17 research outputs found
Constraining Galactic dark matter with gamma-ray pixel counts statistics
Gamma-ray searches for new physics such as dark matter are often driven by
investigating the composition of the extragalactic gamma-ray background (EGB).
Classic approaches to EGB decomposition manifest in resolving individual point
sources and dissecting the intensity spectrum of the remaining unresolved
component. Furthermore, statistical methods have recently been proven to
outperform the sensitivity of classic source detection algorithms in finding
point-source populations in the unresolved flux regime. In this article, we
employ the 1-point photon count statistics of eight years of Fermi-LAT data to
resolve the population of extragalactic point sources and to decompose the
diffuse isotropic background contribution for Galactic latitudes |b|>30 deg. We
use three adjacent energy bins between 1 and 10 GeV. For the first time, we
extend the analysis to incorporate a potential contribution from annihilating
dark matter smoothly distributed in the Galaxy. We investigate the sensitivity
reach of 1-point statistics for constraining the thermally-averaged
self-annihilation cross section of dark matter, using different
template models for the Galactic foreground emission. Given the official
Fermi-LAT interstellar emission model, we set upper bounds on the DM
self-annihilation cross section that are comparable with the
constraints obtained by other indirect detection methods, in particular by the
stacking analysis of several dwarf spheroidal galaxies.Comment: 11 pages, 7 figures, 1 table; v2: major changes improving the
selection of the RO
New Constraints on Hidden Photons using Very High Energy Gamma-Rays from the Crab Nebula
Extensions of the standard model of particle physics, in particular those
based on string theory, often predict a new U(1) gauge symmetry in a hidden
sector. The corresponding gauge boson, called hidden photon, naturally
interacts with the ordinary photon via gauge kinetic mixing, leading to photon
- hidden photon oscillations. In this framework, one expects photon
disappearance as a function of the mass of the hidden photon and the mixing
angle, loosely constrained from theory. Several experiments have been carried
out or are planned to constrain the mass-mixing plane.
In this contribution we derive new constraints on the hidden photon
parameters, using very high energy gamma-rays detected from the Crab Nebula,
whose broad-band spectral characteristics are well understood. The very high
energy gamma-ray observations offer the possibility to provide bounds in a
broad mass range at a previously unexplored energy and distance scale. Using
existing data that were taken with several Cherenkov telescopes, we discuss our
results in the context of current constraints and consider the possibilities of
using astrophysical data to search for hidden photon signatures.Comment: Proceedings of the "Heidelberg International Symposium on High Energy
Gamma-Ray Astronomy", Heidelberg, Germany, July 7-11, 2008, submitted to AIP
Conference Proceedings. 4 pages, 2 figures, 1 tabl
Probing the nature of Dark Matter with the SKA
Dark Matter (DM) is a fundamental ingredient of our Universe and of structure
formation, and yet its nature is elusive to astrophysical probes. Information
on the nature and physical properties of the WIMP (neutralino) DM (the leading
candidate for a cosmologically relevant DM) can be obtained by studying the
astrophysical signals of their annihilation/decay. Among the various e.m.
signals, secondary electrons produced by neutralino annihilation generate
synchrotron emission in the magnetized atmosphere of galaxy clusters and
galaxies which could be observed as a diffuse radio emission (halo or haze)
centered on the DM halo. A deep search for DM radio emission with SKA in local
dwarf galaxies, galaxy regions with low star formation and galaxy clusters
(with offset DM-baryonic distribution, like e.g. the Bullet cluster) can be
very effective in constraining the neutralino mass, composition and
annihilation cross-section. For the case of a dwarf galaxy, like e.g. Draco,
the constraints on the DM annihilation cross-section obtainable with SKA1-MID
will be at least a factor more stringent than the limits obtained
by Fermi-LAT in the -rays. These limits scale with the value of the B
field, and the SKA will have the capability to determine simultaneously both
the magnetic field in the DM-dominated structures and the DM particle
properties. The optimal frequency band for detecting the DM-induced radio
emission is around GHz, with the SKA1-MID Band 1 and 4 important to
probe the synchrotron spectral curvature at low- (sensitive to DM
composition) and at high- (sensitive to DM mass).Comment: 10 pages, 5 figures, to appear as part of 'Cosmic Magnetism' in
proceedings of 'Advancing Astrophysics with the Square Kilometre Array'
PoS(AASKA14)10
Testing gamma-ray models of blazars in the extragalactic sky
The global contribution of unresolved gamma-ray point sources to the
extragalactic gamma-ray background has been recently measured down to gamma-ray
fluxes lower than those reached with standard source detection techniques, and
by employing the statistical properties of the observed gamma-ray counts. We
investigate and exploit the complementarity of the information brought by the
one-point statistics of photon counts (using more than 10 years of Fermi-LAT
data) and by the recent measurement of the angular power spectrum of the
unresolved gamma-ray background (based on 8 years of Fermi-LAT data). We
determine, under the assumption that the source-count distribution of the
brightest unresolved objects is dominated by blazars, their gamma-ray
luminosity function and spectral energy distribution down to fluxes almost two
orders of magnitude smaller than the threshold for detecting resolved sources.
