82 research outputs found
Spectral index variation across X-shaped radio galaxies
The formation mechanism of the enigmatic subclass of radio galaxies, called
'X-shaped radio galaxies' (XRGs), or 'winged' radio galaxies, which account for
of the radio galaxy population, can be effectively constrained
using the radio spectral-index distribution across their twin pairs of radio
lobes. If indeed, the existing claims of no systematic spectral index
difference between the wing and the associated primary lobe are valid in
general, this would provide impetus to the XRG model attributing their origin
to an unresolved binary of active supermassive black holes within the nucleus
of the host galaxy. To investigate this interesting possibility, we have mapped
spatial variation of spectral index for a well-defined sample of 25 XRGs, by
combining their 1.4 GHz VLA (FIRST survey)/uGMRT maps with their 144 MHz maps
(LoTSS-DR2). This has yielded the best available combination of sensitivity,
angular resolution, frequency range and sample size, for spectral mapping of an
XRG sample. A rich diversity of spectral index patterns is thus revealed in our
XRG sample, but we find at most one case where a secondary lobe (wing) exhibits
a flatter spectrum compared to its associated primary lobe. We conclude that
such a spectral pattern is exceedingly rare and by no means a common trait of
XRGs.Comment: 20 pages, 2 figures, 2 tables, accepted for publication in MNRA
Bacterial community structure analysis of soil treated with Parthenium hysterophorus L. derived green medium
The present study encompasses the analysis of bacterial community structure of soil in the presence of Parthenium hysterophorus derived green medium. The 16S microbiome profiling of the soil revealed that it consists of members from 15 bacterial phyla with the most prominent being Proteobacteria. The other predominant phyla were Plantomycetes, Actinobacteria, Acidobacteria, Bacteroidetes, Chloroflexi and Firmicutes. The maximum proportion of the bacterial community remained unclassified at genus and species level. Among the classified population the maximum number of bacteria belonged to Flavisolibacter followed by Kaistobacter, Bacillus, Optitutus, Balneimonas, Steroidobacter, Rhodoplanes and Gemmata
Multi-wavelength variability study of the classical BL Lac object PKS 0735+178 on timescales ranging from decades to minutes
We present the results of our power spectral analysis for the BL Lac object
PKS 0735+178 utilizing the Fermi-LAT survey at high-energy -rays,
several ground-based optical telescopes, and single-dish radio telescopes
operating at GHz frequencies. The novelty of our approach is that, by combining
long-term and densely sampled intra-night light curves in the optical regime,
we were able to construct for the first time the optical power spectrum of the
blazar for a time domain extending from 23 years down to minutes. Our analysis
reveals that: (i) the optical variability is consistent with a pure red noise,
for which the power spectral density can well be approximated by a single
power-law throughout the entire time domain probed; (ii) the slope of power
spectral density at high-energy -rays (), is significantly
flatter than that found at radio and optical frequencies () within the
corresponding time variability range; (iii) for the derived power spectra we
did not detect any low-frequency flattening, nor do we see any evidence for
cut-offs at the highest frequencies down to the noise floor levels due to
measurement uncertainties. We interpret our findings in terms of a model where
the blazar variability is generated by the underlying single stochastic process
(at radio and optical frequencies), or a linear superposition of such processes
(in the -ray regime). Along with the detailed PSD analysis, we also
present the results of our extended (1998-2015) intra-night optical monitoring
program and newly acquired optical photo-polarimetric data for the source.Comment: The Astrophysical Journal, in pres
Catching butterflies in the sky: Extended catalog of winged or X-shaped radio sources from the latest FIRST data release
We present a catalog of 290 "winged" or X-shaped radio galaxies (XRGs)
extracted from the latest (2014 December 17) data release of the "Very Large
Array Faint Images of the Radio Sky at Twenty centimeter." We have combined
these radio images with their counterparts in the TIFR GMRT sky survey at 150
MHz, in an attempt to identify any low surface brightness radio emission
present in these sources. This has enabled us to assemble a sample of 106
"strong" XRG candidates and 184 "probable" XRG candidates whose XRG designation
needs to be verified by further observations. The present sample of 290 XRG
candidates is almost twice as large as the number of XRGs currently known.
