1,176 research outputs found
Giant Pulses from PSR B1937+21 with widths <= 15 nanoseconds and T_b >= 5 x 10^39 K, the Highest Brightness Temperature Observed in the Universe
Giant radio pulses of the millisecond pulsar B1937+21 were recorded with the
S2 VLBI system at 1.65 GHz with NASA/JPL's 70-m radio telescope at Tidbinbilla,
Australia. These pulses have been observed as strong as 65000 Jy with widths <=
15 ns, corresponding to a brightness temperature T_b >= 5 x 10^39 K, the
highest observed in the universe. The vast majority of these pulses occur in a
5.8 mcs and 8.2 mcs window at the very trailing edges of the regular main pulse
and interpulse profiles, respectively. Giant pulses occur in general with a
single spike. Only in one case out of 309 was the structure clearly more
complex. The cumulative distribution is fit by a power law with index -1.40 +/-
0.01 with a low-energy but no high-energy cutoff. We estimate that giant pulses
occur frequently but are only rarely detected. When corrected for the
directivity factor, 25 giant pulses are estimated to be generated in one
neutron star revolution alone. The intensities of the giant pulses of the main
pulses and interpulses are not correlated with each other nor with the
intensities or energies of the main pulses and interpulses themselves. Their
radiation energy density can exceed 300 times the plasma energy density at the
surface of the neutron star and can even exceed the magnetic field energy
density at that surface. We therefore do not think that the generation of giant
pulses is linked to the plasma mechanisms in the magnetosphere. Instead we
suggest that it is directly related to discharges in the polar cap region of
the pulsar.Comment: 14 pages, 13 figures, to be published in ApJ, November 2004, v. 616,
also was presented in Russian National Astronomical Conference VAK-2004,
"Horizons of the Universe" held in Moscow State University, Sternberg
Astronomical Institute, June 3-10, 2004, page 19
Pulsars with the Australian Square Kilometre Array Pathfinder
The Australian Square Kilometre Array Pathfinder (ASKAP) is a 36-element
array with a 30-square-degree field of view being built at the proposed SKA
site in Western Australia. We are conducting a Design Study for pulsar
observations with ASKAP, planning both timing and search observations. We
provide an overview of the ASKAP telescope and an update on pulsar-related
progress.Comment: To appear in proceedings of "Radio Pulsars: An astrophysical key to
unlock the secrets of the Universe
Meixner class of non-commutative generalized stochastic processes with freely independent values I. A characterization
Let be an underlying space with a non-atomic measure on it (e.g.
and is the Lebesgue measure). We introduce and study a
class of non-commutative generalized stochastic processes, indexed by points of
, with freely independent values. Such a process (field),
, , is given a rigorous meaning through smearing out
with test functions on , with being a
(bounded) linear operator in a full Fock space. We define a set
of all continuous polynomials of , and then define a con-commutative
-space by taking the closure of in the norm
, where is the vacuum in the Fock
space. Through procedure of orthogonalization of polynomials, we construct a
unitary isomorphism between and a (Fock-space-type) Hilbert space
, with
explicitly given measures . We identify the Meixner class as those
processes for which the procedure of orthogonalization leaves the set invariant. (Note that, in the general case, the projection of a
continuous monomial of oder onto the -th chaos need not remain a
continuous polynomial.) Each element of the Meixner class is characterized by
two continuous functions and on , such that, in the
space, has representation
\omega(t)=\di_t^\dag+\lambda(t)\di_t^\dag\di_t+\di_t+\eta(t)\di_t^\dag\di^2_t,
where \di_t^\dag and \di_t are the usual creation and annihilation
operators at point
LOFAR discovery of the fastest-spinning millisecond pulsar in the Galactic field
We report the discovery of PSR J09520607, a 707-Hz binary millisecond
pulsar which is now the fastest-spinning neutron star known in the Galactic
field (i.e., outside of a globular cluster). PSR J09520607 was found using
LOFAR at a central observing frequency of 135 MHz, well below the 300 MHz to 3
GHz frequencies typically used in pulsar searches. The discovery is part of an
ongoing LOFAR survey targeting unassociated Fermi Large Area Telescope
-ray sources. PSR J09520607 is in a 6.42-hr orbit around a very
low-mass companion ( M) and we identify a
strongly variable optical source, modulated at the orbital period of the
pulsar, as the binary companion. The light curve of the companion varies by 1.6
mag from at maximum to , indicating that it is
irradiated by the pulsar wind. Swift observations place a 3- upper
limit on the keV X-ray luminosity of erg
s (using the 0.97 kpc distance inferred from the dispersion measure).
Though no eclipses of the radio pulsar are observed, the properties of the
system classify it as a black widow binary. The radio pulsed spectrum of PSR
J09520607, as determined through flux density measurements at 150 and 350
MHz, is extremely steep with (where ).
