96 research outputs found
Pair-production opacity at high and very-high gamma-ray energies
The propagation of high energy (HE, MeV) and very high-energy
gamma-rays (VHE, GeV) in the extra-galactic photon field leads
to pair-production and consequently energy- and distance-dependent attenuation
of the primary intensity. The spectroscopy of an increasing number of
extra-galactic objects at HE and VHE energies has demonstrated indeed the
presence of such an attenuation which in turn has been used to constrain the
photon density in the medium. At large optical depth ()
potential modifications of pair-production due to competing but rare processes
(as, e.g., the presence of sub-neV axion-like particle) may be found.
Indications for a pair-production anomaly have previously been found with
VHE-spectra. Here, we present further indications (at the level of ) for a reduced optical depth at high energies from an analysis of
Fermi-\textit{LAT} data.Comment: 4 pages, 2 figures, to be published in the proceedings
(DESY-PROC-2013-04) of the 9th patras worksho
AstroFit: An Interface Program for Exploring Complementarity in Dark Matter Research
AstroFit is an interface adding astrophysical components to programs for
fitting physics beyond the Standard Model (BSM) to experimental data from
collider searches. The project aims at combining a wide range of experimental
results from indirect, direct and collider serarches for Dark Matter (DM) and
confronting it with theoretical expectations in various DM models. Here, we
introduce AstroFit and discuss first results.Comment: 6 pages, 3 figures, proceedings for the 13th ICATPP Conference on
Astroparticle, Particle, Space Physics and Detectors for Physics
Applications, Villa Olm
Characterization of a Transition-Edge Sensor for the ALPS II Experiment
The ALPS II experiment, Any Light Particle Search II at DESY in Hamburg, will
look for light (m< 10-4 eV) new fundamental bosons (e.g., axion-like particles,
hidden photons and other WISPs) in the next years by the mean of a
light-shining-through-the-wall setup. The ALPS II photosensor is a
Transition-Edge Sensor (TES) optimized for lambda = 1064 nm photons. The
detector is routinely operated at 80 mK, allowing single infrared photon
detections as well as non-dispersive spectroscopy with very low background
rates. The demonstrated quantum efficiency for such TES is up to 95% at lambda
=1064 nm. For 1064 nm photons, the measured background rate is < 10-2 sec-1 and
the intrinsic dark count rate in a dark environment was found to be of 1,0.10-4
sec-1. Latest characterization results are discussed.Comment: Contributed to the 11th Patras Workshop on Axions, WIMPs and WISPs,
Zaragoza, June 22 to 26, 201
Fermi Large Area Telescope Observations of the Fast-dimming Crab Nebula in 60-600 MeV
Context: The Crab pulsar and its nebula are the origin of relativistic
electrons which can be observed through their synchrotron and inverse Compton
emission. The transition between synchrotron-dominated and
inverse-Compton-dominated emissions takes place at eV. Aims: The
short-term (weeks to months) flux variability of the synchrotron emission from
the most energetic electrons is investigated with data from ten years of
observations with the Fermi Large Area Telescope (LAT) in the energy range from
60 MeV to 600 MeV. Methods: The off-pulse light-curve has been reconstructed
from phase-resolved data. The corresponding histogram of flux measurements is
used to identify distributions of flux-states and the statistical significance
of a lower-flux component is estimated with dedicated simulations of mock
light-curves. The energy spectra for different flux states are reconstructed.
Results: We confirm the presence of flaring-states which follow a log-normal
flux distribution. Additionally, we discover a low-flux state where the flux
drops to as low as 18.4% of the intermediate-state average flux and stays there
for several weeks. The transition time is observed to be as short as 2 days.
The energy spectrum during the low-flux state resembles the extrapolation of
the inverse-Compton spectrum measured at energies beyond several GeV energy,
implying that the high-energy part of the synchrotron emission is dramatically
depressed. Conclusions: The low-flux state found here and the transition time
of at most 10 days indicate that the bulk (%) of the synchrotron emission
above eV originates in a compact volume with apparent angular size of
. We tentatively infer that
the so-called inner knot feature is the origin of the bulk of the -ray
emission.Comment: Accepted by A&A on 05.05.2020; Original version submitted on
19.09.201
Probing axion-like particles with the ultraviolet photon polarization from active galactic nuclei in radio galaxies
The mixing of photons with axion-like particles (ALPs) in the large-scale
magnetic field changes the polarization angle of a linearly polarized
photon beam from active galactic nuclei in radio galaxies as it propagates over
cosmological distances. Using available ultraviolet polarization data
concerning these sources we derive a new bound on the product of the photon-ALP
coupling times . We find
GeV nG for ultralight ALPs with eV. We compare
our new bound with the ones present in the literature and we comment about
possible improvements with observations of more sources.Comment: v2: one typo corrected. Added a few comments, matches published
versio
- …