Search

Coherent radio emission with properties similar to planetary auroral signals has been reported from GJ 1151, a quiescent, slow-rotating mid-M star, by the LOFAR Two-metre (120-170 MHz) Sky Survey (LoTSS). The observed {LOFAR} emission is fairly bright at 0.89 mJy with 64% circular polarization, and the emission characteristics are consistent with the interaction between an Earth-sized planet with an orbital period of 1-5 days and the magnetic field of the host star. However, no short-period planet has been detected around GJ 1151. To confirm the reported radio emission caused by the putative planet around GJ 1151 and to investigate the nature of this emission, we carried out uGMRT observations of GJ 1151 at 150, 218, and 400 MHz over 33 hours across ten epochs. No emission was detected at any frequency. While at 150 MHz and 218 MHz, non-detection could be due to the low sensitivity of our observations, at 400 MHz, the rms sensitivities achieved were sufficient to detect the emission observed with LOFAR at $\sim$ 20$\sigma$ level. Our findings suggest that the radio emission is highly time-variable, likely influenced by the star-planet system's phase and the host star's magnetic field. Additional observations below 170 MHz, at more frequent epochs (as the periodicity of the emission is unknown), especially during periods of high stellar magnetic field strength, are needed to confirm the emission., Comment: Accepted at AJ, 8 pages, 2 figures

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

Hub-filament systems (HFSs) being the potential sites of formation of star clusters and high mass stars, provide a test bed for the current theories that attempt to explain star formation globally. It is thus important to study a large number of HFSs using both intensity and velocity information to constrain these objects better observationally. We present here a study of the hub-filament system associated with G6.55-0.1 using newly obtained observations of radio continuum and $J$=2--1 transition of CO, $^{13}$CO, and C$^{18}$O. The radio continuum maps show multiple peaks that coincide with far-infrared dust continuum peaks indicating the presence of more than one young massive stars in the hub of the HFS. We used the velocity information from the C$^{18}$O(2--1) map to (a) show that the source G6.55-0.1 is not physically associated with the SNR W28 and (b) disentangle and identify the velocity components genuinely associated with G6.55-0.1. Among the velocity-coherent structures identified, the two filaments at 13.8 and 17.3 km s$^{-1}$ contribute a total mass accretion rate of $\sim$3000 M$_{\odot}$ Myr$^{-1}$ to the hub. Both the filaments also show V-shaped structure, characteristic of gravitational collapse, in their velocity profile at the location of the hub. Estimated mass per unit length of the segments of the filaments are smaller than the critical line masses derived from virial equilibrium considerations. This suggests that while the filaments are not gravitationally collapsing as a whole, the spectra from the hub indicate that the inner parts are dynamically decoupled and collapsing to form stars., Comment: This paper is accepted in Astrophysical Journal on 04/04/2024

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

The remnant phase of a radio galaxy is characterized by the cessation of AGN activity resulting in the stoppage of jets supplying plasma to radio lobes. In this paper, we present the search and characterization of remnant candidates in 12.5 deg$^{2}$ of the {\em XMM$-$Newton} Large$-$Scale Structure (XMM$-$LSS) field by using deep radio observations at 325 MHz from the Giant Metrewave Radio Telescope (GMRT), at 150 MHz from the LOw Frequency ARray (LOFAR), at 1.4 GHz from the Jansky Very Large Array (JVLA), and at 3 GHz from the VLA Sky Survey (VLASS). By using both morphological criteria {\viz}undetected radio core as well as spectral criteria {\viz}high spectral curvature, and ultra$-$steep spectrum, we identify 21 remnant candidates that are found to reside mostly in non$-$cluster environments, and exhibit diverse properties in terms of morphology, spectral index ($\alpha_{\rm 150}^{\rm 1400}$ in the range of $-1.71$ to $-0.75$ with a median of $-1.10$), and linear radio size (ranging from 242 kpc to 1.3 Mpc with a median of 469 kpc). Our study attempts to identify remnant candidates down to the flux density limit of 6.0 mJy at 325 MHz, and yields an upper limit on the remnant fraction ($f_{\rm rem}$) to be around 5$\%$. The observed $f_{\rm rem}$ seems consistent with the predictions of an evolutionary model assuming power law distributions of the duration of active phase and jet kinetic power with index $-0.8$ to $-1.2$., Comment: 23 pages, 27 figures, 6 tables. Accepted for publication in Astrophysical Journal

