GRB3 - GRBs Observations vs. theory in the Swift era |
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Speaker |
Caito, Letizia |
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Talk Title |
The classification of gamma-ray bursts: the typical cases of GRB 060614 and GRB 07122 |
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Abstract |
The traditional separation between Short Hard Bursts and Long Soft Bursts, yet enabled by many observations of the recent years, has been finally infringed by the explosion of GRB 060614. GRB 060614 is the first clear example of a nearby long duration burst without a bright SN Ib/c emission observed, crucial issue that undermines the fundamental assumption of the standard scenario according to which all long GRBs originate from Supernovae explosions. Although its duration makes it hardly classifiable as a short GRB, it is not either a typical long GRB since it occurs in a low star forming region. This "anomalous" situation finds a natural interpretation within the fireshell scenario: GRB 060614 belongs to the class of "fake" short bursts or, better, of canonical GRBs "disguised" as short ones. Similarly to the prototypical GRB 970228, the morphology, made of an initial spikelike emission followed, in the 15-150 KeV energy band, by a deflated but mostly energetic tail, is due to the particularly low density of the environment. The first, hard spikelike emission is identified with the Proper Gamma-Ray Burst (P-GRB), while the softer tail is the peak of the afterglow. This interpretation is compatible with the merging of a neutron-star/white dwarf binary system as progenitor of the burst. We have considered the possibility that the source GRB 071227, classified in literature as a short GRB and presenting some similar characteristics of GRB 060614, could be another example of disguised short burst. Similarly to GRB 060614 this GRB shows, in addition to its spiky structure followed by a strongly deflated tail, an energetic compatible with that of underluminous and in fact it is very close to us. Though the explosion of this source is in a high-density region, the hipothesys of another disguised burst has been soon ruled out. We have instead checked if it could be an example of "genuine" short burst. The results of our analysis shows that this burst is a typical long GRB within the fireshell scenario. As for GRB 060614, this is not in contradiction with the lack of any SN associated. On the contrary, this is a further confirmation of the same nature and origin of both long and short bursts, that implies the necessity of a new classification scheme based on different criteria and characteristic parameters. |
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