Unifying XRFs and GRBs with a Fisher-shaped universal jet model

Donaghy, T. Q. and Graziani, Carlo and Lamb, D. Q. (2005) Unifying XRFs and GRBs with a Fisher-shaped universal jet model. Il nuovo cimento C, 28 (3). pp. 403-406. ISSN 1826-9885

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We show analytically that GRB jets with an emissivity profile given by the Fisher distribution, epsilon(theta) = A (.) exp[B (.) cos theta], have the unique property of producing equal numbers of bursts per logarithmic interval in E-iso, and therefore in most burst properties. Since this broad distribution of burst properties is a key feature found by HETE-2, a Fisher-shaped universal jet model can explain many of the observed properties of XRFs, X-ray-rich GRBs, and GRBs reasonably well, in contrast to a power law universal model. For small viewing angles, the Fisher distribution can be approximated by a Gaussian, whose properties have been explored by Zhang B. et al. (ApJ, 601 (2004) 1,119). We also show that the Fisher universal jet model produces a broad distribution in the inferred radiated energy E-gamma(inf), in contrast to the narrow distribution predicted by the uniform variable-opening-angle jet model (Lamb D. Q. et al., ApJ, 620 (2005) 335). Here we present Monte Carlo simulations of both a Fisher-shaped universal jet model and a Fisher-shaped variable-opening-angle jet model.

Item Type: Article
Additional Information: Paper presented at the “4th Workshop on Gamma-Ray Burst in the Afterglow Era”, Rome, October 18-22, 2004.
Uncontrolled Keywords: Gamma-ray bursrs ; Standard energy reservoir ; Flashes
Subjects: 500 Scienze naturali e Matematica > 530 Fisica
Depositing User: Marina Spanti
Date Deposited: 16 Mar 2020 10:29
Last Modified: 16 Mar 2020 10:29
URI: http://eprints.bice.rm.cnr.it/id/eprint/15659

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