Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Jet break time -- flux density relationship and constraints on physical
  parameters of GRB afterglows   We derive a relation between the flux density $F_{\nu,j}$ at the light-curve
break of a gamma-ray burst (GRB) afterglow and the break time $t_{j}$. The
break is due to the transition from the spherical-like to jet-like evolution of
the afterglow, when the Lorentz factor of the jet equals the inverse of the
initial half-opening angle, i.e., $\gamma=1/\theta_0$. We show that this
relation indeed behaves as $F_{\nu,j}\propto t_{j}^{-p}$ among GRBs for the
slow-cooling case, where $p$ is the power-law index of electron distribution. A
statistical analysis of the optical jet breaks of nine GRBs gives $p=2.10\pm
0.21$, which is consistent with the shock acceleration theory. The value of $p$
derived in this way is different from the observed temporal index $\alpha_2$
($F_{\nu}\propto t^{-\alpha_{2}}$) of the late-time light curve after $t_{j}$,
which suffers several uncertainties from the unclear hydrodynamics of the
sideways expansion and exhibits a large dispersion. Our results not only
confirm that the remnants of GRBs are standard candles, but also provide the
first evidence that the physical parameters of relativistic shocks are
universal, with the favored values $\epsilon_{e}\sim 0.1$ and $\epsilon_{B}\sim
10^{-3}$.

16
The categories of this paper are: stat
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
0
The categories of this paper are: hep-ph
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
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The categories of this paper are: plasm-ph
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The categories of this paper are: math-ph
17
The categories of this paper are: q-fin
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The categories of this paper are: math
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol