Search

Galactic cosmic rays (GCRs) constitute a significant part of the energy budget of our Galaxy, and the study of their accelerators is of high importance in modern astrophysics. Their main sources are likely supernova remnants (SNRs). These objects are capable to convert a part of their mechanical energy into accelerated charged particles. However, even though the mechanical energy reservoir of SNRs is promising, a conversion rate into particle energy of 10 to 20% is necessary to feed the population of GCRs. Such an efficiency is however not guaranteed. Complementary sources deserve thus to be investigated. This communication aims to address the question of the contribution to the acceleration of GCRs by pre-supernova massive stars in binary or higher multiplicity systems, Comment: 8 pages, 1 figure, Published in the Proceedings of the 3rd BINA Workshop on the Scientific Potential of the Indo-Belgian Cooperation

We measure the specific star formation rates of \textit{K}-band selected galaxies from the ELAIS-N1 by stacking GMRT data at 610 MHz. We identify a sample of SFGs, spanning $\rm{0.1\leq\,\textit{z}\,\leq\,1.5}$ and $\rm{10^{8.5}<\,{\textit{M}_{\star}}/{\textit{M}_{\odot}}<10^{12.4}}$, using a combination of multi-wavelength diagnostics obtained from the deep LoTSS multi-wavelength catalogue. We measure the flux densities in the radio map and estimate the radio SFR in order to probe the nature of the galaxies below the noise and confusion limits. The massive galaxies in our sample have the lowest sSFRs which is in agreement with previous studies. For the different populations, we show that the sSFR-mass relation steepens with redshift, with an average slope of $\rm{\langle \beta_{All} \rangle\,=\, -0.49\pm0.01}$ for the whole sample, and $\rm{\langle \beta_{SFG} \rangle\,=\, -0.42\pm0.02}$ for the SFGs. Our results indicate that galaxy populations undergo 'downsizing', whereby most massive galaxies form their stars earlier and more rapidly than low mass galaxies. Both populations show a strong decrease in their sSFR toward the present epoch. The sSFR evolution with redshift is best described by a power law $\rm{(1\,+\,\textit{z})^\textit{n}}$, where $\rm{\langle \textit{n}_{ALL}\rangle\sim4.94\pm0.53}$ for all galaxies, and $\rm{\langle \textit{n}_{SFG}\rangle \sim3.51\pm0.52}$ for SFGs. Comparing our measured sSFRs to results from literature, we find a general agreement in the \textit{sSFR-M$_{\star}$} plane., Comment: 17 pages, 13 figures, accepted for publication in MNRAS

By combining high-sensitivity LOFAR 150MHz, uGMRT 400MHz and 1,250MHz, GMRT 610MHz, and VLA 5GHz data in the ELAIS-N1 field, we study the radio spectral properties of radio-detected star-forming galaxies (SFGs) at observer-frame frequencies of 150-5,000MHz. We select ~3,500 SFGs that have both LOFAR 150MHz and GMRT 610MHz detections, and obtain a median two-point spectral index of $\alpha_{150}^{610}=-0.51\pm0.01$. The photometric redshift of these SFGs spans $z=0.01-6.21$. We also measure the two-point radio spectral indices at 150-400-610-1,250MHz and 150-610-5,000MHz respectively for the GMRT 610-MHz-detected SFGs, and find that, on average, the radio spectrum of SFGs is flatter at low frequency than at high frequency. At observer-frame 150-5,000MHz, we find that the radio spectrum slightly steepens with increasing stellar mass. However, we only find that the radio spectrum flattens with increasing optical depth at $V$-band at $\nu<1$GHz. We suggest that spectral ageing due to the energy loss of CR electrons and thermal free-free absorption could be among the possible main physical mechanisms that drive the above two correlations respectively. In addition, both of these mechanisms could physically explain why the radio spectrum is flatter at low frequency than at high frequency., Comment: 17 pages, 12 figures, 1 table, published in MNRAS

The Seyfert galaxy NGC 2639 was known to exhibit three episodes of AGN jet/lobe activity. We present here the upgraded Giant Metrewave Radio Telescope (uGMRT) 735 MHz image of NGC 2639 showing a fourth episode as witnessed by the discovery of $\sim9$ kpc radio lobes misaligned with the previously known $\sim1.5$ kpc, $\sim360$ parsec, and $\sim3$ parsec jet features detected through the Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA), respectively. Using the spectral ageing software BRATS, we derive the ages of the $\sim9$ kpc, $\sim1.5$ kpc, and $\sim360$ parsec episodes to be, respectively, $34^{+4}_{-6}$ Myr, $11.8^{+1.7}_{-1.4}$ Myr, and $2.8^{+0.7}_{-0.5}$ Myr, and conclude that minor mergers occurred $9-22$ Myr apart. NGC 2639 shows a deficit of molecular gas in its central $\sim6$ kpc region. The GALEX NUV image also shows a deficiency of recent star-formation in the same region, while the star formation rate (SFR) surface density in NGC 2639 is lower by a factor of $5-18$ compared to the global Schmidt law of star-forming galaxies. This makes NGC 2639 a rare case of a Seyfert galaxy showing episodic jet activity and possible signatures of jet-driven AGN feedback., Comment: 9 pages, 6 figures, 4 tables, accepted for publication to MNRAS

We present for the first time a study of peculiar giant radio galaxy (GRG) J223301+131502 using deep multi-frequency radio observations from GMRT (323, 612, and 1300 MHz) and LOFAR (144 MHz) along with optical spectroscopic observations with the WHT~4.2m optical telescope. Our observations have firmly established its redshift of 0.09956 and unveiled its exceptional jet structure extending more than $\sim$ 200 kpc leading to a peculiar kink structure of $\sim$ 100 kpc. We measure the overall size of this GRG to be $\sim$ 1.83 Mpc; it exhibits lobes without any prominent hotspots and closely resembles a barbell. Our deep low-frequency radio maps clearly reveal the steep-spectrum diffuse emission from the lobes of the GRG. The magnetic field strength of $\sim$ 5 $\mu$G and spectral ages between about 110 to 200 mega years for the radio lobes were estimated using radio data from LOFAR 144 MHz observations and GMRT 323 and 612 MHz observations. We discuss the possible causes leading to the formation of the observed kink feature for the GRG, which includes precession of the jet axis, development of instabilities and magnetic reconnection. Despite its enormous size, the Barbell GRG is found to be residing in a low-mass (M$_{200} \sim 10^{14}$ $\rm M_{\odot}$) galaxy cluster. This GRG with two-sided large-scale jets with a kink and diffuse outer lobes residing in a cluster environment provides an opportunity to explore the structure and growth of GRGs in different environments., Comment: Accepted for publication in A&A. 17 Pages, 7 figures and 6 tables. Comments are welcome

We observed the core region of the giant radio galaxy GRS J0844+4627 with e-MERLIN at 1.52 and 5.07 GHz. These observations revealed that the apparent single feature at the centre of GRS J0844+4627, as seen by GMRT, consists of two components separated by 2.7 kpc in projection. Follow-up observations at 1.66 GHz using the EVN unveiled the complex morphologies of the two components. In particular, the south-western component identified with the SDSS J084408.85+462744.2 galaxy morphologically resembles a compact symmetric object (CSO) with a projected linear size of 115 pc. If the CSO hypothesis turns out to be correct, then the overall radio structure of GRS J0844+4627 is triple-double. Given that CSOs are considered young objects, GRS J0844+4627 would appear as a recently restarted active galaxy., Comment: Matches the version published in MNRAS

Quantifying the energetics and lifetimes of remnant radio-loud active galactic nuclei (AGNs) is much more challenging than for active sources due to the added complexity of accurately determining the time since the central black hole switched off. Independent spectral modelling of remnant lobes enables the derivation of the remnant ratio, $R_\mathrm{rem}$, (i.e. `off-time/source age'), thus reducing this complexity back to that of active sources however, the requirement of high-frequency ($\gtrsim5\,$GHz) coverage makes the application of this technique over large-area radio surveys difficult. In this work we propose a new method, which relies on the observed brightness of backflow of Fanaroff-Riley type~II lobes, combined with the \emph{Radio AGN in Semi-Analytic Environments} (RAiSE) code, to measure the duration of the remnant phase. Sensitive radio observations of the remnant radio galaxy J2253-34 are obtained to provide a robust comparison of this technique with the canonical spectral analysis and modelling methods. We find that the remnant lifetimes modelled by each method are consistent; spectral modelling yields $R_\mathrm{rem} = 0.23\pm0.02$, compared to $R_\mathrm{rem} = 0.26\pm0.02$ from our new method. We examine the viability of applying our proposed technique to low-frequency radio surveys using mock radio source populations, and examine whether the technique is sensitive to any intrinsic properties of radio AGNs. Our results show that the technique can be used to robustly classify active and remnant populations, with the most confident predictions for the remnant ratio, and thus off-time, in the longest-lived radio sources ($>50~$Myr) and those at higher redshifts ($z > 0.1$)., Comment: 20 pages, 9 figures, 8 tables. Accepted for publication to MNRAS

Gamma Cygni is a young supernova remnant located in the Cygnus region. MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescopes detected TeV emission (MAGIC J2019+408) to the north-west of this remnant, about 5 arcmin from its border. We want to identify the radio sources within the region encompassing gamma Cygni and MAGIC J2019+408 to shed light on their nature and investigate if these radio sources could be potential contributors to gamma-ray emission. We carried out a detailed study of the data we obtained with a survey of the Cygnus region at 325 and 610 MHz with the Giant Metrewave Radio Telescope (GMRT). We detected several radio sources in the region where the radio and the TeV emission overlap, as well as several areas of enhanced radio emission. In particular, two of these areas of diffuse enhanced emission may correspond to the supernova remnant interacting with a high density region, which seems to be the best candidate for the MAGIC source. Another two radio sources, which may or may not contribute to the gamma rays, are also spatially coincident with the emission peak of the MAGIC TeV source. One of them displays a rather peculiar extended morphology whose nature is completely unknown. We have identified the radio sources overlapping gamma Cygni and MAGIC J2019+408 and have shown that their potential gamma-ray contribution is likely not dominant. In addition, some of the studied sources show peculiar physical characteristics that deserve deeper multi-wavelength observations., Comment: 8 pages, 6 figures, Accepted for publication in Astronomy & Astrophysics

We present a brief overview of a very extensive studies of the group of active galactic nuclei (AGNs) that transitioned to radio-loud state over the past few decades. The sample consists of twelve sources, both quasars and galaxies, showing the characteristics of gigahertz-peaked spectrum (GPS) objects undergoing relatively rapid changes, due to the evolution of their newly-born radio jets. Discussed objects also show a wide range of physical parameters such as bolometric luminosity, black hole mass and jet power, suggesting a great diversity among young active galactic nuclei and their hosts. Furthermore, we introduce a new observational project, the aim of which will be to investigate and gain a more in-depth understanding of the phenomenon of slow radio transients., Comment: 4 pages, 2 figures

Remnant radio galaxies (RRGs), characterized by the cessation of AGN activity, represent a short-lived last phase of radio galaxy's life-cycle. Hitherto, searches for RRGs, mainly based on the morphological criteria, have identified large angular size sources resulting into a bias towards the remnants of powerful FR-II radio galaxies. In this study we make the first attempt to perform a systematic search for RRGs of small angular sizes ($<$30$^{\prime\prime}$) in the XMM-LSS field. By using spectral curvature criterion we discover 48 remnant candidates exhibiting strong spectral curvature ${\it i.e.}$; ${\alpha}_{\rm 150~MHz}^{\rm 325~MHz}$ - ${\alpha}_{\rm 325~MHz}^{\rm 1.4~GHz}$ $\geq$0.5. Spectral characteristics at higher frequency regime ($>$1.4 GHz) indicate that some of our remnant candidates can depict recurrent AGN activity with an active core. We place an upper limit on the remnant fraction ($f_{\rm rem}$) to be 3.9$\%$, which increases to 5.4$\%$ if flux cutoff limit of S$_{\rm 150~MHz}$ $\geq$10 mJy is considered. Our study unveils, hitherto unexplored, a new population of small-size ($<$200 kpc) remnant candidates that are often found to reside in less dense environments and at higher redshifts ($z$) $>$1.0. We speculate that a relatively shorter active phase and/or low jet power can be plausible reasons for the small size of remnant candidates., Comment: Accepted for publication in Galaxies. 19 pages, 7 figures, 3 tables

Low frequency radio observations of galaxy clusters are a useful probe of the non-thermal intracluster medium (ICM), through observations of diffuse radio emission such as radio halos and relics. Current formation theories cannot fully account for some of the observed properties of this emission. In this study, we focus on the development of interferometric techniques for extracting extended, faint diffuse emissions in the presence of bright, compact sources in wide-field and broadband continuum imaging data. We aim to apply these techniques to the study of radio halos, relics and radio mini-halos using a uniformly selected and complete sample of galaxy clusters selected via the Sunyaev-Zel'dovich (SZ) effect by the Atacama Cosmology Telescope (ACT) project, and its polarimetric extension (ACTPol). We use the upgraded Giant Metrewave Radio Telescope (uGMRT) for targeted radio observations of a sample of 40 clusters. We present an overview of our sample, confirm the detection of a radio halo in ACT-CL J0034.4+0225, and compare the narrowband and wideband analysis results for this cluster. Due to the complexity of the ACT-CL J0034.4+0225 field, we use three pipelines to process the wideband data. We conclude that the experimental SPAM wideband pipeline produces the best results for this particular field. However, due to the severe artefacts in the field, further analysis is required to improve the image quality., Comment: Accepted for publication in Galaxies. 16 pages, 5 figures, and 1 table

We present a collection of double-lobed sources towards a 20 sq deg area of the Cygnus region at the northern sky, observed at 325 and 610~MHz with the Giant Metrewave Radio Telescope. The 10'' resolution achieved at 325 MHz is 5.5 times better than previous studies, while at 610~MHz these are the first results ever of such a large area, mapped with 6'' angular resolution. After a thorough visual inspection of the images at the two bands, we found 43 double-lobed source candidates, proposed as such due to the presence of two bright peaks, within a few arcminutes apart, joined by a bridge or a central nucleus. All but two are presented here as double-lobed candidates for the first time. Thirty-nine of the candidates were covered at both bands, and we provide the spectral index information for them. We have searched for positional coincidences between the detected sources/components and other objects from the literature, along the electromagnetic spectrum. Twenty-three candidates possess radio counterpart(s), 12 present infrared counterparts, and one showed an overlapping X-ray source. We analysed each candidate considering morphology, counterparts, and spectral indices. Out of the 43 candidates, 37 show characteristics compatible with an extragalactic nature, two of probably Galactic origin, three remain as dubious cases, though with feature(s) compatible with an extragalactic nature, and the remaining one, evidence of physically unrelated components. The median spectral index of the 40 putative extragalactic sources is -1.0. Their celestial surface density at 610~MHz resulted in 1.9 per sq deg, across a region lying at the Galactic plane., Comment: The paper has been accepted for publication in PASA (22 pages, 14 Figures, 2 Tables)

We present results from a polarization study of the radio-intermediate quasar, III Zw 2, at a redshift of 0.089, with the upgraded Giant Metrewave Radio Telescope (uGMRT) at 685 MHz and the Karl G. Jansky Very Large Array (VLA) at 5 and 34 GHz. We detect a kpc-scale outflow, exhibiting transverse magnetic (B-) fields. The curved jet terminates in a bow-shock-like radio structure with inferred B-fields aligned with the lobe edges. We suggest that the radio outflow in III Zw 2 is a combination of a collimated jet along with a wind-like component. This "wind" component could be a magnetized accretion disk wind or the outer layers of a broadened jet or a combination of both. The current data cannot differentiate between these possibilities. We also detect kpc-scale lobe emission that is misaligned with the primary lobes in the uGMRT images. The spectral indices and the electron lifetimes in the misaligned lobe are similar to the primary lobe, suggesting that the misaligned lobe is not a relic. We propose that changing spectral states of the accretion disk, and the subsequent intermittent behaviour of the outflow, along with the close interplay between the jet and "wind" could explain the radio-intermediate nature of III Zw 2. Our study shows that radio-intermediate quasars are promising sources for understanding the role of jets and winds in galaxy evolution and demonstrates the power of radio polarization studies towards achieving this., Comment: 12 pages, 6 figures; v2: matches published version