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

The cessation of AGN activity in radio galaxies leads to a remnant phase during which jets are no longer sustained, but lobes can be detected for a period of time before they fade away due to radiative and dynamical energy losses. The time-scale of the remnant phase and AGN duty cycle are vital to understanding the evolution of radio galaxies. In this paper, we report new band-3 observations with the upgraded Giant Meterwave Radio Telescope (uGMRT) for five remnant radio galaxies. Our uGMRT observations reveal emission of low-surface-brightness in all five remnants with 400 MHz surface brightness in the range of 36$-$201 mJy arcmin$^{-2}$. With band-3 uGMRT observations, we discover wing-shaped radio morphology in one of our sample sources. Using radio observations at 150 MHz, 325 MHz, 400 MHz, and 1.5 GHz, we model the radio spectral energy distributions (SEDs) of our sample sources with the continuous injection-off model (CI$_{\rm OFF}$), that assumes an active phase with continuous injection followed by a remnant phase. We obtain total source ages ($t_{\rm s}$) in the range of 20.3 Myr to 41.4 Myr with $t_{\rm OFF}$/$t_{\rm s}$ distributed in the range of 0.16 to 0.63, which in turn suggests them to belong to different evolutionary phases. We note that, in comparison to the remnants reported in the literature, our sample sources tend to show lower spectral ages that can be explained by the combined effects of more dominant inverse Compton losses for our sources present at the relatively higher redshifts and possible rapid expansion of lobes in their less dense environments., Comment: 14 pages, 3 figures, 3 tables, accepted for publication in the Journal of Astrophysics and Astronomy (to appear in the special issue of Indian participation in the SKA)

Radio observations being insensitive to the dust-obscuration, have been exploited to unveil the population of Active Galactic Nuclei (AGN) residing in galaxies with large dust content. In this paper, we investigate the radio characteristics of 321 dust-obscured galaxies (DOGs; S$_{\rm 24 {\mu}m}$/S$_{\rm r band}$ $\geq$1000) by using mainly deep band-3 (250$-$550 MHz) observations from the upgraded Giant Metrewave Radio Telescope (uGMRT) and 1.5 GHz Jansky Very Large Array (JVLA) observations. We find that, for our sample of DOGs, deep (median noise-rms $=$ 30 $\mu$Jy beam$^{-1}$) 400 MHz band-3 uGMRT observations yield the highest detection rate (28 per cent) among those obtained with the JVLA, and the LOw Frequency ARray (LOFAR) radio observations and the ${\it XMM-N}$ X-ray observations. The radio characteristics of our sample sources, ${\it i.e.,}$ linear extent ($<$40 kpc at $z$ $<$1.2), bimodal spectral index (${\alpha}_{\rm 400 MHz}^{\rm 1.5 GHz}$) distribution and the radio luminosities (L$_{\rm 1.5 GHz}$ $>$5.0 $\times$ 10$^{23}$ W Hz$^{-1}$), suggest them to be mainly consist of Compact$-$Steep$-$Spectrum (CSS) or Peaked-Spectrum (PS) sources representing an early phase of the AGN-jet activity in dust-obscured environments. With stacking we find the existence of faint radio emission (S$_{\rm 400 MHz}$ = 72.9 $\mu$Jy beam$^{-1}$ and S$_{\rm 1.5 GHz}$ = 29 $\mu$Jy beam$^{-1}$ with signal-to-noise ratio $\sim$ 20) in otherwise radio-undetected DOGs. Our study revealing the faint emission at a few tens of $\mu$Jy level in high$-z$ DOGs can be used as a test-bed for the deeper radio continuum surveys planned with the Square-Kilometer Array (SKA) and its pathfinders., Comment: 18 pages, 10 figures, 4 tables, accepted for publication in the Journal of Astrophysics and Astronomy (to appear in the special issue of Indian participation in the SKA)

