Pulsars emerge in the Fermi era as a sizable population of gamma-ray sources.
Millisecond pulsars (MSPs) constitute an older subpopulation whose sky
distribution extends to high Galactic latitudes, and it has been suggested that
unresolved members of this class may contribute a significant fraction of the
measured large-scale isotropic gamma-ray background (IGRB). We investigate the
possible energy-dependent contribution of unresolved MSPs to the anisotropy of
the Fermi-measured IGRB. For observationally-motivated MSP population models,
we show that the preliminary Fermi anisotropy measurement places an interesting
constraint on the abundance of MSPs in the Galaxy and the typical MSP flux,
about an order of magnitude stronger than constraints on this population
derived from the intensity of the IGRB alone. We also examine the possibility
of a MSP component in the IGRB mimicking a dark matter signal in
anisotropy-based searches, and conclude that the energy dependence of an
anisotropy signature would distinguish MSPs from all but very light dark matter
candidates.Comment: 10 pages, 7 figures; minor revisions; matches version accepted to
MNRA
Gamma-rays from cosmological sources contain information about gamma-ray interactions. Standard model and non-standard model photon interactions along the path between the source and the observer can lead to changes in the energy or state of the photons, which in turn alters the observed energy spectrum of the source. In general, these interactions are a function of photon energy as well as source distance. Here we show how existing high energy gamma-ray observations of blazars can be used to constrain the coupling of axionlike-particles (ALPs) to the photon. The same ALP-photon coupling that has been invoked to explain the observations of TeV blazars beyond their pair production horizon is shown to have an effect of the data set of Fermi blazars.
Gamma-rays propagating through space are likely to be extinguished via electronpositron pair production off of the ambient extragalactic background light (EBL). The spectrum of the EBL is produced by starlight (and starlight reprocessed by dust) from all galaxies throughout the history of the Universe. The attenuation of 40 -400 GeV gamma-rays has been observed by Fermi and used to measure the EBL spectrum over energies 1 eV -10 eV out to redshift z ∼ 1. Measurements of several TeV blazers are consistent with attenuation, attributed to the EBL at redshift z ∼ 0.1. Here we simultaneously analyze a set of TeV blazers at z ∼ 0.1 to measure the optical depth for 100 GeV -10 TeV gamma-rays, which interact with EBL of energies 0.05 eV -5 eV. Using a suite of models for the EBL, we show that the optical depth indicated by TeV blazar attenuation is in good agreement with the optical depths measured by Fermi at lower gamma-ray energies and higher redshifts.
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