389 research outputs found
Assessment of chromium(VI) release from 848 jewellery items by use of a diphenylcarbazide spot test
Searching for gravitational wave bursts from cosmic string cusps with the Parkes Pulsar Timing Array
Cosmic strings are potential gravitational wave (GW) sources that can be
probed by pulsar timing arrays (PTAs). In this work we develop a detection
algorithm for a GW burst from a cusp on a cosmic string, and apply it to Parkes
PTA data. We find four events with a false alarm probability less than 1%.
However further investigation shows that all of these are likely to be
spurious. As there are no convincing detections we place upper limits on the GW
amplitude for different event durations. From these bounds we place limits on
the cosmic string tension of G mu ~ 10^{-5}, and highlight that this bound is
independent from those obtained using other techniques. We discuss the physical
implications of our results and the prospect of probing cosmic strings in the
era of Square Kilometre Array (SKA).Comment: Accepted for publication by MNRA
The SUrvey for Pulsars and Extragalactic Radio Bursts V:Recent Discoveries and Full Timing Solutions
The SUrvey for Pulsars and Extragalactic Radio Bursts ran from 2014 April to
2019 August, covering a large fraction of the southern hemisphere at mid- to
high-galactic latitudes, and consisting of 9-minute pointings taken with the
20-cm multibeam receiver on the Parkes Radio Telescope. Data up to 2017
September 21 have been searched using standard Fourier techniques, single-pulse
searches, and Fast Folding Algorithm searches. We present 19 new discoveries,
bringing the total to 27 discoveries in the programme, and we report the
results of follow-up timing observations at Parkes for 26 of these pulsars,
including the millisecond pulsar PSR J1421-4409; the faint, highly-modulated,
slow pulsar PSR J1646-1910; and the nulling pulsar PSR J1337-4441. We present
new timing solutions for 23 pulsars, and we report flux densities, modulation
indices, and polarization properties.Comment: Accepted to MNRAS; data available at
https://doi.org/10.5281/zenodo.390098
The NANOGrav 11-Year Data Set: Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries
Observations indicate that nearly all galaxies contain supermassive black
holes (SMBHs) at their centers. When galaxies merge, their component black
holes form SMBH binaries (SMBHBs), which emit low-frequency gravitational waves
(GWs) that can be detected by pulsar timing arrays (PTAs). We have searched the
recently-released North American Nanohertz Observatory for Gravitational Waves
(NANOGrav) 11-year data set for GWs from individual SMBHBs in circular orbits.
As we did not find strong evidence for GWs in our data, we placed 95\% upper
limits on the strength of GWs from such sources as a function of GW frequency
and sky location. We placed a sky-averaged upper limit on the GW strain of at nHz. We also developed a
technique to determine the significance of a particular signal in each pulsar
using ``dropout' parameters as a way of identifying spurious signals in
measurements from individual pulsars. We used our upper limits on the GW strain
to place lower limits on the distances to individual SMBHBs. At the
most-sensitive sky location, we ruled out SMBHBs emitting GWs with
nHz within 120 Mpc for , and
within 5.5 Gpc for . We also determined that
there are no SMBHBs with emitting
GWs in the Virgo Cluster. Finally, we estimated the number of potentially
detectable sources given our current strain upper limits based on galaxies in
Two Micron All-Sky Survey (2MASS) and merger rates from the Illustris
cosmological simulation project. Only 34 out of 75,000 realizations of the
local Universe contained a detectable source, from which we concluded it was
unsurprising that we did not detect any individual sources given our current
sensitivity to GWs.Comment: 10 pages, 11 figures. Accepted by Astrophysical Journal. Please send
any comments/questions to S. J. Vigeland ([email protected]
The Green Bank North Celestial Cap Pulsar Survey. IV: Four New Timing Solutions
We present timing solutions for four pulsars discovered in the Green Bank
Northern Celestial Cap (GBNCC) survey. All four pulsars are isolated with spin
periods between 0.26s and 1.84s. PSR J00382501 has a 0.26s
period and a period derivative of ,
which is unusually low for isolated pulsars with similar periods. This low
period derivative may be simply an extreme value for an isolated pulsar or it
could indicate an unusual evolution path for PSR J00382501, such as a
disrupted recycled pulsar (DRP) from a binary system or an orphaned central
compact object (CCO). Correcting the observed spin-down rate for the Shklovskii
effect suggests that this pulsar may have an unusually low space velocity,
which is consistent with expectations for DRPs. There is no X-ray emission
detected from PSR J00382501 in an archival swift observation, which suggests
that it is not a young orphaned CCO. The high dispersion measure of PSR
J1949+3426 suggests a distance of 12.3kpc. This distance indicates that PSR
J1949+3426 is among the most distant 7% of Galactic field pulsars, and is one
of the most luminous pulsars.Comment: 7 pages, 5 figure
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