The different approaches provide consistent predictions for the gamma-ray
luminosity function of blazars, and they show a significant complementarity.Comment: Matches the published version; extended discussion on detection
efficiency, 4FGL fit improved, comments added. Main results and conclusions
unchange
Hunting for dark halo substructure using submilliarcsecond-scale observations of macrolensed radio jets
Dark halo substructure may reveal itself through secondary, small-scale
gravitational lensing effects on light sources that are macrolensed by a
foreground galaxy. Here, we explore the prospects of using Very Long Baseline
Interferometry (VLBI) observations of multiply-imaged quasar jets to search for
submilliarcsecond-scale image distortions produced by various forms of dark
substructures in the 1e3-1e8 Msolar mass range. We present lensing simulations
relevant for the angular resolutions attainable with the existing European VLBI
Network (EVN), the global VLBI array, and an upcoming observing mode in which
the Atacama Large Millimeter Array (ALMA) is connected to the global VLBI
array. While observations of this type would not be sensitive to standard cold
dark matter subhalos, they can be used to detect more compact forms of halo
substructure predicted in alternative structure formation scenarios. By mapping
~5 strongly lensed systems, it should be possible to detect or robustly rule
out primordial black holes in the 1e3-1e6 Msolar mass range if they constitute
>1% percent of the dark matter in these lenses. Ultracompact minihalos are
harder to detect using this technique, but 1e6-1e8 Msolar ultracompact
minihalos could in principle be detected if they constitute >10% of the dark
matter.Comment: 13 pages, 8 figures; v.2 accepted for publication in MNRA
A Search for Gamma-ray Imprints of Annihilating Dark Matter in the Galaxy, and the Astrophysical Implications of Ultra-light Fundamental Vector Bosons
Standard Model extensions imply new elementary particles that can lead to specific astrophysical signatures. In particular, weakly interacting massive particles (WIMPs) can constitute the unknown non-luminous cold dark matter, which contributes approximately 84% to the matter content of the Universe. Annihilation or decay of WIMPs may lead to high-energy gamma-rays. In this thesis, new methods of searching for gamma-ray signals from annihilating dark matter are developed and applied. Moreover, astrophysical imprints of new ultra-light hidden U(1) gauge bosons in radio data are investigated. Hierarchical structure formation predicts a variety of smaller bound dark matter subhalos in Milky-Way-like galactic hosts. It is shown that the Fermi-LAT is sufficiently sensitive for detecting up to a few nearby dark matter subhalos in terms of faint gamma-ray sources with a moderate angular extent. Searches in the first and second Fermi-LAT source catalogs reveal about ten candidate sources each. To discriminate the source candidates from conventional astrophysical objects, an analysis for spectral, spatial, positional, and temporal gamma-ray properties using 3.5 years of Fermi-LAT data is carried out. In addition, a multi-wavelength analysis of archival data or follow-up observations in the radio, infrared, optical, UV, X-ray, high-energy, and very-high energy gamma-ray bands is carried out. The broad-band spectra of all promising candidates are compatible with AGN, in particular high-energy peaked BL-Lac type objects (HBLs). Dark matter annihilation can contribute to the small-scale angular anisotropy spectrum of the diffuse gamma-ray background (DGB). The detection capabilities of currently operating imaging atmospheric Cherenkov telescopes and the planned Cherenkov Telescope Array (CTA) are studied. With CTA, a relative gamma-ray contribution from annihilating dark matter of 10% to the extragalactic DGB can be resolved via angular anisotropies. In terms of the dark matter velocity-averaged self-annihilation cross section, the sensitivity of CTA corresponds to values below 3x10^{-26} cm^3 s^{-1} for WIMPs lighter than 200 GeV. Standard Model extensions predict the existence of hidden sector U(1) gauge bosons (hidden photons). It is shown how ultra-light hidden photons with masses below 10^{-14} eV can modify broad-band spectra of compact radio sources. The sensitivity of current and planned radio astronomical facilities is investigated. Radio observations are capable of probing mixing angles down to 10^{-3} in a mass range between 10^{-17} eV and 10^{-12} eV