1,329 research outputs found
RFI Identification and Mitigation Using Simultaneous Dual Station Observations
RFI mitigation is a critically important issue in radio astronomy using
existing instruments as well as in the development of next-generation radio
telescopes, such as the Square Kilometer Array (SKA). Most designs for the SKA
involve multiple stations with spacings of up to a few thousands of kilometers
and thus can exploit the drastically different RFI environments at different
stations. As demonstrator observations and analysis for SKA-like instruments,
and to develop RFI mitigation schemes that will be useful in the near term, we
recently conducted simultaneous observations with Arecibo Observatory and the
Green Bank Telescope (GBT). The observations were aimed at diagnosing RFI and
using the mostly uncorrelated RFI between the two sites to excise RFI from
several generic kinds of measurements such as giant pulses from Crab-like
pulsars and weak HI emission from galaxies in bands heavily contaminated by
RFI. This paper presents observations, analysis, and RFI identification and
excision procedures that are effective for both time series and spectroscopy
applications using multi-station data.Comment: 12 pages, 9 figures (4 in ps and 5 in jpg formats), Accepted for
publication in Radio Scienc
A Survey of 56 Mid-latitude EGRET Error Boxes for Radio Pulsars
We have conducted a radio pulsar survey of 56 unidentified gamma-ray sources
from the 3rd EGRET catalog which are at intermediate Galactic latitudes (5 deg.
< |b| < 73 deg.). For each source, four interleaved 35-minute pointings were
made with the 13-beam, 1400-MHz multibeam receiver on the Parkes 64-m radio
telescope. This covered the 95% error box of each source at a limiting
sensitivity of about 0.2 mJy to pulsed radio emission for periods P > 10 ms and
dispersion measures < 50 pc cm-3. Roughly half of the unidentified gamma-ray
sources at |b| > 5 deg. with no proposed active galactic nucleus counterpart
were covered in this survey. We detected nine isolated pulsars and four
recycled binary pulsars, with three from each class being new. Timing
observations suggest that only one of the pulsars has a spin-down luminosity
which is even marginally consistent with the inferred luminosity of its
coincident EGRET source. Our results suggest that population models, which
include the Gould belt as a component, overestimate the number of isolated
pulsars among the mid-latitude Galactic gamma-ray sources and that it is
unlikely that Gould belt pulsars make up the majority of these sources.
However, the possibility of steep pulsar radio spectra and the confusion of
terrestrial radio interference with long-period pulsars (P > 200 ms) having
very low dispersion measures (< 10 pc cm-3, expected for sources at a distance
of less than about 1 kpc) prevent us from strongly ruling out this hypothesis.
Our results also do not support the hypothesis that millisecond pulsars make up
the majority of these sources. Non-pulsar source classes should therefore be
further investigated as possible counterparts to the unidentified EGRET sources
at intermediate Galactic latitudes.Comment: 24 pages, including 4 figures and 3 tables. Accepted for publication
in Ap
Radio timing and optical photometry of the black widow system PSR J1518+0204C in the globular cluster M5
We report on the determination of astrometric, spin and orbital parameters
for PSR J1518+0204C, a "black widow" binary millisecond pulsar in the globular
cluster M5. The accurate position and orbital parameters obtained from radio
timing allowed us to search for the optical companion. By using WFC3/HST images
we identified a very faint variable star (m_F390W > 24.8, m_F606W > 24.3,
m_F814W > 23.1) located at only 0.25" from the pulsar's timing position. Due to
its strong variability, this star is visible only in a sub-sample of images.
However, the light curve obtained folding the available data with the orbital
parameters of the pulsar shows a maximum at the pulsar inferior conjunction and
a possible minimum at the pulsar superior conjunction. Furthermore, the shape
of the optical modulation indicates a heating process possibly due to the
pulsar wind. This is the first identification of an optical companion to a
black widow pulsar in the dense stellar environment of a globular cluster.Comment: Accepted for publication by ApJ; 24 Pages, 5 Figures, 1 Tabl
A Strong Upper Limit on the Pulsed Radio Luminosity of the Compact Object 1RXS J141256.0+792204
The ROSAT X-ray source 1RXS J141256.0+792204 has recently been identified as
a likely compact object whose properties suggest it could be a very nearby
radio millisecond pulsar at d = 80 - 260pc. We investigated this hypothesis by
searching for radio pulsations using the Westerbork Synthesis Radio Telescope.
