918 research outputs found
A deep search for pulsar wind nebulae using pulsar gating
Using the Australia Telescope Compact Array (ATCA) we have imaged the fields
around five promising pulsar candidates to search for radio pulsar wind nebulae
(PWNe). We have used the ATCA in its pulsar gating mode; this enables an image
to be formed containing only off-pulse visibilities, thereby dramatically
improving the sensitivity to any underlying PWN. Data from the Molonglo
Observatory Synthesis Telescope were also used to provide sensitivity on larger
spatial scales. This survey found a faint new PWN around PSR B0906-49; here we
report on non-detections of PWNe towards PSRs B1046-58, B1055-52, B1610-50 and
J1105-6107. Our radio observations of the field around PSR B1055-52 argue
against previous claims of an extended X-ray and radio PWNe associated with the
pulsar. If these pulsars power unseen, compact radio PWN, upper limits on the
radio flux indicate that less than 1e-6 of their spin-down energy is used to
power this emission. Alternatively PSR B1046-58 and PSR B1610-50 may have
relativistic winds similar to other young pulsars and the unseen PWN is
resolved and fainter than our surface brightness sensitivity threshold. We can
then determine upper limits on the local ISM density of 2.2e-3 cm^-3 and 1e-2
cm^-3, respectively. Furthermore we constrain the spatial velocities of these
pulsars to be less than ~450 km/s and thus rule out the association of PSR
B1610-50 with SNR G332.4+00.1 (Kes 32). Strong limits on the ratio of unpulsed
to pulsed emission are also determined for three pulsars.Comment: 10 pages, 5 figures, MNRAS in pres
Gravitational Wave Hotspots: Ranking Potential Locations of Single-Source Gravitational Wave Emission
The steadily improving sensitivity of pulsar timing arrays (PTAs) suggests
that gravitational waves (GWs) from supermassive black hole binary (SMBHB)
systems in the nearby universe will be de- tectable sometime during the next
decade. Currently, PTAs assume an equal probability of detection from every sky
position, but as evidence grows for a non-isotropic distribution of sources, is
there a most likely sky position for a detectable single source of GWs? In this
paper, a collection of galactic catalogs is used to calculate various metrics
related to the detectability of a single GW source resolv- able above a GW
background, assuming that every galaxy has the same probability of containing a
SMBHB. Our analyses of these data reveal small probabilities that one of these
sources is currently in the PTA band, but as sensitivity is improved regions of
consistent probability density are found in predictable locations, specifically
around local galaxy clusters.Comment: 9 pages, 9 figures, accepted for submission in Ap
X-ray Observations of XSS J12270-4859 in a New Low State: A Transformation to a Disk-Free Rotation-Powered Pulsar Binary
We present XMM-Newton and Chandra observations of the low-mass X-ray binary
XSS J12270--4859, which experienced a dramatic decline in optical/X-ray
brightness at the end of 2012, indicative of the disappearance of its accretion
disk. In this new state, the system exhibits previously absent
orbital-phase-dependent, large-amplitude X-ray modulations with a decline in
flux at superior conjunction. The X-ray emission remains predominantly
non-thermal but with an order of magnitude lower mean luminosity and
significantly harder spectrum relative to the previous high flux state. This
phenomenology is identical to the behavior of the radio millisecond pulsar
binary PSR J1023+0038 in the absence of an accretion disk, where the X-ray
emission is produced in an intra-binary shock driven by the pulsar wind. This
further demonstrates that XSS J12270-4859 no longer has an accretion disk and
has transformed to a full-fledged eclipsing "redback" system that hosts an
active rotation-powered millisecond pulsar. There is no evidence for diffuse
X-ray emission associated with the binary that may arise due to outflows or a
wind nebula. An extended source situated 1.5' from XSS J12270--4859 is unlikely
