1,145 research outputs found
ISO/SWS observations of SN 1987A: II. A refined upper limit on the mass of Ti-44 in the ejecta of SN 1987A
ISO/SWS observations of SN 1987A on day 3425 show no emission in [Fe I] 24.05
microns and [Fe II] 25.99 microns down to the limits of roughly 0.39 Jy and
0.64 Jy, respectively. Assuming a homogeneous distribution of Ti-44 inside 2000
km/s and negligible dust cooling, we have made time dependent theoretical
models to estimate an upper limit on the mass of ejected Ti-44. Assessing
various uncertainties of the model, and checking the late optical emission it
predicts, we obtain an upper limit of 1.1EE-4 solar masses. This is lower than
in our previous estimate using other ISO data, and we compare our new result
with other models for the late emission, as well as with expected yields from
explosion models. We also show that steady-state models for the optical
emission are likely to overestimate the mass of ejected Ti-44. The low limit we
find for the mass of ejected Ti-44 could be higher if dust cooling is
important. A direct check on this is provided by the gamma-ray emission at
1.157 Mev as a result of the radioactive decay of Ti-44.Comment: 9 pages including 3 postscript figures (AA Latex vers. 5.01) Accepted
for publication in Astronomy and Astrophysic
Supernova 1998bw - The final phases
The probable association with GRB 980425 immediately put SN 1998bw at the
forefront of supernova research. Here, we present revised late-time BVRI light
curves of the supernova, based on template images taken at the VLT. To follow
the supernova to the very last observable phases we have used HST/STIS. Deep
images taken in June and November 2000 are compared to images taken in August
2001. The identification of the supernova is firmly established. This allows us
to measure the light curve to about 1000 days past explosion. The main features
are a rapid decline up to more than 500 days after explosion, with no sign of
complete positron trapping from the Cobolt-56 decay. Thereafter, the light
curve flattens out significantly. One possible explanation is powering by more
long lived radioactive isotopes, if they are abundantly formed in this
energetic supernova.Comment: 13 pages, 5 figures, A&A, In pres
Resonant Neutrino Spin-Flavor Precession and Supernova Nucleosynthesis and Dynamics
We discuss the effects of resonant spin-flavor precession (RSFP) of Majorana
neutrinos on heavy element nucleosynthesis in neutrino-heated supernova ejecta
and the dynamics of supernovae. In assessing the effects of RSFP, we explicitly
include matter-enhanced (MSW) resonant neutrino flavor conversion effects where
appropriate. We point out that for plausible ranges of neutrino magnetic
moments and proto-neutron star magnetic fields, spin-flavor conversion of
(or ) with a cosmologically significant mass (1--100 eV)
into a light could lead to an enhanced neutron excess in
neutrino-heated supernova ejecta. This could be beneficial for models of
-process nucleosynthesis associated with late-time neutrino-heated ejecta
from supernovae. Similar spin-flavor conversion of neutrinos at earlier epochs
could lead to an increased shock reheating rate and, concomitantly, a larger
supernova explosion energy. We show, however, that such increased neutrino
heating likely will be accompanied by an enhanced neutron excess which could
exacerbate the problem of the overproduction of the neutron number
nuclei in the supernova ejecta from this stage. In all of these scenarios, the
average energy will be increased over those predicted by supernova
models with no neutrino mixings. This may allow the SN1987a data to constrain
RSFP-based schemes.Comment: Latex file, 33 pages including 11 figures, uses psfig.sty, minor
changes about wording and clarification of the text, to be published in Phys.
Rev.
The supernova remnant CTB 37B and its associated magnetar CXOU J171405.7-381031: evidence for a magnetar-driven remnant
We discuss in this Letter the association of the candidate magnetar CXOU
J171405.7-381031 with the supernova remnant CTB 37B. The recent detection of
the period derivative of the object allowed an estimation of a young
characteristic age of only . This value is too small to be
compatible even with the minimum radius of the remnant , the value
corresponding to the {\it lower} limit of the estimated distance of , unless the true distance happens to be even smaller than the lower
limit. We argue that a consistent scenario for the remnant origin, in which the
latter is powered by the energy injected by a young magnetar, is indeed more
accurate to explain the young age, and points out to its non-standard (i.e.
