4,576 research outputs found
Detectable MeV neutrinos from black hole neutrino-dominated accretion flows
Neutrino-dominated accretion flows (NDAFs) around rotating stellar-mass black
holes (BHs) have been theorized as the central engine of relativistic jets
launched in massive star core collapse events or compact star mergers. In this
work, we calculate the electron neutrino/anti-neutrino spectra of NDAFs by
fully taking into account the general relativistic effects, and investigate the
effects of viewing angle, BH spin, and mass accretion rate on the results. We
show that even though a typical NDAF has a neutrino luminosity lower than that
of a typical supernova (SN), it can reach
peaking at MeV, making them potentially detectable with the upcoming
sensitive MeV neutrino detectors if they are close enough to Earth. Based on
the observed GRB event rate in the local universe and requiring that at least 3
neutrinos are detected to claim a detection, we estimate a detection rate up to
(0.10-0.25) per century for GRB-related NDAFs by the Hyper-Kamiokande
(Hyper-K) detector if one neglects neutrino oscillation. If one assumes that
all Type Ib/c SNe have an engine-driven NDAF, the Hyper-K detection rate would
be (1-3) per century. By considering neutrino oscillations, the
detection rate may decrease by a factor of 2-3. Detecting one such event would
establish the observational evidence of NDAFs in the universe.Comment: 7 pages, 2 figures, 2 tables, accepted for publication in PR
An open reading frame upstream from the nifH gene of Klebsiella pneumoniae
An open reading frame upstream from nifHDK operon of Klebsiella pneumoniae had been described. The orientation of this open reading frame is opposite to that of nifHDK and sequence homology was found between the open reading frame promoter and the promoter of nifHDK operon. A recombinant plasmid carrying the promoter region of the open reading frame fused to the beta-galactosidase gene was constructed. Strains of E.coli were transformed with the plasmid containing this open reading frame promoter-lacZ fusion or co-transformed with it and a plasmid carrying the nifA gene. An appreciable activity of beta-galactosidase was found in strains which received both plasmids, indicating that the promoter of the open reading frame can be activated by the product of nifA gene. Thus, the open reading frame found between nifHDK operon and nifJ behaves just like other nif genes of K.pneumoniae in requiring the product of nifA as the positive effector for expression
The vertical composition of neutrino-dominated accretion disks in gamma-ray bursts
We investigate the vertical structure and elements distribution of
neutrino-dominated accretion flows around black holes in spherical coordinates
with the reasonable nuclear statistical equilibrium. According our
calculations, heavy nuclei tend to be produced in a thin region near the disk
surface, whose mass fractions are primarily determined by the accretion rate
and the vertical distribution of temperature and density. In this thin region,
we find that is dominant for the flow with low accretion rate
(e.g., ) but is dominant for the
high counterpart (e.g., ). The dominant
in the special region may provide a clue to understand the bumps in the optical
light curve of core-collapse supernovae.Comment: 15 pages, 2 figures, accepted for publication in Ap
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