OQ208 is a nearby, partially obscured quasar (z=0.077) that is a young, bright, parsec scale radio source. We assemble archival and new high frequency VLBA and VLA observations and optical spectra to form a data-set spanning 39 years. Radio light curves covering 58 years were also compiled. We utilize new spectrophotmetry to calibrate previous spectroscopy using forbidden narrow lines that are expected to be stable on much longer time scales. VLBA and VLA observations of a light-year scale bright nuclear flare at 15.4 GHz and 22 GHz reveal a rise (fade) beginning in mid-1996 (early-2000). Quasi-contemporaneously, from 2/7/1997-6/3/2000, the Hα broad line equivalent widths (EWs) and fluxes dropped dramatically. In the context of the tendency of radio loud quasars to have a depressed extreme ultraviolet (EUV) continuum (the main source of ionizing flux for Hα) relative to radio quiet quasars at matched UV luminosity (the EUV deficit of radio loud quasars), this may not be a coincidence. Analytic models previously developed to explain the relationship between jet power and the EUV deficit are consistent with (but not direct observational proof of) the small EWs being a consequence of transient magnetically arrested accretion states from ∼1997-2001. The 22 GHz VLBA nucleus gradually fades, in 2023 the flux density is <5% of its value in 2000. The environs of the nucleus also fade at 22 GHz, but in a time delayed fashion.

Context. The long-standing question concerning jetted subgalactic-size (JSS) radio sources is whether they will evolve into large radio galaxies, die before escaping the host galaxy, or remain indefinitely confined to their compact size. Aims. Our main goal is to propose a scenario that explains the relative number of JSS radio sources and their general properties. Methods. We studied the parsec-scale radio morphology of a complete sample of 21 objects using Very Long Baseline Array (VLBA) observations at various frequencies and analyzed the morphological characteristics of their optical hosts. Results. Many of these radio sources exhibit radio morphologies consistent with transverse motions of their bright edges and are found in dynamically disturbed galaxies. VLBA images suggest the possible presence of large-angle, short-period precessing jets, and an orbital motion of the radio-loud active galactic nucleus (AGN) in a dual or binary system. The majority of JSS radio sources appear to be in systems in different stages of their merging evolution. Conclusions. We propose a scenario where rapid jet redirection, through precession or orbital motion, prevents the jet from penetrating the interstellar medium (ISM) sufficiently to escape the host galaxy. Most JSS radio sources remain compact due to their occurrence in merging galaxies.

We present a study of quasar host galaxy 3C 297, which is home to a powerful bent-jet radio source suggesting vigorous interaction with a dense interstellar medium (ISM) and/or jet precession. Archival Hubble Space Telescope (HST) imaging showed interestingly perturbed morphology of the host with a bright ∼30 kpc arc feature, extended filamentary structure of line-emitting gas, and clumpy blue excess emission cospatial with the radio hotspots. Our Very Large Telescope (VLA)/SINFONI integral-field observations reveal complex, spatially resolved H α + [N II ] emission in this source. A prominent blueshifted wing in H α indicates an ionized gas flow extending out to ∼8 kpc from the nuclear region. Combining our SINFONI narrow-H α data with archival HST/UV and VLA imaging, we map the young stellar population in the host and compare the spatial distribution of star-forming regions with the ionized gas motion and jet structure. In the attempt to characterize the feedback mechanisms in this chaotic system, we suggest that the powerful radio source dominates the feedback, with possible contribution from radiation pressure due to accretion onto the black hole. We also propose that the expanding jet cocoon likely shocked the ISM, triggering a kpc-scale ionized gas outflow and new starbursts that enhanced ongoing merger-induced star formation.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23060119