magnetar-driven) nature.Comment: 6 pp., 1 figure, to appear in RAA Letter
Predicted gamma-ray line emission from the Cygnus complex
The Cygnus region harbours a huge complex of massive stars at a distance of
1.0-2.0kpc from us. About 170 O stars are distributed over several OB
associations, among which the Cyg OB2 cluster is by far the most important with
about 100-120 O stars. These massive stars inject large quantities of
radioactive nuclei into the interstellar medium, such as 26Al and 60Fe, and
their gamma-ray line decay signals can provide insight into the physics of
massive stars and core-collapse supernovae. Past studies of the nucleosynthesis
activity of Cygnus have concluded that the level of 26Al decay emission as
deduced from CGRO/COMPTEL observations was a factor 2-3 above the predictions
based on the theoretical yields available at that time and on the observed
stellar content of the Cygnus region. We reevaluate the situation from new
measurements of the gamma-ray decay fluxes with INTEGRAL/SPI and new
predictions based on recently improved stellar models including some of the
effects of stellar rotation for the higher mass stars and a coherent estimate
of the contribution from SNIb/c. We developed a population synthesis code to
predict the nucleosynthesis activity and corresponding decay fluxes of a given
stellar population of massive stars. The observed decay fluxes from the Cygnus
complex are found to be consistent with the values predicted by population
synthesis at solar metallicity. The observed extent of the 1809keV emission
from Cygnus is found to be consistent with the result of a numerical simulation
of the diffusion of 26Al inside the superbubble blown by Cyg OB2. Our work
indicates that the past dilemma regarding the gamma-ray line emission from
Cygnus resulted from an overestimate of the 1809keV flux of the Cygnus complex,
combined with an underestimate of the nucleosynthesis yields.Comment: 13 pages, 9 figures, accepted for publication in A&
Neutrino-induced neutron spallation and supernova r-process nucleosynthesis
In order to explore the consequences of the neutrino irradiation for the
supernova r-process nucleosynthesis, we calculate the rates of charged-current
and neutral-current neutrino reactions on neutron-rich heavy nuclei, and
estimate the average number of neutrons emitted in the resulting spallation.
Our results suggest that charged-current captures can be important in
breaking through the waiting-point nuclei at N=50 and 82, while still allowing
the formation of abundance peaks. Furthermore, after the r-process freezes out,
there appear to be distinctive neutral-current and charged-current
postprocessing effects. A subtraction of the neutrino postprocessing effects
from the observed solar r-process abundance distribution shows that two mass
regions, A=124-126 and 183-187, are inordinately sensitive to neutrino
postprocessing effects. This imposes very stringent bounds on the freeze-out
radii and dynamic timescales governing the r-process. Moreover, we find that
the abundance patterns within these mass windows are entirely consistent with
synthesis by neutrino interactions. This provides a strong argument that the
r-process must occur in the intense neutrino flux provided by a core-collapse
supernova.Comment: 34 pages, 4 PostScript figures, RevTe
Helium Star/Black Hole Mergers: a New Gamma-Ray Burst Model
We present a model for gamma-ray bursts (GRB's) in which a stellar mass black
hole acquires a massive accretion disk by merging with the helium core of its
red giant companion. The black hole enters the helium core after it, or its
neutron star progenitor, first experiences a common envelope phase that carries
it inwards through the hydrogen envelope. Accretion of the last several solar
masses of helium occurs on a time scale of roughly a minute and provides a
neutrino luminosity of approximately 10^51 - 10^52 erg/s. Neutrino
annihilation, 0.01% to 0.1% efficient, along the rotational axis then gives a
baryon loaded fireball of electron-positron pairs and radiation (about
10 erg total) whose beaming and relativistic interaction with
circumstellar material makes the GRB (e.g., Rees & Meszaros 1992). The useful
energy can be greatly increased if energy can be extracted from the rotational
energy of the black hole by magnetic interaction with the disk. Such events
should occur at a rate comparable to that of merging neutron stars and black
hole neutron star pairs and may be responsible for long complex GRB's, but not
short hard ones.Comment: 11 pages total, 2 Figures - altered and revised for ApJ letters,
accepte
Bare Quark Matter Surfaces of Strange Stars and Emission
We show that the Coulomb barrier at the quark surface of a hot strange star
may be a powerful source of pairs which are created in an extremely
strong electric field of the barrier and flow away from the star. The
luminosity in the outflowing pair plasma depends on the surface temperature
and may be very high, up to at
K. The effect of pair creation by the Coulomb barrier may
be a good observational signature of strange stars which can give an answer to
the question of whether a compact object is a neutron or strange star.Comment: 5 pages, 1 figure, LATEX, accepted for publication in the Physical
Review Letter
Chandra Observations of the X-ray Environs of SN 1998bw/GRB 980425
(Abrigded) We report X-ray studies of the environs of SN 1998bw and GRB
980425 using the Chandra X-Ray Observatory 1281 days after the GRB. Combining
our observation of the supernova with others of the GRB afterglow, a smooth
X-ray light curve, spanning ~1300 days, is obtained by assuming the burst and
supernova were coincident at 35.6 Mpc. When this X-ray light curve is compared
with those of the X-ray ``afterglows'' of ordinary GRBs, X-ray Flashes, and
ordinary supernovae, evidence emerges for at least two classes of lightcurves,
perhaps bounding a continuum. By three to ten years, all these phenomena seem
to converge on a common X-ray luminosity, possibly indicative of the supernova
underlying them all. This convergence strengthens the conclusion that SN 1998bw
and GRB 980425 took place in the same object. One possible explanation for the
two classes is a (nearly) standard GRB observed at different angles, in which
case X-ray afterglows with intermediate luminosities should eventually be
discovered. Finally, we comment on the contribution of GRB afterglows to the
ULX source population.Comment: 26 pages, 5 figues, submitted to Ap
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