1,899 research outputs found
Gravitational Waves of Jet Precession in Gamma-ray Bursts
The physical nature of gamma-ray bursts (GRBs) are believed to involve an
ultra-relativistic jet. The observed complex structure of light curves motivate
the idea of jet precession. In this work, we study the gravitational waves of
jet precession based on neutrino-dominated accretion disks around black holes,
which may account for the central engine of GRBs. In our model, the jet and the
inner part of the disk may precess along with the black hole, which is driven
by the outer part of the disk. Gravitational waves are therefore expected to be
significant from this black hole-inner disk precession system. By comparing our
numerical results with the sensitivity of some detectors, we find that it is
possible for DECIGO and BBO to detect such gravitational waves, particularly
for GRBs in the Local Group.Comment: 19 pages, 6 figures, accepted for publication in Ap
Understanding Simulations of Thin Accretion Disks by Energy Equation
We study the fluctuations of standard thin accretion disks by linear analysis
of the time-dependent energy equation together with the vertical hydrostatic
equilibrium and the equation of state. We show that some of the simulation
results in Hirose et al. (2009b), such as the time delay, the relationship of
power spectra, and the correlation between magnetic energy and radiation
energy, can be well understood by our analytic results.Comment: 13 pages, 3 figure, accepted for publication in Ap
The influence of outflows on the 1/f-like luminosity fluctuations
In accretion systems, outflows may have significant influence on the
luminosity fluctuations. In this paper, following the Lyubarskii's general
scheme, we revisit the power spectral density of luminosity fluctuations by
taking into account the role of outflows. Our analysis is based on the
assumption that the coupling between the local outflow and inflow is weak on
the accretion rate fluctuations. We find that, for the inflow mass accretion
rate , the power spectrum of flicker noise component will
present a power-law distribution for
advection-dominated flows. We also obtain descriptions of for both
standard thin discs and neutrino-cooled discs, which show that the power-law
index of a neutrino-cooled disc is generally larger than that of a
photon-cooled disc. Furthermore, the obtained relationship between and
indicates the possibility of evaluating the strength of outflows by the
power spectrum in X-ray binaries and gamma-ray bursts. In addition, we discuss
the possible influence of the outflow-inflow coupling on our results.Comment: 6 pages, 1 figure, accepted for publication in MNRA
Neutrino-cooled accretion disks as the central engine of gamma-ray bursts
Neutrino-cooled hyperaccretion disks around stellar mass black holes are plausible candidates for the central engine of gamma-ray bursts. We calculate the one-dimensional structure and the annihilation luminosity of such disks. The resulting neutrino annihilation luminosity is still likely to be adequate for gamma-ray bursts, and it is ejected mainly from the inner region of the disk and has an anisotropic distribution
The LAMOST Complete Spectroscopic Survey of Pointing Area (LaCoSSPAr) in the Southern Galactic Cap I. The Spectroscopic Redshift Catalog
We present a spectroscopic redshift catalog from the LAMOST Complete
Spectroscopic Survey of Pointing Area (LaCoSSPAr) in the Southern Galactic Cap
(SGC), which is designed to observe all sources (Galactic and extra-galactic)
by using repeating observations with a limiting magnitude of in
two fields. The project is mainly focusing on the completeness of
LAMOST ExtraGAlactic Surveys (LEGAS) in the SGC, the deficiencies of source
selection methods and the basic performance parameters of LAMOST telescope. In
both fields, more than 95% of galaxies have been observed. A post-processing
has been applied to LAMOST 1D spectrum to remove the majority of remaining sky
background residuals. More than 10,000 spectra have been visually inspected to
measure the redshift by using combinations of different emission/absorption
features with uncertainty of . In total, there are 1528
redshifts (623 absorption and 905 emission line galaxies) in Field A and 1570
redshifts (569 absorption and 1001 emission line galaxies) in Field B have been
measured. The results show that it is possible to derive redshift from low SNR
galaxies with our post-processing and visual inspection. Our analysis also
indicates that up to 1/4 of the input targets for a typical extra-galactic
spectroscopic survey might be unreliable. The multi-wavelength data analysis
shows that the majority of mid-infrared-detected absorption (91.3%) and
emission line galaxies (93.3%) can be well separated by an empirical criterion
of . Meanwhile, a fainter sequence paralleled to the main population
of galaxies has been witnessed both in / and /
diagrams, which could be the population of luminous dwarf galaxies but
contaminated by the edge-on/highly inclined galaxies ().Comment: 19 pages, 14 figures, 2 MRT, accepted by ApJ
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