arXiv subjects

F. Panessa

Publications and source records attributed to F. Panessa.

At least 37 records · Page 2Linked to original sources

arXiv2023

Multiwavelength monitoring of the nucleus in PBC J2333.9-2343: the giant radio galaxy with a blazar-like core

PBC J2333.9-2343 is a giant radio galaxy at z = 0.047 with a bright central core associated to a blazar nucleus. If the nuclear blazar jet is a new phase of the jet activity, then the small orientation angle suggest a dramatic change of the jet direction. We present observations obtained between September 2018 and January 2019 (cadence larger than three days) with Effeslberg, SMARTS-1.3m, ZTF, ATLAS, Swift, and Fermi-LAT, and between April-July 2019 (daily cadence) with SMARTS-1.3m and ATLAS. Large (>2x) flux increases are observed on timescales shorter than a month, which are interpreted as flaring events. The cross correlation between the SMARTS-1.3m monitoring in the NIR and optical shows that these data do not show significant time lag within the measured errors. A comparison of the optical variability properties between non-blazars and blazars AGN shows that PBC J2333.9-2343 has properties more comparable to the latter. The SED of the nucleus shows two peaks, that were fitted with a one zone leptonic model. Our data and modelling shows that the high energy peak is dominated by External Compton from the dusty torus with mild contribution from Inverse Compton from the jet. The derived jet angle of 3 degrees is also typical of a blazar. Therefore, we confirm the presence of a blazar-like core in the center of this giant radio galaxy, likely a Flat Spectrum Radio Quasar with peculiar properties.

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arXiv2022

Supermassive Black Hole Winds in X-rays -- SUBWAYS. I. Ultra-fast outflows in QSOs beyond the local Universe

We present a new X-ray spectroscopic study of $22$ luminous ($2\times10^{45}\lesssim L_{\rm bol}\rm /erg\,s^{-1} \lesssim 2\times10^{46}$) active galactic nuclei (AGNs) at intermediate-redshift ($0.1 \lesssim z \lesssim 0.4$), as part of the SUpermassive Black hole Winds in the x-rAYS (SUBWAYS) sample, mostly composed of quasars (QSOs) and type\,1 AGN. Here, 17 targets were observed with \textit{XMM-Newton} between 2019--2020 and the remaining 5 are from previous observations. The aim of this large campaign ($1.45\,\rm Ms$ duration) is to characterise the various manifestations of winds in the X-rays driven from supermassive black holes in AGN. In this paper we focus on the search and characterization of ultra-fast outflows (UFOs), which are typically detected through blueshifted absorption troughs in the Fe\,K band ($E>7\,\rm keV$). By following Monte Carlo procedures, we confirm the detection of absorption lines corresponding to highly ionised iron (e.g., Fe\,\textsc{xxv}\,H$α$, Fe\,\textsc{xxvi}\,Ly$α$) in 7/22 sources at the $\gtrsim95\%$ confidence level (for each individual line). The global combined probability of such absorption features in the sample is $>99.9\%$. The SUBWAYS campaign extends at higher luminosity and redshifts than previous local studies on Seyferts, obtained using \xmm and \suzaku observations. We find a UFO detection fraction of $\sim30\%$ on the total sample that is in agreement with the previous findings. This work independently provides further support for the existence of highly-ionised matter propagating at mildly relativistic speed ($\gtrsim0.1c$) in a considerable fraction of AGN over a broad range of luminosities, which is expected to play a key role in the self-regulated AGN feeding-feedback cycle, as also supported by hydrodynamical multiphase simulations.

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arXiv2022

IGR J18249-3243: a new GeV-emitting FR II and the emerging population of high energy radio galaxies

The advent of new all-sky radio surveys such as the VLA Sky Survey (VLASS) and the Rapid ASKAP Continuum Survey (RACS), performed with the latest generation radio telescopes, is opening new possibilities on the classification and study of extragalactic $γ$-ray sources, specially the underrepresented ones like radio galaxies. In particular, the enhanced sensitivity (sub-mJy level) and resolution (a few arcsec) provides a better morphological and spectral classification. In this work, we present the reclassification of a Fermi-LAT source as a new FRII radio galaxy from the INTEGRAL sample found to emit at GeV energies. Through a broad-band spectral fitting from radio to $γ$-ray, we find that the commonly invoked jet contribution is not sufficient to account for the observed $γ$-ray flux. Our modeling suggests that the observed emission could mainly originate in the lobes (rather than in the radio core) by inverse Compton scattering of radio-emitting electrons off the ambient photon fields. In addition, we cross-correlated the latest generation radio surveys with a list of Fermi-LAT objects from the literature considered to be candidate misaligned AGN, finding four new radio galaxies with a double-lobed morphology. Additional four objects could be classified as such thanks to previous studies in the literature, for a total of nine new radio galaxies with GeV emission presented in this work. We foresee that further objects of this class might be found in the near future with the advent of the Square Kilometer Array (SKA), populating the GeV sky.

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arXiv2021

The PG-RQS survey. Building the radio spectral distribution of radio-quiet quasars. I. The 45-GHz data

The origin of the radio emission in radio-quiet quasars (RQQs) remains unclear. Radio emission may be produced by a scaled-down version of the relativistic jets observed in radio-loud (RL) AGN, an AGN-driven wind, the accretion disc corona, AGN photon-ionisation of ambient gas (free-free emission), or star formation (SF). Here, we report a pilot study, part of a radio survey (`PG-RQS') aiming at exploring the spectral distributions of the 71 Palomar-Green (PG) RQQs: high angular resolution observations ($\sim$50 mas) at 45~GHz (7 mm) with the Karl G. Jansky Very Large Array of 15 sources. Sub-mJy radio cores are detected in 13 sources on a typical scale of $\sim$100 pc, which excludes significant contribution from galaxy-scale SF. For 9 sources the 45-GHz luminosity is above the lower frequency ($\sim$1-10 GHz) spectral extrapolation, indicating the emergence of an additional flatter-spectrum compact component at high frequencies. The X-ray luminosity and black hole (BH) mass, correlate more tightly with the 45-GHz luminosity than the 5-GHz. The 45 GHz-based radio-loudness increases with decreasing Eddington ratio and increasing BH mass M$_{\rm BH}$. These results suggest that the 45-GHz emission from PG RQQs nuclei originates from the innermost region of the core, probably from the accretion disc corona. Increasing contributions to 45-GHz emission from a jet at higher M$_{\rm BH}$ and lower Eddington ratios and from a disc wind at large Eddington ratios are still consistent with our results. Future full radio spectral coverage of the sample will help us investigating the different physical mechanisms in place in RQQ cores.

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arXiv2021

LeMMINGs IV: The X-ray properties of a statistically-complete sample of the nuclei in active and inactive galaxies from the Palomar sample

All 280 of the statistically-complete Palomar sample of nearby (<120 Mpc) galaxies dec > 20 degrees have been observed at 1.5 GHz as part of the LeMMINGs e-MERLIN legacy survey. Here, we present Chandra X-ray observations of the nuclei of 213 of these galaxies, including a statistically-complete sub-set of 113 galaxies in the declination range 40 degrees to 65 degrees. We observed galaxies of all optical spectral types, including 'active' galaxies (e.g., LINERs and Seyferts) and 'inactive' galaxies like HII galaxies and absorption line galaxies (ALG). The X-ray flux limit of our survey is 1.65$\times$10$^{-14}$~erg s$^{-1}$ cm$^{-2}$ (0.3$-$10 keV). We detect X-ray emission coincident within 2-arcsec of the nucleus in 150/213 galaxies, including 13/14 Seyferts, 68/77 LINERs, 13/22 ALGs and 56/100 HII galaxies, but cannot completely rule out contamination from non-AGN processes in sources with nuclear luminosities <10$^{39}$ erg s$^{-1}$. We construct an X-ray Luminosity function (XLF) and find that the local galaxy XLF, when including all AGN types, can be represented as a single power-law of slope $-0.54 \pm 0.06$. The Eddington ratio of the Seyferts is usually 2-4 decades higher than that of the LINERs, ALGs and HII galaxies, which are mostly detected with Eddington ratios <10$^{-3}$. Using [O III] line measurements and BH masses from the literature, we show that LINERs, HII galaxies and ALGs follow similar correlations to low luminosities, suggesting that some 'inactive' galaxies may harbour AGN.

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arXiv2021

The Fast Radio Burst FRB 20201124A in a star forming region: constraints to the progenitor and multiwavelength counterparts

We present the results of a multiwavelength campaign of FRB 20201124A, the third closest repeating fast radio burst recently localized in a nearby (z=0.0978) galaxy. Deep VLA observations led to the detection of quiescent radio emission, also marginally visible in X-rays with Chandra. Imaging at 22 GHz allowed us to resolve the source on a scale of $\gtrsim$ 1 arcsec and locate it at the position of the FRB, within an error of 0.2 arcsec. EVN and e-MERLIN observations sampled small angular scales, from 2 to 100 mas, providing tight upper limits on the presence of a compact source and evidence for diffuse radio emission. We argue that this emission is associated with enhanced star formation activity in the proximity of the FRB, corresponding to a star formation rate of $\approx 10\ {\rm M}_\odot {\rm yr}^{-1}$. The surface star formation rate at the location of FRB 20201124A is two orders of magnitude larger than typically observed in other precisely localized FRBs. Such a high SFR is indicative of this FRB source being a new-born magnetar produced from a SN explosion of a massive star progenitor. Upper limits to the X-ray counterparts of 49 radio bursts observed in our simultaneous FAST, SRT and Chandra campaign are consistent with a magnetar scenario.

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arXiv2021

LeMMINGs. III. The e-MERLIN Legacy Survey of the Palomar sample. Exploring the origin of nuclear radio emission in active and inactive galaxies through the [O III] -- radio connection

What determines the nuclear radio emission in local galaxies? We combine optical [O III] line emission, robust black hole (BH) mass estimates, and high-resolution e-MERLIN 1.5-GHz data, from the LeMMINGs survey, of a statistically-complete sample of 280 nearby, optically active (LINER and Seyfert) and inactive HII and Absorption line galaxies [ALG]) galaxies. Using [O III] luminosity ($L_{\rm [O~III]}$) as a proxy for the accretion power, local galaxies follow distinct sequences in the optical-radio planes of BH activity, which suggest different origins of the nuclear radio emission for the optical classes. The 1.5-GHz radio luminosity of their parsec-scale cores ($L_{\rm core}$) is found to scale with BH mass ($M_{\rm BH}$) and [O~III] luminosity. Below $M_{\rm BH} \sim$10$^{6.5}$ M$_{\odot}$, stellar processes from non-jetted HII galaxies dominate with $L_{\rm core} \propto M_{\rm BH}^{0.61\pm0.33}$ and $L_{\rm core} \propto L_{\rm [O~III]}^{0.79\pm0.30}$. Above $M_{\rm BH} \sim$10$^{6.5}$ M$_{\odot}$, accretion-driven processes dominate with $L_{\rm core} \propto M_{\rm BH}^{1.5-1.65}$ and $L_{\rm core} \propto L_{\rm [O~III]}^{0.99-1.31}$ for active galaxies: radio-quiet/loud LINERs, Seyferts and jetted HII galaxies always display (although low) signatures of radio-emitting BH activity, with $L_{\rm 1.5\, GHz}\gtrsim$10$^{19.8}$ W Hz$^{-1}$ and $M_{\rm BH}\gtrsim10^{7}$ M$_{\odot}$, on a broad range of Eddington-scaled accretion rates ($\dot{m}$). Radio-quiet and radio-loud LINERs are powered by low-$\dot{m}$ discs launching sub-relativistic and relativistic jets, respectively. Low-power slow jets and disc/corona winds from moderately high to high-$\dot{m}$ discs account for the compact and edge-brightened jets of Seyferts, respectively. Jetted HII galaxies may host weakly active BHs. Fuel-starved BHs and recurrent activity account for ALG properties. [abridged]

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arXiv2021

Hard X-ray selected giant radio galaxies -- III. The LOFAR view

Giant radio galaxies (GRGs), with extended structures reaching hundreds of kpc, are among the most spectacular examples of ejection of relativistic plasma from super-massive black holes. In this work, third of a series, we present LOw Frequency ARray (LOFAR) images at 144 MHz, collected in the framework of the LOFAR Two-metre Sky Survey Data Release 2 (LoTSS DR2), for nine sources extracted from our sample of hard X-ray selected GRGs (HXGRG, i.e. from INTEGRAL/IBIS and Swift/BAT catalogues at >20 keV). Thanks to the resolution and sensitivity of LoTSS, we could probe the complex morphology of these GRGs, unveiling cases with diffuse (Mpc-scale) remnant emission, presence of faint off-axis wings, or a misaligned inner jet. In particular, for one source (B21144+35B), we could clearly detect a $\sim$300 kpc wide off-axis emission, in addition to an inner jet which orientation is not aligned with the lobes axis. For another source (J1153.9+5848) a structure consistent with jet precession was revealed, appearing as an X-shaped morphology with relic lobes having an extension larger than the present ones, and with a different axis orientation. From an environment analysis, we found 2 sources showing an overdensity of cosmological neighbours, and a correspondent association with a galaxy cluster from catalogues. Finally, a comparison with radio-selected GRGs from LoTSS DR1 suggested that, on average, HXGRG can grow to larger extents. These results highlight the importance of deep low-frequency observations to probe the evolution of radio galaxies, and ultimately estimate the duty cycle of their jets.

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arXiv2020

Multi-messenger astronomy with INTEGRAL

At the time of defining the science objectives of the INTernational Gamma-Ray Astrophysics Laboratory (INTEGRAL), such a rapid and spectacular development of multi-messenger astronomy could not have been predicted, with new impulsive phenomena becoming accessible through different channels. Neutrino telescopes have routinely detected energetic neutrino events coming from unknown cosmic sources since 2013. Gravitational wave detectors opened a novel window on the sky in 2015 with the detection of the merging of two black holes and in 2017 with the merging of two neutron stars, followed by signals in the full electromagnetic range. Finally, since 2007, radio telescopes detected extremely intense and short burst of radio waves, known as Fast Radio Bursts (FRBs) whose origin is for most cases extragalactic, but enigmatic. The exceptionally robust and versatile design of the INTEGRAL mission has allowed researchers to exploit data collected not only with the pointed instruments, but also with the active cosmic-ray shields of the main instruments to detect impulses of gamma-rays in coincidence with unpredictable phenomena. The full-sky coverage, mostly unocculted by the Earth, the large effective area, the stable background, and the high duty cycle (85%) put INTEGRAL in a privileged position to give a major contribution to multi-messenger astronomy. In this review, we describe how INTEGRAL has provided upper limits on the gamma-ray emission from black-hole binary mergers, detected a short gamma-ray burst in coincidence with a binary neutron star merger, contributed to define the spectral energy distribution of a blazar associated with a neutrino event, set upper limits on impulsive and steady gamma-ray emission from cosmological FRBs, and detected a magnetar flare associated with fast radio bursting emission.

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arXiv2020

LeMMINGs. II. The e-MERLIN legacy survey of nearby galaxies. The deepest radio view of the Palomar sample on parsec scale

We present the second data release of high-resolution ($\leq0.2$ arcsec) 1.5-GHz radio images of 177 nearby galaxies from the Palomar sample, observed with the e-MERLIN array, as part of the LeMMINGs (Legacy e-MERLIN Multi-band Imaging of Nearby Galaxy Sample) survey. Together with the 103 targets of the first LeMMINGs data release, this represents a complete sample of 280 local active (LINER and Seyfert) and inactive galaxies HII galaxies and Absorption Line Galaxies, ALG). This large program is the deepest radio survey of the local Universe, $\gtrsim$10$^{17.6}$ W Hz$^{-1}$, regardless of the host and nuclear type: we detect radio emission $\gtrsim$0.25 mJy beam$^{-1}$ for 125/280 galaxies (44.6 per cent) with sizes of typically $\lesssim$100 pc. Of those 125, 106 targets show a core which coincides within 1.2 arcsec with the optical nucleus. Although we observed mostly cores, around one third of the detected galaxies features jetted morphologies. The detected radio core luminosities of the sample range between $\sim$10$^{34}$ and 10$^{40}$ erg s$^{-1}$. LINERs and Seyferts are the most luminous sources, whereas HII galaxies are the least. LINERs show FRI-like core-brightened radio structures, while Seyferts reveal the highest fraction of symmetric morphologies. The majority of HII galaxies have single radio core or complex extended structures, which probably conceal a nuclear starburst and/or a weak active nucleus (seven of them show clear jets). ALGs, which are typically found in evolved ellipticals, although the least numerous, exhibit on average the most luminous radio structures, similar to LINERs.

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arXiv2020

Soft gamma-ray selected giant radio galaxies: an update

We present an update on the sample of soft gamma-ray selected giant radio galaxies (GRGs) extracted from INTEGRAL/IBIS and Swift/BAT surveys; it includes 8 new sources and one candidate object. In the new sample all, but one source, display FR II radio morphologies; the only exception is B21144+35B which is an FR I. The objects belong to both type 1 and 2 AGN optical classes and have redshifts in the range 0.06-0.35, while the radio sizes span from 0.7 to 1 Mpc. In this study, we present for the first time two objects that were never discussed as GRGs before and propose a new candidate GRG. We confirm the correlation between the X-ray luminosity and the radio core luminosity found for other soft gamma-ray selected GRGs and expected for AGNs powered by efficient accretion. We also corroborate previous results that indicate that the luminosity of the radio lobes is relatively low compared with the nuclear X-ray emission. This supports the idea that the nucleus of these GRGs is now more powerful than in the past, consistent with a restarting activity scenario

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arXiv2020

INTEGRAL discovery of a burst with associated radio emission from the magnetar SGR 1935+2154

We report on INTEGRAL observations of the soft $γ$-ray repeater SGR 1935+2154 performed between 2020 April 28 and May 3. Several short bursts with fluence of $\sim10^{-7}-10^{-6}$ erg cm$^{-2}$ were detected by the IBIS instrument in the 20-200 keV range. The burst with the hardest spectrum, discovered and localized in real time by the INTEGRAL Burst Alert System, was spatially and temporally coincident with a short and very bright radio burst detected by the CHIME and STARE2 radio telescopes at 400-800 MHz and 1.4 GHz, respectively. Its lightcurve shows three narrow peaks separated by $\sim$29 ms time intervals, superimposed on a broad pulse lasting $\sim$0.6 s. The brightest peak had a delay of 6.5$\pm$1.0 ms with respect to the 1.4 GHz radio pulse (that coincides with the second and brightest component seen at lower frequencies). The burst spectrum, an exponentially cut-off power law with photon index $Γ=0.7_{-0.2}^{+0.4}$ and peak energy $E_p=65\pm5$ keV, is harder than those of the bursts usually observed from this and other magnetars. By the analysis of an expanding dust scattering ring seen in X-rays with the {\it Neil Gehrels Swift Observatory} XRT instrument, we derived a distance of 4.4$_{-1.3}^{+2.8}$ kpc for SGR 1935+2154, independent of its possible association with the supernova remnant G57.2+0.8. At this distance, the burst 20-200 keV fluence of $(6.1\pm 0.3)\times10^{-7}$ erg cm$^{-2}$ corresponds to an isotropic emitted energy of $\sim1.4\times10^{39}$ erg. This is the first burst with a radio counterpart observed from a soft $γ$-ray repeater and it strongly supports models based on magnetars that have been proposed for extragalactic fast radio bursts.

