873 research outputs found
A Micro-glitch in the Millisecond Pulsar B1821-24 in M28
We report on the observation of a very small glitch observed for the first
time in a millisecond pulsar, PSR B1821-24 located in the globular cluster M28.
Timing observations were mainly conducted with the Nancay radiotelescope
(France) and confirmation comes from the 140ft radiotelescope at Green Bank and
the new Green Bank Telescope data. This event is characterized by a rotation
frequency step of 3 nHz, or 10^-11 in fractional frequency change along with a
short duration limited to a few days or a week. A marginally significant
frequency derivative step was also found. This glitch follows the main
characteristics of those in the slow period pulsars, but is two orders of
magnitude smaller than the smallest ever recorded. Such an event must be very
rare for millisecond pulsars since no other glitches have been detected when
the cumulated number of years of millisecond pulsar timing observations up to
2001 is around 500 for all these objects. However, pulsar PSR B1821-24 is one
of the youngest among the old recycled ones and there is likely a correlation
between age, or a related parameter, and timing noise. While this event happens
on a much smaller scale, the required adjustment of the star to a new
equilibrium figure as it spins down is a likely common cause for all glitches.Comment: Accepted by ApJ Letters, 5 pages, 2 figures, LaTex (uses
emulateapj.sty
Radio Properties of the Auroral Ionosphere, Final Report (Phase I)
It has been found in recent years that a study of the fluctuations
in the signals received from radio stars affords a powerful means of
investigating the irregular structure of the ionosphere. In 1955 studies
of this type, using frequencies of 223 Me and 456 Me, were initiated
at the Geophysical Institute, with a view to investigating the smallscale
structure of the highly disturbed auroral ionosphere. The purpose
of this report is to present a complete description of the initial experimental
arrangement. Further developments of the equipment and some
results of analysis of the data have been presented in Quarterly Progress
Reports covering the period since 1 June 1956,
The report is divided into three sections. Section I contains a
description of the basic philosophy of the experiment with an elementary
discussion of the various parameters involved. Section II contains a
brief description of the actual field installation, and Section III is
devoted to the electronic design features.
The diagrams pertaining to each section are located at the end of
the section.Air Force Contract No. AF 30(635)-2887
Project No. 5535 - Task 45774
Rome Air Development Center, Griffiss Air Force Base
Rome, New YorkABSTRACT AND GENERAL INTRODUCTION -- [SECTION I] Investigation of the Ionosphere Using Extra- Terrestrial Radio Sources : 1.1 Introduction ; 1.2 Extra-Terrestrial Sources ; Apparent Positions ; 1.3 Instrumental Techniques for the Study of Radiation from Radio Stars ; Interferometer Methods ; Advantages of the Phase-Switch Interferometer ; Interferometer Parameters ; 1.5 Limitations on Accuracy -- References -- [SECTION II] The Field Installation : 2.1 Introduction ; 2.2 The Radio Telescope Towers ; 2.3 The Antennas ; 2.4 Acknowledgements -- [SECTION III] Electronic Design of Phase-Switch Interferometers : 3.1 Introduction ; 3.2 223 Mc Phase-Switch Equipment ; 3.3 456 Mc Phase-Switch Equipment ; 3.4 Auxiliary EquipmentYe
The Contribution of the Smectic-Nematic Interface to the Surface Energy
The contribution of the smectic-nematic interface to the surface energy of a
nematic liquid crystal sample is analyzed. By means of a simple model it is
shown that the surface energy depends on the thickness of the region over which
the transition smectic-nematic takes place. For perfectly flat substrates this
thickness is of the order of the correlation length entering in the transition.
An estimate of this contribution shows that it is greater than the one arising
from the nematic-substrate interaction. Moreover, it is also shown that the
surface energy determined in this way presents a non-monotonic behavior with
the temperature.Comment: 10 pages, revte
Simultaneous Absolute Timing of the Crab Pulsar at Radio and Optical Wavelengths
The Crab pulsar emits across a large part of the electromagnetic spectrum.
