1,525 research outputs found
Searching for Millisecond Pulsars: Surveys, Techniques and Prospects
Searches for millisecond pulsars (which we here loosely define as those with
periods 20 ms) in the Galactic field have undergone a renaissance in the
past five years. New or recently refurbished radio telescopes utilizing cooled
receivers and state-of-the art digital data acquisition systems are carrying
out surveys of the entire sky at a variety of radio frequencies. Targeted
searches for millisecond pulsars in point sources identified by the {\it Fermi}
Gamma-ray Space Telescope have proved phenomenally successful, with over 50
discoveries in the past five years. The current sample of millisecond pulsars
now numbers almost 200 and, for the first time in 25 years, now outnumbers
their counterparts in Galactic globular clusters. While many of these searches
are motivated to find pulsars which form part of pulsar timing arrays, a wide
variety of interesting systems are now being found. Following a brief overview
of the millisecond pulsar phenomenon, we describe these searches and present
some of the highlights of the new discoveries in the past decade. We conclude
with predictions and prospects for ongoing and future surveys.Comment: 16 pages, 3 figures, accepted for publication in Classical and
Quantum gravit
Multi-frequency observations and spectral analysis of two gigahertz-peaked spectra pulsars
We report the multi-frequency observations of two pulsars: J1740+1000 and
B1800-21, using the Giant Metrewave Radio Telescope and the Green Bank
Telescope. The main aim of these observations was to estimate the flux density
spectrum of these pulsars, as both of them were previously reported to exhibit
gigahertz-peaked spectra. J1740+1000 is a young pulsar far from the Galactic
plane and the interpretation of its spectrum was inconclusive in the light of
the recent flux density measurements. Our result supports the gigahertz-peaked
interpretation of the PSR J1740+1000 spectrum. B1800-21 is a Vela-like pulsar
near the W30 complex, whose spectrum exhibit a significant change between 2012
and 2014 year. Our analysis shows that the current shape of the spectrum is
similar to that observed before 2009 and confirms that the observed spectral
change happen in a time-scale of a few years.Comment: 9 pages, 7 figure
Depolarization of Pulsar Radio Emission
We show that intensity dependent depolarization of single pulses (e.g.,
Xiluoris et al. 1994) may be due to the nonlinear decay of the "upper" ordinary
mode into an unpolarized extraordinary mode and a backward propagating wave.
The decay occurs in the innermost parts of the pulsar magnetosphere for
obliquely propagating O waves.Comment: 6 pages, 1 postscript figur
The importance of shared understanding within football teams
Within a football team, it is vital for coaches to acknowledge the importance of their players having the knowledge of what is required in specific roles in the team and what their other team members are likely to do in certain situations. This mutual knowledge can be defined as shared understanding – the ability for two or more people to have similar thoughts in specific situations based on their experience together. This paper considers what shared understanding is, its importance within team sports like football and the positive implications for teams who have players with accurate shared understanding. This paper provides practical suggestions for how coaches can develop shared understanding within their team.<br/
A search for rotating radio transients and fast radio bursts in the Parkes high-latitude pulsar survey
Discoveries of rotating radio transients and fast radio bursts (FRBs) in
pulsar surveys suggest that more of such transient sources await discovery in
archival data sets. Here we report on a single-pulse search for dispersed radio
bursts over a wide range of Galactic latitudes (|b| < ) in data
previously searched for periodic sources by Burgay et al. We re-detected 20 of
the 42 pulsars reported by Burgay et al. and one rotating radio transient
reported by Burke-Spolaor. No FRBs were discovered in this survey. Taking into
account this result, and other recent surveys at Parkes, we corrected for
detection sensitivities based on the search software used in the analyses and
the different backends used in these surveys and find that the all-sky FRB
event rate for sources with a fluence above 4.0 Jy ms at 1.4 GHz to be FRBs day sky, where the
uncertainties represent a confidence interval. While this rate is lower
than inferred from previous studies, as we demonstrate, this combined event
rate is consistent with the results of all systematic FRB searches at Parkes to
date and does not require the need to postulate a dearth of FRBs at
intermediate latitudes.Comment: Accepted, 10 pages, 6 figure
Detecting fast radio bursts at decametric wavelengths
Fast radio bursts (FRBs) are highly dispersed, sporadic radio pulses that are likely extragalactic in nature. Here we investigate the constraints on the source population from surveys carried out at frequencies ~GHz. All but one FRB has so far been discovered in the 1--2~GHz band, but new and emerging instruments look set to become valuable probes of the FRB population at sub-GHz frequencies in the near future. In this paper, we consider the impacts of free-free absorption and multi-path scattering in our analysis via a number of different assumptions about the intervening medium. We consider previous low frequency surveys alongwith an ongoing survey with the University of Technology digital backend for the Molonglo Observatory Synthesis Telescope (UTMOST) as well as future observations with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and the Hydrogen Intensity and Real-Time Analysis Experiment (HIRAX). We predict that CHIME and HIRAX will be able to observe 30 or more FRBs per day, even in the most extreme scenarios where free-free absorption and scattering can significantly impact the fluxes below 1~GHz. We also show that UTMOST will detect 1--2 FRBs per month of observations. For CHIME and HIRAX, the detection rates also depend greatly on the assumed FRB distance scale. Some of the models we investigated predict an increase in the FRB flux as a function of redshift at low frequencies. If FRBs are truly cosmological sources, this effect may impact future surveys in this band, particularly if the FRB population traces the cosmic star formation rate. Rajwade, Kaustubh; Lorimer, Dunca
Arecibo timing and single-pulse observations of 17 pulsars
We report on timing and single-pulse observations of 17 pulsars discovered at
the Arecibo observatory. The highlights of our sample are the recycled pulsars
J1829+2456, J1944+0907 and the drifting subpulses observed in PSR J0815+0939.
For the double neutron star binary J1829+2456, in addition to improving upon
our existing measurement of relativistic periastron advance, we have now
measured the pulsar's spin period derivative. This new result sets an upper
limit on the transverse speed of 120 km/s and a lower limit on the
characteristic age of 12.4 Gyr. From our measurement of proper motion of the
isolated 5.2-ms pulsar J1944+0907, we infer a transverse speed of 188 +/- 65
km/s. This is higher than that of any other isolated millisecond pulsar. An
estimate of the speed, using interstellar scintillation, of 235 +/- 45 km/s
indicates that the scattering medium along the line of sight is non-uniform. We
discuss the drifting subpulses detected from three pulsars in the sample, in
particular the remarkable drifting subpulse properties of the 645-ms pulsar
J0815+0939. Drifting is observed in all four components of the pulse profile,
with the sense of drift varying among the different components. This unusual
`bi-drifting'' behaviour challenges standard explanations of the drifting
subpulse phenomenon.Comment: 9 pages, 6 figures. Accepted for publication in MNRA
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