAT observations. We find that the starburst hadronic
component is responsible for NGC 1068's emission above 500\,MeV. However,
below this energy an additional component is required. In the 20-500\,MeV range
the {\it Fermi}-LAT data are consistent with hadronic emission {initiated by
non-thermal ions interacting with gas or photons} in the vicinity of the
central SMBH. This highlights the importance of the MeV band to discover hidden
cosmic-ray accelerators.Comment: Accepted for publication in ApJ Letter
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