G. Ghisellini
A5090088347- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Radio Astronomy Observations and Technology
- Pulsars and Gravitational Waves Research
- Particle Accelerators and Free-Electron Lasers
- Dark Matter and Cosmic Phenomena
- Astro and Planetary Science
- Neutrino Physics Research
- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Stellar, planetary, and galactic studies
- Particle Detector Development and Performance
- Astronomical Observations and Instrumentation
- SAS software applications and methods
- Solar and Space Plasma Dynamics
- Particle accelerators and beam dynamics
- Gyrotron and Vacuum Electronics Research
- Particle physics theoretical and experimental studies
- Computational Physics and Python Applications
- Cosmology and Gravitation Theories
- Nuclear Physics and Applications
- Advanced X-ray Imaging Techniques
- Ionosphere and magnetosphere dynamics
- Advanced X-ray and CT Imaging
Brera Astronomical Observatory
2015-2024
National Institute for Astrophysics
2010-2024
University of Milano-Bicocca
2018
Institute for Space Astrophysics and Planetology
2018
Osservatorio Astronomico di Padova
2018
University of Nova Gorica
2018
American Society for Radiation Oncology
2018
University of Geneva
2016
Marche Polytechnic University
2016
Baden-Wuerttemberg Cooperative State University
2016
The Swift mission, scheduled for launch in 2004, is a multiwavelength observatory gamma-ray burst (GRB) astronomy. It first-of-its-kind autonomous rapid-slewing satellite transient astronomy and pioneers the way future rapid-reaction missions. will be far more powerful than any previous GRB observing 100 bursts yr-1 performing detailed X-ray UV/optical afterglow observations spanning timescales from 1 minute to several days after burst. objectives are (1) determine origin of GRBs, (2)...
We collect data at well-sampled frequencies from the radio to γ-ray range for following three complete samples of blazars: Slew survey, 1-Jy BL Lacs and 2-Jy sample flat-spectrum radio-loud quasars (FSRQs). The fraction objects detected in γ-rays (E ≳ 100 MeV) is ∼ 17, 26 40 per cent respectively. Except survey sample, sources do not differ either other each or all sources, terms distributions redshift, X-ray luminosities broad-band spectral indices (radio optical X-ray). compute average...
view Abstract Citations (912) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Jet Model for the Gamma-Ray--emitting Blazar 3C 279 Maraschi, L. ; Ghisellini, G. Celotti, A. The physical conditions in γ-ray-emitting blazar are discussed. requirement of transparency γ-rays, together with observation rapid variability, imply that high-energy radiation is anisotropic. It proposed γ-rays produced a relativistic jet via synchrotron self-Compton...
The phenomenology of gamma-ray bright blazars can be accounted for by a sequence in the source power and intensity diffuse radiation field surrounding relativistic jet. Correspondingly, equilibrium particle distribution peaks at different energies. This leads to trend observed properties: an increase corresponds to: 1) decrease frequencies synchrotron inverse Compton peaks; 2) ratio powers high low energy spectral components. Objects along this would observationally classified respectively...
We consider all bursts with known redshift and $νF_ν$ peak energy, $E^{obs}_{peak}$. For a good fraction of them an estimate the jet opening angle is available from achromatic break their afterglow light curve. This allows derivation collimation--corrected energy bursts, $E_γ$. The distribution values $E_γ$ more spread respect to previous findings, covering about two orders magnitude. find surprisingly tight correlation between source frame $E_{peak}$: $E^{obs}_{peak}(1+z) \propto...
We studied all blazars of known redshift detected by the Fermi satellite during its first 3-month survey. For majority them, pointed Swift observations ensure a good multiwavelength coverage, enabling us to reliably construct their spectral energy distributions (SEDs). model SEDs using one-zone leptonic and study derived interesting physical parameters as function observed γ-ray luminosity. confirm previous findings concerning relation with source luminosity which are at origin blazar...
view Abstract Citations (540) References (120) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Relativistic Bulk Motion in Active Galactic Nuclei Ghisellini, G. ; Padovani, P. Celotti, A. Maraschi, L. We discuss the evidence for relativistic bulk motion of emitting plasma nuclei ~100 radio sources, which include BL Lacertae objects, quasars, and galaxies, with published VBLI measurements core angular dimension flux. Comparing predicted observed high-frequency...
