1,383 research outputs found
Radial Angular Momentum Transfer and Magnetic Barrier for Short-Type Gamma-Ray Burst Central Engine Activity
Soft extended emission (EE) following initial hard spikes up to 100 seconds
was observed with {\em Swift}/BAT for about half of short-type gamma-ray bursts
(SGRBs). This challenges the conversional central engine models of SGRBs, i.e.,
compact star merger models. In the framework of the black hole-neutron star
merger models, we study the roles of the radial angular momentum transfer in
the disk and the magnetic barrier around the black hole for the activity of
SGRB central engines. We show that the radial angular momentum transfer may
significantly prolong the lifetime of the accretion process and multiple
episodes may be switched by the magnetic barrier. Our numerical calculations
based on the models of the neutrino-dominated accretion flows suggest that the
disk mass is critical for producing the observed EE. In case of the mass being
, our model can reproduce the observed timescale and
luminosity of both the main and EE episodes in a reasonable parameter set. The
predicted luminosity of the EE component is lower than the observed EE with
about one order of magnitude and the timescale is shorter than 20 seconds if
the disk mass being . {\em Swift}/BAT-like instruments may
be not sensitive enough to detect the EE component in this case. We argue that
the EE component would be a probe for merger process and disk formation for
compact star mergers.Comment: 9 pages, 3 figures, accepted for publication in Ap
Speckle Observation of Binary Stars at NTNU
[[abstract]]The binary image will be distorted by atmospheric turbulence, however the angular separation of a binary could be determined with speckle interferometry technology. The binary program with speckle interferometry at NTNU has been set up since 2002.
The commercial CCD, DMK 31AF03 CCD, is suitable for the binary program with the method of speckle interferometry. Because C-14 is the telescope with a moving primary mirror, it is not suitable for speckle observations.
There are 22 binaries chosen for our 2009 program, and the parameters of 13 binaries are determined. Their angular separations are between 0.61 ~ 8 arcsecs. The brightnesses of the primary stars fall between 1.93~5.64 mag.
Extended Emission of Short Gamma-Ray Bursts
Preliminary results of our analysis on the extended emission of short/medium
duration GRBs observed with Swift/BAT are presented. The Bayesian blocks
algorithm is used to analyze the burst durations and the temporal structure of
the lightcurves in different energy bands. We show here the results of three
bursts (GRBs 050724, 061006 and 070714B) that have a prominent soft extended
emission component in our sample. The extended emission of these bursts is a
continuous, flickering-liked component, lasting seconds post the GRB
trigger at 15-25 keV bands. Without considering this component, the three
bursts are classified as short GRBs, with seconds. GRB 060614
has an emission component similar to the extended emission, but this component
has pulse-liked structure, possibly indicating that this emission component is
different from that observed in GRBs 050724, 061006, and 070714B. Further
analysis on the spectral evolution behavior of the extended emission component
is on going.Comment: 2008 Nanjing GRB Conferenc
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