to be associated, and is probably a previously uncatalogued galaxy cluster.Comment: 8 pages, 6 figures; accepted for publication in the Astrophysical
Journa
Limits on radio emission from pulsar wind nebulae
We report on a sensitive survey for radio pulsar wind nebulae (PWN) towards
27 energetic and/or high velocity pulsars. Observations were carried out at 1.4
GHz using the Very Large Array and the Australia Telescope Compact Array, and
utilised pulsar-gating to search for off-pulse emission. These observing
parameters resulted in a considerably more sensitive search than previous
surveys, and could detect PWN over a much wider range of spatial scales (and
hence ambient densities and pulsar velocities). However, no emission clearly
corresponding to a PWN was discovered. Based on these non-detections we argue
that the young and energetic pulsars in our sample have winds typical of young
pulsars, but produce unobservable PWN because they reside in low density (n
approx 0.003 cm^-3) regions of the ISM. However, non-detections of PWN around
older and less energetic pulsars can only be explained if the radio luminosity
of their winds is less than 1e-5 of their spin-down luminosity, implying an
efficiency at least an order of magnitude smaller than that seen for young
pulsars.Comment: 9 pages, 3 embedded EPS files. Accepted to MNRA
Timing models for the long-orbital period binary pulsar PSR B1259-63
The pulsar PSR B1259-63 is in a highly eccentric 3.4-yr orbit with the Be
star SS 2883. Timing observations of this pulsar, made over a 7-yr period using
the Parkes 64-m radio telescope, cover two periastron passages, in 1990 August
and 1994 January. The timing data cannot be fitted by the normal pulsar and
Keplerian binary parameters. A timing solution including a (non-precessing)
Keplerian orbit and timing noise (represented as a polynomial of fifth order in
time) provide a satisfactory fit to the data. However, because the Be star
probably has a significant quadrupole moment, we prefer to interpret the data
by a combination of timing noise, dominated by a cubic phase term, and
and terms. We show that the and are
likely to be a result of a precessing orbit caused by the quadrupole moment of
the tilted companion star. We further rule out a number of possible physical
effects which could contribute to the timing data of PSR B1259-63 on a
measurable level.Comment: LaTeX, 9 pages, 8 figures, accepted for publication in MNRA
X-ray Observations of High-B Radio Pulsars
The study of high-magnetic-field pulsars is important for examining the
relationships between radio pulsars, magnetars, and X-ray-isolated neutron
stars (XINSs). Here we report on X-ray observations of three such
high-magnetic-field radio pulsars. We first present the results of a deep
XMM-Newton observation of PSR J1734-3333, taken to follow up on its initial
detection in 2009. The pulsar's spectrum is well fit by a blackbody with a
temperature of 300 +/- 60 eV, with bolometric luminosity L_bb = 2.0(+2.2
-0.7)e+32 erg/s = 0.0036E_dot for a distance of 6.1 kpc. We detect no X-ray
pulsations from the source, setting a 1 sigma upper limit on the pulsed
fraction of 60% in the 0.5-3 keV band. We compare PSR J1734-3333 to other
rotation-powered pulsars of similar age and find that it is significantly
hotter, supporting the hypothesis that the magnetic field affects the observed
thermal properties of pulsars. We also report on XMM-Newton and Chandra
observations of PSRs B1845-19 and J1001-5939. We do not detect either pulsar,
setting 3 sigma upper limits on their blackbody temperatures of 48 and 56 eV,
respectively. Despite the similarities in rotational properties, these sources
are significantly cooler than all but one of the XINSs, which we attribute to
the two groups having been born with different magnetic fields and hence
evolving differently.Comment: 18 pages, 2 tables, 5 figures, accepted for publication in the
Astrophysical Journa
Evidence for a Massive Neutron Star from a Radial-Velocity Study of the Companion to the Black Widow Pulsar PSR B1957+20
The most massive neutron stars constrain the behavior of ultra-dense matter,
with larger masses possible only for increasingly stiff equations of state.
