2,062 research outputs found
Coronal Mass Ejections - Propagation Time and Associated Internal Energy
In this paper, we analyze 91 coronal mass ejection (CME) events studied by
Manoharan et al. (2004) and Gopalswamy and Xie (2008). These earth-directed
CMEs are large (width 160) and cover a wide range of speeds
(120--2400 {\kmps}) in the LASCO field of view. This set of events also
includes interacting CMEs and some of them take longer time to reach 1 AU than
the travel time inferred from their speeds at 1 AU. We study the link between
the travel time of the CME to 1 AU (combined with its final speed at the Earth)
and the effective acceleration in the Sun-Earth distance. Results indicate that
(1) for almost all the events (85 out of 91 events), the speed of the CME at 1
AU is always less than or equal to its initial speed measured at the near-Sun
region, (2) the distributions of initial speeds, CME-driven shock and CME
speeds at 1 AU clearly show the effects of aero-dynamical drag between the CME
and the solar wind and in consequence, the speed of the CME tends to equalize
to that of the background solar wind, (3) for a large fraction of CMEs (for
50% of the events), the inferred effective acceleration along the
Sun-Earth line dominates the above drag force. The net acceleration suggests an
average dissipation of energy 10 ergs, which is likely provided
by the Lorentz force associated with the internal magnetic energy carried by
the CME.Comment: 18 pages, 6 figure
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
PONDER - A Real time software backend for pulsar and IPS observations at the Ooty Radio Telescope
This paper describes a new real-time versatile backend, the Pulsar Ooty Radio
Telescope New Digital Efficient Receiver (PONDER), which has been designed to
operate along with the legacy analog system of the Ooty Radio Telescope (ORT).
PONDER makes use of the current state of the art computing hardware, a
Graphical Processing Unit (GPU) and sufficiently large disk storage to support
high time resolution real-time data of pulsar observations, obtained by
coherent dedispersion over a bandpass of 16 MHz. Four different modes for
pulsar observations are implemented in PONDER to provide standard reduced data
products, such as time-stamped integrated profiles and dedispersed time series,
allowing faster avenues to scientific results for a variety of pulsar studies.
Additionally, PONDER also supports general modes of interplanetary
scintillation (IPS) measurements and very long baseline interferometry data
recording. The IPS mode yields a single polarisation correlated time series of
solar wind scintillation over a bandwidth of about four times larger (16 MHz)
than that of the legacy system as well as its fluctuation spectrum with high
temporal and frequency resolutions. The key point is that all the above modes
operate in real time. This paper presents the design aspects of PONDER and
outlines the design methodology for future similar backends. It also explains
the principal operations of PONDER, illustrates its capabilities for a variety
of pulsar and IPS observations and demonstrates its usefulness for a variety of
astrophysical studies using the high sensitivity of the ORT.Comment: 25 pages, 14 figures, Accepted by Experimental Astronom
Simultaneous multi-frequency single pulse observations of pulsars
We performed simultaneous observations at 326.5 MHz with the Ooty Radio
Telescope and at 326, 610 and 1308 MHz with the Giant Meterwave Radio Telescope
for a sample of 12 pulsars, where frequency dependent single pulse behaviour
was reported. The single pulse sequences were analysed with fluctuation
analysis, sensitive to both the average fluctuation properties (using longitude
resolved fluctuation spectrum and two-dimensional fluctuation spectrum) as well
as temporal changes in these (using sliding two-dimensional fluctuation
spectrum ) to establish concurrent changes in subpulse drifting over the
multiple frequencies employed. We report subpulse drifting in PSR J09345249
for the first time. We also report pulse nulling measurements in PSRs
J09345249, B1508+55, J18222256, B184519 and J19010906 for the first
time. Our measurements of subpulse drifting and pulse nulling for the rest of
the pulsars are consistent with previously reported values. Contrary to
previous belief, we find no evidence for a frequency dependent drift pattern in
PSR B2016+28 implied by non-simultaneous observations by Oster et al. (1977).
In PSRs B1237+25, J18222256, J19010906 and B204516, our longer and
more sensitive observations reveal multiple drift rates with distinct P3. We
increase the sample of pulsars showing concurrent nulling across multiple
frequencies by more than 100 percent, adding 4 more pulsars to this sample. Our
results confirm and further strengthen the understanding that the subpulse
drifting and pulse nulling are broadband consistent with previous studies
(Gajjar et al. 2014a; Rankin 1986; Weltevrede et al. 2007) and are closely tied
to physics of polar gap.Comment: 22 pages, 44 figures, Single pulse studies of pulsars, accepted by
A&
Multi-frequency scatter broadening evolution of pulsars - II. Scatter broadening of nearby pulsars
We present multi-frequency scatter broadening evolution of 29 pulsars
observed with the LOw Frequency ARray (LOFAR) and Long Wavelength Array (LWA).
We conducted new observations using LOFAR Low Band Antennae (LBA) as well as
utilized the archival data from LOFAR and LWA. This study has increased the
total of all multi-frequency or wide-band scattering measurements up to a
dispersion measure (DM) of 150~pc\,cm by 60\%. The scatter broadening
timescale () measurements at different frequencies are often
combined by scaling them to a common reference frequency of 1\,GHz. Using our
data, we show that the --DM variations are best fitted for reference
frequencies close to 200--300\,MHz, and scaling to higher or lower frequencies
results in significantly more scatter in data. We suggest that this effect
might indicate a frequency dependence of the scatter broadening scaling index
(). However, a selection bias due to our chosen observing frequencies
can not be ruled out with the current data set. Our data did not favour any
particular model of the DM -- relations, and we do not see a
statistically significant break at the low DM range in this relation. The
turbulence spectral index () is found to be steeper than that is
expected from a Kolmogorov spectrum. This indicates that the local ISM
turbulence may have a low wave-number cutoff or presence of large scale
inhomogeneities in the line of sight to some of the reported pulsars.Comment: Accepted for publication in Ap
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