Remnant radio galaxies represent an important phase in the life-cycle of radio active galactic nuclei. It is suggested that in this phase, the jets have switched off and the extended emission is fading rapidly. This phase is not well-studied due to the lack of statistical samples observed at both low and high frequencies. In this work, we study a sample of 23 candidate remnant radio galaxies previously selected using the Low Frequency Array at 150 MHz in the Lockman Hole field. We examine their morphologies and study their spectral properties to confirm their remnant nature and revise the morphological and spectral criteria used to define the initial sample. We present new observations with the Karl G. Jansky Very Large Array at 6000 MHz at both high and low resolution. These observations allowed us to observe the presence or absence of cores and study the spectral curvature and steepness of the spectra of the total emission expected at these high frequencies for the remnant candidates. We confirm 13 out of 23 candidates as remnant radio sources. This corresponds to 7% of the full sample of active, restarted, and remnant candidates from the Lockman Hole field. Surprisingly, only a minority of remnants reside in a cluster (23%). The remnant radio galaxies show a range of properties and morphologies. The majority do not show detection of the core at 6000 MHz and their extended emission often shows ultra-steep spectra (USS). However, there are also remnants with USS total emission and a detection of the core at 6000 MHz, possibly indicating a variety of evolutionary stages in the remnant phase. We confirm the importance of the combination of morphological and spectral criteria and this needs to be taken into consideration when selecting a sample of remnant radio sources., Comment: 24 pages, 7 figures, 7 tables, A&A accepted

A recent multi-year Caltech-NRAO Stripe 82 Survey (CNSS) revealed a group of objects that appeared as new radio sources after $>$5--20 years of absence. They are transient phenomena with respect to the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) survey and constitute the first unbiased sample of renewed radio activity. Here we present the follow-up, radio, optical and X-ray study of them. The group consist of 12 sources, both quasars and galaxies with wide redshift ($\rm 0.04 < z < 1.7$) and luminosity ($\rm 2224.5$) distribution. Their radio properties in the first phase of activity, namely the convex spectra and compact morphology, allow them all to be classified as gigahertz-peaked spectrum (GPS) sources. We conclude that the spectral changes are a consequence of the evolution of newly-born radio jets. Our observations show that over the next few years of activity the GPS galaxies keep the convex shape of the spectrum, while GPS quasars rapidly transform into flat-spectrum sources, which may result in them not being recognized as young sources. The wide range of bolometric luminosities, black hole masses and jet powers among the transient sources indicates even greater population diversity in the group of young radio objects. We also suggest that small changes of the accretion disc luminosity (accretion rate) may be sufficient to ignite low-power radio activity that evolves on the scale of decades.

The remnant phase of a radio galaxy begins when the jets launched from an active galactic nucleus are switched off. To study the fraction of radio galaxies in a remnant phase, we take advantage of a $8.31$\,deg$^2$ sub-region of the GAMA~23~field which comprises of surveys covering the frequency range 0.1--9\,GHz. We present a sample of 104 radio galaxies compiled from observations conducted by the Murchison Wide-field Array (216\,MHz), the Australia Square Kilometer Array Pathfinder (887\,MHz), and the Australia Telescope Compact Array (5.5\,GHz). We adopt an `absent radio core' criterion to identify 10 radio galaxies showing no evidence for an active nucleus. We classify these as new candidate remnant radio galaxies. Seven of these objects still display compact emitting regions within the lobes at 5.5\,GHz; at this frequency the emission is short-lived, implying a recent jet switch-off. On the other hand, only three show evidence of aged lobe plasma by the presence of an ultra-steep spectrum ($\alpha<-1.2$) and a diffuse, low surface-brightness radio morphology. The predominant fraction of young remnants is consistent with a rapid fading during the remnant phase. Within our sample of radio galaxies, our observations constrain the remnant fraction to $4\%\lesssim f_{\mathrm{rem}} \lesssim 10\%$; the lower limit comes from the limiting case in which all remnant candidates with hotspots are simply active radio galaxies with faint, undetected radio cores. Finally, we model the synchrotron spectrum arising from a hotspot to show they can persist for 5--10\,Myr at 5.5\,GHz after the jets switch off -- radio emission arising from such hotspots can therefore be expected in an appreciable fraction of genuine remnants.

We study the cosmic evolution of radio sources out to $z \simeq 1.5$ using a GMRT 610 MHz survey covering $\sim$1.86 deg$^2$ of the ELAIS N1 field with a minimum/median rms noise 7.1/19.5\,$\mu$Jy / beam and an angular resolution of 6\,arcsec. We classify sources as star forming galaxies (SFGs), radio-quiet (RQ) and radio-loud (RL) Active Galactic Nuclei (AGN) using a combination of multi-wavelength diagnostics and find evidence in support of the radio emission in SFGs and RQ AGN arising from star formation, rather than AGN-related processes. At high luminosities, however, both SFGs and RQ AGN display a radio excess when comparing radio and infrared star formation rates. The vast majority of our sample lie along the $\rm{SFR - M_{\star}}$ "main sequence" at all redshifts when using infrared star formation rates. We derive the 610 MHz radio luminosity function for the total AGN population, constraining its evolution via continuous models of pure density and pure luminosity evolution with $\rm{\Phi^{\star}\,\propto\,(\,1+\,z)^{(2.25\pm0.38)-(0.63\pm0.35)z}}$ and $\rm{L_{610\,MHz}\,\propto\,(\,1+\,z)^{(3.45\pm0.53)-(0.55\pm0.29)z}}$ respectively. For our RQ and RL AGN, we find a fairly mild evolution with redshift best fitted by pure luminosity evolution with $\rm{L_{610\,MHz}\,\propto\,(\,1+\,z)^{(2.81\pm0.43)-(0.57\pm0.30)z}}$ for RQ AGN and $\rm{L_{610\,MHz}\,\propto\,(\,1+\,z)^{(3.58\pm0.54)-(0.56\pm0.29)z}}$ for RL AGN. The 610 MHz radio AGN population thus comprises two differently evolving populations whose radio emission is mostly SF-driven or AGN-driven respectively., Comment: 20 pages, 14 figures, Accepted for publication in MNRAS

The view of the gamma-ray universe is being continuously expanded by space high energy (HE) and ground based very-high energy (VHE) observatories. Yet, the angular resolution limitation still precludes a straightforward identification of these gamma-ray emitting sources. Radio observations are an effective tool for searching their possible counterparts at lower energies because the same population of relativistic electrons responsible for radio emission can also produce HE/VHE emission via inverse-Compton scattering. The Cygnus region is crowded by many gamma-ray sources, most of them remaining unidentified. In order to find possible counterparts to unidentified gamma-ray sources, we carried out a deep survey of the Cygnus region using the Giant Metrewave Radio Telescope at 610 MHz and 325 MHz. We did a detailed search for counterparts in the error circle of HE/VHE sources. We report 36 radio sources found in the error ellipse of 15 HE sources, and 11 in those of VHE sources. Eight sources have very steep radio spectral index alpha <-1.5, which are most likely to be pulsars and will be followed up for periodicity search. Such a significant number of pulsar candidates within the error circle of HE/VHE sources prompts fresh look at the energetics and efficacy of pulsars and pulsar wind nebulae in this context., Comment: Accepted for publication in ApJS, 24 pages, 20 figures, 7 tables

Context. The repeating FRB121102 is so far the only extra-galactic Fast Radio Burst found to be associated with a counterpart, a steady radio source with a nearly flat spectral energy distribution (SED) in centimeter wavelengths. Aims. Previous observations of the persistent source down to $1.6$~GHz has shown no sign of a spectral turn-over. Absorption is expected to eventually cause a turn-over at lower frequencies. Better constraints on the physical parameters of the emitting medium can be derived by detecting the self-absorption frequency. Methods. We used the Giant Metre-Wave Radio Telescope (GMRT) during the period of July to December 2017 to observe the source at low radio frequencies down to $400$~MHz. Results. The spectral energy distribution of the source remains optically thin even at $400$~MHz, with a spectral index of $\nu^{-(0.07 \pm 0.03)}$ similar to what is seen in Galactic plerions. Using a generic synchrotron radiation model, we obtain constraints on properties of the non-thermal plasma and the central engine powering it. Conclusions. We present low-frequency detections of the persistent source associated with FRB121102. Its characteristic flat SED extends down to $400$~MHz. Like Galactic plerions, the energy in the persistent source is carried predominantly by leptons. The emitting plasma has a $B< 0.01$~G, and its age is $> 524 \left(\frac{B}{0.01 {\rm G}} \right)^{-3/2}$. We show that the energetics of the persistent source requires an initial spin period shorter than 36~ms, and the magnetic field of the neutron star must exceed $4.5\times 10^{12}$~G. This implies that the persistent source does not necessarily require energetic input from a magnetar., Comment: Submitted to A&A, 8 pages, 4 figures

