561 research outputs found
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
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
Detection of long nulls in PSR B170616, a pulsar with large timing irregularities
Single pulse observations, characterizing in detail, the nulling behaviour of
PSR B170616 are being reported for the first time in this paper. Our regular
long duration monitoring of this pulsar reveals long nulls of 2 to 5 hours with
an overall nulling fraction of 312\%. The pulsar shows two distinct phases
of emission. It is usually in an active phase, characterized by pulsations
interspersed with shorter nulls, with a nulling fraction of about 15 \%, but it
also rarely switches to an inactive phase, consisting of long nulls. The nulls
in this pulsar are concurrent between 326.5 and 610 MHz. Profile mode changes
accompanied by changes in fluctuation properties are seen in this pulsar, which
switches from mode A before a null to mode B after the null. The distribution
of null durations in this pulsar is bimodal. With its occasional long nulls,
PSR B170616 joins the small group of intermediate nullers, which lie between
the classical nullers and the intermittent pulsars. Similar to other
intermediate nullers, PSR B170616 shows high timing noise, which could be
due to its rare long nulls if one assumes that the slowdown rate during such
nulls is different from that during the bursts.Comment: Accepted for publication in MNRA
Glitch Behavior of Pulsars and Contribution from Neutron Star Crust
Pulsars are highly magnetized rotating neutron stars with a very stable
rotation speed. Irrespective of their stable rotation rate, many pulsars have
been observed with the sudden jump in the rotation rate, which is known as
pulsar glitch. The glitch phenomena are considered to be an exhibit of
superfluidity of neutron matter inside the neutron star's crustal region. The
magnitude of such rapid change in rotation rate relative to their stable
rotation frequency can quantify the moment of inertia of the crustal region to
the total moment of inertia of the star called as the fractional moment of
inertia (FMI). In this paper, we have calculated FMI for different masses of
the star using six different representative unified equations of state (EoS)
constructed under Relativistic Mean Field (RMF) framework. We have performed an
event-wise comparison of FMI obtained from data with that of theoretically
calculated values with and without considering the entrainment effect. It is
found that larger glitches can't be explained by crustal FMI alone, even
without the entrainment.Comment: 9 pages, 3 figures, 1 table, revised, accepted for publication in Ap
A Search for Pulsars in Steep Spectrum Radio Sources
We report on a time-domain search for pulsars in 44 steep spectrum radio
sources originally identified from recent imaging surveys. The time-domain
search was conducted at 327 MHz using the Ooty radio telescope, and utilized a
semi-coherent dedispersion scheme retaining the sensitivity even for
sub-millisecond periods up to reasonably high dispersion measures. No new
pulsars were found. We discuss the nature of these steep spectrum sources and
argue that majority of the sources in our sample should either be pulsars or a
new category of Galactic sources. Several possibilities that could hinder
detection of these sources as pulsars, including anomalously high scattering or
alignment of the rotation and magnetic axes, are discussed in detail, and we
suggest unconventional search methods to further probe these possibilities.Comment: Accepted for publication in Ap
Scatter broadening measurements of 124 pulsars at 327 MHz
We present the measurements of scatter broadening time-scales ()
for 124 pulsars at 327 MHz, using the upgraded Ooty Radio Telescope (ORT).
These pulsars lie in the dispersion measure range of 37 503 pc cm
and declination () range of 57. New
estimates for 58 pulsars are presented, increasing the sample of
all such measurements by about 40% at 327 MHz. Using all available
measurements in the literature, we investigate the dependence of on
dispersion measure. Our measurements, together with previously reported values
for , affirm that the ionized interstellar medium upto 3 kpc is
consistent with Kolmogorov spectrum, while it deviates significantly beyond
this distance.Comment: 19 pages, 4 figures, accepted for publication in Ap
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