533 research outputs found
Spin-down evolution and radio disappearance of the magnetar PSR J16224950
We report on 2.4 yr of radio timing measurements of the magnetar PSR
J16224950 using the Parkes telescope, between 2011 November and 2014 March.
During this period the torque on the neutron star (inferred from the rotational
frequency derivative) varied greatly, though much less erratically than in the
2 yr following its discovery in 2009. During the last year of our measurements
the frequency derivative decreased in magnitude monotonically by 20\%, to a
value of s, a factor of 8 smaller than when
discovered. The flux density continued to vary greatly during our monitoring
through 2014 March, reaching a relatively steady low level after late 2012. The
pulse profile varied secularly on a similar timescale as the flux density and
torque. A relatively rapid transition in all three properties is evident in
early 2013. After PSR J16224950 was detected in all of our 87 observations
up to 2014 March, we did not detect the magnetar in our resumed monitoring
starting in 2015 January and have not detected it in any of the 30 observations
done through 2016 September.Comment: 8 pages, 5 figures, submitted to Ap
Spin-down rate and inferred dipole magnetic field of the soft gamma-ray repeater SGR 1627-41
Using Chandra data taken on 2008 June, we detected pulsations at 2.59439(4) s
in the soft gamma-ray repeater SGR 1627-41. This is the second measurement of
the source spin period and allows us to derive for the first time a long-term
spin-down rate of (1.9 +/- 0.4)E-11 s/s. From this value we infer for SGR
1627-41 a characteristic age of 2.2 kyr, a spin-down luminosity of 4E+34 erg/s
(one of the highest among sources of the same class), and a surface dipole
magnetic field strength of 2E+14 G. These properties confirm the magnetar
nature of SGR 1627-41; however, they should be considered with caution since
they were derived on the basis of a period derivative measurement made using
two epochs only and magnetar spin-down rates are generally highly variable. The
pulse profile, double-peaked and with a pulsed fraction of (13 +/- 2)% in the
2-10 keV range, closely resembles that observed by XMM-Newton in 2008
September. Having for the first time a timing model for this SGR, we also
searched for a pulsed signal in archival radio data collected with the Parkes
radio telescope nine months after the previous X-ray outburst. No evidence for
radio pulsations was found, down to a luminosity level 10-20 times fainter (for
a 10% duty cycle and a distance of 11 kpc) than the peak luminosity shown by
the known radio magnetars.Comment: 5 pages, 2 figures; accepted for publication in MNRAS Letter
The Scintillation Velocity of the Relativistic Binary Pulsar PSR J1141-6545
We report a dramatic orbital modulation in the scintillation timescale of the
relativistic binary pulsar J1141--6545 that both confirms the validity of the
scintillation speed methodology and enables us to derive important physical
parameters. We have determined the space velocity, the orbital inclination and
even the longitude of periastron of the binary system, which we find to be in
good agreement with that obtained from pulse timing measurements. Our data
permit two equally-significant physical interpretations of the system. The
system is either an edge-on binary with a high space velocity ( km
s) or is more face-on with a much slower velocity ( km
s). We favor the former, as it is more consistent with pulse timing and
the distribution of known neutron star masses. Under this assumption, the
runaway velocity of 115 km s is much greater than is expected if pulsars
do not receive a natal kick at birth. The derived inclination of the binary
system is (76\pm 2.5^{\circ}) degrees, implying a companion mass of 1.01 (\pm
)~0.02 M(_{\odot}) and a pulsar mass of 1.29 (\pm)~0.02 M(_{\odot}). Our
derived physical parameters indicate that this pulsar should prove to be an
excellent laboratory for tests of gravitational wave emission.Comment: Minor text and figure changes and corrections following referee's
Comments. 14 pages, 3 figures, accepted for publication in Ap
Discovery of Five Recycled Pulsars in a High Galactic Latitude Survey
We present five recycled pulsars discovered during a 21-cm survey of
approximately 4,150 deg^2 between 15 deg and 30 deg from the galactic plane
using the Parkes radio telescope. One new pulsar, PSR J1528-3146, has a 61 ms
spin period and a massive white dwarf companion. Like many recycled pulsars
with heavy companions, the orbital eccentricity is relatively high (~0.0002),
consistent with evolutionary models that predict less time for circularization.
The four remaining pulsars have short spin periods (3 ms < P < 6 ms); three of
these have probable white dwarf binary companions and one (PSR J2010-1323) is
isolated. PSR J1600-3053 is relatively bright for its dispersion measure of
52.3 pc cm^-3 and promises good timing precision thanks to an intrinsically
narrow feature in its pulse profile, resolvable through coherent dedispersion.
