Narrow Results

We discuss the nature of the X-ray emitting plasma of black hole binaries. It is well known that the temperature and optical depth of the Comptonising electrons of the X-ray corona of black hole binaries can be measured using spectroscopy in the 1 keV-1 MeV energy band. We emphasize recent developments in the modeling of high energy radiation processes which allow us to constrain other important physical parameters of the corona, such as the strength of magnetic field, or the temperature of the ions. The results appear to challenge current accretion models. In particular, standard advection dominated accretion flow do not match the observed properties of bright hard state X-ray binaries such as Cygnus X-1 or GX 339-4. On the other hand, we find that all the data would be consistent with a multi-zone magnetically dominated hot accretion flow model. We also emphasize that besides the usual spectral state transitions observed at luminosities above a few percent of Eddington, there is observational evidence for at least two additional, more subtle, radiative transitions occuring at lower luminosities.

We analyze total and polarized intensity images of the quasar 3C273 obtained at 43 GHz monthly during 2008-2010 with the VLBA. We find a strong increase of activity in the parsec-scale jet during a high γ-ray state lasting from 2009 June to 2010 May featuring an increase of the total and polarized flux in the mm-wave core and the appearance of superluminal knots in the jets. Although the optical variability is low, owing to strong contamination by the big blue bump, we observe an increase in optical polarization by a factor of 3 during a gamma-ray flare in 2010 April. We discuss the locations in the jet where high gamma-ray fluxes occur. These include stationary features in the jet flow that we identify with standing shocks.

The analysis of various Gamma Ray Bursts (GRBs) characterized by an isotropic energy E_iso ≲ 10⁵³ ergs within the fireshell model has shown how that the observed N(E) spectrum of their prompt emission can be reproduced in a satisfactory way by assuming a thermal spectrum in the comoving frame of the fireshell. Nevertheless, from the study of higher energetic bursts (E_iso ≳ 10⁵⁴ergs) such as, for example, GRB 080319B, some discrepancies between the numerical simulations and the observational data have been observed. We investigate a different spectrum of photons in the comoving frame of the fireshell in order to better reproduce the spectral properties of GRB prompt emission within the fireshell model. We introduce a phenomenologically modified comoving thermal spectrum: a spectrum characterized by a different asymptotic low energy slope with respect to the thermal one. We test this spectrum by comparing the numerical simulations with the observed prompt emission spectra of various GRBs; we present, as an exaple, the case of GRB 080319B.

The results obtained with the new Laue lens prototype built in the LARIX facility in the Physics Department of University of Ferrara will be present. Thanks to the methods adopted for improving the first prototype (SPIE conference in San Diego, Ferrari et al. 2009) here we present the results of the new prototype with improved performances in terms of point spread function (PSF) and spectral response.

The results of analysis of approximately 3 year gamma-ray observations (August 2008–July 2011) of the core of radio galaxy Centaurus A with the Fermi Large Area Telescope (Fermi LAT) are presented. Binned likelihood analysis method applying to the data shows that below several GeV the spectrum can be described by a single power-law with photon index Γ = 2.73 ± 0.06. However, at higher energies the new data show significant excess above the extrapolation of the energy spectrum from low energies. The comparison of the corresponding Spectral Energy Distribution (SED) at GeV energies with the SED in the TeV energy band reported by the H.E.S.S. collaboration shows that we deal with two or perhaps even three components of gamma-radiation originating from different regions located within the central 10 kpc of Centaurus A.

The analysis of gamma-ray data of Centaurus A lobe accumulated from the beginning of the operation until November 14, 2011 show extension of the HE gamma-ray emission beyond the WMAP radio image in the case of the Northern lobe [9]. The possible origins of gamma-rays from giant radio lobes of Centaurus A are discussed in the context of hadronic and leptonic scenarios.

