4,308 research outputs found
Supernova 1996cr: SN 1987A's Wild Cousin?
We report on new VLT optical spectroscopic and multi-wavelength archival
observations of SN1996cr, a previously identified ULX known as Circinus Galaxy
X-2. Our optical spectrum confirms SN1996cr as a bona fide type IIn SN, while
archival imaging isolates its explosion date to between 1995-02-28 and
1996-03-16. SN1996cr is one of the closest SNe (~3.8 Mpc) in the last several
decades and in terms of flux ranks among the brightest radio and X-ray SNe ever
detected. The wealth of optical, X-ray, and radio observations that exist for
this source provide relatively detailed constraints on its post-explosion
expansion and progenitor history, including an preliminary angular size
constaint from VLBI. The archival X-ray and radio data imply that the
progenitor of SN1996cr evacuated a large cavity just prior to exploding: the
blast wave likely expanded for ~1-2 yrs before eventually striking the dense
circumstellar material which surrounds SN1996cr. The X-ray and radio emission,
which trace the progenitor mass-loss rate, have respectively risen by a factor
of ~2 and remained roughly constant over the past 7 yr. This behavior is
reminiscent of the late rise of SN1987A, but 1000 times more luminous and much
more rapid to onset. Complex Oxygen line emission in the optical spectrum
further hints at a possible concentric shell or ring-like structure. The
discovery of SN1996cr suggests that a substantial fraction of the closest SNe
observed in the last several decades have occurred in wind-blown bubbles. An
Interplanetary Network position allows us to reject a tentative GRB association
with BATSE 4B960202. [Abridged]Comment: 25 pages with tables, 12 figures (color), accepted to ApJ, comments
welcome; v2 - updated to reflect the subsequent rejection of our tentative
GRB association based on a revised error region from the Interplanetary
Network (thanks to Kevin Hurley) and include a few additional references; v3
- corrected some errors in Tables 7 and
The Evolution of Supernovae in Circumstellar Wind Bubbles II: Case of a Wolf-Rayet star
(Abridged) Mass-loss from massive stars leads to the formation of
circumstellar wind-blown bubbles surrounding the star, bordered by a dense
shell. When the star ends its life in a supernova (SN) explosion, the resulting
shock wave will interact with this modified medium. In a previous paper we
discussed the basic parameters of this interaction. In this paper we go a step
further and study the evolution of SNe in the wind blown bubble formed by a 35
\msun star that starts off as an O star, goes through a red supergiant phase,
and ends its life as a Wolf-Rayet star. We model the evolution of the CSM and
then the expansion of the SN shock wave within this medium. Our simulations
clearly reveal fluctuations in density and pressure within the surrounding
medium. The SN shock interacting with these fluctuations, and then with the
dense shell surrounding the wind-blown cavity, gives rise to a variety of
transmitted and reflected shocks in the wind bubble. The interactions between
these various shocks and discontinuities is examined, and its effects on the
X-ray emission is noted. Our simulations reveal the presence of several
hydrodynamic instabilities. They show that the turbulent interior, coupled with
the large fluctuations in density and pressure, gives rise to an extremely
corrugated SN shock wave. The shock shows considerable wrinkles as it impacts
the dense shell, and the impact occurs in a piecemeal fashion, with some parts
of the shock wave interacting with the shell before the others. Therefore
different parts of the shell will `light-up' at different times. The
non-spherical nature of the interaction means that it will occur over a
prolonged period of time, and the spherical symmetry of the initial shock wave
is destroyed.Comment: 50 pages, 19 figures. Accepted to the Astrophysical Journal. For a
version with the original high-resolution color figures please download from
http://astro.uchicago.edu/~vikram/sncsm.htm
Neutron irradiation defects in gallium sulfide : Optical absorption measurements
Gallium sulfide single crystals have been irradiated with different thermal neutron doses. Defects introduced by neutron irradiation turn out to be optically active, giving rise to absorption bands with energies ranging from 1.2 to 3.2 eV. Bands lying in the band-gap exhibit Gaussian shape. Their energies and widths are independent of the irradiation dose, but their intensities are proportional to it. Thermal annealing is completed in two stages, ending at around 500 and 720 K, respectively. Centers responsible for the absorption bands are proposed to be gallium-vacancy-galliuminterstitial complexes in which the distance between the vacancy (acceptor) and the interstitial (donor) determines the energy and intensity of the absorption band, as well as the annealing [email protected]
Young core collapse supernova remnants and their supernovae
Massive star supernovae can be divided into four categories depending on the
amount of mass loss from the progenitor star and the star's radius: red
supergiant stars with most of the H envelope intact (SN IIP), stars with some H
but most lost (IIL, IIb), stars with all H lost (Ib, Ic), and blue supergiant
stars with a massive H envelope (SN 1987A-like). Various aspects of the
immediate aftermath of the supernova are expected to develop in different ways
depending on the supernova category: mixing in the supernova, fallback on the
central compact object, expansion of any pulsar wind nebula, interaction with
circumstellar matter, and photoionization by shock breakout radiation. The
observed properties of young supernova remnants allow many of them to be placed
in one of the supernova categories; all the categories are represented except
for the SN 1987A-like type. Of the remnants with central pulsars, the pulsar
properties do not appear to be related to the supernova category. There is no
evidence that the supernova categories form a mass sequence, as would be
expected in a single star scenario for the evolution. Models for young pulsar
wind nebulae expanding into supernova ejecta indicate initial pulsar periods of
10-100 ms and approximate equipartition between particle and magnetic energies.
