44 research outputs found
Single pulse modeling and the bi-drifting subpulses of radio pulsar B1839-04
We study the bi-drifting pulsar B1839-04, where the observed subpulse drift
direction in the two leading pulse components is opposite from that in the two
trailing components. Such diametrically opposed apparent motions challenge our
understanding of an underlying structure. We find that for the geometry spanned
by the observer and the pulsar magnetic and rotation axes, the observed
bi-drifting in B1839-04 can be reproduced assuming a non-dipolar configuration
of the surface magnetic field. Acceptable solutions are found to either have
relatively weak or strong
surface magnetic fields. Our single pulse modeling shows that a global electric
potential variation at the polar cap that leads to a solid-body-like rotation
of spark forming regions is favorable in reproducing the observed drift
characteristics. This variation of the potential additionally ensures that the
variability is identical in all pulse components resulting in the observed
phase locking of subpulses. Thorough and more general studies of pulsar
geometry show that a low ratio of impact factor to opening angle increases the likelihood of bi-drifting to be observed. We thus conclude
that bi-drifting is visible when our line of sight crosses close to the
magnetic pole.Comment: 15 pages, 14 figures, accepted for publication in Ap
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
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
Detection of radio emission from the gamma-ray pulsar J1732-3131 at 327 MHz
Although originally discovered as a radio-quiet gamma-ray pulsar, J1732-3131
has exhibited intriguing detections at decameter wavelengths. We report an
extensive follow-up of the pulsar at 327 MHz with the Ooty radio telescope.
Using the previously observed radio characteristics, and with an effective
integration time of 60 hrs, we present a detection of the pulsar at a
confidence level of 99.82%. The 327 MHz mean flux density is estimated to be
0.5-0.8 mJy, which establishes the pulsar to be a steep spectrum source and one
of the least-luminous pulsars known to date. We also phase-aligned the radio
and gamma-ray profiles of the pulsar, and measured the phase-offset between the
main peaks in the two profiles to be 0.240.06. We discuss the observed
phase-offset in the context of various trends exhibited by the radio-loud
gamma-ray pulsar population, and suggest that the gamma-ray emission from
J1732-3131 is best explained by outer magnetosphere models. Details of our
analysis leading to the pulsar detection, and measurements of various
parameters and their implications relevant to the pulsar's emission mechanism
are presented.Comment: 8 pages, 6 figures; Accepted for publication in MNRA