Diffusive shock acceleration (DSA) at relativistic shocks is likely to be an important acceleration mechanism in various astrophysical jet sources, including radio-loud AGN. An important recent development for blazar science is the ability of Fermi-LAT data to pin down the power-law index of the high energy portion of emission in these sources, and therefore also the index of the underlying non-thermal particle population. This diagnostic potential was not possible prior to Fermi launch, when gamma-ray information was dominated by the highly-absorbed TeV band. This paper highlights how multiwavelength spectra including X-ray band and Fermi data can be used to probe diffusive acceleration in relativistic, oblique, MHD shocks in blazar jets. The spectral index of the non-thermal particle distributions resulting from Monte Carlo simulations of DSA, and the fraction of thermal particles accelerated to non-thermal energies, depend sensitively on the particles' mean free path scale, and also on the magnetic field obliquity to the shock normal. We investigate self-consistently the radiative synchrotron/Compton signatures of the resulting thermal and non-thermal particle distributions. Important constraints on the frequency of particle scattering and the level of field turbulence are identified for the blazar AO 0235+164. The possible interpretation that turbulence levels decline with remoteness from jet shocks, and a significant role for non-gyroresonant diffusion, are discussed.

We probe the interstellar medium towards the objects Circinus X-1, a low-mass X-ray binary with relativistic jets; and the highly energetic Westerlund 2 stellar cluster, which is located towards TeV gamma-ray emission and interesting arc- and jet-like features seen in Nanten ¹²CO data. We have mapped both regions with the Mopra radio telescope, in 7 mm and 12 mm wavebands, looking for evidence of disrupted/dense gas caused by the interaction between high energy outflows and the ISM. Towards Westerlund 2, peaks in CS(J=1-0) emission indicate high density gas towards the middle of the arc and the endpoint of the jet; and radio recombination line emission is seen overlapping the coincident HII region RCW49. Towards Circinus X-1, ¹²CO(J = 1-0) Nanten data reveals three molecular clouds that lie in the region of Cir X-1. Gas parameters for each cloud are presented here.

PKS 1510-089 (z = 0.361), one of only a handful of flat spectrum radio quasars detected in the very high energy (VHE, E > 100 GeV) γ-rays, is known for its flux variability and complex multiwavelength behaviour. VHE observations by H.E.S.S. and MAGIC in May 2016 detected an unprecedented flare, both in intensity and in the shortness of its variability timescale. The flare lasted less than 48 hours, during which time the flux reached about 80 per cent of the Crab Nebula flux above 200 GeV. In addition, the intranight variability of this source was detected for the first time. Simultaneous observations in high energy (HE, E > 100 MeV) γ-rays performed with Fermi-LAT and optical R-band performed with ATOM show behaviour not consistent with simple simultaneous brightening in all bands. While a significant hardening of the spectrum is visible in HE, the flux increased only moderately. A simultaneous rise in daily-averaged optical flux was seen in the R-band. However, the intranight R-band flux evolution shows two prominent peaks, while only one is visible in the VHE range. These intriguing features of the flare will be presented in detail. We will also discuss possible explanations for the observed emission.

Here we present results from an in-depth search for pulsed emission from both close binary systems AE Aquarii (AE Aqr) and AR Scorpii (AR Sco) in radio and gamma-ray energies. Both systems were observed recently with the MeerKAT telescope, and combined with this, we utilized the combined 10 year Pass 8 Fermi-LAT dataset to search for pulsed gamma-ray emission from both white dwarfs in these systems. Pulsed emission was detected in MeerKAT data from both these close binary systems at a period that is at, or close to, the spin period of the white dwarf. The search for pulsed gamma-ray emission revealed pulsed emission at the spin period of the white dwarf of AE Aqr after selecting data sets with duration of 2 weeks that show excess emission above the 2 σ significance level. Braking these two-week sets up in 10 minute intervals and stacking the power spectra revealed pulsed emission at both the spin (P * = 33.08 s) and its associated first harmonic (P₁ = 16.54 s). A full 10 year analysis of the AR Sco data revealed pulsed emission at the spin period/beat period of the white dwarf, albeit at a lower significance level. Several control analyses were performed to verify the authenticity of the emission in both radio and gamma-rays, which will be discussed in the main text. The results of this study definitely reveal that both white dwarfs in these systems contain a particle accelerator that accelerates charged particles to high energies resulting in associated non-thermal radio and gamma-ray emission.

The location of the main emitting region responsible for the bulk of the Blazar emission is a puzzling issue in our understanding of jetted Active Galactic Nuclei. Fast flares and a high Compton dominance are more easily explained if the gamma-ray zone is well inside the Broad Line Region (BLR), while the absence of γ-γ absorption features in the Fermi-LAT spectra as well as the detection at Very High Energies (VHE) of some FSRQ put the blazar zone at much larger distances along the jet, beyond the BLR. The latter seems now to be the most typical behavior in FSRQ, questioning SED models based on the external Compton process on BLR photons.