Browsing by Author "Tavecchio, F"

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    Multiepoch multiwavelength spectra and models for blazar 3C 279
    (2001) Hartman, RC; Böttcher, M; Aldering, G; Aller, H; Aller, M; Backman, DE; Balonek, TJ; Bertsch, DL; Bloom, SD; Bock, H; Boltwood, P; Carini, MT; Collmar, W; De Francesco, G; Ferrara, EC; Freudling, W; Gear, WK; Hall, PB; Heidt, J; Hughes, P; Hunter, SD; Jogee, S; Johnson, WN; Kanbach, G; Katajainen, S; Kidger, M; Kii, T; Koskimies, M; Kraus, A; Kubo, H; Kurtanidze, O; Lanteri, L; Lawson, A; Lin, YC; Lisenfeld, U; Madejski, G; Makino, F; Maraschi, L; Marscher, AP; McFarland, JP; McHardy, I; Miller, HR; Nikolashvili, M; Nilsson, K; Noble, JC; Nucciarelli, G; Ostorero, L; Pian, E; Pursimo, T; Raiteri, CM; Reich, W; Rekola, R; Richter, GM; Robson, EI; Sadun, A; Savolainen, T; Sillanpää, A; Smale, A; Sobrito, G; Sreekumar, P; Stevens, JA; Takalo, LO; Tavecchio, F; Teräsranta, H; Thompson, DJ; Tornikoski, M; Tosti, G; Ungerechts, H; Urry, CM; Valtaoja, E; Villata, M; Wagner, SJ; Wehrle, AE; Wilson, JW
    Of the blazars detected by EGRET in GeV gamma -rays, 3C 279 is not only the best observed by EGRET but also one of the best monitored at lower frequencies. We have assembled 11 spectra, from GHz radio through GeV gamma -rays, from the time intervals of EGRET observations. Although some of the data have appeared in previous publications, most are new, including data taken during the high states in early 1999 and early 2000. All of the spectra show substantial gamma -ray contribution to the total luminosity of the object; in a high state, the gamma -ray luminosity dominates over that at all other frequencies by a factor of more than 10. There is no clear pattern of time correlation; different bands do not always rise and fall together, even in the optical, X-ray, and gamma -ray bands. The spectra are modeled using a leptonic jet, with combined synchrotron self-Compton plus external Compton gamma -ray production. Spectral variability of 3C 279 is consistent with variations of the bulk Lorentz factor of the jet, accompanied by changes in the spectral shape of the electron distribution. Our modeling results are consistent with the UV spectrum of 3C 279 being dominated by accretion disk radiation during times of low gamma -ray intensity.
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    Optical and NIR observations of the afterglow of GRB020813
    (2003) Covino, S; Malesani, D; Tavecchio, F; Antonelli, LA; Arkharov, A; Di Paola, A; Fugazza, D; Ghisellini, G; Larionov, V; Lazzati, D; Mannucci, F; Masetti, N; Barrena, R; Benetti, S; Castro-Tirado, AJ; Alighieri, SD; Fiore, F; Frontera, F; Fruchter, A; Ghinassi, F; Gladders, M; Hall, PB; Israel, GL; Klose, S; Magazzù, A; Palazzi, E; Pedani, M; Pian, E; Romano, P; Stefanon, M; Stella, L
    We present optical and near-infrared (NIR) photometry of the bright afterglow of GRB020813. Our data span from 3 hours to 4 days after the GRB event. A rather sharp achromatic break is present in the light curve, 14 hours after the trigger. In the framework of jetted fireballs, this break corresponds to a jet half-opening angle of 1.9degrees +/- 0.2degrees, the smallest value ever inferred for a GRB. We discuss our results in the framework of currently available models, and find that they have problems in explaining the joint temporal and spectral properties, and in particular the slow decay before the break.