C. Righi

The Fermi blazar sequence

We revisit the blazar sequence exploiting the complete, flux limited sample of blazars with known redshift detected by the Fermi satellite after 4 years of operations (the 3LAC sample). We divide the sources into gamma-ray luminosity bins, collect all the archival data for all blazars, and construct their spectral energy distribution (SED). We describe the average SED of blazars in the same luminosity bin through a very simple, completely phenomenological function consisting of two broken power laws connecting with a power law of fixed slope describing the radio emission. We do that separately for BL Lacs and for flat spectrum radio quasars (FSRQs) and also for all blazars together. The main results are: i) FSRQs display approximately the same SED as the luminosity increases, except for the fact that the relative importance of the high energy peak increases; ii) as a consequence, X-ray spectra of FSRQs become harder for larger luminosities; iii) BL Lacs form indeed a sequence: they become redder (i.e. the peak frequencies becomes smaller) for increasing luminosities, with a steeper gamma-ray slope and a larger dominance of the high energy peak; iv) for all blazars (BL Lacs+FSRQs) these properties becomes more prominent, as the highest luminosity bin is populated mostly by FSRQs and the lowest luminosity bin mostly by BL Lacs. This agrees with the original blazar sequence, although BL Lacs never have an average gamma-ray slope as hard as found in the original sequence. v) At high luminosities, a large fraction of FSRQs shows signs of thermal emission from the accretion disc, contributing in the optical-UV.

On the Redshift of TeV BL Lac Objects

We report results of a spectroscopic campaign carried out at the 10 m Gran Telescopio Canarias for a sample of 22 BL Lac objects detected (or candidates) at TeV energies, aimed to determine or constrain their redshift. This is of fundamental importance for the interpretation of their emission models, for population studies and also mandatory to study the interaction of high energy photons with the extragalactic background light using TeV sources. High signal-to-noise optical spectra in the range 4250 - 10000 {AA} were obtained to search for faint emission and/or absorption lines from both the host galaxy or the nucleus. We determine a new redshift for PKS 1424+240 (z = 0.604) and a tentative one for 1ES 0033+595 (z = 0.467). We are able to set new spectroscopic redshift lower limits for other three sources on the basis of Mg II and Ca II intervening absorption features: BZB J1243+3627 (z > 0.483), BZB J1540+8155 (z > 0.672), and BZB 0J2323+4210 (z > 0.267). We confirm previous redshift estimates for four blazars: S3 0218+357 (z = 0.944), 1ES 1215+303 (z = 0.129), W Comae (z = 0.102), and MS 1221.8+2452 (z = 0.218). For the remaining targets, in seven cases (S2 0109+22, 3C 66A, VER J0521+211, S4 0954+65, BZB J1120+4214, S3 1227+25, BZB J2323+4210), we do not validate the proposed redshift. Finally for all sources of still unknown redshift, we set a lower limit based on the minimum equivalent width of absorption features expected from the host galaxy.

High-energy emitting BL Lacs and high-energy neutrinos - Prospects for the direct association with IceCube and KM3NeT

Context. The origin of the high-energy flux of neutrinos detected by IceCube remains unknown. Recent works report evidence for a possible positional correlation between the reconstructed neutrino arrival directions and the positions in the sky of low-power, high-energy-emitting BL Lac objects (HBL). Aims. Assuming that γ -ray-emitting HBL form the bulk of the sources of high-energy neutrinos above 100 TeV, we intend to calculate the number of events expected to be detected for each source by IceCube and KM3NeT. Methods. Based on a simple theoretically-motivated framework inspired by the structured jet scenario for these sources, we postulate a direct proportionality between high-energy γ -ray and neutrino fluxes. We calculate the expected neutrino event rate for the HBL sources of the Second Fermi -LAT Catalog of High-Energy Sources (2FHL) for IceCube and the presently under-construction KM3NeT using declination-dependent and exposure-weighted effective areas. Results. We provide a list of 2FHL HBL with the calculated number of events. For IceCube, the derived count rate for several sources is relatively high, of the order of ≲1 yr -1 , consistent with the recent findings of a possible positional correlation. For KM3NeT, the calculated rates are higher, with several sources with expected rates exceeding 1 yr -1 . This, coupled with the improved angular resolution, implies that the HBL origin can be effectively tested with few years of observation of KM3NeT (and IceCube Gen2, for which similar performances are foreseen) through the direct association of neutrinos and single HBL. Conclusions. Our results show that if, as suggested by recent works, HBL represent a possible population of high-energy neutrino emitters, several single sources should be identified in a few years of exposure of KM3NeT, highlighting the importance of the improved angular resolution anticipated for KM3NeT and IceCube Gen2.

High-energy neutrinos from FR0 radio-galaxies?

The sources responsible for the emission of high-energy (

Holographic diffraction gratings based on photopolymers: achieved results and new opportunities in astronomical spectroscopy

gtrsim

New over-octave VPHG architecture for DOLORES spectrograph at TNG

100 TeV) neutrinos detected by IceCube are still unknown. Among the possible candidates, active galactic nuclei with relativistic jets are often examined, since the outflowing plasma seems to offer the ideal environment to accelerate the required parent high-energy cosmic rays. The non-detection of single point sources or -- almost equivalently -- the absence, in the IceCube events, of multiplets originating from the same sky position, constrains the cosmic density and the neutrino output of these sources, pointing to a numerous population of faint sources. Here we explore the possibility that FR0 radiogalaxies, the population of compact sources recently identified in large radio and optical surveys and representing the bulk of radio-loud AGN population, can represent suitable candidates for neutrino emission. Modeling the spectral energy distribution of a FR0 radiogalaxy recently associated to a