ABSTRACT The Narrow Line Seyfert 1 Galaxy IRAS17020+4544 is one of the few active galactic nuclei (AGNs) where a galaxy-scale energy-conserving outflow was revealed. This paper reports on NOEMA observations addressed to constrain the spatial scale of the CO emission in outflow. The molecular outflowing gas is resolved in five components tracing approaching and receding gas, all located at a distance of 2–3 kpc on the west and east sides of the active nucleus. This high-velocity gas (up to vout = ±1900 km s−1) is not coincident with the rotation pattern of the CO gas in the host galaxy disc. The estimated mass outflow rate shows that with a global mass output of $\dot{M}_{H_2}$ = 139$\pm 20~\, \mathrm{M}_\odot$ yr−1, this powerful galaxy-scale outflow is consistent with the wind conserving its energy, and with a momentum rate boost of a factor of ∼30 compared to the momentum rate of the nuclear X-ray wind. Preliminary results from ancillary X-ray (Chandra) and radio images (e-MERLIN) are reported. While the nature of the radio source is not conclusive, the Chandra image may tentatively trace extended emission, as expected by an expanding bubble of hot X-ray gas. The outcome of the NOEMA analysis and of the past and ongoing publications dedicated to the description of the outflow multiband phenomenology in IRAS17020+4544 concur to provide compelling reasons to postulate that an outflow shocking with the galaxy interstellar medium is driving the multiphase wind in this peculiar AGN.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23060119

In 1908, a massive explosion known as the Tunguska Event (TE) occurred in Central Siberia. However, its origin remains widely discussed and environmental impacts are not known in detail. We investigated evidence of the TE in sediments of Suzdalevo Lake, which is located near the explosion epicenter. According to local nomads (Evenkis), Suzdalevo Lake did not exist before the TE and was considered as a possible impact-origin water body. However, apart from oral testimony, there is no evidence of the lake formation process. Two short sediment cores (SUZ1 and SUZ3) were retrieved from the lake and dated using 210 Pb and 137 Cs. The sedimentary record was characterized using magnetic susceptibility, X-ray fluorescence, and the screening for melted magnetic microspherules. To study possible effects of the TE on the lake ecosystem, we performed diatom and freshwater fauna remains analyses. Results indicate that the lake contains sediments that originated before the TE and thus its formation was not related to the impact. Also, the depth to diameter ratio of the lake basin is too low (<1/100) for a young impact crater. In one of the two cores (SUZ1), we documented distinct changes in the lake-catchment ecosystem that occurred within a 5-cm-thick depth interval calculated for the best fit depths for the year 1908 using three alternative age-depth models (CRS, CIC, CFCS), namely, increases in terrestrial matter input (abundant fine plant macroremains, peaks in magnetic susceptibility and the Sr to Rb ratio) and taxonomic diversity and relative abundance of benthic taxa. The shifts in aquatic biota assemblages were likely caused by nutrient supply and improved water column mixing following a catchment disturbance. Nevertheless, precise timing of the observed abrupt changes in relation to the TE is not clear due to uncertainty of the 210 Pb dating method and absence of melted magnetic microspherules or an event layer. The disturbance signals in the proxy data may postdate the TE. Our results demonstrate potential usefulness of the paleolimnological approach to understand the possible environmental consequences of the TE and similar events elsewhere.

ABSTRACTThe radio, optical, and γ-ray light curves of the blazar S5 1803+784, from the beginning of the Fermi-Large Area Telescope (LAT) mission in 2008 August–2018 December, are presented. The aim of this work is to look for correlations among different wavelengths useful for further theoretical studies. We analysed all the data collected by Fermi-LAT for this source, taking into account the presence of nearby sources, and we collected optical data from our own observations and public archive data to build the most complete optical and γ-ray light curve possible. Several γ-ray flares (F > 2.3 10−7ph(E > 0.1 GeV) cm−2 s−1) with optical coverage were detected, all but one with corresponding optical enhancement; we also found two optical flares without a γ-ray counterpart. We obtained two Swift Target of Opportunity observations during the strong flare of 2015. Radio observations performed with VLBA and EVN through our proposals in the years 2016–2020 were analysed to search for morphological changes after the major flares. The optical/γ-ray flux ratio at the flare peak varied for each flare. Very minor optical V − I colour changes were detected during the flares. The X-ray spectrum was well fitted by a power law with photon spectral index α = 1.5, nearly independent of the flux level: No clear correlation with the optical or the γ-ray emission was found. The γ-ray spectral shape was well fitted by a power law with average photon index α = 2.2. These findings support an inverse-Compton origin for the high-energy emission of the source, nearly co-spatial with the optically emitting region. The radio maps showed two new components originating from the core and moving outwards, with ejection epochs compatible with the dates of the two largest γ-ray flares.

