8,216 research outputs found
Radio sources near the core of globular cluster 47 Tucanae
We present ATCA radio images of the globular cluster 47 Tucanae made at 1.4
and 1.7 GHz and provide an analysis of the radio sources detected within 5
arcmin of the cluster centre. 11 sources are detected, most of which are
clustered about the core of 47 Tuc. Both of the pulsars in 47 Tuc whose
positions are known can be identified with sources in the 1.4 GHz image. The
source distribution has a characteristic radius of ~100 arcsec, larger than the
23 arcsec radius of the cluster core. We compare source positions with the
positions of nine X-ray sources and find no correspondence.Comment: 6 pages, 4 postscript figures, LaTeX with MNRAS macro; Accepted by
MNRA
Time-scales of Radio Emission in PSR J0437-4715 at 327 MHz
Time-scales of radio emission are studied in PSR J0437-4715 at 327 MHz using
almost half a million periods of high quality data from Ooty Radio Telescope.
The radio emission in this milli second pulsar occurs on a short (s) time-scale
of approximately 0.026 +- 0.001 periods, and on a (l) time-scale that is much
longer than the widths of the components of the integrated profile
(approximately 0.05 periods). The width of the s emission increases with its
increasing relative contribution to the total radio emission. This may provide
constraints for the details of discharge of vacuum gaps above pulsar polar
caps. The s emission occasionally takes place in the form of intense spikes,
which are confined to the main component of the integrated profile for 90 per
cent of the time. The positions of spikes within a component of the integrated
profile have no simple relation to the shape of that component. This may have
impact on the interpretation of the integrated profile components in terms of
independent regions of emission on the polar cap.Comment: Accepted for publication in Vol 543 (1 Nov 2000) of The Astrophysical
Journa
Determination of failure limits for sterilizable solid rocket motor
A structural evaluation to establish probable failure limits and a series of environmental tests involving temperature cycling, sustained acceleration, and vibration were conducted on an 18-inch diameter solid rocket motor. Despite the fact that thermal, acceleration and vibration loads representing a severe overtest of conventional environmental requirements were imposed on the sterilizable motor, no structural failure of the grain or flexible support system was detected. The following significant conclusions are considered justified. It is concluded that: (1) the flexible grain retention system, which permitted heat sterilization at 275 F on the test motor, can readily be adopted to meet the environmental requirements of an operational motor design, and (2) if further substantiation of structural integrity is desired, the motor used is considered acceptable for static firing
Design features and results from fatigue reliability research machines
Design and performance tests for reversed bending with steady torque fatigue test machine using notched steel specimen
Differential rotation enhanced dissipation of tides in the PSR J0045-7319 Binary
Recent observations of PSR J0045-7319, a radio pulsar in a close eccentric
orbit with a massive B-star companion, indicate that the system's orbital
period is decreasing on a timescale of years, which is
much shorter than the timescale of 10^9 years given by the standard
theory of tidal dissipation in radiative stars. Observations also provide
strong evidence that the B-star is rotating rapidly, perhaps at nearly its
break up speed. We show that the dissipation of the dynamical tide in a star
rotating in the same direction as the orbital motion of its companion (prograde
rotation) with a speed greater than the orbital angular speed of the star at
periastron results in an increase in the orbital period of the binary system
with time. Thus, since the observed time derivative of the orbital period is
large and negative, the B-star in the PSR J0045-7319 binary must have
retrograde rotation if tidal effects are to account for the orbital decay. We
also show that the time scale for the synchronization of the B-star's spin with
the orbital angular speed of the star at periastron is comparable to the
orbital evolution time. From the work of Goldreich and Nicholson (1989) we
therefore expect that the B-star should be rotating differentially, with the
outer layers rotating more slowly than the interior. We show that the
dissipation of the dynamical tide in such a differentially rotating B-star is
enhanced by almost three orders of magnitude leading to an orbital evolution
time for the PSR J0045-7319 Binary that is consistent with the observations.Comment: 8 pages, tex. Submitted to Ap
The radio luminosity distribution of pulsars in 47 Tucanae
We have used the Australia Telescope Compact Array to seek the integrated
radio flux from all the pulsars in the core of the globular cluster 47 Tucanae.
We have detected an extended region of radio emission and have calibrated its
flux against the flux distribution of the known pulsars in the cluster. We find
the total 20-cm radio flux from the cluster's pulsars to be S = 2.0 +/- 0.3
mJy. This implies the lower limit to the radio luminosity distribution to be
L_1400 = 0.4 mJy kpc^2 and the size of the observable pulsar population to be N
< 30.Comment: 7 pages, 4 figures, MNRAS in pres
Hard X‐ray polarimetry of solar flares with BATSE
We describe a technique for measuring the polarization of hard X‐rays from solar flares based on the angular distribution of that portion of the flux which is scattered off the top of the Earth’s atmosphere. The scattering cross section depends not only on the scatter angle itself, but on the orientation of the scatter angle with respect to the incident polarization vector. Consequently, the distribution of the observed albedo flux will depend on the direction and the polarization properties (i.e., the level of polarization and polarization angle) of the source. Since the albedo component can represent a relatively large fraction (up to 40%) of the direct source flux, there will generally be sufficient signal for making such a measurement. The sensitivity of this approach is therefore dictated by the effective area and the ability of a detector system to ‘image’ the albedo flux. The 4π coverage of the BATSE detectors on the Compton Gamma‐RayObservatory provides an opportunity to measure both the direct and the albedo flux from a given solar flare event. Although the BATSE design (with its large field‐of‐view for each detector) is not optimized for albedo polarimetry, we have nonetheless investigated the feasibility of this technique using BATSE data
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