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 $\sim 10\%$ 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 $\gamma$-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 $\gamma$-rays ($\sim 1$), is significantly flatter than that found at radio and optical frequencies ($\sim 2$) 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 $\gamma$-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 journa