arXiv subjects

Ievgen Vovk

Publications and source records attributed to Ievgen Vovk.

21 records · Page 2Linked to original sources

arXiv2012

Fermi/LAT observations of 1ES 0229+200: implications for extragalactic magnetic fields and background light

We report the observation in the GeV band of the blazar 1ES 0229+200, which over recent years has become one the primary sources used to put constraints on the Extragalactic Background Light (EBL) and Extragalactic Magnetic Field (EGMF). We derive constraints on both the EBL and EGMF from the combined Fermi-HESS data set taking into account the direct and cascade components of the source spectrum. We show that the limit on the EBL depends on the EGMF strength and vice versa. In particular, an EBL density twice as high as that derived by Franceschini et al. (2008) is allowed if the EGMF is strong enough. On the other hand, an EGMF strength as low as 6x10^-18 G is allowed if the EBL density is at the level of the lower bound from the direct source counts. We present the combined EBL and EGMF limits on as an exclusion plot in two dimensional parameter space: EGMF strength vs. EBL density.

astro-ph.CO↗

arXiv2010

Fast variability of gamma-ray emission from supermassive black hole binary OJ 287

We report the discovery of fast variability of gamma-ray flares from blazar OJ 287. This blazar is known to be powered by binary system of supermassive black holes. The observed variability time scale T_var < 3-10 hr is much shorter than the light crossing time of more massive (1.8x10^10 solar masses) black hole and is comparable to the light crossing time of the less massive (1.3x10^8 solar masses) black hole. This indicates that gamma-ray emission is produced by relativistic jet ejected by the black hole of smaller mass. Detection of gamma rays s with energies in excess of 10 GeV during the fast variable flares constrains the Doppler factor of the jet to be larger than 4. Possibility of the study of orbital modulation of emission from relativistic jet makes OJ 287 a unique laboratory for the study of the mechanism(s) of formation of jets by black holes, in particular, of the response of the jet parameters to the changes of the parameters of the medium from which the black hole accretes and into which the jet expands.

astro-ph.HE↗

arXiv2010

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

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 $B\ge 3\times 10^{-16}$~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-ray in intergalactic medium. The bound improves as $λ_B^{-1/2}$ if magnetic field correlation length, $λ_B$, is much smaller than a megaparsec. This lower bound constrains models for the origin of cosmic magnetic fields.

astro-ph.HE↗