4,653 research outputs found
Gamma-Ray Burst Afterglows with Energy Injection: Homogeneous Versus Wind External Media
Assuming an adiabatic evolution of a gamma-ray burst (GRB) fireball
interacting with an external medium, we calculate the hydrodynamics of the
fireball with energy injection from a strongly magnetic millisecond pulsar
through magnetic dipole radiation, and obtain the light curve of the optical
afterglow from the fireball by synchrotron radiation. Results are given both
for a homogeneous external medium and for a wind ejected by GRB progenitor. Our
calculations are also available in both ultra-relativistic and non-relativistic
phases. Furthermore, the observed R-band light curve of GRB{000301C} can be
well fitted in our model, which might provide a probe of the properties of GRB
progenitors.Comment: revised version for publication in Chin. Phys. Let
The Inverse Compton Emission Spectra in the Very Early Afterglows of Gamma-Ray Bursts
We calculate the spectra of inverse Compton (IC) emissions in gamma-ray burst
(GRB) shocks produced when relativistic ejecta encounters the external
interstellar medium, assuming a broken power-law approximation to the
synchrotron seed spectrum. Four IC processes, including the synchrotron
self-Compton (SSC) processes in GRB forward and reverse shocks, and two
combined-IC processes (i.e. scattering of reverse shock photons on the
electrons in forward shocks and forward shock photons on the electrons in
reverse shocks), are considered. We find that the SSC emission from reverse
shocks dominates over other emission processes in energy bands from tens of MeV
to tens of GeV, for a wide range of shock parameters. This mechanism may be
responsible for the prompt high energy gamma-rays detected by the Energetic
Gamma Ray Experiment Telescope (EGRET). At TeV energy bands, however, the
combined-IC emissions and/or the SSC emission from the forward shocks become
increasingly dominant for a moderately steep distribution of shocked electrons.Comment: 15 pages, 4 EPS figures, Latex, accepted for publication in ApJ,
scheduled for the v556 n2 Aug 1, 2001 issu
Broad-lined type Ic supernova iPTF16asu: A challenge to all popular models
It is well-known that ordinary supernovae (SNe) are powered by 56Ni cascade
decay. Broad-lined type Ic SNe (SNe Ic-BL) are a subclass of SNe that are not
all exclusively powered by 56Ni decay. It was suggested that some SNe Ic-BL are
powered by magnetar spin-down. iPTF16asu is a peculiar broad-lined type Ic
supernova discovered by the intermediate Palomar Transient Factory. With a
rest-frame rise time of only 4 days, iPTF16asu challenges the existing popular
models, for example, the radioactive heating (56Ni-only) and the magnetar+56Ni
models. Here we show that this rapid rise could be attributed to interaction
between the SN ejecta and a pre-existing circumstellar medium ejected by the
progenitor during its final stages of evolution, while the late-time light
curve can be better explained by energy input from a rapidly spinning magnetar.
This model is a natural extension to the previous magnetar model. The mass-loss
rate of the progenitor and ejecta mass are consistent with a progenitor that
experienced a common envelope evolution in a binary. An alternative model for
the early rapid rise of the light curve is the cooling of a shock propagating
into an extended envelope of the progenitor. It is difficult at this stage to
tell which model (interaction+magnetar+56Ni or cooling+magnetar+56Ni) is better
for iPTF16asu. However, it is worth noting that the inferred envelope mass in
the cooling+magnetar+56Ni is very high.Comment: 11 pages, 4 figures, 3 table
Measurement of the branching fractions of psi(2S) -> 3(pi+pi-) and J/psi -> 2(pi+pi-)
Using data samples collected at sqrt(s) = 3.686GeV and 3.650GeV by the BESII
detector at the BEPC, the branching fraction of psi(2S) -> 3(pi+pi-) is
measured to be [4.83 +- 0.38(stat) +- 0.69(syst)] x 10^-4, and the relative
branching fraction of J/psi -> 2(pi+pi-) to that of J/psi -> mu+mu- is measured
to be [5.86 +- 0.19(stat) +- 0.39(syst)]% via psi(2S) -> (pi+pi-)J/psi, J/psi
-> 2(pi+pi-). The electromagnetic form factor of 3(pi+pi-) is determined to be
0.21 +- 0.02 and 0.20 +- 0.01 at sqrt(s) = 3.686GeV and 3.650GeV, respectively.Comment: 17pages, 7 figures, submitted to Phys. Rev.
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