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arXiv2020

The lowest frequency Fast Radio Bursts: Sardinia Radio Telescope detection of the periodic FRB 180916 at 328 MHz

We report on the lowest-frequency detection to date of three bursts from the fast radio burst FRB 180916, observed at 328 MHz with the Sardinia Radio Telescope (SRT). The SRT observed the periodic repeater FRB 180916 for five days from 2020 February 20 to 24 during a time interval of active radio bursting, and detected the three bursts during the first hour of observations; no more bursts were detected during the remaining ~ 30 hours. Simultaneous SRT observations at 1548 MHz did not detect any bursts. Burst fluences are in the range 37 to 13 Jy ms. No relevant scattering is observed for these bursts. We also present the results of the multi-wavelength campaign we performed on FRB 180916, during the five days of the active window. Simultaneously with the SRT observations, others with different time spans were performed with the Northern Cross at 408 MHz, with XMM-Newton, NICER, INTEGRAL, AGILE, and with the TNG and two optical telescopes in Asiago, which are equipped with fast photometers. XMM-Newton obtained data simultaneously with the three bursts detected by the SRT, and determined a luminosity upper limit in the 0.3-10 keV energy range of ~$10^{45}$ erg/s for the burst emission. AGILE obtained data simultaneously with the first burst and determined a fluence upper limit in the MeV range for millisecond timescales of $ 10^{-8}$ erg cm$^{-2}$.Our results show that absorption from the circumburst medium does not significantly affect the emission from FRB 180916, thus limiting the possible presence of a superluminous supernova around the source, and indicate that a cutoff for the bursting mechanism, if present, must be at lower frequencies. Our multi-wavelength campaign sensitively constrains the broadband emission from FRB 180916, and provides the best limits so far for the electromagnetic response to the radio bursting of this remarkable source of fast radio bursts.

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arXiv2020

Hard - X-rays selected Active Galactic Nuclei. I. A radio view at high-frequencies

A thorough study of radio emission in Active Galactic Nuclei (AGN) is of fundamental importance to understand the physical mechanisms responsible for the emission and the interplay between accretion and ejection processes. High frequency radio observations can target the nuclear contribution of smaller emitting regions and are less affected by absorption. We present JVLA 22 and 45 GHz observations of 16 nearby (0.003$\le$z$\le$0.3) hard - X-rays selected AGN at the (sub)-kpc scale with tens uJy beam$^{-1}$ sensitivity. We detected 15/16 sources, with flux densities ranging from hundreds uJy beam$^{-1}$ to tens Jy (specific luminosities from $\sim$10$^{20}$ to $\sim$10$^{25}\,W\,Hz^{-1}$ at 22 GHz). All detected sources host a compact core, with 8 being core-dominated at either frequencies, the others exhibiting also extended structures. Spectral indices range from steep to flat/inverted. We interpret this evidence as either due to a core+jet system (6/15), a core accompanied by surrounding star formation (1/15), to a jet oriented close to the line of sight (3/15), to emission from a corona or the base of a jet (1/15), although there might be degeneracies between different processes. Four sources require more data to shed light on their nature. We conclude that, at these frequencies, extended, optically-thin components are present together with the flat-spectrum core. The ${L_R}/{L_X}\sim10^{-5}$ relation is roughly followed, indicating a possible contribution to radio emission from a hot corona. A weakly significant correlation between radio core (22 and 45 GHz) and X-rays luminosities is discussed in the light of an accretion-ejection framework.

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arXiv2020

The curious activity in the nucleus of NGC 4151: jet interaction causing variability?

A key characteristic of many active galactic nuclei (AGN) is their variability, but its origin is poorly understood, especially in the radio domain. Williams et al. (2017) reported a ~50 per cent increase in peak flux density of the AGN in the Seyfert galaxy NGC 4151 at 1.5 GHz with the e-MERLIN array. We present new high resolution e-MERLIN observations at 5 GHz and compare these to archival MERLIN observations to investigate the reported variability. Our new observations allow us to probe the nuclear region at a factor three times higher-resolution than the previous e-MERLIN study. We separate the core component, C4, into three separate components: C4W, C4E and X. The AGN is thought to reside in component C4W, but this component has remained constant between epochs within uncertainties. However, we find that the Eastern-most component, C4E, has increased in peak flux density from 19.35$\pm$1.10 to 37.09$\pm$1.86 mJy/beam, representing a 8.2 sigma increase on the MERLIN observations. We attribute this peak flux density increase to continued interaction between the jet and the emission line region (ELR), observed for the first time in a low-luminosity AGN such as NGC 4151. We identify discrete resolved components at 5 GHz along the jet axis, which we interpret as areas of jet-ELR interaction.

