A. Neronov

Evidence for strong extragalactic magnetic fields from Fermi observations of TeV blazars.

On the Origins of Magnetism The magnetic fields in galaxies and galaxy clusters are thought to result from the amplification of weak primordial magnetic fields, which, according to one class of theories, should exist in the voids between galaxies and galaxy clusters. Neronov and Vovk (p. 73) present evidence for the existence of intergalactic magnetic fields and derive a lower limit for their strength, based on an analysis of data from the Fermi Large Area Telescope. The results place constraints on magnetogenesis models and suggest that magnetic fields originated in the early universe before galaxy formation took place. An analysis of data from the Fermi Large Area Telescope sets a lower limit for the strength of intergalactic magnetic fields. Magnetic fields in galaxies are produced via the amplification of seed magnetic fields of unknown nature. The seed fields, which might exist in their initial form in the intergalactic medium, were never detected. We report a lower bound B ≥ 3 × 10−16 gauss on the strength of intergalactic magnetic fields, which stems from the nonobservation of GeV gamma-ray emission from electromagnetic cascade initiated by tera–electron volt gamma rays in intergalactic medium. The bound improves as λB−1/2 if magnetic field correlation length, λB, is much smaller than a megaparsec. This lower bound constrains models for the origin of cosmic magnetic fields.

Cosmological Magnetic Fields: Their Generation, Evolution and Observation

We review the possible mechanisms for the generation of cosmological magnetic fields, discuss their evolution in an expanding Universe filled with the cosmic plasma and provide a critical review of the literature on the subject. We put special emphasis on the prospects for observational tests of the proposed cosmological magnetogenesis scenarios using radio and gammaray astronomy and ultra high energy cosmic rays. We argue that primordial magnetic fields are observationally testable. They lead to magnetic fields in the intergalactic medium with magnetic field strength and correlation length in a well defined range. We also state the unsolved questions in this fascinating open problem of cosmology and propose future observations to address them.

Extragalactic magnetic fields constraints from simultaneous GeV-TeV observations of blazars

Attenuation of the TeV gamma-ray flux from distant blazars through pair production with extragalactic background light leads to the development of electromagnetic cascades and subsequent, lower energy, GeV secondary gamma-ray emission. Due to the deflection of VHE cascade electrons by extragalactic magnetic fields (EGMF), the spectral shape of this arriving cascade gamma-ray emission is dependent on the strength of the EGMF. Thus, the spectral shape of the GeV-TeV emission from blazars has the potential to probe the EGMF strength along the line of sight to the object. We investigate constraints on the EGMF derived from observations of blazars for which TeV observations simultaneous with those by the Fermi telescope were reported. We study the dependence of the EGMF bound on the hidden assumptions it rests upon. We select blazar objects for which simultaneous Fermi/LAT GeV and Veritas, MAGIC or HESS TeV emission have been published. We model the development of electromagnetic cascades along the gamma-ray beams from these sources using Monte Carlo simulations, including the calculation of the temporal delay incurred by cascade photons, relative to the light propagation time of direct gamma-rays from the source. Constraints on EGMF could be derived from the simultaneous GeV-TeV data on the blazars RGB J0710+591, 1ES 0229+200, and 1ES 1218+304. The measured source flux level in the GeV band is lower than the expected cascade component calculated under the assumption of zero EGMF. Assuming that the reason for the suppression of the cascade component is the extended nature of the cascade emission, we find that B>10^{-15} G (assuming EGMF correlation length of ~1 Mpc) is consistent with the data. Alternatively, the assumption that the suppression of the cascade emission is caused by the time delay of the cascade photons the data are consistent with B>10^{-17} G for the same correlation length.

Constraints on sterile neutrinos as dark matter candidates from the diffuse X-ray background

Sterile neutrinos with masses in the keV range are viable candidates for the warm dark matter. We analyze existing data for the extragalactic diffuse X-ray background for signatures of sterile neutrino decay. The absence of detectable signal within current uncertainties of background measurements puts model-independent constraints on allowed values of sterile neutrino mass and mixing angle, which we present in this work.

Strategy for searching for a dark matter sterile neutrino

We propose a strategy of how to look for dark matter (DM) particles possessing a radiative decay channel and derive constraints on their parameters from observations of X-rays from our own Galaxy and its dwarf satellites. When applied to the sterile neutrinos in keV mass range, it allows a significant improvement of restrictions to its parameters, as compared with previous works.

Constraints on 3.55 keV line emission from stacked observations of dwarf spheroidal galaxies

Several recent works have reported the detection of an unidentified x-ray line at 3.55 keV, which could possibly be attributed to the decay of dark matter (DM) particles in the halos of galaxy clusters and in the M31 galaxy. We analyze all publicly available XMM-Newton satellite data of dwarf spheroidal galaxies to test the possible DM origin of the line. Dwarf spheroidal galaxies have high mass-to-light ratios, and their interstellar medium is not a source of diffuse x-ray emission; thus, they are expected to provide the cleanest DM decay line signal. Our analysis shows no evidence for the presence of the line in the stacked spectra of the dwarf galaxies. It excludes the sterile neutrino DM decay origin of the 3.5 keV line reported by Bulbul et al. (2014) at the level of

FERMI/LAT OBSERVATIONS OF 1ES 0229+200: IMPLICATIONS FOR EXTRAGALACTIC MAGNETIC FIELDS AND BACKGROUND LIGHT

4.1\ensuremath{\sigma}

INTEGRAL and XMM-Newton observations of LSI +61 303

under standard assumptions about the Galactic DM column density in the direction of selected dwarf galaxies and at the level of

The Masses of active neutrinos in the nuMSM from X-ray astronomy

3.2\ensuremath{\sigma}

A compact pulsar wind nebula model of the γ-ray-loud binary LS I +61°303

assuming minimal Galactic DM column density. Our analysis is still consistent with the estimate of sterile neutrino DM parameters by Boyarsky et al. (2014) because of its larger uncertainty. However, the central value of their estimate of the mixing angle is inconsistent with our dwarf spheroidals data at the