331 research outputs found
Flux-density spectral analysis for several pulsars and two newly-identified gigahertz-peaked spectra
In this paper we present results from flux density measurements for 21
pulsars over a wide frequency range, using the Giant Metrewave Radio Telescope
(GMRT) and the Effelsberg telescope. Our sample was a set of mostly newly
discovered pulsars from the selection of candidates for gigahertz-peaked
spectra (GPS) pulsars. Using the results of our observations along with
previously published data, we identify two new GPS pulsars. One of them, PSR
J1740+1000, with dispersion measure of 24 pc cm, is the first GPS pulsar
with such a low DM value.We also selected several strong candidates for objects
with high frequency turnover in their spectra which require further
investigation.We also revisit our source selection criteria for future searches
for GPS pulsars.Comment: 10 pages, 2 tables, 9 figures, accepted for publication in MNRA
A multiwavlength study of PSR B0628-28: The first overluminous rotation-powered pulsar?
The ROSAT source RX J0630.8-2834 was suggested by positional coincidence to
be the X-ray counterpart of the old field pulsar PSR B0628-28. This
association, however, was regarded to be unlikely based on the computed
energetics of the putative X-ray counterpart. In this paper we report on
multiwavelength observations of PSR B0628-28 made with the ESO/NTT observatory
in La Silla, the Jodrell Bank radio observatory and XMM-Newton. Although the
optical observations do not detect any counterpart of RX J0630.8-2834 down to a
limiting magnitude of V=26.1 mag and B=26.3 mag, XMM-Newton observations
finally confirmed it to be the pulsar's X-ray counterpart by detecting X-ray
pulses with the radio pulsar's spin-period. The X-ray pulse profile is
characterized by a single broad peak with a second smaller peak leading the
main pulse component by ~144 degree. The fraction of pulsed photons is (38 +-
7)% with no strong energy dependence in the XMM-Newton bandpass. The pulsar's
X-ray spectrum is well described by a single component power law with photon
index 2.63^{+0.23}_{-0.15}, indicating that the pulsar's X radiation is
dominated by non-thermal emission processes. A low level contribution of
thermal emission from residual cooling or from heated polar caps, cannot be
excluded. The pulsar's spin-down to X-ray energy conversion efficiency is
obtained to be ~16% for the radio dispersion measure inferred pulsar distance.
If confirmed, PSR B0628-28 would be the first X-ray overluminous
rotation-powered pulsar identified among all ~1400 radio pulsars known today.Comment: Accepted for publication in ApJ. Find a paper copy with higher
resolution images at
ftp://ftp.xray.mpe.mpg.de/people/web/astro-ph-0505488_rev2.pd
The Effelsberg Search for Pulsars in the Galactic Centre
We report the status of a search for pulsars in the Galactic Centre, using acompletely revised and improved high-sensitivity double-horn system at4.85-GHz. We also present calculations about the success rate of periodicitysearches for such a survey, showing that in contrast to conclusions in recentliterature pulsars can be indeed detected at the chosen search frequency
Pulse to pulse flux density modulation from pulsars at 8.35 GHz
Aims. To investigate the flux density modulation from pulsars and the
existence of specific behaviour of modulation index versus frequency. Methods.
Several pulsars have been observed with the Effelsberg radio telescope at 8.35
GHz. Their flux density time series have been corrected for interstellar
scintillation effects. Results. We present the measurement of modulation
indices for 8 pulsars. We confirm the presence of a critical frequency at ~1
GHz for these pulsars (including 3 new ones from this study). We derived
intrinsic modulation indices for the resulting flux density time series. Our
data analysis revealed strong single pulses detected from 5 pulsars.Comment: accepted for publication in A&
On Pair Production in the Crab Pulsar
We consider the widespread assumption that coherent pulsar radio emission is
based on extended pair production leading to plasma densities highly exceeding
the Goldreich-Julian density. We show as an example that the observed low
frequency (160 MHz) emission of the Crab pulsar is incompatible to the model of
extended pair production. Our results rule out significant pair production if a
plasma process is responsible for coherence and the radio emission originates
from inside the light cylinder.Comment: accepted for publication in ApJ Letters; 4 pages, no figure
Polarized radio emission from a magnetar
We present polarization observations of the radio emitting magnetar AXP
J1810-197. Using simultaneous multi-frequency observations performed at 1.4,
4.9 and 8.4 GHz, we obtained polarization information for single pulses and the
average pulse profile at several epochs. We find that in several respects this
magnetar source shows similarities to the emission properties of normal radio
pulsars while simultaneously showing striking differences. The emission is
nearly 80-95% polarized, often with a low but significant degree of circular
polarization at all frequencies which can be much greater in selected single
pulses. The position angle swing has a low average slope of only 1 deg/deg,
deviating significantly from an S-like swing as often seen in radio pulsars
which is usually interpreted in terms of a rotating vector model and a dipolar
magnetic field. The observed position angle is consistent at all frequencies
while showing significant secular variations. On average the interpulse is less
linearly polarized but shows a higher degree of circular polarization. Some
epochs reveal the existence of non-orthogonal emission modes in the main pulse
and systematic wiggles in the PA swing, while the interpulse shows a large
variety of position angle values. We interprete many of the emission properties
as propagation effects in a non-dipolar magnetic field configuration where
emission from different multipole components is observed.Comment: accepted for publication in MNRAS, 15 pages, 11 figures. Figure 9 in
reduced quality, full resolution preprint at
ftp://ftp.jb.man.ac.uk/pub/mk/preprint/ksj+07.pdf, typos fixe
- âŠ