Browsing by Author "Benetti, S"

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    A new faint type Ia supernova: SN 1997cn in NGC 5490
    (1998) Turatto, M; Piemonte, A; Benetti, S; Cappellaro, E; Mazzali, PA; Danziger, IJ; Patat, F
    Observations of the recent supernova (SN) 1997cn in the elliptical galaxy NGC 5490 show that this object closely resembles, both photometrically and spectroscopically, the faint SN Ia SN 1991bg. The two objects have similar light curves, which do not show secondary maxima in the near-IR as normal type Ia supernova. The host galaxy, NGC 5490, lies in the Hubble flow. Adopting for SN 1997cn a reddening E(B-V) = 0, the absolute magnitude is faint: M-V = - 17.98 using H-0 = 65 and M-V = - 17.40 using H-0 = 85 km s(-1) Mpc(-1). The latter value is in close agreement with the absolute magnitude of SN 1991bg on the SBF/PNLF/TF distance scale. The photospheric spectra of the two SNe show the same peculiarities, the deep Ti n trough between 4000 and 4500 A, the strong Ca n IR triplet, the narrow absorption at about 5700 A, and the slow expansion velocity. Analogous to SN 1991bg, the observed spectrum of SN 1997cn has been successfully modeled by scaling down the W7 model by a factor of 2, assuming a rise time to B maximum of 18 days, a photospheric velocity, and an effective temperature low compared to normal SNe Ia. The influence of the distance scale adopted on the input parameters of the best-fit model is also discussed.
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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.
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    The peculiar type II supernova 1997D
    (1998) Turatto, M; Mazzali, PA; Young, TR; Nomoto, K; Iwamoto, K; Benetti, S; Cappellaro, E; Danziger, IJ; de Mello, DF; Phillips, MM; Suntzeff, NB; Clocchiatti, A; Piemonte, A; Leibundgut, B; Covarrubias, R; Maza, J; Sollerman, J
    SN 1997D in NGC 1536 is possibly the least luminous and energetic Type II supernova discovered to date. The entire light curve is subluminous, never reaching M-v = -14.65. The radioactive tail follows the Co-56 decay slope. In the case of a nearly complete trapping of the gamma-rays, the Ni-56 mass derived from the tail brightness is extremely small, similar to 0.002 M.. At discovery, the spectra showed a red continuum and line velocities on the order of 1000 km s(-1). The luminosity and the photospheric expansion velocity suggest that the explosion occurred about 50 days before discovery and that a plateau probably followed. Model light curves and spectra of the explosion of a 26 M. star successfully fitted the observations. Low-mass models are inconsistent with the observations. The radius of the progenitor, constrained by the prediscovery upper limits, is R-0 less than or similar to 300 R.. A low explosion energy of similar to 4 x 10(50) ergs is then required in the modeling. The strong Pa II lines in the photospheric spectra are reproduced with a solar abundance and low T-eff. A scenario in which the low Ni-56 mass observed in SN 1997D is due to fallback of material onto the collapsed remnant of the explosion of a 25-40 M. star appears to be favored over the case of the explosion of an 8-10 M. star with low Ni-56 production.