arXiv subjects

Luigi Foschini

Publications and source records attributed to Luigi Foschini.

At least 19 recordsLinked to original sources

arXiv2026

Hunting the nature of the Seyfert 1 galaxy GRS 1734-292: can it be a gamma-ray emitter?

It has been proposed that the radio-weak Seyfert galaxy GRS 1734-292 is the counterpart of 3EG J1736-2908 and of the nearby Fermi/LAT source. I examine this identification, considering that the radio weakness could result from free-free absorption of a relativistic jet. An association with the EGRET detections is plausible, whereas the latest Fermi/LAT localization no longer favors GRS 1734-292. New observations, especially at radio frequencies of tens of GHz, would help to settle the issue.

astro-ph.HE↗

arXiv2026

Flagging Super-Eddington Candidates among Jetted, {\gamma}-Ray-Emitting AGN

The quasar Eigenvector-1/Main Sequence (E1/MS) provides a physically motivated empirical framework to organize the spectroscopic diversity of type~1 active galactic nuclei (AGN). In its optical plane, the full width at half maximum of H$\beta$ and the Fe\,II strength ratio $R_{\mathrm{FeII}}$ define a sequence that is primarily driven by Eddington ratio, with important secondary roles played by black-hole mass, orientation, spectral energy distribution, and chemical enrichment. The E1/MS framework is therefore well suited to identify highly accreting and possibly super-Eddington (SE) sources, usually associated with the extreme Population~A (xA) spectral types. We discuss why E1/MS is a useful tool to search for SE accretors among jetted AGN and, conversely, to place $\gamma$-ray-detected AGN in the broader context of quasar phenomenology. We summarize two complementary results: (1) some candidate SE accretors show radio properties such as high brightness temperature non-thermal cores or radio lobes} consistent with jet activity; and (2) a subset of low-redshift $\gamma$-ray narrow-line Seyfert~1 galaxies exhibit optical spectra consistent with xA or borderline-xA classification. We also expand the discussion of recent developments in E1/MS studies, including metallicity trends, the spectral energy distribution of xA quasars, and the role of highly accreting quasars as discovery tools for extreme accretion states, as probes of quasars at the reionization epoch, and as possible cosmological probes.

astro-ph.GA↗

arXiv2026

The growing family of gamma-ray narrow-line Seyfert 1 galaxies

The revision of the fourth Fermi Large Area Telescope (LAT) catalog of gamma-ray point sources (rev4FGL) revealed that the gamma-ray sky is populated by emerging populations of jetted active galactic nuclei (AGN) other than blazars and radio galaxies. Narrow-Line Seyfert 1, Seyfert 1, intermediate, and Seyfert 2 galaxies, changing-look AGN, plus a number of ambiguous or unclassified sources. After a short historical introduction on the gamma-ray observations of Seyfert-type AGN, I explore the main statistical properties of 1477 jetted AGN from the rev4FGL with spectroscopic redshift, and also the cross-match with Very Large Baseline Array (VLBA) radio observations at 15~GHz from the Monitoring Of Jets in Active galactic nuclei with VLBA Experiments (MOJAVE) program. I then discuss the difference between gamma and non-gamma jetted AGN, and the implications on the classification.

astro-ph.HE↗

arXiv2025

The jetted NLS1 1H 0323+342: the Rosetta stone for accretion/ejection in AGN

1H 0323+342 is the nearest gamma-ray narrow-line Seyfert 1 galaxy (z=0.063). Its X-ray spectrum (0.3-10 keV) is characterised by significant spectral variability observed by many authors, with a backbone with photon index ~2 occasionally superimposed by a hard tail. This spectral variability has been interpreted as the interplay between the X-ray corona and the relativistic jet. The X-ray fluxes in the 0.3-10 keV energy band are generally around ~10^-11 erg cm^-2 s^-1, making it easier to get sufficient statistics even with short exposures. Here I present a reanalysis of all the available X-ray observations with Swift (181 obs), XMM-Newton (7 obs), Chandra (1 obs), and Suzaku (2 obs) performed between 2006 and 2025. Possible interpretations are proposed and discussed.

astro-ph.HE↗

arXiv2025

Accretion and ejection at work in the Narrow Line Seyfert 1 galaxy 1H 0323+342 -- A case of intermittent activity?

