A. N. Cillis

Diffusion of Cosmic Rays and the Gamma-Ray Large Area Telescope: Phenomenology at the 1-100 GeV Regime

This paper analyzes astrophysical scenarios that may be detected at the upper end of the energy range of the Gamma-Ray Large Area Space Telescope (GLAST), as a result of cosmic-ray (CR) diffusion in the interstellar medium (ISM). Hadronic processes are considered the source of γ-ray photons from localized molecular enhancements nearby accelerators. Two particular cases are presented: (1) the possibility of detecting spectral energy distributions (SEDs) with maxima above 1 GeV, which may be constrained by detection or nondetection at very high energies (VHEs) with observations by ground-based Cerenkov telescopes, and (2) the possibility of detecting V-shaped, inverted spectra, due to confusion of a nearby (to the line of sight) arrangement of accelerator/target scenarios with different characteristic properties. We show that finding these signatures (in particular, a peak at the 1-100 GeV energy region) indicates the underlying mechanism producing the γ-rays that is realized by nature, which accelerator (age and relative position to the target cloud) and under which diffusion properties CRs propagate.

A Novel Method for Measuring the Extragalactic Background Light: Fermi Application to the Lobes of Fornax A

We describe a new method for measuring the extragalactic background light (EBL) through the detection of γ-ray inverse Compton (IC) emission due to scattering of the EBL photons off relativistic electrons in the lobes of radio galaxies. Our method has no free physical parameters and is a powerful tool when the lobes are characterized by a high-energy sharp break or cutoff in their electron energy distribution (EED). We show that such a feature will produce a high-energy IC imprint of the EBL spectrum in which the radio lobes are embedded and show how this imprint can be used to derive the EBL. We apply our method to the bright nearby radio galaxy Fornax A, for which we demonstrate, using Wilkinson Microwave Anisotropy Probe (WMAP) and EGRET observations, that the EED of its lobes is characterized by a conveniently located cutoff, bringing the IC EBL emission into the Fermi Gamma-Ray Space Telescope energy range. We show that Fermi will set upper limits to the optical EBL and measure the more elusive infrared EBL.

Egret upper limits and stacking searches of gamma-ray observations of luminous and ultraluminous infrared galaxies

We present a stacking analysis of EGRET γ-ray observations at the positions of luminous and ultraluminous infrared galaxies. The latter were selected from the recently presented HCN survey, which is thought to contain the most active star-forming regions of the universe. Different sorting criteria are used, and since there is no positive collective detection of γ-ray emission from these objects, we determined both collective and individual upper limits. The uppermost excess we find appears in the case of ULIRGs ordered by redshift, at a value of 1.8 σ.

The effects of magnetic field, age and intrinsic luminosity on Crab-like pulsar wind nebulae

We investigate the time-dependent behavior of Crab-like pulsar wind nebulae (PWNe) generating a set of models using 4 different initial spin-down luminosities (

EGRET Diffuse Gamma-Ray Maps between 30 MeV and 10 GeV

L_0 =\{1,0.1,0.01,0.001\} \times L_{0, {\rm Crab}}

Cosmic rays in the surroundings of SNR G35.6−0.4

), 8 values of magnetic fraction (

Building up the spectrum of cosmic rays in star-forming regions

\eta =

Is there room for highly magnetized pulsar wind nebulae among those non-detected at TeV?

0.001, 0.01, 0.03, 0.1, 0.5, 0.9, 0.99, and 0.999, i.e., from fully particle dominated to fully magnetically dominated nebulae), and 3 distinctive ages: 940, 3000, and 9000 years. We find that the self-synchrotron Compton (SSC) contribution is irrelevant for

Gamma-ray source stacking analysis at low galactic latitudes

L_{SD}

Digging the Cosmic Infrared Background out of the lobes of a radio galaxy

=0.1, 1, and 10% of the Crab power, disregarding the age and the magnetic fraction. SSC only becomes relevant for highly energetic (