1,362 research outputs found
Extragalactic gamma-ray background from AGN winds and star-forming galaxies in cosmological galaxy formation models
We derive the contribution to the extragalactic gamma-ray background (EGB)
from AGN winds and star-forming galaxies by including a physical model for the
gamma-ray emission produced by relativistic protons accelerated by AGN-driven
and supernova-driven shocks into a state-of-the-art semi-analytic model of
galaxy formation. This is based on galaxy interactions as triggers of AGN
accretion and starburst activity and on expanding blast wave as the mechanism
to communicate outwards the energy injected into the interstellar medium by the
active nucleus. We compare the model predictions with the latest measurement of
the EGB spectrum performed by the Fermi-LAT in the range between 100 MeV and
820 GeV. We find that AGN winds can provide ~3515% of the observed EGB in
the energy interval E_{\gamma}=0.1-1 GeV, for ~7315% at E_{\gamma}=1-10
GeV, and for ~6020% at E_{\gamma}>10 GeV. The AGN wind contribution to the
EGB is predicted to be larger by a factor of 3-5 than that provided by
star-forming galaxies (quiescent plus starburst) in the hierarchical clustering
scenario. The cumulative gamma-ray emission from AGN winds and blazars can
account for the amplitude and spectral shape of the EGB, assuming the standard
acceleration theory, and AGN wind parameters that agree with observations. We
also compare the model prediction for the cumulative neutrino background from
AGN winds with the most recent IceCube data. We find that for AGN winds with
accelerated proton spectral index p=2.2-2.3, and taking into account internal
absorption of gamma-rays, the Fermi-LAT and IceCube data could be reproduced
simultaneously.Comment: 12 pages, 8 figures, accepted for publication in A&
ASTRI SST-2M prototype and mini-array simulation chain, data reduction software, and archive in the framework of the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) is a worldwide project aimed at building
the next-generation ground-based gamma-ray observatory. Within the CTA project,
the Italian National Institute for Astrophysics (INAF) is developing an
end-to-end prototype of the CTA Small-Size Telescopes with a dual-mirror
(SST-2M) Schwarzschild-Couder configuration. The prototype, named ASTRI SST-2M,
is located at the INAF "M.C. Fracastoro" observing station in Serra La Nave
(Mt. Etna, Sicily) and is currently in the scientific and performance
validation phase. A mini-array of (at least) nine ASTRI telescopes has been
then proposed to be deployed at the Southern CTA site, by means of a
collaborative effort carried out by institutes from Italy, Brazil, and
South-Africa. The CTA/ASTRI team is developing an end-to-end software package
for the reduction of the raw data acquired with both ASTRI SST-2M prototype and
mini-array, with the aim of actively contributing to the global ongoing
activities for the official data handling system of the CTA observatory. The
group is also undertaking a massive Monte Carlo simulation data production
using the detector Monte Carlo software adopted by the CTA consortium.
Simulated data are being used to validate the simulation chain and evaluate the
ASTRI SST-2M prototype and mini-array performance. Both activities are also
carried out in the framework of the European H2020-ASTERICS (Astronomy ESFRI
and Research Infrastructure Cluster) project. A data archiving system, for both
ASTRI SST-2M prototype and mini-array, has been also developed by the CTA/ASTRI
team, as a testbed for the scientific archive of CTA. In this contribution, we
present the main components of the ASTRI data handling systems and report the
status of their development.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Bexco, Busan, Korea. All CTA contributions at arXiv:1709.0348
Multiwavelength observation from radio through very-high-energy Gamma-ray of OJ 287 during the 12-year cycle flare in 2007
We performed simultaneous multiwavelength observations of OJ 287 with the
Nobeyama Millimeter Array for radio, the KANATA telescope and the KVA telescope
for optical, the Suzaku satellite for X-ray and the MAGIC telescope for very
high energy (VHE) gamma-ray in 2007. The observations were conducted for a
quiescent state in April and in a flaring state in November-December. We
clearly observed increase of fluxes from radio to X-ray bands during the
flaring state while MAGIC could not detect significant VHE gamma-ray emission
from the source. We could derive an upper limit (95% confidence level) of 1.7%
of the Crab Nebula flux above 150 GeV from about 41.2 hours of the MAGIC
observation. A simple SSC model suggests that the observed flaring activity
could be caused by evolutions in the distribution of the electron population
rather than changes of the magnetic field strength or Doppler beaming factor in
the jet.Comment: Contribution to the 31st ICRC, Lodz, Poland, July 200
Gamma rays from microquasars Cygnus X-1 and Cygnus X-3
Gamma-ray observations of microquasars at high and very-high energies can
provide valuable information of the acceleration processes inside the jets, the
jet-environment interaction and the disk-jet coupling. Two high-mass
microquasars have been deeply studied to shed light on these aspects: Cygnus
X-1 and Cygnus X-3. Both systems display the canonical hard and soft X-ray
spectral states of black hole transients, where the radiation is dominated by
non-thermal emission from the corona and jets and by thermal emission from the
disk, respectively. Here, we report on the detection of Cygnus X-1 above 60 MeV
using 7.5 yr of Pass8 Fermi-LAT data, correlated with the hard X-ray state. A
hint of orbital flux modulation was also found, as the source is only detected
in phases around the compact object superior conjunction. We conclude that the
high-energy gamma-ray emission from Cygnus X-1 is most likely associated with
jets and its detection allow us to constrain the production site. Moreover, we
include in the discussion the final results of a MAGIC long-term campaign on
Cygnus X-1 that reaches almost 100 hr of observations at different X-ray
states. On the other hand, during summer 2016, Cygnus X-3 underwent a flaring
activity period in radio and high-energy gamma rays, similar to the one that
led to its detection in the high-energy regime in 2009. MAGIC performed
comprehensive follow-up observations for a total of about 70 hr. We discuss our
results in a multi-wavelength context.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Bexco, Busan, Korea (arXiv:1708.05153
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