We present a comprehensive investigation into the properties of 1H 0323+342, a prominent jetted narrow-line Seyfert 1 galaxy. The primary objective is to understand the interplay between the relativistic jet, the hot corona, and the accretion disk around the supermassive black hole. This study spans the years 2006 to 2023, incorporating a rich dataset with 172 Swift observations, including the optical, UV, and X-ray bands, integrated with Fermi Large Area Telescope (LAT) observations. Spectral analysis was conducted on the X-ray observations using the XSPEC software, and the results were compared with optical, UV, and gamma-ray flux measurements and photon index values. Our key findings include the identification of three distinct zones in the X-ray photon index-flux plot, characterized by high flux and a hard photon index (zone 1), high flux and a soft photon index (zone 2), and low flux and a soft photon index (zone 3). Before 2017, 1H 0323+342 moved back and forth between zones 1 and 2; after that epoch, it transitioned to zones 2 and 3. Correspondingly, we observed a decreasing jet activity in the Fermi/LAT data and a reduction in the accretion rate in optical/UV data from Swift/UVOT. We interpret these observations in the framework of an intermittent jet scenario, driven by radiation-pressure instability in the accretion disk.

astro-ph.HE↗

arXiv2024

Searching for quantum-gravity footprint around stellar-mass black holes

According to the asymptotically safe gravity, black holes may have characteristics different from those described according to general relativity if the running of the gravitational constant coupling happens at low energies. Particularly, they should be more compact, with a smaller event horizon, which in turn affects the other quantities dependent on it, like the photon ring and the size of the innermost stable circular orbit. We decided to test the latter hypothesis by searching in the literature for observational measurements of the inner radius of the accretion disk around stellar-mass black holes. We selected the smallest values measured when the disk was in high/soft state, made them homogeneous by taking into account the most recent and more reliable values of mass, spin, viewing angle, and distance from the Earth, and compared with the expectations of the Kerr metric. We do not find any significant deviation. Some doubtful cases can be easily understood as due to specific states of the object during the observation or instrumental biases. We set the tightest constraint on the parameter $\xi$ obtained to date.

gr-qc↗

arXiv2024

The power of relativistic jets: a comparative study

We present the results of a comparison between different methods to estimate the power of relativistic jets from active galactic nuclei (AGN). We selected a sample of 32 objects (21 flat-spectrum radio quasars, 7 BL Lacertae Objects, 2 misaligned AGN, and 2 changing-look AGN) from the Very Large Baseline Array (VLBA) observations at 43 GHz of the Boston University blazar program. We then calculated the total, radiative, and kinetic jet power from both radio and high-energy gamma-ray observations, and compare the values. We found an excellent agreement between the radiative power calculated by using the Blandford and K\"onigl model with 37 or 43 GHz data, and the values derived from the high-energy $\gamma-$ray luminosity. The agreement is still acceptable if 15 GHz data are used, although with a larger dispersion, but it improves if we use a constant fraction of the $\gamma-$ray luminosity. We found a good agreement also for the kinetic power calculated with Blandford and K\"onigl model with 15 GHz data, and the value from the extended radio emission. We also propose some easy-to-use equations to estimate the jet power.

astro-ph.HE↗

arXiv2024

X-ray properties of two complementary samples of intermediate Seyfert galaxies

We present the X-ray spectral analysis of two complementary sets of intermediate Seyfert galaxies (ISs). Analyzing X-ray data, we estimate the hydrogen abundance $N_H$ and test its connection with the [O III] luminosity acquired from optical observations. The results confirm the conclusions drawn in a previous study concerning the lack of a direct correlation between the obscuration measure ($N_H$) and the intrinsic characteristics of the active nuclei ([O III] luminosity). Instead, we validate the existence of a correlation between the Seyfert type and the $N_H$ parameter, employing a separation threshold of approximately 10$^{22}$ atoms cm$^{-2}$. Simultaneously, our findings align with prior research, corroborating the relationship between X-ray luminosity and the [O III] luminosity.

