374 research outputs found
Control in the technical societies: a brief history
By the time control engineering emerged as a coherent body of knowledge and practice (during and just after WW2) professional engineering societies had existed for many decades. Since control engineering is an interdisciplinary branch of the profession, new sections devoted to control were quickly established within the various existing technical societies. In addition, some new bodies devoted specifically or primarily to control were established. This article, a revised version of a paper presented at the IEEE 2009 Conference on the History of Technical Societies, describes how control engineering as a distinct branch of engineering became represented in technical societies in a number of countries
Neutron star spin-kick velocity correlation effect on binary neutron star coalescence rates and spin-orbit misalignment of the components
We study the effect of the neutron star spin -- kick velocity alignment
observed in young radio pulsars on the coalescence rate of binary neutron
stars. Two scenarios of the neutron star formation are considered: when the
kick is always present and when it is small or absent if a neutron star is
formed in a binary system due to electron-capture degenerate core collapse. The
effect is shown to be especially strong for large kick amplitudes and tight
alignments, reducing the expected galactic rate of binary neutron star
coalescences compared to calculations with randomly directed kicks. The
spin-kick correlation also leads to a much narrower NS spin-orbit misalignment.Comment: 7 pages, 5 figures, accepted for publiction in MNRA
On the Eccentricities and Merger Rates of Double Neutron Star Binaries and the Creation of "Double Supernovae"
We demonstrate that a natural consequence of an asymmetric kick imparted to
neutron stars at birth is that the majority of double neutron star binaries
should possess highly eccentric orbits. This leads to greatly accelerated
orbital decay, due to the enormous increase in the emission of gravitational
radiation at periastron as originally demonstrated by Peters (1964). A uniform
distribution of kick velocities constrained to the orbital plane would result
in ~24% of surviving binaries coalescing at least 10,000 times faster than an
unperturbed circular system. Even if the planar kick constraint is lifted, ~6%
of bound systems still coalesce this rapidly. In a non-negligible fraction of
cases it may even be possible that the system could coalesce within 10 years of
the final supernova, resulting in what we might term a "double supernova''. For
systems resembling the progenitor of PSR J0737-3039A, this number is as high as
\~9% (in the planar kick model). Whether the kick velocity distribution extends
to the range required to achieve this is still unclear. We do know that the
observed population of binary pulsars has a deficit of highly eccentric systems
at small orbital periods. In contrast, the long-period systems favour large
eccentricities, as expected. We argue that this is because the short-period
highly eccentric systems have already coalesced and are thus selected against
by pulsar surveys. This effect needs to be taken into account when using the
scale-factor method to estimate the coalescence rate of double neutron star
binaries. We therefore assert that the coalesence rate of such binaries is
underestimated by a factor of several.Comment: 7 pages, 6 figures, submitted to Ap
The Vela Pulsar and its Synchrotron Nebula
(Abridged) We present high-resolution Chandra X-ray observations of PSR
B0833-45, the 89 ms pulsar associated with the Vela supernova remnant. We have
acquired two observations separated by one month to search for changes in the
pulsar and its environment following an extreme glitch in its rotation
frequency. We find a well-resolved nebula with a toroidal morphology remarkably
similar to that observed in the Crab Nebula, along with an axial Crab-like jet.
