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According to radiative models, radio galaxies and quasars are predicted to produce gamma rays from the earliest stages of their evolution. Exploring their high-energy emission is crucial for providing information on the most energetic processes, the origin and the structure of the newly born radio jets. Taking advantage of more than 11 years of textit{Fermi}-LAT data, we investigate the gamma-ray emission of 162 young radio sources (103 galaxies and 59 quasars), the largest sample of young radio sources used so far for such a gamma-ray study. We separately analyze each source and perform the first stacking analysis of this class of sources to investigate the gamma-ray emission of the undetected sources. We detect significant gamma-ray emission from 11 young radio sources, four galaxies and seven quasars, including the discovery of significant gamma-ray emission from the compact radio galaxy PKS 1007+142 (z=0.213). The cumulative signal of below-threshold young radio sources is not significantly detected. However, it is about one order of magnitude below than those derived from the individual sources, providing stringent upper limits on the gamma-ray emission from young radio galaxies ($F_{gamma}< 4.6 times 10^{-11}$ ph cm$^{-2}$ s$^{-1}$) and quasars ($F_{gamma}< 10.1 times 10^{-11}$ ph cm$^{-2}$ s$^{-1}$), and enabling a comparison with the models proposed. With this analysis of more than a decade of textit{Fermi}-LAT observations, we can conclude that while individual young radio sources can be bright gamma-ray emitters, the collective gamma-ray emission of this class of sources is not bright enough to be detected by textit{Fermi}-LAT.
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According to radiative models, radio galaxies are predicted to produce gamma rays from the earliest stages of their evolution onwards.The study of the high-energy emission from young radio sources is crucial for providing information on the most energetic processes associated with these sources, the actual region responsible for this emission, as well as the structure of the newly born radio jets. Despite systematic searches for young radio sources at gamma-ray energies, only a handful of detections have been reported so far. Taking advantage of more than 11 years of textit{Fermi}-LAT data, we investigate the gamma-ray emission of 162 young radio sources (103 galaxies and 59 quasars), the largest sample of young radio sources used so far for a gamma-ray study. We analyse the textit{Fermi}-LAT data of each individual source separately to search for a significant detection. In addition, we perform the first stacking analysis of this class of sources in order to investigate the gamma-ray emission of the young radio sources that are undetected at high energies. We report the detection of significant gamma-ray emission from 11 young radio sources, including the discovery of significant gamma-ray emission from the compact radio galaxy PKS 1007+142. Although the stacking analysis of below-threshold young radio sources does not result in a significant detection, it provides stringent upper limits to constrain the gamma-ray emission from these objects. In this talk we present the results of our study and we discuss their implications for the predictions of gamma-ray emission from this class of sources.
We review the high energy properties of Misaligned AGNs associated with gamma-ray sources detected by Fermi in 24 months of survey. Most of them are nearby emission low power radio galaxies (i.e FRIs) which probably have structured jets. On the contrary, high power radio sources (i.e FRIIs) with GeV emission are rare. The small number of FRIIs does not seem to be related to their higher redshifts. Assuming proportionality between the radio core flux and the gamma-ray flux, several of them are expected to be bright enough to be detected above 100 MeV in spite of their distance. We suggest that beaming/jet structural differences are responsible for the detection rate discrepancy observed between FRIs and FRIIs.
We present an analysis of the multiwavelength behaviour of the blazar OJ 248 at z = 0.939 in the period 2006-2013. We use low-energy data (optical, near-infrared, and radio) obtained by 21 observatories participating in the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT), as well as data from the Swift (optical-UV and X-rays) and Fermi (gamma-rays) satellites, to study flux and spectral variability and correlations among emissions in different bands. We take into account the effect of absorption by the Damped Lyman Alpha intervening system at z = 0.525. Two major outbursts were observed in 2006-2007 and in 2012-2013 at optical and near-IR wavelengths, while in the high-frequency radio light curves prominent radio outbursts are visible peaking at the end of 2010 and beginning of 2013, revealing a complex radio-optical correlation. Cross-correlation analysis suggests a delay of the optical variations after the gamma-ray ones of about a month, which is a peculiar behaviour in blazars. We also analyse optical polarimetric and spectroscopic data. The average polarization percentage P is less than 3 per cent, but it reaches about 19 per cent during the early stage of the 2012-2013 outburst. A vague correlation of P with brightness is observed. There is no preferred electric vector polarisation angle and during the outburst the linear polarization vector shows wide rotations in both directions, suggesting a complex behaviour or structure of the jet and possible turbulence. The analysis of 140 optical spectra acquired at the Steward Observatory reveals a strong Mg II broad emission line with an essentially stable flux of 6.2 e-15 erg cm-2 s-1 and a full width at half-maximum of 2053 km s-1.
Star-forming galaxies (SFGs) emit non-thermal radiation from radio to gamma-rays. We aim to investigate the main mechanisms of global CR transport and cooling in SFGs. The way they contribute in shaping the relations between non-thermal luminosities and SFR could shed light onto their nature. We develop a model to compute the CR populations of SFGs, taking into account their production, transport, and cooling. The model is parameterised only through global galaxy properties, and describes the non-thermal emission in both radio and gamma-rays. We focus on the role of diffusive and advective transport by galactic winds, either driven by turbulent or thermal instabilities. We compare model predictions to observations, for which we compile a homogeneous set of luminosities in these radio bands, and update those available in gamma-rays. Our model reproduces reasonably well the observed relations between the gamma-ray or 1.4 GHz radio luminosities and the SFR, assuming a single power-law scaling of the magnetic field with the latter with index beta=0.3, and winds blowing either at Alfvenic speeds or typical starburst wind velocities. Escape of CR is negligible for > 30 Mo/yr. A constant ionisation fraction of the interstellar medium fails to reproduce the 150 MHz radio luminosity throughout the whole SFR range. Our results reinforce the idea that galaxies with high SFR are CR calorimeters, and that the main mechanism driving proton escape is diffusion, whereas electron escape also proceeds via wind advection. They also suggest that these winds should be CR or thermally-driven at low and intermediate SFR, respectively. Our results globally support that magnetohydrodynamic turbulence is responsible for the dependence of the magnetic field strength on the SFR and that the ionisation fraction is strongly disfavoured to be constant throughout the whole SFR range.
SPI on INTEGRAL has provided spectra and a map of the sky in the emission from annihilations of positrons in the interstellar medium of our Galaxy. From high-resolution spectra we learned that a warm, partially-ionized medium is the site where the observed gamma-rays originate. The gamma-ray emission map shows a major puzzle for broader astrophysics topics, as it is dominated by a bright and extended apparently spherical emission region centered in the Galaxys center. Only recently has the disk of the Galaxy been detected with SPI. This may be regarded as confirmation of earlier expectations that positrons should arise predominantly from sources of nucleosynthesis distributed throughout the plane of the Galaxy, which produce proton-rich unstable isotopes. But there are other plausible sources of positrons, among them pulsars and accreting binaries such as microquasars. SPI results may be interpreted also as hints that these are more significant as positron sources on the Galactic scale than thought before, in the plane and therefore also in the bulge of the Galaxy. This is part of the attempt to understand the surprisingly-bright emission from the central region in the Galaxy, which otherwise also could be interpreted as a first rather direct detection of dark matter annihilations in the Galaxys gravitational well. INTEGRAL has a unique potential to shed light on the various aspects of positron astrophysics, through its capability for imaging spectroscopy.
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