TeV BL Lacertae objects require extreme relativistic bulk motion in the gamma-ray emission region, but at VLBI scale their radio knots hardly move. The same sources show evidence, radio, of a structure made fast spine plus slow layer. We propose that this exists even on spatial regions responsible for emission. One component sees (beamed) radiation produced by other, and enhances inverse Compton both components. In addition, allows magnetic field to be nearly equipartition with emitting...
We estimate the power of relativistic, extragalactic jets by modelling spectral energy distribution a large number blazars. adopt simple one-zone, homogeneous, leptonic synchrotron and inverse Compton model, taking into account seed photons originating both locally in jet externally. The blazars under study have an often dominant high component, which, if interpreted as due to radiation, limits value magnetic field within emission region. As consequence, corresponding Poynting flux cannot be...
The jets of powerful blazars propagate within regions relatively dense radiation produced externally to the jet. This is a key ingredient understand origin high energy emission blazars, from X-ray gamma-ray band. These external fields control amount inverse Compton with respect synchrotron flux. Therefore predicted spectral distribution (SED) will depend on where jet dissipates part its produce observed radiation. We investigate in detail how SED changes as function location dissipation...
We revisit the blazar sequence exploiting complete, flux-limited sample of blazars with known redshift detected by Fermi satellite after 4 yr operations (the 3LAC sample). divide sources into γ-ray luminosity bins, collect all archival data for blazars, and construct their spectral energy distribution (SED). describe average SED in same bin through a simple phenomenological function consisting two broken power laws connecting law describing radio emission. do that separately BL Lacs flat...
We report our observation of the short gamma-ray burst (GRB) GRB 170817A, associated to binary neutron star merger gravitational wave (GW) event GW 170817, performed in X-ray band with XMM-Newton 135 d after (on 29 December, 2017). find evidence for a flattening light curve respect previously observed brightening. This is also supported by nearly simultaneous optical Hubble Space Telescope and successive Chandra low-frequency radio observations recently reported literature. Since...
The binary neutron star merger event GW170817 was detected through both electromagnetic radiation and gravitational waves. Its afterglow emission may have been produced by either a narrow relativistic jet or an isotropic outflow. High-spatial-resolution measurements of the source size displacement can discriminate between these scenarios. We present very-long-baseline interferometry observations, performed 207.4 days after using global network 32 radio telescopes. apparent is constrained to...
We assess non-thermal Comptonization models for the high-energy emission of EGRET blazar sources. argue that copious γ-ray radiation originates from a region is transparent to pair-production processes, at some distance central engine. In opposite case, absorbed γ power would be largely reprocessed into softer X-ray photons, contrary observations. Our model consists low-entropy inner jet and dissipative outer jet, where kinetic or Poynting primary flux converted energetic emitting particles....
The central engine causing the production of jets in radio sources may work intermittently, accelerating shells plasma with different mass, energy and velocity. Faster but later can then catch up slower earlier ones. In resulting collisions shocks develop, converting some ordered bulk kinetic into magnetic field random electrons which radiate. We propose that this internal shock scenario, is scenario generally thought to explain observed gamma-ray burst radiation, also for general, blazars...
We consider the constraints on physical parameters of a homogeneous SSC model that can be derived from spectral shape and variability TeV blazars. Assuming relativistic electron spectrum is broken power law, where break energy $γ_b$ free parameter, we write analytical formulae allow to connect observable quantities. The summarized in plane coordinates are Doppler factor magnetic field. consistency between balance cooling escape interpretation soft photon lags measured some sources as...
The presence of an obscuring torus around the nucleus a Seyfert galaxy, as supposed in popular unification scheme, can strongly modify X-ray spectrum for both type 1 and 2 galaxies. We study this problem by means Monte Carlo simulations, finding that, if is Compton-thick, it scatter at small angles significant fraction nuclear radiation, contribute to continuum galaxies above ∼ 10 keV, fluorescence iron line 6.4 keV. At large inclination column densities, attenuated photoabsorption Compton...