Context. According to radiative models, radio galaxies may produce γ-ray emission from the first stages of their evolution. However, very few such galaxies have been detected by the Fermi Large Area Telescope (LAT) so far. Aims. NGC 3894 is a nearby (z = 0.0108) object that belongs to the class of compact symmetric objects (CSOs, i.e., the most compact and youngest radio galaxies), which is associated with a γ-ray counterpart in the Fourth Fermi-LAT source catalog. Here we present a study of the source in the γ-ray and radio bands aimed at investigating its high-energy emission and assess its young nature. Methods. We analyzed 10.8 years of Fermi-LAT data between 100 MeV and 300 GeV and determined the spectral and variability characteristics of the source. Multi-epoch very long baseline array (VLBA) observations between 5 and 15 GHz over a period of 35years were used to study the radio morphology of NGC 3894 and its evolution. Results. NGC 3894 is detected in γ-rays with a significance >9σ over the full period, and no significant variability has been observed in the γ-ray flux on a yearly time-scale. The spectrum is modeled with a flat power law (Γ = 2.0 ± 0.1) and a flux on the order of 2.2 × 10−9 ph cm−2 s−1. For the first time, the VLBA data allow us to constrain with high precision the apparent velocity of the jet and counter-jet side to be βapp, NW = 0.132 ± 0.004 and βapp, SE = 0.065 ± 0.003, respectively. Conclusions. Fermi-LAT and VLBA results favor the youth scenario for the inner structure of this object, with an estimated dynamical age of 59 ± 5 years. The estimated range of viewing angle (10° < θ < 21°) does not exclude a possible jet-like origin of the γ-ray emission.

This paper presents a survey of microwave front-end receivers installed at radio telescopes throughout the world. This unprecedented analysis was conducted as part of a review of front-end developments for Italian radio telescopes, initiated by the Italian National Institute for Astrophysics in 2016. Fifteen international radio telescopes have been selected to be representative of the instrumentation used for radio astronomical observations in the frequency domain from 300 MHz to 116 GHz. A comprehensive description of the existing receivers is presented and their characteristics are compared and discussed. The observing performances of the complete receiving chains are also presented. An overview of ongoing developments illustrates and anticipates future trends in front-end projects to meet the most ambitious scientific research goals.

The 1908 Tunguska Event is one of the best studied cases of a cosmic body impacting the Earth with global effects. However, still today, significant doubts are casted on the different proposed event reconstructions. In the present work, we would like to revisit the atmospheric fragmentation of the Tunguska Cosmic Body (TCB) by taking into account the possibility that a metre-sized fragment caused the formation of the Lake Cheko, located at about 9km NW the epicentre. Our work favours the hypothesis that the TCB was a rubble-pile asteroid composed by boulders with very different materials with different mechanical strengths, density, and porosity. The TCB was divided at least into two pieces by a close encounter with the Earth, short before the impact with our Planet: the main body (60m) produced the well-known airburst that devastated more than 2000km^2 of Siberian taig`a, while the secondary one (6-10m) fell without fragmentation in the Kimchu river region and excavated a 50m depression, which presently hosts the Lake Cheko. This hypothesis requires that the secondary body was an extremely compact stone with high mechanical strength (300MPa). It is a high, but not unrealistic, value, as shown by a similar case that occurred in 2007 near the village of Carancas (Peru). An extreme compactness is not necessary, if one considers that the crater excavation could be enhanced by the explosion of permafrost-trapped methane released and ignited during the impact process. In this case, a smaller fragment (2m) with an average mechanical strength could reach the ground without fragmentation and is sufficient to excavate the Lake Cheko. We exclude the hypothesis of a single cosmic body ejecting a metre-sized fragment during or shortly before the airburst, because the resulting lateral velocity of such a large boulder was not enough to deviate to reach the alleged impact site.

