arXiv subjects

Biny Sebastian

Publications and source records attributed to Biny Sebastian.

23 records · Page 2Linked to original sources

arXiv2019

The filamentary radio lobes of the Seyfert-Starburst composite galaxy NGC3079

We present results from multi-frequency polarization-sensitive Very Large Array observations of the Seyfert-starburst composite galaxy NGC3079. Our sensitive radio observations reveal a plethora of radio filaments comprising the radio lobes in this galaxy. We analyze the origin of these radio filaments in the context of existing Chandra X-ray and HST emission-line data. We do not find a one-to-one correlation of the radio filaments with the emission line filaments. The north-eastern lobe is highly polarized with polarization fractions $\sim$33% at 5 GHz. The magnetic fields are aligned with the linear extents of the optically-thin filaments, as observed in our, as well as other observations in the literature. Our rotation measure images show evidence for rotation measure inversion in the north-eastern lobe. Our data best fit a model where the cosmic rays follow the magnetic field lines generated as a result of the dynamo mechanism. There could be additional effects like shock acceleration that might also be playing a role. We speculate that the peculiar radio lobe morphology is a result of an interplay between both the superwinds and the AGN jet that are present in the galaxy. The jet, in fact, might be playing a major role in providing the relativistic electron population that is present in the radio lobes.

astro-ph.GA↗

arXiv2019

GMRT Low-frequency Imaging of an Extended Sample of X-shaped Radio Galaxies

We present a low-frequency imaging study of an extended sample of X-shaped radio sources using the Giant Metrewave radio telescope (GMRT) at two frequencies (610 and 240 MHz). The sources were drawn from a Very Large Array FIRST-selected sample and extends an initial GMRT study at the same frequencies, of 12 X-shaped radio galaxies predominantly from the 3CR catalog (Lal & Rao 2007). Both the intensity maps and spectral index maps of the 16 newly observed sources are presented. With the combined sample of 28 X-shaped radio sources, we found no systematic differences in the spectral properties of the higher surface brightness, active lobes versus the lower surface brightness, off-axis emission. The properties of the combined sample are discussed, including the possible role of a twin active galactic nuclei model in the formation of such objects.

astro-ph.GA↗

arXiv2018

A Curved 150 Parsec Long Jet in the Double-Peaked Emission-Line AGN KISSR 434

Double-peaked emission lines in the narrow- and/or broad-line spectra of AGN have been suggested to arise due to disky broad/narrow line regions, jet-medium interaction, or the presence of binary supermassive black holes. We present the results from 1.5 and 4.9 GHz phase-referenced Very Long Baseline Interferometry (VLBI) observations of the Seyfert type 2 galaxy KISSR 434, which exhibits double-peaked emission lines in its optical spectrum. We detect a steep-spectrum ($α<-1$), curved and long (~150 parsec) jet in the VLBI images of KISSR 434. The jet curvature could be a result of precession rather than ram-pressure bending from a rotating ISM. Precession could in turn arise due to a warped accretion disk or the presence of a binary black hole with a separation of 0.015 parsec, not accessible to present day telescopes. An examination of the emission line ratios with the MAPPINGS III code reveals that AGN photoionization is likely to be responsible for the observed line ratios and not shock-ionization due to the jet. A light (with jet-to-ambient medium density ratio of $η\sim0.01$) and fast (with speed $v_j\gtrsim0.75c$) precessing jet in KISSR 434 may have stirred up the emission-line gas clouds to produce the observed splits in the narrow line peaks but is not powerful enough to shock-ionise the gas.

astro-ph.GA↗

arXiv2017

Discovery of a new, 2.2 Mpc Giant Radio Galaxy at a redshift of 0.57

We report the discovery of one of the largest and most distant Giant Radio Galaxy (GRG) in the Lynx field which was discovered using deep Giant Metre-wave Radio Telescope (GMRT) 150 MHz observations. The core is detected at 150 MHz and also in the VLA FIRST survey. Spectroscopic observations carried out using the IUCAA Giravali Observatory(IGO) provided a redshift value of 0.57. This redshift was later confirmed with data from the Sloan Digital Sky Survey (Data Release 12). The angular size of the GRG is 5.5 arcmin and at the redshift of 0.57, its linear size is 2.2 Mpc. At this high redshift, only a few radio sources are known to have such large linear size. In order to estimate the spectral index of the bridge emission as well as the spectral age of the source, we observed this source at L-band, 610 MHz and 325 MHz bands with the GMRT. We present the spectral ageing analysis of the source which puts an upper limit of 20 Myr on the spectral age. The better resolution maps presented here as opposed to the original 150 MHz map shows evidence for a second episode of emission. We also find that the core is detected at all four frequencies with a spectral index of 0.85, which is steeper than normal, hence we speculate that the core may be a compact steep spectrum source (CSS), which makes this giant radio galaxy a candidate triple-double radio galaxy.

astro-ph.GA↗

arXiv2017

Giant Metrewave Radio Telescope Observations of Head-Tail Radio Galaxies

We present results from a study of seven large known head-tail radio galaxies based on observations using the Giant Metrewave Radio Telescope at 240 and 610 MHz. These observations are used to study the radio morphologies and distribution of the spectral indices across the sources. The overall morphology of the radio tails of these sources is suggestive of random motions of the optical host around the cluster potential. The presence of the multiple bends an d wiggles in several head-tail sources is possibly due to the precessing radio jets. We find steepening of the spectral index along the radio tails. The prevailing equipartition magnetic field also decreases a long the radio tails of these sources. These steepening trends are attributed to the synchrotron aging of plasma toward the ends of the tails. The dynamical ages of these sample sources have been estimated to be ~100 Myr, which is a factor of six more than the age estimates from the radiative losses due to synchrotron cooling.

astro-ph.GA↗