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26 April 2024 |
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Variable jet properties in GRB110721A: Time resolved observations of the jet photosphere | | Shabnam Iyyani
; Felix Ryde
; Magnus Axelsson
; James Michael Burgess
; Sylvain Guiriec
; Josefin Larsson
; Christoffer Lundman
; Elena Moretti
; Sinead McGlynn
; Tanja Nymark
; Kjell Rosquist
; | | Date: |
15 May 2013 | | Abstract: | {it Fermi Gamma-ray Space Telescope} observations of GRB110721A have
revealed two emission components from the relativistic jet: emission from the
photosphere, peaking at $sim 100$ keV and a non-thermal component, which peaks
at $sim 1000$ keV. We use the photospheric component to calculate the
properties of the relativistic outflow. We find a strong evolution in the flow
properties: the Lorentz factor decreases with time during the bursts from
$Gamma sim 1000$ to $sim 150$ (assuming a redshift $z=2$; the values are
only weakly dependent on unknown efficiency parameters). Such a decrease is
contrary to the expectations from the internal shocks and the isolated magnetar
birth models. Moreover, the position of the flow nozzle measured from the
central engine, $r_0$, increases by more than two orders of magnitude. Assuming
a moderately magnetised outflow we estimate that $r_0$ varies from $10^6$ cm to
$sim 10^9$ cm during the burst. We suggest that the maximal value reflects the
size of the progenitor core. Finally, we show that these jet properties
naturally explain the observed broken power-law decay of the temperature which
has been reported as a characteristic for GRB pulses. | | Source: | arXiv, 1305.3611 | | Services: | Forum | Review | PDF | Favorites | |
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