Between the two observations the flux from the pulsar is found to be steady to
within 0.75%; the 3 sigma limit on the fractional increase in the pulsar's
X-ray flux is < ~10^-5 of the inferred glitch energy. We use this limit to
constrain parameters of glitch models and neutron star structure. We do find a
significant increase in the flux of the nebula's outer arc; if associated with
the glitch, the inferred propagation velocity is > 0.7c, similar to that seen
in the brightening of the Crab Nebula wisps. We propose an explanation for the
X-ray structure of the Vela synchrotron nebula based on a model originally
developed for the Crab Nebula. In a departure from the Crab model, the
magnetization parameter "sigma" of the Vela pulsar wind is allowed to be of
order unity; this is consistent with the simplest MHD transport of magnetic
field from the pulsar to the nebula, where B < 4 X 10^-4 G. We review effects
that may enhance the probability of alignment between the spin axis and space
velocity of a pulsar, and speculate that short-period, slowly moving pulsars
are just the ones best-suited to producing synchrotron nebulae with such
aligned structures.Comment: 16 pages with 8 figures, uses LaTex, emulateapj.sty. Refereed
version. To appear in The Astrophysical Journa
COMPTEL detection of pulsed gamma-ray emission from B1509-58 up to at least 10 MeV
We report on the first firm detection of pulsed gamma-ray emission from PSR
B1509-58 in the 0.75-30 MeV energy range in CGRO COMPTEL data collected over
more than 6 years. The modulation significance in the 0.75-30 MeV pulse-phase
distribution is 5.4 sigma and the lightcurve is similar to the lightcurves
found earlier between 0.7 and 700 keV: a single broad asymmetric pulse reaching
its maximum 0.38 +/- 0.03 in phase after the radio peak, compared to the offset
of 0.30 found in the CGRO BATSE soft gamma-ray data, and 0.27 +/- 0.01 for RXTE
(2-16 keV), compatible with ASCA (0.7-2.2 keV). Spectral analysis based on the
excess counts in the broad pulse of the lightcurve shows that extrapolation of
the OSSE power-law spectral fit with index -1.68 describes our data well up to
10 MeV. Above 10 MeV the spectrum breaks abruptly. The precise location of the
break/bend between 10 and 30 MeV depends on the interpretation of the structure
in the lightcurve measured by COMPTEL and EGRET above 10 MeV.Comment: 15 pages, 10 figures, accepted for publication in Astronomy and
Astrophysic
Local Pulsars; A note on the Birth-Velocity Distribution
We explore a simple model for the representation of the observed
distributions of the motions, and the characteristic ages of the local
population of pulsars. The principal difference from earlier models is the
introduction of a unique value, S, for the kick velocity with which pulsars are
born. We consider separately the proper motion components in galactic longitude
and latitude, and find that the distributions of the velocity components
parallel and perpendicular to the galactic plane are represented satisfactorily
by S=200 km/sec, and leave no room for a significant fraction of much higher
velocities. The successful proposition of a unique value for the kick velocity
may provide an interesting tool in attempts to understand the physical process
leading to the expulsion of the neutron star.Comment: To be published in JAA, 14 pages, 7 figure
The UTMOST Survey for Magnetars, Intermittent pulsars, RRATs and FRBs I: System description and overview
We describe the ongoing `Survey for Magnetars, Intermittent pulsars, Rotating
radio transients and Fast radio bursts' (SMIRF), performed using the newly
refurbished UTMOST telescope. SMIRF repeatedly sweeps the southern Galactic
plane performing real-time periodicity and single-pulse searches, and is the
first survey of its kind carried out with an interferometer. SMIRF is
facilitated by a robotic scheduler which is capable of fully autonomous
commensal operations. We report on the SMIRF observational parameters, the data
analysis methods, the survey's sensitivities to pulsars, techniques to mitigate
radio frequency interference and present some early survey results. UTMOST's
wide field of view permits a full sweep of the Galactic plane to be performed
every fortnight, two orders of magnitude faster than previous surveys. In the
six months of operations from January to June 2018, we have performed
sweeps of the Galactic plane with SMIRF. Notable blind re-detections include
the magnetar PSR J16224950, the RRAT PSR J09413942 and the eclipsing
pulsar PSR J17482446A. We also report the discovery of a new pulsar, PSR
J170554. Our follow-up of this pulsar with the UTMOST and Parkes telescopes
at an average flux limit of mJy and mJy respectively,
categorizes this as an intermittent pulsar with a high nulling fraction of Comment: Submitted to MNRAS, comments welcom
Detecting sterile dark matter in space
Space-based instruments provide new and, in some cases, unique opportunities
to search for dark matter. In particular, if dark matter comprises sterile
neutrinos, the x ray detection of their decay line is the most promising
strategy for discovery. Sterile neutrinos with masses in the keV range could
solve several long-standing astrophysical puzzles, from supernova asymmetries
and the pulsar kicks to star formation, reionization, and baryogenesis. The
best current limits on sterile neutrinos come from Chandra and XMM-Newton.
Future advances can be achieved with a high-resolution x-ray spectrometry in
space.Comment: 11 pages, 1 figure, to appear in proceedings "From Quantum to Cosmos:
fundametal physics research in space", Washington, DC, May 22-24, 200
- …