3,002 research outputs found
Fast radio bursts: recent discoveries and future prospects
Fast radio bursts (FRBs) are quickly becoming a subject of intense interest
in time-domain astronomy. The progenitors of FRBs remain unknown but a wide
variety of models exist from cataclysmic to repeating scenarios. Advances in
FRB detection using current and next-generation radio telescopes will enable
the growth of the population in the next few years. Real-time discovery of FRBs
is now possible with 6 sources detected in real-time within the past 2 years at
the Parkes telescope. Here we discuss the developing strategies for maximising
real-time science with FRBs including polarisation capture and multi-wavelength
follow-up, with particular focus on real-time detections with the Parkes
telescope as a test bed for fast radio burst science. We also discuss how our
response to these events can pave the way for the next generation of FRB
searches with wide-field interferometers.Comment: Published in Proceedings from 11th INTEGRAL Conference: Gamma-ray
Astrophysics in Multi-Wavelenth Perspectiv
Fast Radio Bursts
The discovery of radio pulsars over a half century ago was a seminal moment
in astronomy. It demonstrated the existence of neutron stars, gave a powerful
observational tool to study them, and has allowed us to probe strong gravity,
dense matter, and the interstellar medium. More recently, pulsar surveys have
led to the serendipitous discovery of fast radio bursts (FRBs). While FRBs
appear similar to the individual pulses from pulsars, their large dispersive
delays suggest that they originate from far outside the Milky Way and hence are
many orders-of-magnitude more luminous. While most FRBs appear to be one-off,
perhaps cataclysmic events, two sources are now known to repeat and thus
clearly have a longer-lived central engine. Beyond understanding how they are
created, there is also the prospect of using FRBs -- as with pulsars -- to
probe the extremes of the Universe as well as the otherwise invisible
intervening medium. Such studies will be aided by the high implied all-sky
event rate: there is a detectable FRB roughly once every minute occurring
somewhere on the sky. The fact that less than a hundred FRB sources have been
discovered in the last decade is largely due to the small fields-of-view of
current radio telescopes. A new generation of wide-field instruments is now
coming online, however, and these will be capable of detecting multiple FRBs
per day. We are thus on the brink of further breakthroughs in the
short-duration radio transient phase space, which will be critical for
differentiating between the many proposed theories for the origin of FRBs. In
this review, we give an observational and theoretical introduction at a level
that is accessible to astronomers entering the field.Comment: Invited review article for The Astronomy and Astrophysics Revie
Fast Radio Bursts
The discovery of radio pulsars over a half century ago was a seminal moment
in astronomy. It demonstrated the existence of neutron stars, gave a powerful
observational tool to study them, and has allowed us to probe strong gravity,
dense matter, and the interstellar medium. More recently, pulsar surveys have
led to the serendipitous discovery of fast radio bursts (FRBs). While FRBs
appear similar to the individual pulses from pulsars, their large dispersive
delays suggest that they originate from far outside the Milky Way and hence are
many orders-of-magnitude more luminous. While most FRBs appear to be one-off,
perhaps cataclysmic events, two sources are now known to repeat and thus
clearly have a longer-lived central engine. Beyond understanding how they are
created, there is also the prospect of using FRBs -- as with pulsars -- to
probe the extremes of the Universe as well as the otherwise invisible
intervening medium. Such studies will be aided by the high implied all-sky
event rate: there is a detectable FRB roughly once every minute occurring
somewhere on the sky. The fact that less than a hundred FRB sources have been
discovered in the last decade is largely due to the small fields-of-view of
current radio telescopes. A new generation of wide-field instruments is now
coming online, however, and these will be capable of detecting multiple FRBs
per day. We are thus on the brink of further breakthroughs in the
short-duration radio transient phase space, which will be critical for
differentiating between the many proposed theories for the origin of FRBs. In
this review, we give an observational and theoretical introduction at a level
that is accessible to astronomers entering the field.Comment: Invited review article for The Astronomy and Astrophysics Revie
The Effectiveness of Day Reporting Centers in Reducing the Likelihood of Probation Violations