We present the results from 685 MHz observations with the upgraded Giant Metrewave Radio Telescope (uGMRT) of 22 quasars belonging to the Palomar-Green (PG) quasar sample. Only four sources reveal extended radio structures on $\sim$10-30 kpc scales, while the rest are largely a combination of a radio core unresolved at the uGMRT resolution of $\sim$3-5 arcsec, surrounded by diffuse emission on few kpc to $\sim$10 kpc scales. A few sources reveal signatures of barely resolved jets and lobes in their spectral index images that are created using the uGMRT 685 MHz data and similar resolution GHz-frequency data from the Very Large Array. On the basis of their position on the radio-IR correlation as well as the spectral index images, we find that the radio emission in the two radio-loud (RL) quasars and nearly one-third of the radio-quiet (RQ) quasars is active galactic nucleus (AGN) dominated whereas the remaining sources appear to have significant contributions from stellar-related processes along with the AGN. While the two RL sources exhibit inverted spectral index in their cores, the RQ sources exhibit a range of spectral indices varying from flat to steep ($-0.1\gtrsim\alpha_{R}\gtrsim-1.1$) indicating the presence of unresolved jets/lobes or winds. Except for a significant correlation between the 685~MHz radio luminosity and the Eddington ratio, we do not find strong correlations between other 685 MHz radio properties and black hole (BH) properties in the RQ PG sources. This lack of correlations could be explained by the contribution of stellar-related emission, or radio emission from previous AGN activity episodes which may not be related to the current BH activity state., Comment: 25 pages, 20 figures; v2: matches published version

In this paper we present a wide-area 610 MHz survey of the ELAIS\,N1 field with the GMRT, covering an area of 12.8 deg$^2$ at a resolution of 6 arcsec and with an rms noise of $\sim 40$ $\mu$Jy beam$^{-1}$. This is equivalent to $\sim 20$ $\mu$Jy beam$^{-1}$ rms noise at 1.4 GHz for a spectral index of $-0.75$. The primary goal of the survey was to study the polarised sky at sub-mJy flux densities at $<$ GHz frequencies. In addition, a range of other science goals, such as investigations in to the nature of the low-frequency $\mu$Jy source populations and alignments of radio jets. A total of 6,400 sources were found in this region, the vast majority of them compact. The sample jointly detected by GMRT at 610 MHz and by VLA FIRST at 1.4\,GHz has a median spectral index of $-0.85 \pm 0.05$ and a median 610 MHz flux density of 4.5 mJy. This region has a wealth of ancillary data which is useful to characterize the detected sources. The multi-wavelength cross matching resulted optical/IR counterparts to $\sim 90$ per~cent of the radio sources, with a significant fraction having at least photometric redshift. Due to the improved sensitivity of this survey over preceding ones, we have discovered six giant radio sources (GRS), with three of them at $z \sim 1$ or higher. This implies that the population of GRS may be more abundant and common than known to date and if true this has implications for the luminosity function and the evolution of radio sources. We have also identified several candidate extended relic sources., Comment: 13 pages, 11 figures, 1 table. Accepted for publication in MNRAS

Context: Observations at the radio continuum band below the gigahertz band are key when the nature and properties of nonthermal sources are investigated because their radio radiation is strongest at these frequencies. The low radio frequency range is therefore the best to spot possible counterparts to very high-energy (VHE) sources: relativistic particles of the same population are likely to be involved in radio and high-energy radiation processes. Some of these counterparts to VHE sources can be stellar sources. Aims: The Cygnus region in the northern sky is one of the richest in this type of sources that are potential counterparts to VHE sources. We surveyed the central ~15sq deg of the Cygnus constellation at the 325 and 610~MHz bands with angular resolutions and sensitivities of 10" and 6", and 0.5 and 0.2 mJy/beam, respectively. Methods: The data were collected during 172 hours in 2013 - 2017, using the Giant Metrewave Radio Telescope (GMRT) with 32MHz bandwidth, and were calibrated using the SPAM routines. The source extraction was carried out with the PyBDSF tool, followed by verification through visual inspection of every putative catalog candidate source in order to determine its reliability. Results: In this first paper we present the catalog of sources, consisting of 1048 sources at 325 MHz and 2796 sources at 610MHz. By cross-matching the sources from both frequencies with the objects of the SIMBAD database, we found possible counterparts for 143 of them. Most of the sources from the 325-MHz catalog (993) were detected at the 610MHz band, and their spectral index alpha was computed adopting S(nu) ~ nu^alpha. The maximum of the spectral index distribution is at alpha=-1, which is characteristic of nonthermal emitters and might indicate an extragalactic population., Comment: 17 pages, 15 figures, 6 tables, accepted for publication in A&A

We report the discovery of a remnant radio AGN J1615+5452 in the field of ELAIS-N1. GMRT continuum observations at 150, 325 and 610 MHz combined with archival data from the 1.4 GHz NVSS survey were used to derive the radio spectrum of the source. At a redshift $z \sim$ 0.33, J1615+5452 has a linear size of $\sim$ 100 kpc and spectral indices ranging between $\alpha^{1400}_{610} < -1.5$ and $\alpha^{325}_{150} = -0.61 \pm 0.12$. While the source has a diffuse radio emission at low frequencies, we do not find evidence of core, jets or hotspots in the 1.4\,GHz VLA data of $\sim 5$ arcsec angular resolution. Such morphological properties coupled with a curved radio spectrum suggest that the AGN fueling mechanisms undergo a shortage of energy supply which is typical of a dying radio AGN. This is consistent with the observed steep curvature in the spectrum $\Delta\alpha \approx -1$, the estimated synchrotron age of $t_{\rm s}=76.0^{+7.4}_{-8.7}$ Myr and a $t_{\rm off}/t_{\rm s}$ ratio of $\sim 0.3$., Comment: 9 pages, 3 figures, accepted for publication in MNRAS

Massive, early type stars have been detected as radio sources for many decades. Their thermal winds radiate free-free continuum and in binary systems hosting a colliding-wind region, non-thermal emission has also been detected. To date, the most abundant data have been collected from frequencies higher than 1 GHz. We present here the results obtained from observations at 325 and 610 MHz, carried out with the Giant Metrewave Radio Telescope, of all known Wolf-Rayet and O-type stars encompassed in area of ~15 sq degrees centred on the Cygnus region. We report on the detection of 11 massive stars, including both Wolf-Rayet and O-type systems. The measured flux densities at decimeter wavelengths allowed us to study the radio spectrum of the binary systems and to propose a consistent interpretation in terms of physical processes affecting the wide-band radio emission from these objects. WR 140 was detected at 610 MHz, but not at 325 MHz, very likely because of the strong impact of free-free absorption. We also report - for the first time - on the detection of a colliding-wind binary system down to 150 MHz, pertaining to the system of WR 146, making use of complementary information extracted from the TIFR GMRT Sky Survey. Its spectral energy distribution clearly shows the turnover at a frequency of about 600 MHz, that we interpret to be due to free-free absorption. Finally, we report on the identification of two additional particle-accelerating colliding-wind binaries, namely Cyg OB2 12 and ALS 15108 AB., Comment: 20 pages, 20 figures, 6 tables, accepted in PASA

One of the key science goals for the most sensitive telescopes, both current and upcoming, is the detection of the redshifted 21-cm signal from the Cosmic Dawn and Epoch of Reionization. The success of detection relies on accurate foreground modeling for their removal from data sets. This paper presents the characterization of astrophysical sources in the Lockman Hole region. Using 325 MHz data obtained from the GMRT, a $6^\circ \times 6^\circ$ mosaiced map is produced with an RMS reaching 50 $\mu$Jy $\mathrm{beam}^{-1}$. A source catalog containing 6186 sources is created, and the Euclidean normalized differential source counts have been derived from it, consistent with previous observations as well as simulations. A detailed comparison of the source catalog is also made with previous findings - at both lower and higher frequencies. The angular power spectrum (APS) of the diffuse Galactic synchrotron emission is determined for three different galactic latitudes using the Tapered Gridded Estimator. The values of the APS lie between $\sim$1 mK$^2$ to $\sim$100 mK$^2$. Fitting a power law of the form $A\ell^{-\beta}$ gives values of $A$ and $\beta$ varying across the latitudes considered. This paper demonstrates, for the first time, the variation of the power-law index for diffuse emission at very high galactic locations. It follows the same trend that is seen at locations near the galactic plane, thus emphasizing the need for low-frequency observations for developing better models of the diffuse emission., Comment: 16 Pages, 11 Figures, Accepted for publication in MNRAS