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arXiv2020

Hard X-ray selected giant radio galaxies -- II. Morphological evidence of restarted radio activity

About 6% of Radio Galaxies (RG) can reach linear sizes larger than 0.7 Mpc, and are then classified as Giant Radio Galaxies (GRG). The conditions that make possible the formation of such big structures is still not clear - either core accretion properties or environmental factors. Recent studies have shown that GRG can be up to four times more abundant in hard X-ray selected (i.e. from INTEGRAL/IBIS and Swift/BAT at >20 keV) RG samples. Moreover, a high fraction of young radio sources found in their cores suggests a recently restarted activity, as suggested from the discrepancy between the measured jet and lobes power, with respect to the one expected from core X-ray luminosity. Here we present a radio morphological study of a sample of 15 hard X-ray selected GRG, discussing low-frequency images from our GMRT campaign complemented with others from the literature: among them, 7/15 show evidence of restarted radio activity either in the form of double-double/X-shaped morphology, or as a cocoon emission embedding more recent jets. This, together with the objects from this sample already found hosting a young radio source in their core, suggests that at least 13 over 15 of these hard X-ray selected GRG show features which are consistent with the possibility of restarted radio activity.

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arXiv2019

A young and obscured AGN embedded in the giant radio galaxy Mrk 1498

Mrk 1498 is part of a sample of galaxies with extended emission line regions (extended outwards up to a distance of $\sim$7 kpc) suggested to be photo-ionized by an AGN that has faded away or that is still active but heavily absorbed. Interestingly, the nucleus of Mrk 1498 is at the center of two giant radio lobes with a projected linear size of 1.1 Mpc. Our multi-wavelength analysis reveals a complex nuclear structure, with a young radio source (Giga-hertz Peaked Spectrum) surrounded by a strong X-ray nuclear absorption, a mid-infrared spectrum that is dominated by the torus emission, plus a circum-nuclear extended emission in the [OIII] image (with radius of $\sim$ 1 kpc), most likely related to the ionization of the AGN, aligned with the small and large scale radio jet and extended also at X-rays. In addition a large-scale extended emission (up to $\sim$ 10 kpc) is only visible in [OIII]. These data show conclusive evidence of a heavily absorbed nucleus and has recently restarted its nuclear activity. To explain its complexity, we propose that Mrk 1498 is the result of a merging event or secular processes, such as a minor interaction, that has triggered the nuclear activity and produced tidal streams. The large-scale extended emission that gives place to the actual morphology could either be explained by star formation or outflowing material from the AGN.

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arXiv2019

A discovery of young radio sources in the cores of giant radio galaxies selected at hard X-rays

Giant Radio Galaxies (GRG) are the largest single entities in the Universe, having a projected linear size exceeding 0.7 Mpc, which implies that they are also quite old objects. They are not common, representing a fraction of only about 6% in samples of bright radio galaxies. While a census of about 300 of these objects has been built in the past years, still no light has been shed on the conditions necessary to allow such an exceptional growth, whether of environmental nature or linked to the inner accretion properties. Recent studies found that samples of radio galaxies selected from hard X-ray AGN catalogs selected from INTEGRAL/IBIS and Swift/BAT (thus at energies >20 keV) present a fraction of GRG four times larger than what found in radio-selected samples. We present radio observations of 15 nuclei of hard X-ray selected GRG, finding for the first time a large fraction (61%) of young radio sources at the center of Mpc-scale structures. Being at the center of GRG, these young nuclei may be undergoing a restarting activity episode, suggesting a link between the detected hard X-ray emission - due to the ongoing accretion - and the reactivation of the jets.

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