Determining the time delay between the emission at different wavelengths will
allow to better constrain the site and mechanism of the emission. We have
simultaneously observed the Crab Pulsar in the optical with S-Cam, an
instrument based on Superconducting Tunneling Junctions (STJs) with s time
resolution and at 2 GHz using the Nan\c{c}ay radio telescope with an instrument
doing coherent dedispersion and able to record giant pulses data. We have
studied the delay between the radio and optical pulse using simultaneously
obtained data therefore reducing possible uncertainties present in previous
observations. We determined the arrival times of the (mean) optical and radio
pulse and compared them using the tempo2 software package. We present the most
accurate value for the optical-radio lag of 255 21 s and suggest the
likelihood of a spectral dependence to the excess optical emission asociated
with giant radio pulses.Comment: 8 pages; accepted for publication in Astronomy and Astrophysic
Quarterly Progress Reports Nos. 1-5, 7, 8
This report, prepared during May 1958, summarizes the analysis of over twelve months of amplitude and angular scintillation data obtained using phase-switch interferometers at 223 Mc and 456 Mc on the Cygnus and
Cassiopeia radio sources. The main parameters of the equipment used are
first discussed. The method of scaling the records, involving the arbitrary
division of the records into four (456 Mc) or six (223 Mc) levels of activity
is then described. The probability distributions of the amplitude variations,
as derived using a phase-sweep interferometer, are given for the main levels
of scintillation activity at 223 Mc. Values of mean fractional deviation of
power, -A.P. } for the main levels of activity at 223 Mc are also given.
Preliminary probability distributions of angular deviation, and values of
mean angular deviation, are also given for the different levels of activity
at 223 Mc. The solar-time dependence and sidereal-time (elevation angle)
dependence of the scintillation activity are presented arid c6mpared with
similar data from temperate latitudes. The report concludes with a section
in which a recent theory of radio star scintillations^ is modified to
include the effect of an elongation of the irregularities along the earth's
magnetic lines of force.Air Force Contract No. AF 30(635)-2837
Project No. 5535 - Task 45774
Rome Air Development Center, Griffiss Air Force Base
Rome, New YorkTABLE OF CONTENTS -- ABSTRACT -- [SECTION I] The Phase-Switch Interferometers : Main Parameters of the Equipment ; Method of Operation -- [SECTION II] Analysis of Phase-Switch Interferometer Records : Scaling of Records ; Probability of Occurrence of Different Indexes of Scintillation Activity ; Preparation of Monthly Diurnal Curve of the Mean Value A? at 223 Mc. ; Preparation of Mean Solar Time and Sidereal Time Variation of Mean -AP. at 223 Mc. ; Solar Time Dependence of the Mean Values of -4£ at 223 Mc. ; Sidereal Time Dependence of 223 Me Scintillation Activity -- Analysis of Angular Scintillation Information -- [SECTION III] Discussion of Results [SECTION IV] Adaptation to an Anisotropic Ionosphere of
Booker's Formulae for Radio Star Scintillations -- [SECTION V] Proposed Program of Further Research [SUMMARY] [REFERENCES]Ye
An improved solar wind electron-density model for pulsar timing
Variations in the solar wind density introduce variable delays into pulsar
timing observations. Current pulsar timing analysis programs only implement
simple models of the solar wind, which not only limit the timing accuracy, but
can also affect measurements of pulsar rotational, astrometric and orbital
parameters. We describe a new model of the solar wind electron density content
which uses observations from the Wilcox Solar Observatory of the solar magnetic
field. We have implemented this model into the tempo2 pulsar timing package. We
show that this model is more accurate than previous models and that these
corrections are necessary for high precision pulsar timing applications.Comment: Accepted by ApJ, 13 pages, 4 figure
Pulsed Gamma Rays from the Original Millisecond and Black Widow Pulsars: a case for Caustic Radio Emission?
We report the detection of pulsed gamma-ray emission from the fast
millisecond pulsars (MSPs) B1937+21 (also known as J1939+2134) and B1957+20
(J1959+2048) using 18 months of survey data recorded by the \emph{Fermi} Large
Area Telescope (LAT) and timing solutions based on radio observations conducted
at the Westerbork and Nan\c{c}ay radio telescopes. In addition, we analyzed
archival \emph{RXTE} and \emph{XMM-Newton} X-ray data for the two MSPs,
confirming the X-ray emission properties of PSR B1937+21 and finding evidence
() for pulsed emission from PSR B1957+20 for the first time. In
both cases the gamma-ray emission profile is characterized by two peaks
separated by half a rotation and are in close alignment with components
observed in radio and X-rays. These two pulsars join PSRs J0034-0534 and
J2214+3000 to form an emerging class of gamma-ray MSPs with phase-aligned peaks
in different energy bands. The modeling of the radio and gamma-ray emission
profiles suggests co-located emission regions in the outer magnetosphere.Comment: Accepted for publication in the Astrophysical Journa
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