253,480 research outputs found
LS 5039 - the counterpart of the unidentified MeV source GRO J1823-12
The COMPTEL experiment on CGRO observed the gamma-ray sky at energies from
0.75 MeV to 30 MeV between April 1991 and June 2000. COMPTEL detected many
gamma-ray sources, among them an unidentified one labeled GRO J1823-12, which
is positionally consistent with the prominent high-mass X-ray binary LS 5039.
Because LS 5039 was established as gamma-ray emitter during recent years, whose
gamma-radiation radiation is modulated along its binary orbit, we reanalysed
the COMPTEL data of GRO J1823-12 including an orbital resolved analysis. We
find a significant MeV source, showing evidence for a modulated MeV flux
corresponding to the orbital period of LS 5039 of about 3.9 days. We show that
its MeV emission is stronger at the orbital part around the inferior conjuction
than at the part of the superior conjunction, being in phase with X-rays and
TeV gamma-rays, however being in anti-phase with GeV gamma-rays. We conclude
that the COMPTEL source GRO J1823-12 is the counterpart of the microquasar
candidate LS 5039, at least for the majority of its MeV emission. The COMPTEL
fluxes, put into multifrequency perspective, provide new constraints on the
modelling of the high-energy emission of LS 5039.Comment: accepted by Astronomy & Astrophysics; 11 pages, 9 figure
Spectral constraints on unidentified EGRET gamma-ray sources from COMPTEL MeV observations
We investigated the MeV properties of 173 unidentified or only tentatively
identified EGRET sources listed in the third EGRET catalogue, by analyzing the
simultaneously collected COMPTEL MeV data for each individual source. The
sources can generally be divided into 4 groups. In this paper we focus on one
of these, a group of 22 EGRET sources for which we can provide additional
constraining information: their spectral extrapolations from the energy range
above 100 MeV towards lower energies overshoot the fluxes or upper limits
derived simultaneously at MeV energies. This means that for these sources a
spectral turnover/break between 1 MeV and 100 MeV is required. At least two of
these sources, but most likely the majority of this sample, have the maxima of
their gamma-ray luminosities in this energy band. The sources have rather soft
EGRET spectra (average photon index: 2.72), and seem to spatially cluster in
the inner Galaxy. Variability analyses revealed 11 out of the 22 sources to be
significantly variable. Object classes proposed as possible counterparts for
the unidentified EGRET sources are discussed in the light of these additional
constraints.Comment: 9 pages including 4 figures; A&A accepte
Auxiliary-field quantum Monte Carlo study of first- and second-row post-d elements
A series of calculations for the first- and second-row post-d elements (Ga-Br
and In-I) are presented using the phaseless auxiliary-field quantum Monte Carlo
(AF QMC) method. This method is formulated in a Hilbert space defined by any
chosen one-particle basis, and maps the many-body problem into a linear
combination of independent-particle solutions with external auxiliary fields.
The phase/sign problem is handled approximately by the phaseless formalism
using a trial wave function, which in our calculations was chosen to be the
Hartree-Fock solution. We used the consistent correlated basis sets of Peterson
and coworkers, which employ a small core relativistic pseudopotential. The AF
QMC results are compared with experiment and with those from density-functional
(GGA and B3LYP) and coupled-cluster CCSD(T) calculations. The AF QMC total
energies agree with CCSD(T) to within a few milli-hartrees across the systems
and over several basis sets. The calculated atomic electron affinities,
ionization energies, and spectroscopic properties of dimers are, at large basis
sets, in excellent agreement with experiment.Comment: 10 pages, 2 figures. To be published in Journal of Chemical Physic
Octupole degree of freedom for the critical-point candidate nucleus Sm in a reflection-asymmetric relativistic mean-field approach
The potential energy surfaces of even-even Sm are investigated in
the constrained reflection-asymmetric relativistic mean-field approach with
parameter set PK1. It is shown that the critical-point candidate nucleus
Sm marks the shape/phase transition not only from U(5) to SU(3)
symmetry, but also from the octupole-deformed ground state in Sm to the
quadrupole-deformed ground state in Sm. By including the octupole
degree of freedom, an energy gap near the Fermi surface for single-particle
levels in Sm with is found, and the
important role of the octupole deformation driving pair and is demonstrated.Comment: 11 pages, 3 figure
The Central Engines of Gamma-Ray Bursts
Leading models for the "central engine" of long, soft gamma-ray bursts (GRBs)
are briefly reviewed with emphasis on the collapsar model. Growing evidence
supports the hypothesis that GRBs are a supernova-like phenomenon occurring in
star forming regions, differing from ordinary supernovae in that a large
fraction of their energy is concentrated in highly relativistic jets. The
possible progenitors and physics of such explosions are discussed and the
important role of the interaction of the emerging relativistic jet with the
collapsing star is emphasized. This interaction may be responsible for most of
the time structure seen in long, soft GRBs. What we have called "GRBs" may
actually be a diverse set of phenomena with a key parameter being the angle at
which the burst is observed. GRB 980425/SN 1988bw and the recently discovered
hard x-ray flashes may be examples of this diversity.Comment: 8 pages, Proc. Woods Hole GRB meeting, Nov 5 - 9 WoodsHole
Massachusetts, Ed. Roland Vanderspe
- …