A review of the possible relationship between γ-ray sources and supernova remnants (SNRs) is presented. Particular emphasis is given to the analysis of the observational status of the problem of cosmic ray acceleration at SNR shock fronts. All positional coincidences between SNRs and unidentified γ-ray sources listed in the Third EGRET Catalog at low Galactic latitudes are discussed on a case b...

Almost all the X-ray afterglows of gamma-ray bursts (GRBs) observed by the Swift satellite have a shallow decay phase in the first thousands of seconds. We show that in an inhomogeneous jet (multiple-subjet or patchy-shell) model the superposition of the afterglows of off-axis subjets (patchy shells) can have the shallow decay phase. The necessary condition for obtaining the shallow decay phase...

As shown by Maraschi (this volume) the overall spectral energy distribution (SED) of the blazars detected by EGRET shows two peaks, in a ν–νF (ν) plot. With few exceptions, the minimum between these two peaks occurs in the X–ray range. We can exploit this observational fact to constrain the models proposed to account for the SED of blazars, and to reach an important conclusion: the conversion o...

Aims. We present X-ray and 12CO(J=1–0) observations of the very-high-energy (VHE) γ-ray source HESS J1813–178 with the aim of understanding the origin of the γ-ray emission. Methods. High-angular resolution X-ray studies of the VHE γ-ray emission region are performed using 18.6 ks of XMM-Newton data, taken on HESS J1813–178 in October 2005. Using this dataset we are able to undertake spectral a...

Supernovae 1998bw and its corresponding relativistically expanding radio source are coincident with the γ-ray burst source GRB 980425. We show that of six recent SN Ib/c for which an outburst epoch can be estimated with some reliability, four have radio outbursts and all are correlated in time and space with BATSE γ-ray bursts. The joint probability of all six correlations is 1.5×10. No such co...

Starting in 1991 we have performed a regular monitoring of EGRET sources with the Effelsberg 100-m telescope and the IRAM 30-m at Pico Veleta. In comparison with data on a sample of flat-spectrum quasars which have not been seen by EGRET we search for correlations of any kind in the behaviour of FSRQ's in the radio and gamma-ray regime. While there is no radio-to-gamma-ray luminosity correlatio...

The prompt γ-ray emission in γ-ray bursts is believed to be produced by internal shocks within a relativistic unsteady outflow. The recent detection of prompt optical emission accompanying the prompt γ-ray emission appears to be inconsistent with this model since the out flowing plasma is expected to be highly optically thick to optical photons. We show here that fluctuations in flow properties...

ABSTRACT Radio and γ-ray loud narrow-line Seyfert 1 galaxies (NLS1s) are unique objects to study the formation evolution of relativistic jets, as they believed have high accretion rates powered by low mass black holes contrary that known for blazars. However, only about a dozen γ-ray-detected NLS1s (γ-NLS1s) date all them at $z$ ≤ 1. Here, we report identification new γ-ray-emitting NLS1 TXS 12...