A&A 447, 121-132 (2006)
DOI: 10.1051/0004-6361:20052803

Gamma-ray bursts associated with supernovae: a systematic analysis of BATSE GRB candidates

Z. Bosnjak¹, A. Celotti¹, G. Ghirlanda², M. Della Valle³ and E. Pian<sup>4

1</sup>  SISSA/ISAS, via Beirut 2-4, 34014 Trieste, Italy
    e-mail: celotti@sissa.it
²  INAF - Observatory of Brera, via Bianchi 46, 23807 Merate (LC), Italy
³  INAF - Observatory of Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁴  INAF - Observatory of Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy

(Received 1 February 2005 / Accepted 25 September 2005)

Abstract
We examined the properties of a sample of BATSE Gamma-Ray Bursts (GRBs) comprising events which have indications of association with a supernova (SN), some on the basis of indications of re-brightening in the optical afterglow light curve, but in most cases based only on the "loose" temporal and directional coincidence inferred from the cross correlation of catalogs. Despite the large uncertainties in the latter selection method, the temporal and spectral analysis reveal three interesting statistical results when the sample is compared with that of all the BATSE GRBs: the GRBs tentatively associated with SNe are found to predominantly (in ~80% of the cases) have single-peaked light curves, a softer spectrum (i.e. low energy power law index ) and tend not to follow the Lag-Luminosity and Isotropic Energy-Peak Energy correlations. These three independent statistical properties point toward the existence of a significant number of under-luminous, GRB 980425-like events constituting - at least from an observational point of view - a tail or a separate class with respect to the whole of the BATSE GRB events. The unusually high percentage of SN Ibc among those identified by the catalog cross-correlation (a factor ~four higher than expected from SN catalog statistics) reinforces the non-randomness of some of the selected events.

Key words: gamma rays: bursts -- methods: data analysis -- stars: supernovae: general

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© ESO 2006

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