In this survey, the recycled pulsar discovery rate was one per four days of
telescope time or one per 600 deg^2 of sky. The variability of these sources
implies that there are more millisecond pulsars that might be found by
repeating this survey.Comment: 15 pages, 3 figures, accepted for publication in Ap
Simian immunodeficiency virus infection in wild-caught chimpanzees from Cameroon
Simian immunodeficiency viruses (SIVcpz) infecting chimpanzees (Pan troglodytes) in west central Africa are the closest relatives to all major variants of human immunodeficiency virus type 1 ([HIV-1]; groups M, N and O), and have thus been implicated as the source of the human infections; however, information concerning the prevalence, geographic distribution, and subspecies association of SIVcpz still remains limited. In this study, we tested 71 wild-caught chimpanzees from Cameroon for evidence of SIVcpz infection. Thirty-nine of these were of the central subspecies (Pan troglodytes troglodytes), and 32 were of the Nigerian subspecies (Pan troglodytes vellerosus), as determined by mitochondrial DNA analysis. Serological analysis determined that one P. t. troglodytes ape (CAM13) harbored serum antibodies that cross-reacted strongly with HIV-1 antigens; all other apes were seronegative. To characterize the newly identified virus, 14 partially overlapping viral fragments were amplified from fecal virion RNA and concatenated to yield a complete SIVcpz genome (9,284 bp). Phylogenetic analyses revealed that SIVcpzCAM13 fell well within the radiation of the SIVcpzPtt group of viruses, as part of a clade including all other SIVcpzPtt strains as well as HIV-1 groups M and N. However, SIVcpzCAM13 clustered most closely with SIVcpzGAB1 from Gabon rather than with SIVcpzCAM3 and SIVcpzCAM5 from Cameroon, indicating the existence of divergent SIVcpzPtt lineages within the same geographic region. These data, together with evidence of recombination among ancestral SIVcpzPtt lineages, indicate long-standing endemic infection of central chimpanzees and reaffirm a west central African origin of HIV-1. Whether P. t. vellerosus apes are naturally infected with SIVcpz requires further study
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
Transformation of a Star into a Planet in a Millisecond Pulsar Binary
Millisecond pulsars are thought to be neutron stars that have been spun-up by
accretion of matter from a binary companion. Although most are in binary
systems, some 30% are solitary, and their origin is therefore mysterious. PSR
J1719-1438, a 5.7 ms pulsar, was detected in a recent survey with the Parkes
64m radio telescope. We show that it is in a binary system with an orbital
period of 2.2 h. Its companion's mass is near that of Jupiter, but its minimum
density of 23 g cm suggests that it may be an ultra-low mass carbon
white dwarf. This system may thus have once been an Ultra Compact Low-Mass
X-ray Binary, where the companion narrowly avoided complete destruction.Comment: 16 pages, 3 figures. Science Express, in pres
Timing stability of millisecond pulsars and prospects for gravitational-wave detection
Analysis of high-precision timing observations of an array of approx. 20
millisecond pulsars (a so-called "timing array") may ultimately result in the
detection of a stochastic gravitational-wave background. The feasibility of
such a detection and the required duration of this type of experiment are
determined by the achievable rms of the timing residuals and the timing
stability of the pulsars involved. We present results of the first long-term,
high-precision timing campaign on a large sample of millisecond pulsars used in
gravitational-wave detection projects. We show that the timing residuals of
most pulsars in our sample do not contain significant low-frequency noise that
could limit the use of these pulsars for decade-long gravitational-wave
detection efforts. For our most precisely timed pulsars, intrinsic
instabilities of the pulsars or the observing system are shown to contribute to
timing irregularities on a five-year timescale below the 100 ns level. Based on
those results, realistic sensitivity curves for planned and ongoing timing
array efforts are determined. We conclude that prospects for detection of a
gravitational-wave background through pulsar timing array efforts within five
years to a decade are good.Comment: 21 pages, 5 figures, submitted to MNRA
The High Time Resolution Universe Survey - V: Single-pulse energetics and modulation properties of 315 pulsars
We report on the pulse-to-pulse energy distributions and phase-resolved
modulation properties for catalogued pulsars in the southern High Time
Resolution Universe intermediate-latitude survey. We selected the 315 pulsars
detected in a single-pulse search of this survey, allowing a large sample
unbiased regarding any rotational parameters of neutron stars. We found that
the energy distribution of many pulsars is well-described by a log-normal
distribution, with few deviating from a small range in log-normal scale and
location parameters. Some pulsars exhibited multiple energy states
corresponding to mode changes, and implying that some observed "nulling" may
actually be a mode-change effect. PSRJ1900-2600 was found to emit weakly in its
previously-identified "null" state. We found evidence for another state-change
effect in two pulsars, which show bimodality in their nulling time scales; that
is, they switch between a continuous-emission state and a single-pulse-emitting
state. Large modulation occurs in many pulsars across the full integrated
profile, with increased sporadic bursts at leading and trailing sub-beam edges.
Some of these high-energy outbursts may indicate the presence of "giant pulse"
phenomena. We found no correlation with modulation and pulsar period, age, or
other parameters. Finally, the deviation of integrated pulse energy from its
average value was generally quite small, despite the significant phase-resolved
modulation in some pulsars; we interpret this as tenuous evidence of energy
regulation between distinct pulsar sub-beams.Comment: Before full MNRAS publication, supplementary material is available
temporarily at http://dl.dropbox.com/u/22076931/supplementary_material.pd
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