The 1908 June 30 Tunguska Event (TE) is one of the best studied cases of cosmic body impacting the Earth with global effects. However, still today, significant doubts are casted on the different proposed event reconstructions, because of shortage of reliable information and uncertainties of available data. In the present work, we would like to revisit the atmospheric fragmentation of the Tunguska Cosmic Body (TCB) by taking into account the possibility that a metre-sized fragment could cause the formation of the Lake Cheko, located at about $9$~km North-West from the epicentre. We performed order-of-magnitude calculations by using the classical single-body theory for the atmospheric dynamics of comets/asteroids, with the addition of the fragmentation conditions by Foschini (2001). We calibrated the numerical model by using the data of the Chelyabinsk Event (CE) of 2013 February 15. Our work favours the hypothesis that the TCB could have been a rubble-pile asteroid composed by boulders with very different materials with different mechanical strengths, density, and porosity. Before the impact, a close encounter with the Earth stripped at least one boulder, which fell aside the main body and excavated the Lake Cheko. We exclude the hypothesis of a single compact asteroid ejecting a metre-sized fragment during, or shortly before, the airburst, because there is no suitable combination of boulder mass and lateral velocity.

This paper describes a reigorous process started within the Italian National Institute for Astrophysics (INAF)to review existing and future radio astronomical front-end receivers for the INAF radio telescopes. The main goal of the review was to increase the level of coordination in receiver development, improving at the same time the scientific impact from the national facilities. The working group in charge of the review collected information on the front-ends in operation and under development at the INAF radio telescopes and new idea for future receivers from the Italian astronomical community. The outcome of the working group consists of recommendations on receivers under development and on strategies for future receivers at the suite of Italian radio telescopes.

We present a multiwavelength study of IC 1531 (z = 0.02564), an extragalactic radio source associated with the γ-ray object 3FGL J0009.9 − 3206 and classified as a blazar of uncertain type in the Third Fermi-Large Area Telescope AGN catalog (3LAC). A core-jet structure, visible in radio and X-rays, is enclosed within a ∼220 kpc wide radio structure. The morphology and spectral characteristics of the kiloparsec jet in radio and X-rays are typical of Fanaroff–Riley type I galaxies. The analysis of the radio data and optical spectrum and different diagnostic methods based on the optical, infrared, and γ-ray luminosities also support a classification as a low-power RG seen at moderate angles (θ = 10°–20°). In the framework of leptonic models, the high-energy peak of the non-thermal nuclear spectral energy distribution can be explained in terms of synchrotron-self-Compton emission from a jet seen at θ ∼ 15°. Similarly to other misaligned AGNs detected by Fermi, the required bulk motion is lower (Γbulk = 4) than the values inferred in BL Lac objects, confirming that, because of the de-boosting of emission from the highly relativistic blazar region, these nearby systems are valuable targets to probe the existence of multiple sites of production of the most energetic emission in the jets.