We present a detailed analysis of the radio galaxy PKS 2250-351, a giant of 1.2 Mpc projected size, its host galaxy, and its environment. We use radio data from the Murchison Widefield Array, the upgraded Giant Metre-wavelength Radio Telescope, the Australian Square Kilometre Array Pathfinder, and the Australia Telescope Compact Array to model the jet power and age. Optical and infra-red data come from the Galaxy And Mass Assembly (GAMA) survey and provide information on the host galaxy and environment. GAMA spectroscopy confirms that PKS 2250-351 lies at z=0.2115 in the irregular, and likely unrelaxed, cluster Abell 3936. We find its host is a massive, `red and dead' elliptical galaxy with negligible star formation but with a highly obscured active galactic nucleus dominating the mid-infrared emission. Assuming it lies on the local M-sigma relation it has an Eddington accretion rate of lambda_EDD~0.014. We find that the lobe-derived jet power (a time-averaged measure) is an order of magnitude greater than the hotspot-derived jet power (an instantaneous measure). We propose that over the lifetime of the observed radio emission (~300 Myr) the accretion has switched from an inefficient advection dominated mode to a thin-disc efficient mode, consistent with the decrease in jet power. We also suggest that the asymmetric radio morphology is due to its environment, with the host of PKS 2250-351 lying to the west of the densest concentration of galaxies in Abell 3936., Comment: 16 pages and 8 figures, accepted for publication in PASA

We study the properties of star-forming galaxies selected at 610 MHz with the GMRT in a survey covering $\sim$1.86 deg$^2$ down to a noise of $\sim$7.1\,$\mu$Jy / beam. These were identified by combining multiple classification diagnostics: optical, X-ray, infrared and radio data. Of the 1685 SFGs from the GMRT sample, 496 have spectroscopic redshifts whereas 1189 have photometric redshifts. We find that the IRRC of star-forming galaxies, quantified by the infrared-to-1.4 GHz radio luminosity ratio $\rm{q_{IR}}$, decreases with increasing redshift: $\rm{q_{IR}\,=\,2.86\pm0.04(1\,+\,z)^{-0.20\pm0.02}}$ out to $z \sim 1.8$. We use the $\rm{V/V_{max}}$ statistic to quantify the evolution of the co-moving space density of the SFG sample. Averaged over luminosity our results indicate $\rm{\langle V/V_{max} \rangle}$ to be $\rm{0.51\,\pm\, 0.06}$, which is consistent with no evolution in overall space density. However we find $\rm V/V_{max}$ to be a function of radio luminosity, indicating strong luminosity evolution with redshift. We explore the evolution of the SFGs radio luminosity function by separating the source into five redshift bins and comparing to theoretical model predictions. We find a strong redshift trend that can be fitted with a pure luminosity evolution of the form $\rm{L_{610\,MHz}\,\propto\,(\,1+\,z)^{(2.95\pm0.19)-(0.50\pm0.15)z}}$. We calculate the cosmic SFR density since $\rm{z \sim 1.5}$ by integrating the parametric fits of the evolved 610\,MHz luminosity function. Our sample reproduces the expected steep decline in the star formation rate density since $\rm{z\,\sim\,1}$., Comment: 16 pages, 11 figures and 6 tables in the main text plus additional figure and table in the appendix. Accepted for publication in MNRAS

This is the first of a series of papers based on sensitive 610 MHz observations of the ELAIS N1 field using the Giant Metrewave Radio Telescope. We describe the observations, processing and source catalogue extraction from a deep image with area of 1.86\,deg$^{2}$ and minimum noise of $\sim$7.1\,$\mu$Jy/beam. We compile a catalogue of 4290 sources with flux densities in the range 28.9\,$\mu$Jy - 0.503\,Jy, and derive the Euclidean-normalized differential source counts for sources with flux densities brighter than $\rm{35.5\,\mu\,Jy}$. Our counts show a flattening at 610 MHz flux densities below 1 mJy. Below the break the counts are higher than previous observations at this frequency, but generally consistent with recent models of the low-frequency source population. The radio catalogue is cross-matched against multi-wavelength data leading to identifications for 92\% and reliable redshifts for 72\% of our sample, with 19\% of the redshifts based on spectroscopy. For the sources with redshifts we use radio and X-ray luminosity, optical spectroscopy and mid-infrared colours to search for evidence of the presence of an Active Galactic Nucleus (AGN). We compare our identifications to predictions of the flux density distributions of star forming galaxies (SFGs) and AGN, and find a good agreement assuming the majority of the sources without redshifts are SFGs. We derive spectral index distributions for a sub-sample. The majority of the sources are steep spectra, with a median spectral index that steepens with frequency; $\mathrm{\alpha^{325}_{610}\,=\,-0.80\,\pm\,0.29}$, $\mathrm{\alpha^{610}_{1400}\,=\,-0.83\,\pm\,0.31}$ and $\mathrm{\alpha^{610}_{5000}\,=\,-1.12\,\pm\,0.15}$., Comment: 21 pages, 18 figures, 7 tables, accepted for publication in MNRAS

Binary millisecond pulsars (MSPs) provide several opportunities for research of fundamental physics. However, finding them can be challenging. Several subdwarf B (sdB) binary systems with possible neutron star companions have been identified, allowing us to perform a targeted search for MSPs within these systems. Six sdBs with companions in the neutron star mass range, as determined from their optical light curves, were observed with the Green Bank and Westerbork radio telescopes. The data were searched for periodic signals as well as single pulses. No radio pulsations from sdB systems were detected, down to an average sensitivity limit of 0.11 mJy. We did, however, discover a pulsar in the field of sdB HE0532-4503. Follow-up observations with the Giant Metrewave Radio Telescope showed that this pulsar, J0533-4524, is not spatially coincident with the sdB system. The pulsar has a relatively low magnetic field but still emits giant pulses. We place an upper limit of three to the number of radio pulsars in the six sdB systems. The non-detections may be explained by a combination of the MSP beaming fraction, luminosity, and a recycling fraction <0.5. Alternatively, the assumption of co-rotation between the MSP and sdB may break down, which implies the systems are more edge-on than previously thought. This would shift the predicted companion masses into the white dwarf range. It would also explain the relative lack of edge-on sdB systems with massive companions., Comment: 12 pages, 8 figures. Accepted for publication in MNRAS

Our knowledge of the variety of galaxy clusters has been increasing in the last few years thanks to our progress in understanding the severity of selection effects on samples. To understand the reason for the observed variety, we study CL2015, a cluster easily missed in X-ray selected observational samples. Its core-excised X-ray luminosity is low for its mass M500, well below the mean relation for an X-ray selected sample, but only ~1.5 sigma below that derived for an X-ray unbiased sample. We derived thermodynamic profiles and hydrostatic masses with the acquired deep Swift X-ray data, and we used archival Einstein, Planck, and SDSS data to derive additional measurements, such as integrated Compton parameter, total mass, and stellar mass. The pressure and the electron density profiles of CL2015 are systematically outside the +/- 2 sigma range of the universal profiles; in particular the electron density profile is even lower than the one derived from Planck-selected clusters. CL2015 also turns out to be fairly different in the X-ray luminosity versus integrated pressure scaling compared to an X-ray selected sample, but it is a normal object in terms of stellar mass fraction. CL2015's hydrostatic mass profile, by itself or when is considered together with dynamical masses, shows that the cluster has an unusual low concentration and an unusual sparsity compared to clusters in X-ray selected samples. The different behavior of CL2015 is caused by its low concentration. When concentration differences are accounted for, the properties of CL2015 become consistent with comparison samples. CL2015 is perhaps the first known cluster with a remarkably low mass concentration for which high quality X-ray data exist. Objects similar to CL2015 fail to enter observational X-ray selected samples because of their low X-ray luminosity relative to their mass., Comment: A&A, appeared

We present observations of the Cygnus OB2 region obtained with the Giant Metrewave Radio Telescope (GMRT) at the frequencies of 325 MHz and 610 MHz. In this contribution we focus on the study of proplyd-like objects (also known as free-floating Evaporating Gas Globules or frEGGs) that typically show an extended cometary morphology. We identify eight objects previously studied at other wavelengths and derive their physical properties by obtaining their optical depth at radio-wavelengths. Using their geometry and the photoionization rate needed to produce their radio-continuum emission, we find that these sources are possibly ionized by a contribution of the stars Cyg OB2 #9 and Cyg OB2 #22. Spectral index maps of the eight frEGGs were constructed, showing a flat spectrum in radio frequencies in general. We interpret these as produced by optically-thin ionized gas, although it is possible that a combination of thermal emission, not necessarily optically thin, produced by a diffuse gas component and the instrument response (which detects more diffuse emission at low frequencies) can artificially generate negative spectral indices. In particular, for the case of the Tadpole we suggest that the observed emission is not of non-thermal origin despite the presence of regions with negative spectral indices in our maps., Comment: Acepted Astronomy & Astrophysics, 9 pages, 4 figures