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

This paper presents a multiwavelength investigation of the Galactic HII IRAS 17149$-$3916. Using the Giant Meterwave Radio Telescope, India, first low-frequency radio continuum observations at 610 and 1280 MHz for this region are presented. The ionized gas emission displays an interesting cometary morphology which is likely powered by the early type source, E4 (IRS-1). The origin of the cometary morphology is discussed under the framework of the widely accepted bow shock, champagne flow, and clumpy cloud mechanisms. The mid- and far-infrared data from Spitzer-GLIMPSE and Herschel-Hi-GAL reveal a complex network of pillars, clumps, bubble, filaments, and arcs suggesting the profound influence of massive stars on the surrounding medium. Triggered star formation at the tip of an observed pillar structure is reported. High-resolution ALMA continuum data show a string of cores detected within the identified clumps. The core masses are well explained by thermal Jeans fragmentation and support the hierarchical fragmentation scenario. Four `super-Jeans' cores are identified which, at the resolution of the present data set, are suitable candidates to form high-mass stars., Comment: 17 pages, 10 figures, accepted for publication in MNRAS

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

We present archival Giant Metrewave Radio Telescope (GMRT) observations of two exoplanetary systems, $\tau$ Bo\"otis, and 55 Cancri, at 610 MHz and 150 MHz, respectively. Theoretical models predict these systems to have some of the highest expected flux densities at radio wavelengths. Both $\tau$ Bo\"otis and 55 Cancri have been previously observed at low frequency ($\sim$ 30 MHz) with Low-Frequency Array (LOFAR) (Turner et al. 2020). $\tau$ Bo\"otis shows tentative signatures of circularly polarized emission at 30 MHz, while no emission was detected from 55 Cancri. We do not detect radio emission from both the systems, but the GMRT observations set $3\sigma$ upper limits of 0.6 mJy at 610 MHz for $\tau$ Bo\"otis and 4.6 mJy at 150 MHz for 55 Cancri. The sensitivity achieved at 610 MHz in these observations is comparable to some of the deepest images of an exoplanet field., Comment: 3 pages, 1 Figure, Accepted for publication in RNASS

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.

This paper reports Giant Metrewave Radio Telescope (GMRT) observations of the binary system HD 41004 that are among the deepest images ever obtained at 150~MHz and 400 MHz in the search for radio emission from exoplanets. The HD 41004 binary system consists of a K1 V primary star and an M2 V secondary; both stars are host to a massive planet or brown dwarf. Analogous to planets in our solar system that emit at radio wavelengths due to their strong magnetic fields, one or both of the planet or brown dwarf in the HD 41004 binary system are also thought to be sources of radio emission. Various models predict HD~41004Bb to have one of the largest expected flux densities at 150 MHz. The observations at 150 MHz cover almost the entire orbital period of HD 41004Bb, and about $20\%$ of the orbit is covered at 400 MHz. We do not detect radio emission, setting 3$\sigma$ limits of 1.8 mJy at 150 MHz and 0.12 mJy at 400 MHz. We also discuss some of the possible reasons why no radio emission was detected from the HD 41004 binary system., Comment: 11 pages, 5 figures, accepted for publication in MNRAS

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 first fully automated pipeline for making images from the interferometric data obtained from the upgraded Giant Metrewave Radio Telescope (uGMRT) called CAsa Pipeline-cum-Toolkit for Upgraded Giant Metrewave Radio Telescope data REduction - CAPTURE. It is a python program that uses tasks from the NRAO Common Astronomy Software Applications (CASA) to perform the steps of flagging of bad data, calibration, imaging and self-calibration. The salient features of the pipeline are: i) a fully automatic mode to go from the raw data to a self-calibrated continuum image, ii) specialized flagging strategies for short and long baselines that ensure minimal loss of extended structure, iii) flagging of persistent narrow band radio frequency interference (RFI), iv) flexibility for the user to configure the pipeline for step-by-step analysis or special cases and v) analysis of data from the legacy GMRT. CAPTURE is available publicly on github (https://github.com/ruta-k/uGMRT-pipeline, release v1.0.0). The primary beam correction for the uGMRT images produced with CAPTURE is made separately available at https://github.com/ruta-k/uGMRTprimarybeam. We show examples of using CAPTURE on uGMRT and legacy GMRT data. In principle, CAPTURE can be tailored for use with radio interferometric data from other telescopes., Comment: 15 pages, 5 figures, 3 tables, Accepted for publication in Experimental Astronomy

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