The high brightness temperatures, T-b greater than or similar to 10(13) K, detected in several active galactic nuclei by RadioAstron space VLBI observations challenge theoretical limits. Refractive scattering by the interstellar medium may affect such measurements. We quantify the scattering properties and the sub-mas scale source parameters for the quasar B0529+483. Using RadioAstron correlated flux density measurements at 1.7, 4.8, and 22 GHz on projected baselines up to 240 000 km we find two characteristic angular scales in the quasar core, about 100 and 10 mu as. Some indications of scattering substructure are found. Very high brightness temperatures, T-b >= 10(13) K, are estimated at 4.8 and 22 GHz even taking into account the refractive scattering. Our findings suggest a clear dominance of the particle energy density over the magnetic field energy density in the core of this quasar.

In September 2016, the microquasar Cygnus X-3 underwent a giant radio flare, which was monitored for 6 days with the Medicina Radio Astronomical Station and the Sardinia Radio Telescope. Long observations were performed in order to follow the evolution of the flare on a hourly scale, covering six frequency ranges from 1.5 GHz to 25.6 GHz. The radio emission reached a maximum of 13.2 +/- 0.7 Jy at 7.2 GHz and 10 +/- 1 Jy at 18.6 GHz. Rapid flux variations were observed at high radio frequencies at the peak of the flare, together with rapid evolution of the spectral index: alpha steepened from 0.3 to 0.6 within 5 hours. This is the first time that such fast variations are observed, giving support to the evolution from optically thick to optically thin plasmons in expansion moving outward from the core. Based on the Italian network (Noto, Medicina and SRT) and extended to the European antennas (Torun, Yebes, Onsala), VLBI observations were triggered at 22 GHz on five different occasions, four times prior to the giant flare, and once during its decay phase. Flux variations of 2-hour duration were recorded during the first session. They correspond to a mini-flare that occurred close to the core ten days before the onset of the giant flare. From the latest VLBI observation we infer that four days after the flare peak the jet emission was extended over 30 mas.

[Abridged] The Sardinia Radio Telescope (SRT) is the new 64-m dish operated by INAF (Italy). Its active surface will allow us to observe at frequencies of up to 116 GHz. At the moment, three receivers, one per focal position, have been installed and tested. The SRT was officially opened in October 2013, upon completion of its technical commissioning phase. In this paper, we provide an overview of the main science drivers for the SRT, describe the main outcomes from the scientific commissioning of the telescope, and discuss a set of observations demonstrating the SRT's scientific capabilities. One of the main objectives of scientific commissioning was the identification of deficiencies in the instrumentation and/or in the telescope sub-systems for further optimization. As a result, the overall telescope performance has been significantly improved. As part of the scientific commissioning activities, different observing modes were tested and validated, and first astronomical observations were carried out to demonstrate the science capabilities of the SRT. In addition, we developed astronomer-oriented software tools, to support future observers on-site. The astronomical validation activities were prioritized based on technical readiness and scientific impact. The highest priority was to make the SRT available for joint observations as part of European networks. As a result, the SRT started to participate (in shared-risk mode) in EVN (European VLBI Network) and LEAP (Large European Array for Pulsars) observing sessions in early 2014. The validation of single-dish operations for the suite of SRT first light receivers and backends continued in the following years, and was concluded with the first call for shared-risk/early-science observations issued at the end of 2015.

ABSTRACT We present new rest-frame UV and visible observations of 22 high- z (1 < z < 2.5) 3C radio galaxies and QSOs obtained with the Hubble Space Telescope ’s Wide Field Camera 3 instrument. Using a custom data reduction strategy in order to assure the removal of cosmic rays, persistence signal, and other data artifacts, we have produced high-quality science-ready images of the targets and their local environments. We observe targets with regions of UV emission suggestive of active star formation. In addition, several targets exhibit highly distorted host galaxy morphologies in the rest frame visible images. Photometric analyses reveal that brighter QSOs generally tend to be redder than their dimmer counterparts. Using emission line fluxes from the literature, we estimate that emission line contamination is relatively small in the rest frame UV images for the QSOs. Using archival VLA data, we have also created radio map overlays for each of our targets, allowing for analysis of the optical and radio axes alignment.