Ages are obtained for pulsar nebulae, including an age of 2400 pm 500 yr for
3C58, which is not consistent with an origin in SN 1181. There is no evidence
that mass fallback plays a role in neutron star properties.Comment: 43 pages, ApJ, revised, discussion of 3C58 changed, in press for Feb.
1, 200
Light-induced transmission nonlinearities in gallium selenide
The intensity of a He–Ne laser (633 nm, 5 mW) transmitted by different GaSe samples is observed to change in correlation with a Nd-yttrium–aluminum–garnet laser pulse (532 nm, 7.8 ns, 3 mJ) which excites them. Such time response has been attributed to a nonlinear optical effect, i.e., a decrease in the refractive index due to the exciton screening by the photogenerated carriers. A calculation of the absorption coefficient and refractive index at different carrier concentrations has led to a reconstruction of transmittance transients which fully agree with the experimental data at different incident intensities and [email protected] ; [email protected] ; [email protected] ; [email protected]
Late Emission from the Type Ib/c SN 2001em: Overtaking the Hydrogen Envelope
The Type Ib/c supernova SN 2001em was observed to have strong radio, X-ray,
and Halpha emission at an age of about 2.5 yr. Although the radio and X-ray
emission have been attributed to an off-axis gamma-ray burst, we model the
emission as the interaction of normal SN Ib/c ejecta with a dense, massive (3
Msun) circumstellar shell at a distance about 7 x 10^{16} cm. We investigate
two models, in which the circumstellar shell has or has not been overtaken by
the forward shock at the time of the X-ray observation. The circumstellar shell
was presumably formed by vigorous mass loss with a rate (2-10) x 10^{-3}
Msun/yr at 1000-2000 yr prior to the supernova explosion. The hydrogen envelope
was completely lost, and subsequently was swept up and accelerated by the fast
wind of the presupernova star up to a velocity of 30-50 km/s. Although
interaction with the shell can explain most of the late emission properties of
SN 2001em, we need to invoke clumping of the gas to explain the low absorption
at X-ray and radio wavelengths.Comment: 26 pages, 4 figures, ApJ submitte
Copper deposition on fabrics by rf plasma sputtering for medical applications
https://www.scopus.com/inward/record.url?eid=2-s2.0-84938151607&partnerID=40&md5=bf2da795caced442546f442aa330773aThe present work is about preparation and characterization of RF sputtered Cu films on cotton by the usage of a Magnetron Sputter Source and 99.995% purity Cu target at room temperature. Cotton fabric samples of 1, 2 and 4 min of sputtering time at discharge pressure of 1×10-2 Torr and distance between target and sample of 8 cm were used. The main goal was to qualitatively test the antimicrobial action of copper on fabrics. For that purpose, a reference strain of Escherichia Coli ATCC 35218 that were grown in TSA plates was implemented. Results indicated a decrease in the growth of bacteria by contact with Cu; for fabric samples with longer sputtering presented lower development of E. coli colonies. The scope of this research focused on using these new textiles in health field, for example socks can be made with this textile for the treatment of athlete's foot and the use in pajamas, sheets, pillow covers and robes in hospital setting for reducing the spread of microorganisms. © Published under licence by IOP Publishing Ltd.Ad Astra Rocket Company,Instituto Tecnologico de Costa Rica,International Atomic Energy Agency (IAEA),Universidad Nacional de Costa Ric
The application of the photoacoustic transmittance oscillations for determining elastic constants in gallium and indium selenides
Transmittance periodic oscillations are observed in GaSe and InSe on excitation with optical pulses. Such oscillations are explained in terms of photoacoustic generation of dilatational waves, which become resonant within the crystal. Spectral analysis of those oscillations in samples of different thickness has led to an accurate determination of the longitudinal acoustic‐wave velocity along the crystallographic axis [email protected] ; [email protected] ; [email protected]
A Search for Core-Collapse Supernova Progenitors In Hubble Space Telescope Images
Identifying the massive progenitor stars that give rise to core-collapse
supernovae (SNe) is one of the main pursuits of supernova and stellar evolution
studies. Using ground-based images of recent, nearby SNe obtained primarily
with KAIT, astrometry from 2MASS, and archival images from HST, we have
attempted the direct identification of the progenitors of 16 SNe II and SNe
Ib/c. We may have identified the progenitors of the SNe II 1999br, 1999ev, and
2001du as supergiant stars with M^0_V ~ -6 mag in all three cases. We may have
also identified the progenitors of the SNe Ib 2001B and 2001is as very luminous
supergiants with M^0_V ~ -8 to -9 mag, and possibly the progenitor of the SN Ic
1999bu as a supergiant with M^0_V ~ -7.5 mag. Additionally, we have recovered
at late times SNe 1999dn, 2000C, and 2000ew, although none of these had
detectable progenitors on pre-SN images. In fact, for the remaining SNe only
limits can be placed on the absolute magnitude and color (when available) of
the progenitor. The detected SN II progenitors and limits are consistent with
red supergiants as progenitor stars, although possibly not as red as we had
expected. Our results for the SNe Ib/c do not strongly constrain either
Wolf-Rayet stars or massive interacting binary systems as progenitors.Comment: 19 pages, 23 figures, to appear in PASP (2003 Jan
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