arXiv subjects

A. A. Mokrushina

Publications and source records attributed to A. A. Mokrushina.

3 recordsLinked to original sources

arXiv2018

Exploring the connection between parsec-scale jet activity and broadband outbursts in 3C 279

We use a combination of high-resolution very long baseline interferometry (VLBI) radio and multi-wavelength flux density and polarization observations to constrain the physics of the dissipation mechanism powering the broadband flares in 3C 279 during an episode of extreme flaring activity in 2013-2014. Six bright flares superimposed on a long-term outburst are detected at $γ$-ray energies. Four of the flares have optical and radio counterparts. The two modes of flaring activity (faster flares sitting on top of a long term outburst) present at radio, optical, $γ$-ray frequencies are missing in X-rays. X-ray counterparts are only observed for two flares. The first three flares are accompanied by ejection of a new VLBI component (NC2) suggesting the 43 GHz VLBI core as the site of energy dissipation. Another new component, NC3, is ejected after the last three flares, which suggests that the emission is produced upstream from the core (closer to the black hole). The study therefore indicates multiple sites of energy dissipation in the source. An anti-correlation is detected between the optical percentage polarization (PP) and optical/$γ$-ray flux variations, while the PP has a positive correlation with optical/$γ$-rays spectral indices. Given that the mean polarization is inversely proportional to the number of cells in the emission region, the PP vs. optical/$γ$-ray anti-correlation could be due to more active cells during the outburst than at other times. In addition to the turbulent component, our analysis suggests the presence of a combined turbulent and ordered magnetic field, with the ordered component transverse to the jet axis.

astro-ph.HE↗

arXiv2018

Multiwavelength observations of the blazar BL Lacertae: a new fast TeV gamma-ray flare

Combined with very-long-baseline interferometry measurements, the observations of fast TeV gamma-ray flares probe the structure and emission mechanism of blazar jets. However, only a handful of such flares have been detected to date, and only within the last few years have these flares been observed from lower-frequency-peaked BL~Lac objects and flat-spectrum radio quasars. We report on a fast TeV gamma-ray flare from the blazar BL~Lacertae observed by VERITAS, with a rise time of $\sim$2.3~hr and a decay time of $\sim$36~min. The peak flux above 200 GeV is $(4.2 \pm 0.6) \times 10^{-6} \;\text{photon} \;\text{m}^{-2}\; \text{s}^{-1}$ measured with a 4-minute-binned light curve, corresponding to $\sim$180\% of the flux which is observed from the Crab Nebula above the same energy threshold. Variability contemporaneous with the TeV gamma-ray flare was observed in GeV gamma-ray, X-ray, and optical flux, as well as in optical and radio polarization. Additionally, a possible moving emission feature with superluminal apparent velocity was identified in VLBA observations at 43 GHz, potentially passing the radio core of the jet around the time of the gamma-ray flare. We discuss the constraints on the size, Lorentz factor, and location of the emitting region of the flare, and the interpretations with several theoretical models which invoke relativistic plasma passing stationary shocks.

astro-ph.HE↗

arXiv2017

Multiwavelength observations of the blazar BL Lacertae: a new fast TeV $γ$-ray flare

Observations of fast TeV $γ$-ray flares from blazars reveal the extreme compactness of emitting regions in blazar jets. Combined with very-long-baseline radio interferometry measurements, they probe the structure and emission mechanism of the jet. We report on a fast TeV $γ$-ray flare from BL Lacertae observed by VERITAS, with a rise time of about 2.3 hours and a decay time of about 36 minutes. The peak flux at $>$200 GeV measured with the 4-minute binned light curve is $(4.2 \pm 0.6) \times 10^{-6} \;\text{photons} \;\text{m}^{-2}\, \text{s}^{-1}$, or $\sim$180% the Crab Nebula flux. Variability in GeV $γ$-ray, X-ray, and optical flux, as well as in optical and radio polarization was observed around the time of the TeV $γ$-ray flare. A possible superluminal knot was identified in the VLBA observations at 43 GHz. The flare constrains the size of the emitting region, and is consistent with several theoretical models with stationary shocks.

astro-ph.HE↗