250 research outputs found
X-Ray Observations of Black Widow Pulsars
We describe the first X-ray observations of five short orbital period ( day), -ray emitting, binary millisecond pulsars. Four of these, PSRs
J0023+0923, J11243653, J1810+1744, and J22561024 are `black-widow'
pulsars, with degenerate companions of mass , three of which
exhibit radio eclipses. The fifth source, PSR J2215+5135, is an eclipsing
`redback' with a near Roche-lobe filling 0.2 solar mass non-degenerate
companion. Data were taken using the \textit{Chandra X-Ray Observatory} and
covered a full binary orbit for each pulsar. Two pulsars, PSRs J2215+5135 and
J22561024, show significant orbital variability while PSR J11243653 shows
marginal orbital variability. The lightcurves for these three pulsars have
X-ray flux minima coinciding with the phases of the radio eclipses. This
phenomenon is consistent with an intrabinary shock emission interpretation for
the X-rays. The other two pulsars, PSRs J0023+0923 and J1810+1744, are fainter
and do not demonstrate variability at a level we can detect in these data. All
five spectra are fit with three separate models: a power-law model, a blackbody
model, and a combined model with both power-law and blackbody components. The
preferred spectral fits yield power-law indices that range from 1.3 to 3.2 and
blackbody temperatures in the hundreds of eV. The spectrum for PSR J2215+5135
shows a significant hard X-ray component, with a large number of counts above 2
keV, which is additional evidence for the presence of intrabinary shock
emission and is similar to what has been detected in the low-mass X-ray binary
to millisecond pulsar transition object PSR J1023+0038.Comment: 8 pages, 6 figures, 2 tables, submitted to Ap
Spectroscopic analysis of a-C and a-CNx films prepared by ultrafast high repetition rate pulsed laser deposition
Arecibo timing and single-pulse observations of 17 pulsars
We report on timing and single-pulse observations of 17 pulsars discovered at
the Arecibo observatory. The highlights of our sample are the recycled pulsars
J1829+2456, J1944+0907 and the drifting subpulses observed in PSR J0815+0939.
For the double neutron star binary J1829+2456, in addition to improving upon
our existing measurement of relativistic periastron advance, we have now
measured the pulsar's spin period derivative. This new result sets an upper
limit on the transverse speed of 120 km/s and a lower limit on the
characteristic age of 12.4 Gyr. From our measurement of proper motion of the
isolated 5.2-ms pulsar J1944+0907, we infer a transverse speed of 188 +/- 65
km/s. This is higher than that of any other isolated millisecond pulsar. An
estimate of the speed, using interstellar scintillation, of 235 +/- 45 km/s
indicates that the scattering medium along the line of sight is non-uniform. We
discuss the drifting subpulses detected from three pulsars in the sample, in
particular the remarkable drifting subpulse properties of the 645-ms pulsar
J0815+0939. Drifting is observed in all four components of the pulse profile,
with the sense of drift varying among the different components. This unusual
`bi-drifting'' behaviour challenges standard explanations of the drifting
subpulse phenomenon.Comment: 9 pages, 6 figures. Accepted for publication in MNRA
Discovery of the Optical Counterparts to Four Energetic Fermi Millisecond Pulsars
In the last few years, over 43 millisecond radio pulsars have been discovered
by targeted searches of unidentified gamma-ray sources found by the Fermi
Gamma-Ray Space Telescope. A large fraction of these millisecond pulsars are in
compact binaries with low-mass companions. These systems often show eclipses of
the pulsar signal and are commonly known as black widows and redbacks because
the pulsar is gradually destroying its companion. In this paper, we report on
the optical discovery of four strongly irradiated millisecond pulsar
companions. All four sources show modulations of their color and luminosity at
the known orbital periods from radio timing. Light curve modelling of our
exploratory data shows that the equilibrium temperature reached on the
companion's dayside with respect to their nightside is consistent with about
10-30% of the available spin-down energy from the pulsar being reprocessed to
increase the companion's dayside temperature. This value compares well with the
range observed in other irradiated pulsar binaries and offers insights about
the energetics of the pulsar wind and the production of gamma-ray emission. In
addition, this provides a simple way of estimating the brightness of irradiated
pulsar companions given the pulsar spin-down luminosity. Our analysis also
suggests that two of the four new irradiated pulsar companions are only
partially filling their Roche lobe. Some of these sources are relatively bright
and represent good targets for spectroscopic follow-up. These measurements
could enable, among other things, mass determination of the neutron stars in
these systems.Comment: 11 pages, 5 tables, 1 figure, 4 online tables. ApJ submitted and
referee
New Pulsars from an Arecibo Drift Scan Search
