8,397 research outputs found
Supernova SN 2012dn: A spectroscopic clone of SN 2006gz
We present optical and UV analysis of the luminous type Ia supernova SN
2012dn covering the period 11 to +109 days with respect to the band
maximum, that occurred on JD 2456132.89 0.19, with an apparent magnitude
of = 14.38 0.02. The absolute magnitudes at maximum in
and bands are and
, respectively. SN 2012dn is marginally
luminous compared to normal type Ia supernovae. The peak bolometric luminosity
of erg s suggests that
M of Ni was synthesized in the explosion. The
decline rate mag is lower than
that of normal type Ia supernovae, and similar to the luminous SN 1991T.
However, the photometric and spectroscopic behaviour of SN 2012dn is different
from that of SN 1991T. Early phase light curves in and bands are very
broad. The band peak has a plateau-like appearance similar to the
super-Chandra SN 2009dc. Pre-maximum spectra show clear evidence of C\,{\sc ii}
6580 \AA\, line, indicating the presence of unburned materials. The velocity
evolution of C\,{\ sc ii} line is peculiar. Except for the very early phase
(13 d), the C\,{\sc ii} line velocity is lower than the velocity
estimated using the Si\,{\sc ii} line. During the pre-maximum and close to
maximum phase, to reproduce observed shape of the spectra, the synthetic
spectrum code {\sc syn++} needs significantly higher blackbody temperature than
those required for normal type Ia events. The photospheric velocity evolution
and other spectral properties are similar to those of the carbon-rich SN
2006gz.Comment: Accepted for publication in MNRAS, 19 pages, 20 figure
ASASSN-14dq: A fast-declining type II-P Supernova in a low-luminosity host galaxy
Optical broadband (UBVRI) photometric and low-resolution spectroscopic
observations of the type II-P supernova (SN) ASASSN-14dq are presented.
ASASSN-14dq exploded in a low-luminosity/metallicity host galaxy UGC 11860, the
signatures of which are present as weak iron lines in the photospheric phase
spectra. The SN has a plateau duration of 90 d, with a plateau decline
rate of 1.38 in V-band which is higher than most type
II-P SNe. ASASSN-14dq is a luminous type II-P SN with a peak -band absolute
magnitude of -17.70.2 mag. The light curve of ASASSN-14dq indicates it
to be a fast-declining type II-P SN, making it a transitional event between the
type II-P and II-L SNe. The empirical relation between the steepness parameter
and mass for type II SNe was rebuilt with the help of
well-sampled light curves from the literature. A mass of
0.029 M was estimated for ASASSN-14dq, which is slightly
lower than the expected mass for a luminous type II-P SN. Using
analytical light curve modelling, a progenitor radius of cm, an ejecta mass of and a total
energy of ergs was estimated for this event. The
photospheric velocity evolution of ASASSN-14dq resembles a type II-P SN, but
the Balmer features (H and H) show relatively slow velocity
evolution. The high-velocity H feature in the plateau phase, the
asymmetric H emission line profile in the nebular phase and the
inferred outburst parameters indicate an interaction of the SN ejecta with the
circumstellar material (CSM).Comment: 28 pages, 29 figures, Accepted in MNRA
Optical Photometry of the GRB 010222 Afterglow
The optical afterglow of GRB 010222 was observed using the recently installed
2-m telescope at the Indian Astronomical Observatory, Hanle, and the telescopes
at the Vainu Bappu Observatory, Kavalur, beginning ~ 0.6 day after the
detection of the event. The results based on these photometric observations
combined with others reported in the literature are presented in this paper.
The R band light curve shows an initial decline of intensities proportional to
t^{-0.542} which steepens, after 10.3 hours, to t^{-1.263}. Following the model
of collimated outflow, the early break in the light curve implies a very narrow
beam angle (~ 2-3 deg). The two decay rates are consistent with the standard
jet model in a uniform density ambient medium, but require a hard spectrum of
electron power density with p ~ 1.5. The R band light between 14 and 17 hours
since outburst departs from the power law fit by 0.1 mag and shows some
evidence for fluctuations over timescales of an hour in the observer's frame.
