1,296 research outputs found
Ultraviolet Observations of Supernovae
The motivations to make ultraviolet (UV) studies of supernovae (SNe) are
reviewed and discussed in the light of the results obtained so far by means of
IUE and HST observations. It appears that UV studies of SNe can, and do lead to
fundamental results not only for our understanding of the SN phenomenon, such
as the kinematics and the metallicity of the ejecta, but also for exciting new
findings in Cosmology, such as the tantalizing evidence for "dark energy" that
seems to pervade the Universe and to dominate its energetics. The need for
additional and more detailed UV observations is also considered and discussed.Comment: 10 pages, 5 figures - Invited talk at the "Supernova 1987A: 20 Years
after: Supernovae and Gamma-Ray Bursters" Conference, February 19-23, 2007,
Aspen, CO, (AIP Conf. Proc.), eds. S. Immler, R. McCray and K.W. Weiler, in
press. Slightly revised version that clarifies some confusing statement
Circumstellar Interaction Around Type Ib/c Supernovae and the GRB Connection
Radio observations of Type Ib/c supernovae suggest that circumstellar
interaction takes place with a wide range of wind densities, comparable to that
seen in Galactic Wolf-Rayet stars. Efficient production of magnetic field in
the shocked region is needed. The X-ray emission observed from some Type Ib/c
supernovae is higher than would be expected by the thermal or inverse Compton
mechanisms; a synchrotron interpretation requires a flattening of the electron
energy spectrum at high energies, as might occur in a cosmic ray dominated
shock wave. The wind density variations that are indicated in two supernovae
may be due to a binary companion, although variable mass loss from a single
star remains a possibility. Other than the optical supernova radiation, the
emission from the nearby SN 2006aj/GRB 060218 appears to be powered by a
central engine, while that from SN 1998bw/GRB 980425 could be powered by either
a central engine or the outer supernova ejecta.Comment: 8 pages, to appear in Circumstellar Media and Late Stages of Massive
Stellar Evolution, RevMexA
SN Shock Evolution in the Circumstellar Medium surrounding SN 1987A
We study the structure of the circumstellar medium surrounding SN 1987A in
the equatorial plane. Furthermore, we study the evolution of the SN shock
within this medium during the first 25 years, and the resulting hard X-ray and
radio emission from the remnant.Comment: 5 pages, 3 Figures. To be published in the proceedings of the
conference on "Supernova 1987A: 20 Years After: Supernovae and Gamma-Ray
Bursters" AIP, New York, eds. S. Immler, K.W. Weiler, and R. McCra
The Radio Properties of Type Ibc Supernovae
Over the past few years, long-duration gamma-ray bursts (GRBs), including the
subclass of X-ray flashes (XRFs), have been revealed to be a rare variety of
Type Ibc supernova (SN Ibc). While all these events result from the death of
massive stars, the electromagnetic luminosities of GRBs and XRFs exceed those
of ordinary Type Ibc SNe by many orders of magnitude. The observed diversity of
stellar death corresponds to large variations in the energy, velocity, and
geometry of the explosion ejecta. Using multi-wavelength (radio, optical,
X-ray) observations of the nearest GRBs, XRFs, and SNe Ibc, I show that while
GRBs and XRFs couple at least 10^48 erg to relativistic material, SNe Ibc
typically couple less than 10^48 erg to their fastest (albeit non-relativistic)
outflows. Specifically, I find that less than 3% of local SNe Ibc show any
evidence for association with a GRB or XRF. Recently, a new class of GRBs and
XRFs has been revealed which are under-luminous in comparison with the
statistical sample of GRBs. Owing to their faint high-energy emission, these
sub-energetic bursts are only detectable nearby (z < 0.1) and are likely 10
times more common than cosmological GRBs. In comparison with local SNe Ibc and
typical GRBs/XRFs, these explosions are intermediate in terms of both
volumetric rate and energetics. Yet the essential physical process that causes
a dying star to produce a GRB, XRF, or sub-energetic burst, and not just a SN,
remains a crucial open question. Progress requires a detailed understanding of
ordinary SNe Ibc which will be facilitated with the launch of wide-field
optical surveys in the near future.Comment: 8 pages, Proceedings for "Supernova 1987A: 20 Years After: Supernovae
and Gamma-Ray Bursters" AIP, New York, eds. S. Immler, K.W. Weiler, and R.
McCra
Hypercharged Naturalness
We present an exceptional twin-Higgs model with the minimal symmetry
structure for an exact implementation of twin parity along with custodial
symmetry. Twin particles are mirrors of the Standard Model yet they carry
hypercharge, while the photon is identified with its twin. We thoroughly
explore the phenomenological signatures of hypercharged naturalness: long-lived
charged particles, a colorless twin top with electric charge that once
pair-produced, bounds via twin-color interactions and can annihilate to
dileptons or a Higgs plus a photon or a , and glueballs produced from Higgs
decays and twin-quarkonium annihilation that either decay displaced, or are
stable on collider scales and eventually decay to diphotons. Prospects for
detection of these signatures are also discussed.Comment: 37 pages, 7 figure
High Resolution Spectroscopy of SN1987A's Rings: He I 10830 and H-alpha from the Hotspots
We present the first high-dispersion spectroscopy of He I 10830 from the
hotspots in the ring around SN1987A, obtained at Gemini South, spatially
resolving the near and far sides of the ring. We compare these line profiles to
similar echelle spectra of H and [N II] 6583 obtained at the Magellan
Observatory. We find that the He I profiles are much broader than H-alpha or [N
II], but the He I profiles also have different shapes -- they have enhanced
emission at high speeds, with extra blueshifted emission on the north side of
the ring, and extra redshifted emission on the south side. To explain this, we
invoke a simple geometric picture where the extra He I emission traces hotter
gas from faster shocks that strike the apex of the hotspots directly, while the
H-alpha preferentially traces cooler lower-ionization gas from slower
transverse shocks that penetrate into the sides of the ring.Comment: 3 pages. To appear in proceedings: "Supernova 1987A: 20 Years After:
Supernovae and Gamma-Ray Bursters" AIP, New York, eds. S. Immler, K.W.
Weiler, and R. McCra
Dust-Gas Interaction in SNR 1987A
Multiwavelength observations of SNR 1987A show that its morphology is rapidly
changing at X-ray, radio, and optical wavelengths as the blast wave from the
explosion expands into the circumstellar equatorial ring. Infrared emission
arises from the interaction of dust grains with the hot X-ray emitting gas. We
show that the IR emission provides important complementary information on the
interaction of the SN blast wave with the circumstellar equatorial ring that
cannot be obtained at any other wavelength.Comment: 8 pages, 4 figures; review talk to appear in the AIP Proceedings of
the Conference " Supernova 1987A: 20 Years after - Supernovae and Gamma-Ray
Bursters" held in Aspen Co USA, Feb 19-23, 200
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