astro-ph.GA↗

arXiv2023

A large jet narrow-line Seyfert 1 galaxy: observations from pc to 100 kpc scales

We present new 1.5-8.5 GHz Very Long Baseline Array (VLBA) observations and 0.32-1.26 GHz Giant Meterwave Radio Telescope (GMRT) observations of J0354-1340, which is the only known radio-quiet (RQ) or radio-intermediate (RI) narrow-line Seyfert 1 galaxy with a 100-kpc two-sided radio jet. A pc-scale one-sided jet in the southeast direction from the core emission is found in the VLBA observations, while the kpc-scale jet observed with Karl G. Jansky Very Large Array (VLA) and GMRT is in the south-north direction. The core spectra on pc and kpc scales are presented in combination with the archival VLASS observations at 3.0 GHz and the VLA C configuration observations at 5.5 GHz. The pc-scale emission dominates the kpc-scale emission above ~ 5 GHz, and the spectrum is inverted due to synchrotron self-absorption. This indicates a compact synchrotron source with a size of ~ 0.04 pc, which is associated with either the jet base or the corona. A sub-kpc scale jet, which is unresolved on scales of ~ 3 arcsec, probably dominates the emission below ~ 5 GHz. Future radio observations can explore the jet structure between the pc and 100 kpc scales, the origin of their direction mismatch, and the pc-scale jet proper motion. It remains to be explored how common such large-scale jets are in RQ or RI AGN.

astro-ph.GA↗

arXiv2023

Optical properties of two complementary samples of intermediate Seyfert galaxies

We present preliminary results of the analysis of optical spectra of two complementary samples of Seyfert galaxies. The first sample was extracted from a selection of the 4th Fermi Gamma-ray Large Area Telescope (4FGL) catalog, and consists of 9 $γ$-ray emitting jetted Seyfert galaxies. The second one was extracted from the Swift-BAT AGN Spectroscopic Survey (BASS), and is composed of 38 hard-X ray selected Active Galactic Nuclei (AGN). These two samples are complementary, with the former expected to have smaller viewing angles, while the latter may include objects with larger viewing angles. We measured emission line ratios to investigate whether the behavior of these Seyferts can be explained in terms of obscuration, as suggested by the well-known Unified Model (UM) of AGN, or if there are intrinsic differences due to the presence of jets, outflows, or the evolution. We found no indications of intrinsic differences. The UM remains the most plausible interpretation for these classes of objects even if some results can be challenging for this model.

astro-ph.GA↗

arXiv2022

The reification of the word against science

Research in foundations of physics is stagnant, as claimed by many scientists during the last years. I suggest that one reason might be the reification of language, particularly of mathematics, which favour the search for answers to wrong questions.

physics.hist-ph↗

arXiv2022

A New Sample of Gamma-Ray Emitting Jetted Active Galactic Nuclei

We considered the fourth catalog of gamma-ray point sources produced by the Fermi Large Area Telescope (LAT) and selected only jetted active galactic nuclei (AGN) or sources with no specific classification, but with a low-frequency counterpart. Our final list is composed of 2980 gamma-ray point sources. We then searched for optical spectra in all the available literature and publicly available databases, to measure redshifts and to confirm or change the original LAT classification. Our final list of gamma-ray emitting jetted AGN is composed of BL Lac Objects (40%), flat-spectrum radio quasars (23%), misaligned AGN (2.8%), narrow-line Seyfert 1, Seyfert, and low-ionization nuclear emission-line region galaxies (1.9%). We also found a significant number of objects changing from one type to another, and vice versa (changing-look AGN, 1.1%). About 30% of gamma-ray sources still have an ambiguous classification or lack one altogether.

astro-ph.HE↗

arXiv2021

Some notes about the current researches on the physics of relativistic jets

Some highlights of the recent researches in the field of relativistic jets are reviewed and critically analyzed. Given the extent of the available literature, this essay symbolically takes the baton from the outstanding and recent review by Blandford, Meier, and Readhead (2019). Therefore, I focus mostly on the results published during the latest few years, with specific reference to jets from active galactic nuclei.

astro-ph.HE↗

arXiv2021

Matter without mass: do we really need the concept of mass?