Such deviations are expected due to density inhomogeneities if the ambient
medium is similar to the local interstellar medium. GRB 010222 is thus an
example of a highly collimated outflow with a hard spectrum of electron energy
distribution in normal interstellar environment.Comment: 15 pages, Latex, including 2 postscript figures, to appear in the
Bull. astro. Soc. India, September 2001 issu
A relativistic quark model for the Omega- electromagnetic form factors
We compute the Omega- electromagnetic form factors and the decuplet baryon
magnetic moments using a quark model application of the Covariant Spectator
Theory. Our predictions for the Omega- electromagnetic form factors can be
tested in the future by lattice QCD simulations at the physical strange quark
mass.Comment: 13 pages, 5 figure
The Progenitor of the New COMPTEL/ROSAT Supernova Remnant in Vela
We show that (1) the newly discovered supernova remnant (SNR), GRO
J0852--4642/RX J0852.0--4622, was created by a core-collapse supernova of a
massive star, and (2) the same supernova event which produced the Ti
detected by COMPTEL from this source is probably also responsible for a large
fraction of the observed Al emission in the Vela region detected by the
same instrument. The first conclusion is based on the fact that the remnant is
currently expanding too slowly given its young age for it to be caused by a
Type Ia supernova. If the current SNR shell expansion speed is greater than
3000 km/s, a Type II supernova with a moderate kinetic energy
exploding at about 150 pc away is favored. If the SNR expansion speed is lower
than 2000 km s, as derived naively from the X-ray data, a much more
energetic supernova is required to have occurred at pc away in a
dense environment at the edge of the Gum nebula. This progenitor has a
preferred ejecta mass of and therefore, it is probably a Type
Ib or Type Ic supernova. However, the required high ambient density of in this scenario is difficult to reconcile with the regional CO
data. A combination of our estimates of the age/energetics of the new SNR and
the almost perfect positional coincidence of the new SNR with the centroid of
the COMPTEL Al emission feature of the Vela region strongly favors a
causal connection. If confirmed, this will be the first case where both
Ti and Al are detected from the same young SNR and together they
can be used to select preferred theoretical core-collapse supernova models.Comment: Revised, 10 pages, 2 figures, to appear in ApJ Lett Vol.514 on April
1, 199
UV Interstellar Absorption Lines towards the Starburst Dwarf Galaxy NGC 1705
Archival Goddard High Resolution Spectrograph low-resolution spectra of NGC
1705, with wavelength ranges 1170.3 to 1461.7 A and 1453.5 to 1740.1 A and a
velocity resolution of about 100 km\s, have been used to derive the velocity
structure and equivalent widths of the absorption lines of Si II 1190.42,
1260.42, 1304.37 and 1526.71 A, S II 1253 , Al II 1670.79 Aand Fe II 1608.45 A
in this sightline. Three relatively narrow absorption components are seen at
LSR velocities --20 km/s, 260 km/sand 540 km/s. Arguments are presented to show
these absorption features are interstellar rather than stellar in origin based
on a comparison with the C III 1175.7 A absorption feature. We identify the
--20 km/s component with Milky Way disk/halo gas and the 260 km/s component
with an isolated high-velocity cloud HVC 487. This small HVC is located about
10 degrees from the H I gas which envelops the Magellanic Clouds and the
Magellanic Stream (MS). The (Si/H) ratio for this HVC is > 0.6 (Si/H)solar
which together with velocity agreement, suggests association with the
Magellanic Cloud and MS gas. H-alpha emission line kinematics of NGC 1705 show
the presence of a kpc-scale expanding supershell of ionized gas centered on the
central nucleus with a blue-shifted emission component at 540 km/s (Meurer et
al. 1992). We identify the 540 km/s absorption component seen in the GHRS
spectra with the front side of this expanding, ionized supershell. The most
striking feature of this component is strong Si II and Al II absorption but
weak Fe II 1608 A absorption. The low Fe II column density derived is most
likely intrinsic since it cannot be accounted for by ionization corrections or
dust depletion. Due to their shallow gravitational potential wells, dwarf
galaxies have small gravitational binding energies and are vulnerable to largeComment: 15 pages, LaTEX, 1 figure. Accepted for publication in Astrophysical
Journal Letter
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