Here, we present evidence that the black widow pulsar, PSR B1957+20, has a high
mass. We took spectra of its strongly irradiated companion and found an
observed radial-velocity amplitude of K_obs=324+/-3 km/s. Correcting this for
the fact that, due to the irradiation, the center of light lies inward relative
to the center of mass, we infer a true radial-velocity amplitude of K_2=353+/-4
km/s and a mass ratio q=M_PSR/M_2=69.2+/-0.8. Combined with the inclination
i=65+/-2 deg inferred from models of the lightcurve, our best-fit pulsar mass
is M_PSR=2.40+/-0.12 M_sun. We discuss possible systematic uncertainties, in
particular in the lightcurve modeling. Taking an upper limit of i<85 deg based
on the absence of radio eclipses at high frequency, combined with a
conservative lower-limit to the motion of the center of mass, K_2>343 km/s
(q>67.3), we infer a lower limit to the pulsar mass of M_PSR>1.66 M_sun.Comment: 7 pages, 3 figures, 1 table, accepted for publication in ApJ;
revision includes more detail on the spectral classification and discussion
of other recent high neutron-star masse
A new limit on the Ultra-High-Energy Cosmic-Ray flux with the Westerbork Synthesis Radio Telescope
A particle cascade (shower) in a dielectric, for example as initiated by an
ultra-high energy cosmic ray, will have an excess of electrons which will emit
coherent \v{C}erenkov radiation, known as the Askaryan effect. In this work we
study the case in which such a particle shower occurs in a medium just below
its surface. We show, for the first time, that the radiation transmitted
through the surface is independent of the depth of the shower below the surface
when observed from far away, apart from trivial absorption effects. As a direct
application we use the recent results of the NuMoon project, where a limit on
the neutrino flux for energies above \,eV was set using the Westerbork
Synthesis Radio Telescope by measuring pulsed radio emission from the Moon, to
set a limit on the flux of ultra-high-energy cosmic rays.Comment: Accepted for publication in Phys. Rev.
A Cosmic Census of Radio Pulsars with the SKA
The Square Kilometre Array (SKA) will make ground breaking discoveries in
pulsar science. In this chapter we outline the SKA surveys for new pulsars, as
well as how we will perform the necessary follow-up timing observations. The
SKA's wide field-of-view, high sensitivity, multi-beaming and sub-arraying
capabilities, coupled with advanced pulsar search backends, will result in the
discovery of a large population of pulsars. These will enable the SKA's pulsar
science goals (tests of General Relativity with pulsar binary systems,
investigating black hole theorems with pulsar-black hole binaries, and direct
detection of gravitational waves in a pulsar timing array). Using SKA1-MID and
SKA1-LOW we will survey the Milky Way to unprecedented depth, increasing the
number of known pulsars by more than an order of magnitude. SKA2 will
potentially find all the Galactic radio-emitting pulsars in the SKA sky which
are beamed in our direction. This will give a clear picture of the birth
properties of pulsars and of the gravitational potential, magnetic field
structure and interstellar matter content of the Galaxy. Targeted searches will
enable detection of exotic systems, such as the ~1000 pulsars we infer to be
closely orbiting Sgr A*, the supermassive black hole in the Galactic Centre. In
addition, the SKA's sensitivity will be sufficient to detect pulsars in local
group galaxies. To derive the spin characteristics of the discoveries we will
perform live searches, and use sub-arraying and dynamic scheduling to time
pulsars as soon as they are discovered, while simultaneously continuing survey
observations. The large projected number of discoveries suggests that we will
uncover currently unknown rare systems that can be exploited to push the
boundaries of our understanding of astrophysics and provide tools for testing
physics, as has been done by the pulsar community in the past.Comment: 20 pages, 7 figures, to be published in: "Advancing Astrophysics with
the Square Kilometre Array", Proceedings of Science, PoS(AASKA14)04
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