The GMRT Online Archive now houses over 120 terabytes of interferometric observations obtained with the GMRT since the observatory began operating as a facility in 2002. The utility of this vast data archive, likely the largest of any Indian telescope, can be significantly enhanced if first look (and where possible, science ready) processed images can be made available to the user community. We have initiated a project to pipeline process GMRT images in the 150, 240, 325 and 610 MHz bands. The thousands of processed continuum images that we will produce will prove useful in studies of distant galaxy clusters, radio AGN, as well as nearby galaxies and star forming regions. Besides the scientific returns, a uniform data processing pipeline run on a large volume of data can be used in other interesting ways. For example, we will be able to measure various performance characteristics of the GMRT telescope and their dependence on waveband, time of day, RFI environment, backend, galactic latitude etc. in a systematic way. A variety of data products such as calibrated UVFITS data, sky images and AIPS processing logs will be delivered to users via a web-based interface. Data products will be compatible with standard Virtual Observatory protocols., Comment: To appear in the Proceedings of Astronomical Data Analysis Software & Systems (ADASS) XXVIII published by the Astronomical Society of the Pacific (ASP) conference series

Narrow-Line Seyfert 1 galaxies (NLS1s) are generally believed to be radio-quiet Active Galactic Nuclei (AGN) with relatively less-massive (10$^{5}$$-$10$^{8}$~M$_{\odot}$) Super-Massive Black Holes (SMBH). Using the FIRST radio detections of hitherto the largest sample of 11101 optically-selected NLS1s we find a rather uncommon population of 55 NLS1s with Kiloparsec-Scale Radio structures (KSRs). We note that the number of NLS1s with KSRs found in our study is only a lower limit considering the effects of sensitivity, spatial resolution and projection, and hence, the number of NLS1s with KSRs may be more common than thought earlier. The NLS1s with KSRs are distributed across a wide range of redshifts, flux densities and luminosities. NLS1s with KSRs tend to exhibit steep radio spectra and are likely to be misaligned version of blazar-like NLS1s. The ratio of IR to radio flux density (q$_{\rm 22~{\mu}m}$ $=$ log[S$_{\rm 22~{\mu}m}$/S$_{\rm 1.4~GHz}$]) versus radio luminosity plot suggests that KSRs are mostly powered by AGN, while KSRs in NLS1s with low radio luminosity (L$_{\rm 1.4~GHz}$ $<$ 10$^{23.5}$ W~Hz$^{-1}$) may have a contribution from circumnuclear starburst. The trend shown by KSRs in radio luminosity versus radio-size plot indicates that the radio-jets resulting in KSRs are either in the early phase of their evolution or inefficient to grow beyond the host galaxy., Comment: 6 pages, 4 figures, 1 table, accepted for publication in Proceedings of Science. Contributed article in the conference on "Revisiting narrow-line Seyfert 1 galaxies and their place in the Universe'' held in Padova university, Italy, 9-13 April 2018

We present a multiwavelength study of the filamentary infrared dark cloud (IRDC) G333.73+0.37. The region contains two distinct mid-infrared sources S1 and S2 connected by dark lanes of gas and dust. Cold dust emission from the IRDC is detected at seven wavelength bands and we have identified 10 high density clumps in the region. The physical properties of the clumps such as temperature: 14.3-22.3 K and mass: 87-1530 M_sun are determined by fitting a modified blackbody to the spectral energy distribution of each clump between 160 micron and 1.2 mm. The total mass of the IRDC is estimated to be $~4700 M_sun. The molecular line emission towards S1 reveals signatures of protostellar activity. Low frequency radio emission at 1300 and 610 MHz is detected towards S1 (shell-like) and S2 (compact morphology), confirming the presence of newly formed massive stars in the IRDC. Photometric analysis of near and mid-infrared point sources unveil the young stellar object population associated with the cloud. Fragmentation analysis indicates that the filament is supercritical. We observe a velocity gradient along the filament, that is likely to be associated with accretion flows within the filament rather than rotation. Based on various age estimates obtained for objects in different evolutionary stages, we attempt to set a limit to the current age of this cloud., Comment: 26 pages, 20 figures, accepted by ApJ

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., Comment: Accepted for publication in MNRAS; 6 pages, 6 figures

Binary neutron-star mergers (BNSMs) are among the most readily detectable gravitational-wave (GW) sources with LIGO. They are also thought to produce short $\gamma$-ray bursts (SGRBs), and kilonovae that are powered by r-process nuclei. Detecting these phenomena simultaneously would provide an unprecedented view of the physics during and after the merger of two compact objects. Such a Rosetta Stone event was detected by LIGO/Virgo on 17 August 2017 at a distance of $\sim 44$ Mpc. We monitored the position of the BNSM with ALMA at 338.5 GHz and GMRT at 1.4 GHz, from 1.4 to 44 days after the merger. Our observations rule out any afterglow more luminous than $3\times 10^{26}~{\rm erg\,s}^{-1}\,{\rm Hz}^{-1}$ in these bands, probing $>$2--4 dex fainter than previous SGRB limits. We match these limits, in conjunction with public data announcing the appearance of X-ray and radio emission in the weeks after the GW event, to templates of off-axis afterglows. Our broadband modeling suggests that GW170817 was accompanied by a SGRB and that the GRB jet, powered by $E_{\rm AG,\,iso}\sim10^{50}$~erg, had a half-opening angle of $\sim20^\circ$, and was misaligned by $\sim41^\circ$ from our line of sight. The data are also consistent with a more collimated jet: $E_{\rm AG,\,iso}\sim10^{51}$~erg, $\theta_{1/2,\,\rm jet}\sim5^\circ$, $\theta_{\rm obs}\sim17^\circ$. This is the most conclusive detection of an off-axis GRB afterglow and the first associated with a BNSM-GW event to date. Assuming a uniform top-hat jet, we use the viewing angle estimates to infer the initial bulk Lorentz factor and true energy release of the burst., Comment: Accepted for publication in the Astrophysical Journal Letter. 12 pages, 4 figures

Infrared-Faint Radio Sources (IFRSs) are an unusual class of objects that are relatively bright at radio wavelengths but have faint or undetected infrared counterparts even in deep surveys. We identify and investigate the nature of IFRSs using deep radio (S$_{\rm 1.4~GHz}$ $\sim$ 100 $\mu$Jy beam$^{-1}$ at 5$\sigma$), optical (m$_{\rm r}$ $\sim$ 26 - 27.7 at 5$\sigma$), and near-IR (S$_{\rm 3.6~{\mu}m}$ $\sim$ 1.3 - 2.0 $\mu$Jy beam$^{-1}$ at 5$\sigma$) data available in two deep fields namely the Subaru X-ray Deep Field (SXDF) and the Very Large Array - VIMOS VLT Deep Survey (VLA-VVDS) field. In 1.8 deg$^{2}$ of the two fields we identify a total of nine confirmed and ten candidate IFRSs. We find that our IFRSs are high-redshift radio-loud AGN, with 12/19 sources having redshift estimates in the range of $z$ $\sim$ 1.7 - 4.3, while a limit of $z$ $\geq$ 2.0 is placed for the remaining seven sources. Notably, our study finds, for the first time, IFRSs with measured redshift $>$ 3.0, and also, the redshift estimates for IFRSs in the faintest 3.6 $\mu$m flux regime i.e., S$_{\rm 3.6~{\mu}m}$ $<$ 1.3 ${\mu}$Jy. Radio observations show that our IFRSs exhibit both compact unresolved as well as extended double-lobe morphologies, and have predominantly steep radio spectra between 1.4 GHz and 325 MHz. The non-detection of all but one IFRSs in the X-ray band and the optical-to-MIR colour (m$_{\rm r}$ - m$_{\rm 24~{\mu}m}$) suggest that a significant fraction of IFRSs are likely to be hosted in dusty obscured galaxies., Comment: 20 pages, 8 figures, 4 tables, accepted for publication in MNRAS