Einstein's most famous equation -- $E=mc^2$ -- generated a short-circuit between the concepts of mass and energy, which also affects other concepts like matter, radiation, and vacuum. Physics currently has a mixture of classical, relativistic, and quantum concepts of mass, which generates a great deal of confusion and many problems. Clear definitions need to be established if one wants to avoid ghost hunting. In particular, by abandoning the idea of mass and focusing on time and energy, some interesting implications are emerging. It is noted that the cutoff frequency of the quantum vacuum energy, consistent with the observations of the cosmological constant, corresponds to that of the Cosmic Microwave Background. This might be consistent with the hypothesis of a rotating and expanding universe described by a Kerr-de Sitter metric with the observed cosmological constant. To verify this hypothesis is crucial to prove the rotation of the universe.

physics.gen-ph↗

arXiv2020

Jetted Narrow-Line Seyfert 1 Galaxies & Co.: where do we stand?

The discovery in 2008 of high-energy gamma-rays from Narrow-Line Seyfert 1 Galaxies (NLS1s) made it clear that there were active galactic nuclei (AGN) other than blazars and radio galaxies that can eject powerful relativistic jets. In addition to NLS1s, the great performance of the Fermi Large Area Telescope made it possible to discover MeV-GeV photons emitted from more classes of AGN, like Seyferts, Compact Steep Spectrum Gigahertz Peaked Sources (CSS/GPS), and disk-hosted radio galaxies. Although observations indicate a variety of objects, their physical characteristics point to a central engine powered by a relatively small-mass black hole (but, obviously, there are interpretations against this view). This essay critically reviews the literature published on these topics during the last eight years and analyses the perspectives for the forthcoming years.

astro-ph.HE↗

arXiv2020

High-energy and Very High-energy Constraints from Log-parabolic Spectral Models in Narrow-line Seyfert 1 Galaxies

Narrow-line Seyfert 1 galaxies (NLSy1s) are a well-established class of $γ$-ray sources, showing the presence of a jet like the more common flat-spectrum radio quasars. The evidence of $γ$-ray emission poses the issue of the location of the $γ$-ray emitting zone and of the contribution of the $γ$-$γ$ absorption within the broad-line region (BLR), since such objects have been detected by Fermi-LAT in the MeV-GeV energy range but not by imaging atmospheric Cherenkov telescopes beyond 100 GeV. We discuss how the spectral properties of three NLSy1s (SBS 0846+513, PMN J0948+0022, and PKS 1502+036) derived from the Fermi Large Area Telescope Fourth Source Catalog (4FGL) compare with theoretical models based on the observed properties of the BLR. In particular, we focus on the question on how simple power-law spectral models and log-parabolic ones could be disentangled in $γ$-ray narrow-line Seyfert 1 galaxies by means of current Fermi-LAT or future imaging atmospheric Cherenkov telescopes data. We find that the only possibility for a log-parabolic model to mimic a power-law model in the energy band above $E \sim 100$ GeV is to have a very small value of the curvature parameter $ β\sim 0.05$.

astro-ph.HE↗

arXiv2019

Mapping the narrow-line Seyfert 1 galaxy 1H 0323+342

Taking advantage of the most recent measurements by means of high-resolution radio observations and other multiwavelength campaigns, it is possible to elaborate a detailed map of the narrow-line Seyfert 1 Galaxy 1H 0323+342. This map will open the possibility of intriguing hypotheses about the generation of high-energy gamma rays in the narrow-line region.

astro-ph.GA↗

arXiv2019

The cut of time

After a short review on the use of time in various branches of physics, I suggest to change the interpretation of time, from a duration to a cut. A reassessment of terminology is also required to avoid meaning traps. I also address the problem of estimating the energy needed by a physical object to shift in time without any other interaction or motion, that is, only to exist.

physics.gen-ph↗