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Register a new userDiagnostics of timing noise in middle aged pulsars
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Radio pulsars are often used as clocks in a wide variety of experiments. Imperfections in the clock, known as timing noise, have the potential to reduce the significance of, or even thwart e.g. the attempt to find a stochastic gravitational wave (GW) background. We measure the timing noise in a group of 129 mostly middle-aged pulsars (i.e. characterstic ages near 1~Myr) observed with the Parkes radio telescope on a monthly basis since 2014. We examine four different metrics for timing noise, but it remains unclear which, if any, provides the best determination. In spite of this, it is evident that these pulsars have significantly less timing noise than their younger counterparts, but significantly more than the (much older) millisecond pulsars (MSPs). As with previous authors, we find a strong correlation between timing noise and the pulsar spin-down rate, $dot{ u}$. However, for a given $dot{ u}$ there is a spread of about a factor 30 in the strength of the timing noise likely indicating that nuclear conditions in the interior of the stars differs between objects. We briefly comment on the implications for GW detection through pulsar timing arrays as the level of timing noise in MSPs may be less than predicted.
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Electrons/positrons produced in a pulsar magnetosphere emit synchrotron radiation, which is widely believed as the origin of the non-thermal X-ray emission detected from pulsars. Particles are produced by curvature photons emitted from accelerated particles in the magnetosphere. These curvature photons are detected as pulsed $gamma$-ray emissions from pulsars with age $lesssim10^6$ yr. Using $gamma$-ray observations and analytical model, we impose severe constraints on the synchrotron radiation as a mechanism of the non-thermal X-ray emission. In most middle-aged pulsars ($sim10^5-10^6$ yr) which photon-photon pair production is less efficient in their magnetosphere, we find that the synchrotron radiation model is difficult to explain the observed non-thermal X-ray emission.
We analyze timing noise from five years of Arecibo and Green Bank observations of the seventeen millisecond pulsars of the North-American Nanohertz Observatory for Gravitational Waves (NANOGrav) pulsar timing array. The weighted autocovariance of the timing residuals was computed for each pulsar and compared against two possible models for the underlying noise process. The first model includes red noise and predicts the autocovariance to be a decaying exponential as a function of time lag. The second model is Gaussian white noise whose autocovariance would be a delta function. We also perform a ``nearest-neighbor correlation analysis. We find that the exponential process does not accurately describe the data. Two pulsars, J1643-1224 and J1910+1256, exhibit weak red noise, but the rest are well described as white noise. The overall lack of evidence for red noise implies that sensitivity to a (red) gravitational wave background signal is limited by statistical rather than systematic uncertainty. In all pulsars, the ratio of non-white noise to white noise is low, so that we can increase the cadence or integration times of our observations and still expect the root-mean-square of timing residual averages to decrease by the square-root of observation time, which is key to improving the sensitivity of the pulsar timing array.
We used the 10.4m Gran Telescopio Canarias to search for the optical counterparts to four isolated $gamma$-ray pulsars, all detected in the X-rays by either xmm or chan but not yet in the optical. Three of them are middle-aged pulsars -- PSR, J1846+0919 (0.36 Myr), PSR, J2055+2539 (1.2 Myr), PSR, J2043+2740 (1.2 Myr) -- and one, PSR, J1907+0602, is a young pulsar (19.5 kyr). For both PSR, J1907+0602 and PSR, J2055+2539 we found one object close to the pulsar position. However, in both cases such an object cannot be a viable candidate counterpart to the pulsar. For PSR, J1907+0602, because it would imply an anomalously red spectrum for the pulsar and for PSR, J2055+2539 because the pulsar would be unrealistically bright ($r=20.34pm0.04$) for the assumed distance and interstellar extinction. For PSR, J1846+0919, we found no object sufficiently close to the expected position to claim a possible association, whereas for PSR, J2043+2740 we confirm our previous findings that the object nearest to the pulsar position is an unrelated field star. We used our brightness limits ($g approx 27$), the first obtained with a large-aperture telescope for both PSR, J1846+0919 and PSR, J2055+2539, to constrain the optical emission properties of these pulsars and investigate the presence of spectral turnovers at low energies in their multi-wavelength spectra.
We report the discovery and timing results for five millisecond pulsars (MSPs) from the Arecibo PALFA survey: PSRs J1906+0055, J1914+0659, J1933+1726, J1938+2516, and J1957+2516. Timing observations of the 5 pulsars were conducted with the Arecibo and Lovell telescopes for time spans ranging from 1.5 to 3.3 yr. All of the MSPs except one (PSR J1914+0659) are in binary systems with low eccentricities. PSR J1957+2516 is likely a redback pulsar, with a ~0.1 $M_odot$ companion and possible eclipses that last ~10% of the orbit. The position of PSR J1957+2516 is also coincident with a NIR source. All 5 MSPs are distant (>3.1 kpc) as determined from their dispersion measures, and none of them show evidence of $gamma$-ray pulsations in a search of Fermi Gamma-Ray Space Telescope data. These 5 MSPs bring the total number of MSPs discovered by the PALFA survey to 26 and further demonstrate the power of this survey in finding distant, highly dispersed MSPs deep in the Galactic plane.
We report observed and derived timing parameters for three millisecond pulsars (MSPs) from observations collected with the Parkes 64-m telescope, Murriyang. The pulsars were found during re-processing of archival survey data by Mickaliger et al. One of the new pulsars (PSR J1546-5925) has a spin period $P=7.8$ ms and is isolated. The other two (PSR J0921-5202 with $P=9.7$ ms and PSR J1146-6610 with $P=3.7$ ms) are in binary systems around low-mass ($>0.2 M_{odot}$) companions. Their respective orbital periods are $38$.2 d and $62.8$ d. While PSR J0921-5202 has a low orbital eccentricity $e=1.3 times 10^{-5}$, in keeping with many other Galactic MSPs, PSR J1146-6610 has a significantly larger eccentricity, $e = 7.4 times 10^{-3}$. This makes it a likely member of a group of eccentric MSP-He white dwarf binary systems in the Galactic disk whose formation is poorly understood. Two of the pulsars are co-located with previously unidentified point sources discovered with the Fermi satellites Large Area Telescope, but no $gamma$-ray pulsations have been detected, likely due to their low spin-down powers. We also show that, particularly in terms of orbital diversity, the current sample of MSPs is far from complete and is subject to a number of selection biases.
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