We present the first quick look analysis of data from nine {\it AstroSat}'s LAXPC observations of GRS 1915+105 during March 2016 when the source had the characteristics of being in Radio-quiet $\chi$ class. We find that a simple empirical model of a disk blackbody emission, with Comptonization and a broad Gaussian Iron line can fit the time averaged 3--80 keV spectrum with a systematic uncertainty of 1.5\% and a background flux uncertainty of 4\%. A simple deadtime-corrected Poisson noise level spectrum matches well with the observed high frequency power spectra till 50 kHz and as expected the data show no significant high frequency ($> 20$ Hz) features. Energy dependent power spectra reveal a strong low frequency (2 - 8 Hz) Quasi-periodic oscillation (LFQPO) and its harmonic along with broad band noise. The QPO frequency changes rapidly with flux (nearly 4 Hz in ~ 5 hours). With increasing QPO frequency, an excess noise component appears significantly in the high energy regime (> 8 keV). At the QPO frequencies, the time-lag as a function of energy has a non-monotonic behavior such that the lags decrease with energy till about 15 -20 keV and then increase for higher energies. These first look results benchmark the performance of LAXPC at high energies and confirms that its data can be used for more sophisticated analysis such as flux or frequency-resolved spectro-timing studies., Comment: 9 pages, 11 figures

We report the discovery of a `Triple-Double Radio Galaxy (TDRG)' J1216+0709 detected in deep low-frequency Giant Metrewave Radio Telescope (GMRT) observations. J1216+0709 is only the third radio galaxy, after B0925+420 and Speca, with three pairs of lobes resulting from three different episodes of AGN jet activity. The 610 MHz GMRT image clearly displays an inner pair of lobes, a nearly co-axial middle pair of lobes and a pair of outer lobes that is bent w.r.t. the axis of inner pair of lobes. The total end-to-end projected sizes of the inner, middle, and outer lobes are 40$^{{\prime}{\prime}}$ ($\sim$ 95 kpc), 1$^{\prime}$.65 ($\sim$ 235 kpc) and 5$^{\prime}$.7 ($\sim$ 814 kpc), respectively. Unlike the outer pair of lobes both the inner and middle pairs of lobes exhibit asymmetries in arm-lengths and flux densities, but in opposite sense, i.e., the eastern sides are farther and also brighter that the western sides, thus suggesting the possibility of jet being intrinsically asymmetric rather than due to relativistic beaming effect. The host galaxy is a bright elliptical (m$_{\rm r}$ $\sim$ 16.56) with M$_{\rm SMBH}$ $\sim$ 3.9 $\times$ 10$^{9}$ M$\odot$ and star-formation rate of $\sim$ 4.66$_{\rm -1.61}^{\rm +4.65}$ M$_{\odot}$ yr$^{-1}$. The host galaxy resides is a small group of three galaxies (m$_{\rm r}$ $\leq$ 17.77) and is possibly going through the interaction with faint, dwarf galaxies in the neighbourhood, which may have triggered the recent episodes of AGN activity., Comment: 8 pages, 2 figures, 2 tables, accepted for publication in ApJ

Low frequency observations at 325 and 610 MHz have been carried out for two "radio-loud" Seyfert galaxies, NGC4235 and NGC4594 (Sombrero galaxy), using the Giant Meterwave Radio Telescope (GMRT). The 610 MHz total intensity and 325-610 MHz spectral index images of NGC4235 tentatively suggest the presence of a "relic" radio lobe, most likely from a previous episode of AGN activity. This makes NGC4235 only the second known Seyfert galaxy after Mrk6 to show signatures of episodic activity. Spitzer and Herschel infrared spectral energy distribution (SED) modelling using the clumpyDREAM code predicts star formation rates (SFR) that are an order of magnitude lower than those required to power the radio lobes in these Seyferts (~0.13-0.23 M_sun/yr compared to the required SFR of ~2.0-2.7 M_sun/yr in NGC4594 and NGC4235, respectively). This finding along with the detection of parsec and sub-kpc radio jets in both Seyfert galaxies, that are roughly along the same position angles as the radio lobes, strongly support the suggestion that Seyfert lobes are AGN-powered. SED modelling supports the "true" type 2 classification of NGC4594: this galaxy lacks significant dust obscuration as well as a prominent broad-line region. Between the two Seyfert galaxies, there is an inverse relation between their radio-loudness and Eddington ratio and a direct relation between their Eddington-scaled jet power and bolometric power., Comment: 22 pages, 11 figures, MNRAS, accepted

LS I +61 303 is a gamma-ray binary that exhibits an outburst at GHz frequencies each orbital cycle of $\approx$ 26.5 d and a superorbital modulation with a period of $\approx$ 4.6 yr. We have performed a detailed study of the low-frequency radio emission of LS I +61 303 by analysing all the archival GMRT data at 150, 235 and 610 MHz, and conducting regular LOFAR observations within the Radio Sky Monitor (RSM) at 150 MHz. We have detected the source for the first time at 150 MHz, which is also the first detection of a gamma-ray binary at such a low frequency. We have obtained the light-curves of the source at 150, 235 and 610 MHz, all of them showing orbital modulation. The light-curves at 235 and 610 MHz also show the existence of superorbital variability. A comparison with contemporaneous 15-GHz data shows remarkable differences with these light-curves. At 15 GHz we see clear outbursts, whereas at low frequencies we see variability with wide maxima. The light-curve at 235 MHz seems to be anticorrelated with the one at 610 MHz, implying a shift of $\sim$ 0.5 orbital phases in the maxima. We model the shifts between the maxima at different frequencies as due to changes in the physical parameters of the emitting region assuming either free-free absorption or synchrotron self-absorption, obtaining expansion velocities for this region close to the stellar wind velocity with both mechanisms., Comment: 12 pages, 10 figures, accepted for publication in MNRAS

We present observations at 610 MHz and 235 MHz using the Giant Metrewave Radio Telescope (GMRT) of the recurrent nova V745 Scorpii which recorded its last outburst on 6 February 2014. This is the second symbiotic recurrent nova whose light curve at low frequencies has been followed in detail, the first being RS Ophiuchi in 2006. We fitted the 610 MHz light curve by a model of synchrotron emission from an expanding shell being modified by radiative transfer effects due to local absorbing gas consisting of a uniformly distributed and a clumpy component. Using our model parameters, we find that the emission at 235 MHz peaked around day 35 which is consistent with our GMRT observations. The two main results of our study are: (1) The radio emission at a given frequency is visible sooner after the outburst in successive outbursts of both V745 Scorpii and RS Ophiuchi. The earlier detection of radio emission is interpreted to be caused by decreasing foreground densities. (2) The clumpy material, if exists, is close to the white dwarf and can be interpreted as being due to the material from the hot accretion disk. The uniform density gas is widespread and attributed to the winds blown by the white dwarf. We present implications of these results on the evolution of both novae. Such studies alongwith theoretical understanding have the potential of resolving several outstanding issues such as why all recurrent novae are not detectable in synchrotron radio and whether recurrent novae are progenitor systems of type 1a supernova., Comment: Revised, matches version in print

Double-lobe radio galaxies in the local Universe have traditionally been found to be hosted in elliptical or lenticular galaxies. We report the discovery of four spiral-host double-lobe radio galaxies (J0836+0532, J1159+5820, J1352+3126 and J1649+2635) that are discovered by cross-matching a large sample of 187005 spiral galaxies from SDSS DR7 to the full catalogues of FIRST and NVSS. J0836+0532 is reported for the first time. The host galaxies are forming stars at an average rate of 1.7 $-$ 10 M$_{\odot}$ yr$^{-1}$ and possess Super Massive Black Holes (SMBHs) with masses of a few times 10$^{8}$ M$_{\odot}$. Their radio morphologies are similar to FR-II radio galaxies with total projected linear sizes ranging from 86 kpc to 420 kpc, but their total 1.4 GHz radio luminosities are only in the range 10$^{24}$ $-$ 10$^{25}$ W Hz$^{-1}$. We propose that the formation of spiral-host double-lobe radio galaxies can be attributed to more than one factor, such as the occurrence of strong interactions, mergers, and the presence of unusually massive SMBHs, such that the spiral structures are not destroyed. Only one of our sources (J1649+2635) is found in a cluster environment, indicating that processes other than accretion through cooling flows e.g., galaxy-galaxy mergers or interactions could be plausible scenarios for triggering radio-loud AGN activity in spiral galaxies., Comment: 18 pages, 6 figures, 9 tables, accepted for publication in MNRAS