We discuss the growing evidence that the fastest-spinning radio pulsars have
exceptionally steep radio spectra, as well as the prospects for finding more
sources like PSR J09520607.Comment: 9 pages, 3 figures, 1 table, published in ApJ letter
A Radio Pulsar/X-ray Binary Link
Radio pulsars with millisecond spin periods are thought to have been spun up
by transfer of matter and angular momentum from a low-mass companion star
during an X-ray-emitting phase. The spin periods of the neutron stars in
several such low-mass X-ray binary (LMXB) systems have been shown to be in the
millisecond regime, but no radio pulsations have been detected. Here we report
on detection and follow-up observations of a nearby radio millisecond pulsar
(MSP) in a circular binary orbit with an optically identified companion star.
Optical observations indicate that an accretion disk was present in this system
within the last decade. Our optical data show no evidence that one exists
today, suggesting that the radio MSP has turned on after a recent LMXB phase.Comment: published in Scienc
An Eccentric Binary Millisecond Pulsar in the Galactic Plane
Binary pulsar systems are superb probes of stellar and binary evolution and
the physics of extreme environments. In a survey with the Arecibo telescope, we
have found PSR J1903+0327, a radio pulsar with a rotational period of 2.15 ms
in a highly eccentric (e = 0.44) 95-day orbit around a solar mass companion.
Infrared observations identify a possible main-sequence companion star.
Conventional binary stellar evolution models predict neither large orbital
eccentricities nor main-sequence companions around millisecond pulsars.
Alternative formation scenarios involve recycling a neutron star in a globular
cluster then ejecting it into the Galactic disk or membership in a hierarchical
triple system. A relativistic analysis of timing observations of the pulsar
finds its mass to be 1.74+/-0.04 Msun, an unusually high value.Comment: 28 pages, 4 figures inc Supplementary On-Line Material. Accepted for
publication in Science, published on Science Express: 10.1126/science.115758
LOFAR tied-array imaging and spectroscopy of solar S bursts
Context. The Sun is an active source of radio emission that is often associated with energetic phenomena ranging from nanoflares to coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), numerous millisecond duration radio bursts have been reported, such as radio spikes or solar S bursts (where S stands for short). To date, these have neither been studied extensively nor imaged because of the instrumental limitations of previous radio telescopes.
Aims. Here, LOw Frequency ARray (LOFAR) observations were used to study the spectral and spatial characteristics of a multitude of S bursts, as well as their origin and possible emission mechanisms.
Methods. We used 170 simultaneous tied-array beams for spectroscopy and imaging of S bursts. Since S bursts have short timescales and fine frequency structures, high cadence (~50 ms) tied-array images were used instead of standard interferometric imaging, that is currently limited to one image per second.
Results. On 9 July 2013, over 3000 S bursts were observed over a time period of ~8 h. S bursts were found to appear as groups of short-lived (<1 s) and narrow-bandwidth (~2.5 MHz) features, the majority drifting at ~3.5 MHz s-1 and a wide range of circular polarisation degrees (2−8 times more polarised than the accompanying Type III bursts). Extrapolation of the photospheric magnetic field using the potential field source surface (PFSS) model suggests that S bursts are associated with a trans-equatorial loop system that connects an active region in the southern hemisphere to a bipolar region of plage in the northern hemisphere.
Conclusions. We have identified polarised, short-lived solar radio bursts that have never been imaged before. They are observed at a height and frequency range where plasma emission is the dominant emission mechanism, however, they possess some of the characteristics of electron-cyclotron maser emission
The Green Bank Northern Celestial Cap Pulsar Survey - I: Survey Description, Data Analysis, and Initial Results
We describe an ongoing search for pulsars and dispersed pulses of radio
emission, such as those from rotating radio transients (RRATs) and fast radio
bursts (FRBs), at 350 MHz using the Green Bank Telescope. With the Green Bank
Ultimate Pulsar Processing Instrument, we record 100 MHz of bandwidth divided
into 4,096 channels every 81.92 . This survey will cover the entire sky
visible to the Green Bank Telescope (, or 82% of the sky)
and outside of the Galactic Plane will be sensitive enough to detect slow
pulsars and low dispersion measure (30 ) millisecond
pulsars (MSPs) with a 0.08 duty cycle down to 1.1 mJy. For pulsars with a
spectral index of 1.6, we will be 2.5 times more sensitive than previous and
ongoing surveys over much of our survey region. Here we describe the survey,
the data analysis pipeline, initial discovery parameters for 62 pulsars, and
timing solutions for 5 new pulsars. PSR J02145222 is an MSP in a long-period
(512 days) orbit and has an optical counterpart identified in archival data.
PSR J06365129 is an MSP in a very short-period (96 minutes) orbit with a
very low mass companion (8 ). PSR J06455158 is an isolated MSP
with a timing residual RMS of 500 ns and has been added to pulsar timing array
experiments. PSR J14347257 is an isolated, intermediate-period pulsar that
has been partially recycled. PSR J18164510 is an eclipsing MSP in a
short-period orbit (8.7 hours) and may have recently completed its spin-up
phase.Comment: 18 pages, 10 figures, 5 tables, accepted by Ap
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