382 research outputs found
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
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 Green Bank Northern Celestial Cap Pulsar Survey II: The Discovery and Timing of Ten Pulsars
We present timing solutions for ten pulsars discovered in 350 MHz searches
with the Green Bank Telescope. Nine of these were discovered in the Green Bank
Northern Celestial Cap survey and one was discovered by students in the Pulsar
Search Collaboratory program in analysis of drift-scan data. Following
discovery and confirmation with the Green Bank Telescope, timing has yielded
phase-connected solutions with high precision measurements of rotational and
astrometric parameters. Eight of the pulsars are slow and isolated, including
PSR J09302301, a pulsar with nulling fraction lower limit of 30\% and
nulling timescale of seconds to minutes. This pulsar also shows evidence of
mode changing. The remaining two pulsars have undergone recycling, accreting
material from binary companions, resulting in higher spin frequencies. PSR
J05572948 is an isolated, 44 \rm{ms} pulsar that has been partially recycled
and is likely a former member of a binary system which was disrupted by a
second supernova. The paucity of such so-called `disrupted binary pulsars'
(DRPs) compared to double neutron star (DNS) binaries can be used to test
current evolutionary scenarios, especially the kicks imparted on the neutron
stars in the second supernova. There is some evidence that DRPs have larger
space velocities, which could explain their small numbers. PSR J1806+2819 is a
15 \rm{ms} pulsar in a 44 day orbit with a low mass white dwarf companion. We
did not detect the companion in archival optical data, indicating that it must
be older than 1200 Myr.Comment: 9 pages, 5 figure
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]
Giant pulses from J1823-3021A observed with the MeerKAT telescope
The millisecond pulsar J1823-3021A is a very active giant pulse emitter in
the globular cluster NGC 6624. New observations with the MeerKAT radio
telescope have revealed 14350 giant pulses over 5 hours of integration time,
with an average wait time of about 1 second between giant pulses. The giant
pulses occur in phases compatible with the ordinary radio emission, follow a
power-law distribution with an index of -2.63 0.02 and contribute 4
percent of the total integrated flux. The spectral index of the giant pulses
follows a Gaussian distribution centered around -1.9 with a standard deviation
of 0.6 and is on average flatter than the integrated emission, which has a
spectral index of -2.81 0.02. The waiting times between the GPs are
accurately described by a Poissonian distribution, suggesting that the time of
occurrence of a GP is independent from the times of occurrence of other GPs. 76
GPs show multiple peaks within the same rotation, a rate that is also
compatible with the mutual independence of the GP times of occurrence. We
studied the polarization properties of the giant pulses finding, on average,
linear polarization only at the 1 percent level and circular polarization at
the 3 percent level, similar to the polarization percentages of the total
integrated emission. In 4 cases it was possible to measure the RM of the GPs
which are highly variable and, in two cases, is inconsistent with the mean RM
of the total integrated pulsar signal.Comment: Accepted for publication in MNRAS. 8 Pages, 11 Figure
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