Probing Intergalactic Magnetic Fields from [gamma]-ray Observations PDF Download

Author: Wenlei Chen
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 171

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Book Description
The large-scaled magnetic fields in intergalactic space may contain detailed information of the primordial magnetic fields produced in the early Universe. The generation of the cosmological matter-antimatter asymmetry may produce helical magnetic fields via CP (charge conjugation and parity) violating interactions during matter-genesis. Thus, the study of the intergalactic magnetic field (IGMF) could provide a new window on early-Universe cosmology. IGMFs deflect the electron-positron pairs produced by TeV gamma-rays from blazars, resulting in broadened beams of cascade GeV gamma-rays known as pair halos. In the presence of helical IGMFs, cascade GeV gamma-rays at different energies from a distant source fall into patterns in the observation plane in the GeV gamma-ray sky that have a similar chirality. These signatures of the IGMF on the gamma-ray emission from extragalactic sources, i.e. pair halos and helical patterns, can be observed using data from the Fermi Large Area Telescope (Fermi-LAT). In this dissertation, I describe methods for probing the IGMF using gamma-ray observations. I report on the results of a search for gamma-ray pair halos with a stacking analysis of low-redshift blazars using data from Fermi-LAT. For this analysis we used a number of a priori selection criteria, including the spatial and spectral properties of the Fermi sources. The angular distribution of ~1 GeV photons around 24 stacked isolated high-synchrotron-peaked BL Lacs with redshift z 0.5 shows an excess over that of point-like sources. A frequentist test yields a p-value of p ~0.01 for the extended emission against the point-source hypothesis. A Bayesian estimation provides the common logarithm of Bayes factors 2, consistent with expectations for pair halos produced in the IGMF with strength of ~10−17 to 10−15 Gauss. In addition, I present a search for parity violating signatures of helical IGMFs in the GeV gamma-ray sky. In this study, the IGMF helicity is examined by evaluating a parity-odd statistic using gamma-ray data obtained from Fermi-LAT observations at high galactic latitudes. The resulting negative values of the parity-odd statistic imply that there is an excess of left-handed spirals in the gamma-ray sky, indicating a left-handed helicity consistent with a helical magnetic field with strength of ~10−14 Gauss on ~10 Mpc scales.