We report the discovery of a relic Giant Radio Galaxy (GRG) J021659-044920 at redshift $z \sim 1.3$ that exhibits large-scale extended, nearly co-spatial, radio and X-ray emission from radio lobes, but no detection of Active Galactic Nuclei core, jets and hotspots. The total angular extent of the GRG at the observed frame 0.325 GHz, using Giant Metrewave Radio Telescope observations is found to be ${\sim}$ 2.4 arcmin, that corresponds to a total projected linear size of $\sim$ 1.2 Mpc. The integrated radio spectrum between 0.240 and 1.4 GHz shows high spectral curvature (${\alpha}_{\rm 0.610~GHz}^{\rm 1.4~GHz} - {\alpha}_{\rm 0.240~GHz}^{\rm 0.325~GHz}$ $>$ 1.19) with sharp steepening above 0.325 GHz, consistent with relic radio emission that is $\sim$ 8 $\times$ 10$^{6}$ yr old. The radio spectral index map between observed frame 0.325 and 1.4~GHz for the two lobes varies from 1.4 to 2.5 with the steepening trend from outer-end to inner-end, indicating backflow of plasma in the lobes. The extended X-ray emission characterized by an absorbed power-law with photon index $\sim$ 1.86 favours inverse-Compton scattering of the Cosmic Microwave Background (ICCMB) photons as the plausible origin. Using both X-ray and radio fluxes under the assumption of ICCMB we estimate the magnetic field in the lobes to be 3.3 $\mu$G. The magnetic field estimate based on energy equipartition is $\sim$ 3.5 $\mu$G. Our work presents a case study of a rare example of a GRG caught in dying phase in the distant Universe., Comment: 10 pages, 5 figures, 3 tables. Published in MNRAS. Corrected typos and added a reference

We have studied in detail the 0.15-15 GHz radio spectrum of the gamma-ray binary LS 5039 to look for a possible turnover and absorption mechanisms at low frequencies, and to constrain the physical properties of its emission. We have analysed two archival VLA monitorings, all the available archival GMRT data and a coordinated quasi-simultaneous observational campaign conducted in 2013 with GMRT and WSRT. The data show that the radio emission of LS 5039 is persistent on day, week and year timescales, with a variability $\lesssim 25~\%$ at all frequencies, and no signature of orbital modulation. The obtained spectra reveal a power-law shape with a curvature below 5 GHz and a turnover at $\sim0.5$ GHz, which can be reproduced by a one-zone model with synchrotron self-absorption plus Razin effect. We obtain a coherent picture for a size of the emitting region of $\sim0.85~\mathrm{mas}$, setting a magnetic field of $B\sim20~\mathrm{mG}$, an electron density of $n_{\rm e}\sim4\times10^5~{\rm cm^{-3}}$ and a mass-loss rate of $\dot M\sim5\times10^{-8}~{\rm M_{\odot} yr^{-1}}$. These values imply a significant mixing of the stellar wind with the relativistic plasma outflow from the compact companion. At particular epochs the Razin effect is negligible, implying changes in the injection and the electron density or magnetic field. The Razin effect is reported for first time in a gamma-ray binary, giving further support to the young non-accreting pulsar scenario., Comment: 16 pages, 9 figures, accepted for publication in MNRAS

We present Giant Metrewave Radio Telescope (GMRT) 240 MHz observations of the nearby luminous FR I radio source 3C 270, in the group-central elliptical NGC 4261. Combining these data with reprocessed Very Large Array (VLA) 1.55 and 4.8 GHz observations, we produce spectral index maps that reveal a constant spectral index along the jets and a gradual steepening from the ends of the jets through the lobes towards the nucleus. A Jaffe & Perola (JP) model fitted to the integrated spectrum of the source gives an asymptotic low-frequency index of $\alpha_{inj}=0.53_{-0.02}^{+0.01}$, while JP models fitted to the observed spectral index trend along the lobes allow us to estimate radiative ages of $\sim29$ Myr and $\sim37$ Myr for the west and east lobes respectively. Our age estimates are a factor of two lower than the 75-Myr upper limit derived from X-ray data (O'Sullivan et al. 2011). We find unlikely the scenario of an early supersonic phase in which the lobe expanded into the ISM at approximately Mach 6 (3500 km s$^{-1}$), and suggest that either the source underwent multiple AGN outbursts with possible large changes in jet power, or possibly that the source age that we find is due to a backflow that transports young electrons from the jet tips through the lobes toward the nucleus relatively quickly. We calculate that in the lobes the energy ratio of non-radiating to radiating particles is $\sim4-24$ indicating significant gas entrainment. If the lobes are in pressure balance with their surroundings, the total energy required to heat the entrained material is $10^{58}$ erg, $\sim$40% of the total enthalpy of the lobes., Comment: 14 pages, 11 figures, 8 tables. Accepted for publication by MNRAS. Revised throughout in response to referee's comments

We study the radio--far infrared (FIR) correlation in "blue cloud" galaxies chosen from the PRism MUltiobject Survey (PRIMUS) up to redshift ($z$) of 1.2 in the XMM-LSS field. We use rest-frame emission at 1.4 GHz in the radio and both monochromatic (at 70$\mu$m) and bolometric (between $8-1000~\mu$m) emission in the FIR. To probe the nature of the correlation up to $z\sim1.2$, where direct detection of blue star-forming galaxies is impossible with current technology, we employ the technique of image stacking at 0.325 and 1.4 GHz in the radio and in six infrared bands, viz. 24, 70, 160, 250, 350 and $500~\mu$m. For comparison, we also study the correlation for more luminous galaxies that are directly detected. The stacking analysis allows us to probe the radio--FIR correlation for galaxies that are up to 2 orders of magnitude fainter than the ones detected directly. The $k-$correction in the infrared wavebands is obtained by fitting the observed spectral energy distribution (SED) with a composite mid-IR power law and a single temperature greybody model. We find that the radio luminosity at 1.4 GHz ($L_{\rm 1.4GHz}$) is strongly correlated with monochromatic FIR luminosity at 70 $\mu$m ($L_{\rm 70\mu m}$) having slope $1.09\pm0.05$ and with bolometric luminosity ($L_{\rm TIR}$) having slope $1.11\pm0.04$. The quantity $q_{\rm TIR} (=\log_{10}[L_{\rm TIR}/(3.75\times 10^{12} L_{\rm 1.4 GHz})])$ is observed to decrease with redshift as $q_{\rm TIR} \propto (1+z)^{-0.16\pm0.03}$ probably caused due to the non-linear slope of the radio--FIR correlation. Within the uncertainties of our measurement and the limitations of our flux-limited and color-selected sample, we do not find any evolution of the radio--FIR correlation with redshift., Comment: 17 pages, 8 figures. Accepted to be published in Astrophysical Journal

Seyfert and LINER galaxies are known to exhibit compact radio emission on $\sim$ 10 to 100 parsec scales, but larger Kiloparsec-Scale Radio structures (KSRs) often remain undetected in sub-arcsec high resolution observations. We investigate the prevalence and nature of KSRs in Seyfert and LINER galaxies using the 1.4 GHz VLA FIRST and NVSS observations. Our sample consists of 2651 sources detected in FIRST and of these 1737 sources also have NVSS counterparts. Considering the ratio of total to peak flux density ($\theta$ $=$ ${\rm (S_{\rm int}/S_{\rm peak})^{1/2}}$) as a parameter to infer the presence of extended radio emission we show that $\geq$ 30$\%$ of FIRST detected sources possess extended radio structures on scales larger than 1.0 kpc. The use of low-resolution NVSS observations help us to recover faint extended KSRs that are resolved out in FIRST observations and results in $\geq$ 42.5$\%$ KSR sources in FIRST-NVSS subsample. This fraction is only a lower limit owing to the combination of projection, resolution and sensitivity effects. Our study demonstrates that KSRs may be more common than previously thought and are found across all redshifts, luminosities and radio-loudness. The extranuclear radio luminosity of KSR sources is found to be positively correlated with the core radio luminosity as well as the [O~III] $\lambda$5007{\AA} line luminosity and this can be interpreted as KSRs being powered by AGN rather than star-formation. The distributions of the FIR-to-radio ratios and mid-IR colors of KSR sources are also consistent with their AGN origin. However, contribution from star-formation cannot be ruled out particularly in sources with low radio luminosities., Comment: 15 pages, 13 figures, 4 tables, accepted for publication in MNRAS