The following research goals were established to guide the research and answer the problem: 1. Does intensive supervision provided by Day Reporting Centers reduce the likelihood of probationers violating their conditions of probation? 2. Is intensive supervision provided by Day Reporting Centers more effective in ensuring public safety then regular supervision? 3. Do violations of probation initiated by Day Reporting Centers result in more sentence revocations than violations of offenders on regular supervision? 4. Do special programs such as life skills and substance abuse counseling provided by Day Reporting Centers reduce recidivism
Low-speed aerodynamic characteristics of a 0.08-scale YF-17 airplane model at high angles of attack and sideslip
Data were obtained with and without the nose boom and with several strake configurations; also, data were obtained for various control surface deflections. Analysis of the results revealed that selected strake configurations adequately provided low Reynolds number simulation of the high Reynolds number characteristics. The addition of the boom in general tended to reduce the Reynolds number effects
Low speed aerodynamic characteristics of an 0.075-scale F-15 airplane model at high angles of attack and sideslip
An 0.075 scale model representative of the F-15 airplane was tested in the Ames 12 foot pressure wind tunnel at a Mach number of 0.16 to determine static longitudinal and lateral directional characteristics at spin attitudes for Reynolds numbers from 1.48 to 16.4 million per meter (0.45 to 5.0 million per foot). Angles of attack ranged from 0 to +90 deg and from -40 deg to -80 deg while angles of sideslip were varied from -20 deg to +30 deg. Data were obtained for nacelle inlet ramp angles of 0 to 11 deg with the left and right stabilators deflected 0, -25 deg, and differentially 5 deg and -5 deg. The normal pointed nose and two alternate nose shapes were also tested along with several configurations of external stores. Analysis of the results indicate that at higher Reynolds numbers there is a slightly greater tendency to spin inverted than at lower Reynolds numbers. Use of a hemispherical nose in place of the normal pointed nose provided an over correction in simulating yawing moment effects at high Reynolds numbers
A fast radio burst with a low dispersion measure
Fast radio bursts (FRBs) are millisecond pulses of radio emission of seemingly extragalactic origin. More than 50 FRBs have now been detected, with only one seen to repeat. Here we present a new FRB discovery, FRB 110214, which was detected in the high-latitude portion of the High Time Resolution Universe South survey at the Parkes telescope. FRB 110214 has one of the lowest dispersion measures of any known FRB (DM = 168.8 ± 0.5 pc cm^(−3)), and was detected in two beams of the Parkes multibeam receiver. A triangulation of the burst origin on the sky identified three possible regions in the beam pattern where it may have originated, all in sidelobes of the primary detection beam. Depending on the true location of the burst the intrinsic fluence is estimated to fall in the range of 50–2000 Jy ms, making FRB 110214 one of the highest fluence FRBs detected with the Parkes telescope. No repeating pulses were seen in almost 100 h of follow-up observations with the Parkes telescope down to a limiting fluence of 0.3 Jy ms for a 2 ms pulse. Similar low DM, ultrabright FRBs may be detected in telescope sidelobes in the future, making careful modelling of multibeam instrument beam patterns of utmost importance for upcoming FRB surveys
Radiative cascades in charged quantum dots
We measured, for the first time, two photon radiative cascades due to
sequential recombination of quantum dot confined electron hole pairs in the
presence of an additional spectator charge carrier. We identified direct, all
optical cascades involving spin blockaded intermediate states, and indirect
cascades, in which non radiative relaxation precedes the second recombination.
Our measurements provide also spin dephasing rates of confined carriers.Comment: 4 pages, 3 figure
Two-photon- photoluminescence excitation spectroscopy of single quantum-dots
We present experimental and theoretical study of single semiconductor quantum
dots excited by two non-degenerate, resonantly tuned variably polarized lasers.
The first laser is tuned to excitonic resonances. Depending on its polarization
it photogenerates a coherent single exciton state. The second laser is tuned to
biexciton resonances. By scanning the energy of the second laser for various
polarizations of the two lasers, while monitoring the emission from the
biexciton and exciton spectral lines, we map the biexciton photoluminescence
excitation spectra. The resonances rich spectra of the second photon absorption
are analyzed and fully understood in terms of a many carrier theoretical model
which takes into account the direct and exchange Coulomb interactions between
the quantum confined carriers.Comment: Accepted for publication in PR
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