Aims: Gamma Ray Bursts (GRBs) are sometimes preceded by dimmer emission episodes, called "precursors", whose nature is still a puzzle: they could either have the same origin as the main emission episode or they could be due to another mechanism. We investigate if precursors have some spectral distinctive feature with respect to the main GRB episodes. Methods: To this aim we compare the spectral evolution of the precursor with that of the main GRB event. We also study if and how the spectral parameters, and in particular the peak of the vFv spectrum of time resolved spectra, correlates with the flux. This allows us to test if the spectra of the precursor and of the main event belong to the same correlation (if any). We searched GRBs with precursor activity in the complete sample of 2704 bursts detected by BATSE finding that 12% of GRBs have one or more precursors. Among these we considered the bursts with time resolved spectral analysis performed by Kaneko et al. 2006, selecting those having at least two time resolved spectra for the precursor. Results: We find that precursors and main events have very similar spectral properties. The spectral evolution within precursors has similar trends as the spectral evolution observed in the subsequent peaks. Also the typical spectral parameters of the precursors are similar to those of the main GRB events. Moreover, in several cases we find that within the precursors the peak energy of the spectrum is correlated with the flux similarly to what happens in the main GRB event. This strongly favors models in which the precursor is due to the same fireball physics of the main emission episodes.

Time resolved spectral behaviour of bright BATSE precursors / Burlon, D; Ghirlanda, G; Ghisellini, G; Greiner, J; Celotti, Anna Lisa. - In: ASTRONOMY & ASTROPHYSICS. - ISSN 0004-6361. - 505:2(2009), pp. 569-575. [10.1051/0004-6361/200912662]

Time resolved spectral behaviour of bright BATSE precursors

Celotti, Anna Lisa
2009-01-01

Abstract

Aims: Gamma Ray Bursts (GRBs) are sometimes preceded by dimmer emission episodes, called "precursors", whose nature is still a puzzle: they could either have the same origin as the main emission episode or they could be due to another mechanism. We investigate if precursors have some spectral distinctive feature with respect to the main GRB episodes. Methods: To this aim we compare the spectral evolution of the precursor with that of the main GRB event. We also study if and how the spectral parameters, and in particular the peak of the vFv spectrum of time resolved spectra, correlates with the flux. This allows us to test if the spectra of the precursor and of the main event belong to the same correlation (if any). We searched GRBs with precursor activity in the complete sample of 2704 bursts detected by BATSE finding that 12% of GRBs have one or more precursors. Among these we considered the bursts with time resolved spectral analysis performed by Kaneko et al. 2006, selecting those having at least two time resolved spectra for the precursor. Results: We find that precursors and main events have very similar spectral properties. The spectral evolution within precursors has similar trends as the spectral evolution observed in the subsequent peaks. Also the typical spectral parameters of the precursors are similar to those of the main GRB events. Moreover, in several cases we find that within the precursors the peak energy of the spectrum is correlated with the flux similarly to what happens in the main GRB event. This strongly favors models in which the precursor is due to the same fireball physics of the main emission episodes.
2009
505
2
569
575
https://doi.org/10.1051/0004-6361/200912662
Burlon, D; Ghirlanda, G; Ghisellini, G; Greiner, J; Celotti, Anna Lisa
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11767/12428
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