We observed 1RXS J141256.0+792204 at 385 and 1380MHz, recording at high time
and frequency resolution in order to maintain sensitivity to millisecond
pulsations. These data were searched both for dispersed single pulses and using
Fourier techniques sensitive to constant and orbitally modulated periodicities.
No radio pulsations were detected in these observations, resulting in pulsed
radio luminosity limits of L_400 ~ 0.3 (d/250pc)^2 mJy kpc^2 and L_1400 ~ 0.03
(d/250pc)^2 mJy kpc^2 at 400 and 1400MHz respectively. The lack of detectable
radio pulsations from 1RXS J141256.0+792204 brings into question its
identification as a nearby radio pulsar, though, because the pulsar could be
beamed away from us, this hypothesis cannot be strictly ruled out.Comment: To appear in A&A. 3 page
Pulsars in Globular Clusters with the SKA
Globular clusters are highly efficient radio pulsar factories. These pulsars
can be used as precision probes of the clusters' structure, gas content,
magnetic field, and formation history; some of them are also highly interesting
in their own right because they probe exotic stellar evolution scenarios as
well as the physics of dense matter, accretion, and gravity. Deep searches with
SKA1-MID and SKA1-LOW will plausibly double to triple the known population.
Such searches will only require one to a few tied-array beams, and can be done
during early commissioning of the telescope - before an all-sky pulsar survey
using hundreds to thousands of tied-array beams is feasible. With SKA2 it will
be possible to observe most of the active radio pulsars within a large fraction
of the Galactic globular clusters, an estimated population of 600 - 3700
observable pulsars (those beamed towards us). This rivals the total population
of millisecond pulsars that can be found in the Galactic field; fully
characterizing it will provide the best-possible physical laboratories as well
as a rich dynamical history of the Galactic globular cluster system.Comment: 15 pages, 5 figures, to be published in: "Advancing Astrophysics with
the Square Kilometre Array", Proceedings of Science, PoS(AASKA14)04
Discovery of three new millisecond pulsars in Terzan 5
We report on the discovery of three new millisecond pulsars (namely
J1748-2446aj, J1748-2446ak and J1748-2446al) in the inner regions of the dense
stellar system Terzan 5. These pulsars have been discovered thanks to a method,
alternative to the classical search routines, that exploited the large set of
archival observations of Terzan 5 acquired with the Green Bank Telescope over 5
years (from 2010 to 2015). This technique allowed the analysis of stacked power
spectra obtained by combining ~206 hours of observation. J1748-2446aj has a
spin period of ~2.96 ms, J1748-2446ak of ~1.89 ms (thus it is the fourth
fastest pulsar in the cluster) and J1748-2446al of ~5.95 ms. All the three
millisecond pulsars are isolated and currently we have timing solutions only
for J1748-2446aj and J1748-2446ak. For these two systems, we evaluated the
contribution to the measured spin-down rate of the acceleration due to the
cluster potential field, thus estimating the intrinsic spin-down rates, which
are in agreement with those typically measured for millisecond pulsars in
globular clusters. Our results increase to 37 the number of pulsars known in
Terzan 5, which now hosts 25% of the entire pulsar population identified, so
far, in globular clusters.Comment: 10 pages, 6 figures. ApJ (accepted
VLA Observations of Single Pulses from the Galactic Center Magnetar
We present the results of a 7-12 GHz phased-array study of the Galactic
center magnetar J1745-2900 with the Karl G. Jansky Very Large Array (VLA).
Using data from two 6.5 hour observations from September 2014, we find that the
average profile is comprised of several distinct components at these epochs and
is stable over day timescales and GHz frequencies. Comparison with
additional phased VLA data at 8.7 GHz shows significant profile changes on
longer timescales. The average profile at 7-12 GHz is dominated by the jitter
of relatively narrow pulses. The pulses in each of the four main profile
components seen in September 2014 are uncorrelated in phase and amplitude,
though there is a small but significant correlation in the occurrence of pulses
in two of the profile components. Using the brightest pulses, we measure the
dispersion and scattering parameters of J1745-2900. A joint fit of 38 pulses
gives a 10 GHz pulse broadening time of and a dispersion measure of . Both of these results are consistent with previous measurements,
which suggests that the scattering and dispersion measure of J1745-2900 may be
stable on timescales of several years.Comment: 20 pages, 10 figures, published in Ap
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