14,276 research outputs found
X-ray and radio prompt emission from a hypernova SN 2002ap
Here we report on combined X-ray and radio observations of SN 2002ap with
XMM-Newton ToO observation and GMRT observations aided with VLA published
results. In deriving the X-ray flux of SN 2002ap we account for the
contribution of a nearby source, found to be present in the pre-SN explosion
images obtained with Chandra observatory. We also derive upper limits on mass
loss rate from X-ray and radio data. We suggest that the prompt X-ray emission
is non-thermal in nature and its is due to the repeated compton boosting of
optical photons. We also compare SN's early radiospheric properties with two
other SNe at the same epoch.Comment: 4 pages, 5 figures. Uses espcrc2.sty. To appear in proceedings of
symposium on X-ray astronomy "The Restless High-Energy Universe", May 2003,
Amsterdam, The Netherlands, eds. E.P.J. van den Heuvel, J.J.M. in 't Zand,
and R.A.M.J. Wijer
Hidden Order in
We review current attempts to characterize the underlying nature of the
hidden order in . A wide variety of experiments point to the
existence of two order parameters: a large primary order parameter of unknown
character which co-exists with secondary antiferromagnetic order. Current
theories can be divided into two groups determined by whether or not the
primary order parameter breaks time-reversal symmetry. We propose a series of
experiments designed to test the time-reversal nature of the underlying primary
order in and to characterize its local single-ion physics
Velocity vectors of a quiescent prominence observed by Hinode/SOT and the MSDP (Meudon)
The dynamics of prominence fine structures is a challenge to understand the
formation of cool plasma prominence embedded in the hot corona. Recent
observations from the high resolution Hinode/SOT telescope allow us to compute
velocities perpendicularly to the line-of-sight or transverse velocities.
Combining simultaneous observations obtained in H-alpha with Hinode/SOT and the
MSDP spectrograph operating in the Meudon solar tower we derive the velocity
vectors of a quiescent prominence. The velocities perpendicular to the
line-of-sight are measured by time slice technique, the Dopplershifts by the
bisector method. The Dopplershifts of bright threads derived from the MSDP
reach 15 km/s at the edges of the prominence and are between +/- 5 km/s in the
center of the prominence. Even though they are minimum values due to seeing
effect, they are of the same order as the transverse velocities. These
measurements are very important because they suggest that the
verticalstructures shown in SOT may not be real vertical magnetic structures in
the sky plane. The vertical structures could be a pile up of dips in more or
less horizontal magnetic field lines in a 3D perspective, as it was proposed by
many MHD modelers. In our analysis we also calibrate the Hinode H-alpha data
using MSDP observations obtained simultaneously.Comment: 7 pages, 7 figures, submitted to A &
Biodiesel: Freedom from Dependence on Fossil Fuels?
In view of the depleting oil reserves and exponential rise in petroleum prices, the search for alternative sources of fuel is very timely and important. The present paper addresses the underlying issues in biodiesel production from biomaterials and sustainable production and supply of first-generation biofuels, especially the one from jatropha. The agencies and research institutions involved in the production of biofuels and the national and international efforts made in this regard are discussed here. There is also a dire need of a step towards large-scale production and supply of second-generation biofuels, although in infant stage, to strengthen the world economy in general and Indian economy in particular. However, the production of biofuels are likely to have serious socio-economic implications especially to the lesser developed societies. This needs serious attention from policy makers and public at large
Multi-frequency scatter broadening evolution of pulsars - I
We present multi-wavelength scatter broadening observations of 47 pulsars,
made with the Giant Metre-wave Radio Telescope (GMRT), Ooty Radio Telescope
(ORT) and Long Wavelength Array (LWA). The GMRT observations have been made in
the phased array mode at 148, 234, and 610 MHz and the ORT observations at 327
MHz. The LWA data sets have been obtained from the LWA pulsar data archive. The
broadening of each pulsar as a function of observing frequency provides the
frequency scaling index, . The estimations of have been
obtained for 39 pulsars, which include entirely new estimates for 31 pulsars.
This study increases the total sample of pulsars available with
estimates by 50\%. The overall distribution of with the
dispersion measure (DM) of pulsar shows interesting variations, which are
consistent with the earlier studies. However, for a given value of DM a range
of values are observed, indicating the characteristic turbulence along
each line of sight. For each pulsar, the estimated level of turbulence,
, has also been compared with and DM. Additionally, we
compare the distribution of with the theoretically predicated model to
infer the general characteristics of the ionized interstellar medium (ISM).
Nearly 65\% of the pulsars show a flatter index (i.e., ) than
that is expected from the Kolmogorov turbulence model. Moreover, the group of
pulsars having flatter index is typically associated with an enhanced value of
than those with steeper index.Comment: 13 pages, 4 figures, 3 tables. Accepted for publication in Ap
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