We report the discovery of pulsars J0030+0451, J0711+0931, and J1313+0931
that were found in a search of 470 square degrees at 430 MHz using the 305m
Arecibo telescope. The search has an estimated sensitivity for long period, low
dispersion measure, low zenith angle, and high Galactic latitude pulsars of ~1
mJy, comparable to previous Arecibo searches. Spin and astrometric parameters
for the three pulsars are presented along with polarimetry at 430 MHz. PSR
J0030+0451, a nearby pulsar with a period of 4.8 ms, belongs to the less common
category of isolated millisecond pulsars. We have measured significant
polarization in PSR J0030+0451 over more than 50% of the period, and use these
data for a detailed discussion of its magnetospheric geometry. Scintillation
observations of PSR J0030+0451 provide an estimate of the plasma turbulence
level along the line of sight through the local interstellar medium.Comment: 21 pages, 4 figures, Accepted for Publication in Ap
Electronic properties of a-CNx thin films: An x-ray-absorption and photoemission spectroscopy study
[[notice]]補正完畢[[booktype]]紙本[[booktype]]電子
A 350-MHz GBT Survey of 50 Faint Fermi Gamma-ray Sources for Radio Millisecond Pulsars
We have used the Green Bank Telescope at 350MHz to search 50 faint,
unidentified Fermi Gamma-ray sources for radio pulsations. So far, these
searches have resulted in the discovery of 10 millisecond pulsars, which are
plausible counterparts to these unidentified Fermi sources. Here we briefly
describe this survey and the characteristics of the newly discovered MSPs.Comment: 4 pages, 2 figures, to appear in AIP Conference Proceedings of Pulsar
Conference 2010 "Radio Pulsars: a key to unlock the secrets of the Universe",
Sardinia, October 201
Electronic structure and bonding properties of Si-doped hydrogenated amorphous carbon films
[[abstract]]This work investigates the C K-edge x-ray absorption near-edge structure (XANES), valence-band photoelectron spectroscopy (PES), and Fourier transform infrared (FTIR) spectra of Si-doped hydrogenated amorphous carbon films. The C K-edge XANES and valence-band PES spectra indicate that the sp2/sp3 population ratio decreases as the amount of tetramethylsilane vapor precursor increases during deposition, which suggest that Si doping% enhances sp3 and reduces sp2-bonding configurations. FTIR spectra show the formation of a polymeric sp3 C–Hn structure and Si–Hn bonds, which causes the Young’s modulus and hardness of the films to decrease with the increase of the Si content.[[incitationindex]]SCI[[booktype]]紙
X-Ray and Optical Properties of Black Widows and Redbacks
Black widows and redbacks are binary systems consisting of a millisecond
pulsar in a close binary with a companion having matter driven off of its
surface by the pulsar wind. X-rays due to an intra-binary shock have been
observed from many of these systems, as well as orbital variations in the
optical emission from the companion due to heating and tidal distortion. We
have been systematically studying these systems in radio, optical and X-rays.
Here we will present an overview of X-ray and optical studies of these systems,
including new XMM-Newton and NuStar data obtained from several of them, along
with new optical photometry.Comment: 4 pages, 1 figure, Proceedings of IAU Symposium 337 "Pulsar
Astrophysics - The Next 50 Years" held in Jodrell Bank Observatory, UK Sept.
4-8 201
Surveying the Dynamic Radio Sky with the Long Wavelength Demonstrator Array
This paper presents a search for radio transients at a frequency of 73.8 MHz
(4 m wavelength) using the all-sky imaging capabilities of the Long Wavelength
Demonstrator Array (LWDA). The LWDA was a 16-dipole phased array telescope,
located on the site of the Very Large Array in New Mexico. The field of view of
the individual dipoles was essentially the entire sky, and the number of
dipoles was sufficiently small that a simple software correlator could be used
to make all-sky images. From 2006 October to 2007 February, we conducted an
all-sky transient search program, acquiring a total of 106 hr of data; the time
sampling varied, being 5 minutes at the start of the program and improving to 2
minutes by the end of the program. We were able to detect solar flares, and in
a special-purpose mode, radio reflections from ionized meteor trails during the
2006 Leonid meteor shower. We detected no transients originating outside of the
solar system above a flux density limit of 500 Jy, equivalent to a limit of no
more than about 10^{-2} events/yr/deg^2, having a pulse energy density >~ 1.5 x
10^{-20} J/m^2/Hz at 73.8 MHz for pulse widths of about 300 s. This event rate
is comparable to that determined from previous all-sky transient searches, but
at a lower frequency than most previous all-sky searches. We believe that the
LWDA illustrates how an all-sky imaging mode could be a useful operational
model for low-frequency instruments such as the Low Frequency Array, the Long
Wavelength Array station, the low-frequency component of the Square Kilometre
Array, and potentially the Lunar Radio Array.Comment: 20 pages; accepted for publication in A
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