Twenty-five of our 290 XRG candidates (9 "strong" and 16 "probable") are
identified as quasars. Double-peaked narrow emission lines are seen in the
optical spectra of three of the XRG candidates (two "strong" and one
"probable"). Nearly 90% of the sample is located in the FR II domain of the
Owen-Ledlow diagram. A few of the strong XRG candidates have a rather flat
radio spectrum (spectral index alpha flatter than -0.3) between 150 MHz and 1.4
GHz, or between 1.4 and 5 GHz. Since this is not expected for lobe-dominated
extragalactic radio sources (like nearly all known XRGs), these sources are
particularly suited for follow-up radio imaging and near-simultaneous
measurement of the radio spectrum.Comment: 22 pages, 9 figures, 3 tables, accepted for publication in ApJ
Plant growth promoting traits of psychrotolerant bacteria: A boon for agriculture in hilly terrains
Plant growth promoting bacteria (PGPB) are well known to promote plant growth in a number of ways. It is important to study plant growth promoting potential of bacteria capable of growing in extreme environments to establish their role in promoting agricultural yield under harsh conditions. Psychrophilic or psychrotolerant bacteria with plant growth promoting traits may improve the quality of agricultural practices in hilly terrain. The agricultural importance of such microbes stems from the fact that the world over temperate agro-ecosystems are characterized by low temperatures and short growing seasons that subject both plant and microbial life to cold temperature induced stress. Hence, there is a need to identify potential microbes that retain their functional traits under low temperature conditions. Such microbes can be used to enhance the agricultural yields in low temperature areas of the world. This review describes plant growth promoting activities identified in cold adapted bacteria
Rapid optical variability of TeV blazars
In this first systematic attempt to characterise the intranight optical
variability (INOV) of TeV detected blazars, we have monitored a well defined
set of 9 TeV blazars on total 26 nights during 2004-2010. In this R (or V)-band
monitoring programme only one blazar was monitored per night for a minimum
duration of 4 hours. Using the CCD, an INOV detection threshold of ~ 1-2 % was
achieved in the densely sampled DLCs. We have further expanded the sample by
including another 13 TeV blazars from literature. This enlarged sample of 22
TeV blazars, monitored on a total of 116 nights (including 55 nights newly
reported here), has enabled us to arrive at the first estimate of the INOV duty
cycle of TeV detected blazars. Applying the C-test, the INOV DC is found to be
59 %, which decreases to 47 % if only INOV fractional amplitudes above 3 % are
considered. These observations also permit, for the first time, a comparison of
the INOV characteristics of the two major subclasses of TeV detected BL Lacs,
namely LBLs and HBLs, for which we find the INOV DCs to be ~ 63 % and ~ 38 %,
respectively. This demonstrates that the INOV differential between LBLs and
HBLs persists even when only their TeV detected subsets are considered. Despite
dense sampling, the intranight light curves of the 22 TeV blazars have not
revealed even a single feature on time scale substantially shorter than 1 hour,
even though the inner jets of TeV blazars are believed to have exceptionally
large bulk Lorentz factors (and correspondingly stronger time compression). An
intriguing feature, clearly detected in the light curve of the HBL J1555+1111,
is a 4 per cent `dip' on a 1 hour timescale. This unique feature could have
arisen from absorption in a dusty gas cloud, occulting a superluminally moving
optical knot in the parsec scale jet of this relatively luminous BL Lacs
object.Comment: 39 pages, 3 figures, accepted for publication in MNRA
Optical microvariability properties of BALQSOs
We present optical light curves of 19 radio quiet (RQ) broad absorption line
(BAL) QSOs and study their rapid variability characteristics. Systematic CCD
observations, aided by a careful data analysis procedure, have allowed us to
clearly detect any such microvariability exceeding 0.01--0.02 mag. Our
observations cover a total of 13 nights (~72 hours) with each quasar monitored
for about 4 hours on a given night. Our sample size is a factor of three larger
than the number of radio-quiet BALQSOs previously searched for
microvariability. We introduce a scaled F-test statistic for evaluating the
presence of optical microvariability and demonstrate why it is generally
preferable to the statistics usually employed for this purpose. Considering
only unambiguous detections of microvariability we find that ~11 per cent of
radio-quiet BALQSOs (two out of 19 sources) show microvariability for an
individual observation length of about 4 hr. This new duty cycle of 11 per cent
is similar to the usual low microvariability fraction of normal RQQSOs with
observation lengths similar to those of ours. This result provides support for
models where radio-quiet BALQSO do not appear to be a special case of the
RQQSOs in terms of their microvariability properties.Comment: 13 pages, 3 figures, 3 tables, accepted for publication in MNRAS main
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