Direct detection of low-frequency gravitational waves (GWs,
Hz) is the main goal of pulsar timing array (PTA) projects. One of the main targets for the PTAs is to measure the stochastic background of ...gravitational waves (GWB) whose characteristic strain is expected to approximately follow a power-law of the form
, where f is the GW frequency. In this paper we use the current data from the European PTA to determine an upper limit on the GWB amplitude A as a function of the unknown spectral slope α with a Bayesian algorithm, by modelling the GWB as a random Gaussian process. For the case α=−2/3, which is expected if the GWB is produced by supermassive black hole binaries, we obtain a 95 per cent confidence upper limit on A of 6 × 10−15, which is 1.8 times lower than the 95 per cent confidence GWB limit obtained by the Parkes PTA in 2006. Our approach to the data analysis incorporates the multitelescope nature of the European PTA and thus can serve as a useful template for future intercontinental PTA collaborations.
A glitch in the millisecond pulsar J0613−0200 McKee, J. W; Janssen, G. H; Stappers, B. W ...
Monthly notices of the Royal Astronomical Society,
09/2016, Letnik:
461, Številka:
3
Journal Article
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We present evidence for a small glitch in the spin evolution of the millisecond pulsar J0613−0200, using the EPTA Data Release 1.0, combined with Jodrell Bank analogue filterbank times of arrival ...(TOAs) recorded with the Lovell telescope and Effelsberg Pulsar Observing System TOAs. A spin frequency step of 0.82(3) nHz and frequency derivative step of −1.6(39) × 10−19 Hz s−1 are measured at the epoch of MJD 50888(30). After PSR B1821−24A, this is only the second glitch ever observed in a millisecond pulsar, with a fractional size in frequency of Δν/ν = 2.5(1) × 10−12, which is several times smaller than the previous smallest glitch. PSR J0613−0200 is used in gravitational wave searches with pulsar timing arrays, and is to date only the second such pulsar to have experienced a glitch in a combined 886 pulsar-years of observations. We find that accurately modelling the glitch does not impact the timing precision for pulsar timing array applications. We estimate that for the current set of millisecond pulsars included in the International Pulsar Timing Array, there is a probability of ∼50 per cent that another glitch will be observed in a timing array pulsar within 10 years.
Pulsar timing observations have revealed companions to neutron stars that include other neutron stars, white dwarfs, main-sequence stars, and planets. We demonstrate that the correlated and ...apparently stochastic residual times of arrival from the millisecond pulsar B1937+21 are consistent with the signature of an asteroid belt having a total mass <, ~0.05 M sub(+ in circle). Unlike the solar system's asteroid belt, the best fit pulsar asteroid belt extends over a wide range of radii, consistent with the absence of any shepherding companions. We suggest that any pulsar that has undergone accretion-driven spin-up and subsequently evaporated its companion may harbor orbiting asteroid mass objects. The resulting timing variations may fundamentally limit the timing precision of some of the other millisecond pulsars. Observational tests of the asteroid belt model include identifying periodicities from individual asteroids, which are difficult; testing for statistical stationarity, which becomes possible when observations are conducted over a longer observing span; and searching for reflected radio emission.
We present results from the high-precision timing analysis of the pulsar-white dwarf (WD) binary PSR J1012+5307 using 15 years of multitelescope data. Observations were performed regularly by the ...European Pulsar Timing Array (EPTA) network, consisting of Effelsberg, Jodrell Bank, Westerbork and Nançay. All the timing parameters have been improved from the previously published values, most by an order of magnitude. In addition, a parallax measurement of π= 1.2(3) mas is obtained for the first time for PSR J1012+5307, being consistent with the optical estimation from the WD companion. Combining improved 3D velocity information and models for the Galactic potential, the complete evolutionary Galactic path of the system is obtained. A new intrinsic eccentricity upper limit of e < 8.4 × 10−7 is acquired, one of the smallest calculated for a binary system and a measurement of the variation of the projected semimajor axis also constrains the system's orbital orientation for the first time. It is shown that PSR J1012+5307 is an ideal laboratory for testing alternative theories of gravity. The measurement of the change of the orbital period of the system of is used to set an upper limit on the dipole gravitational wave emission that is valid for a wide class of alternative theories of gravity. Moreover, it is shown that in combination with other binary pulsars PSR J1012+5307 is an ideal system to provide self-consistent, generic limits, based only on millisecond pulsar data, for the dipole radiation and the variation of the gravitational constant .
Pulsars with gigahertz-peaked spectra Kijak, J.; Lewandowski, W.; Maron, O. ...
Astronomy and astrophysics (Berlin),
07/2011, Letnik:
531
Journal Article
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Aims. We investigate a high frequency turn-over effect in radio spectra for pulsars with positive or flat spectral index. Methods. Using GMRT and Effelsberg observatory, we estimated the flux density ...to reconstruct pulsar spectra. Results. We find objects that have a maximum flux in their spectrum above 1 GHz, whose emitted energy decreases below 1 GHz and whose spectral indices are positive at lower frequencies. Some pulsars with a turn-over in their spectrum at high frequencies are found to exist in very interesting environments. We call these objects gigahertz-peaked spectra pulsars.
In this paper, we present results from flux-density measurements for 21 pulsars over a wide frequency range, using the Giant Metrewave Radio Telescope (GMRT) and the Effelsberg telescope. Our sample ...was a set of mostly newly discovered pulsars from the selection of candidates for gigahertz-peaked spectra (GPS) pulsars. Using the results of our observations along with previously published data, we identify two new GPS pulsars. One of them, PSR J1740+1000, with dispersion measure (DM) of 24 pc cm−3, is the first GPS pulsar with such a low DM value. We also selected several strong candidates for objects with high-frequency turnover in their spectra, which require further investigation. We also revisit our source selection criteria for future searches for GPS pulsars.
We report on 22 yr of radio timing observations of the millisecond pulsar J1024−0719 by the telescopes participating in the European Pulsar Timing Array (EPTA). These observations reveal a ...significant second derivative of the pulsar spin frequency and confirm the discrepancy between the parallax and Shklovskii distances that has been reported earlier. We also present optical astrometry, photometry and spectroscopy of 2MASS J10243869−0719190. We find that it is a low-metallicity main-sequence star (K7V spectral type, M/H = −1.0, T
eff = 4050 ± 50 K) and that its position, proper motion and distance are consistent with those of PSR J1024−0719. We conclude that PSR J1024−0719 and 2MASS J10243869−0719190 form a common proper motion pair and are gravitationally bound. The gravitational interaction between the main-sequence star and the pulsar accounts for the spin frequency derivatives, which in turn resolves the distance discrepancy. Our observations suggest that the pulsar and main-sequence star are in an extremely wide (P
b > 200 yr) orbit. Combining the radial velocity of the companion and proper motion of the pulsar, we find that the binary system has a high spatial velocity of 384 ± 45 km s−1 with respect to the local standard of rest and has a Galactic orbit consistent with halo objects. Since the observed main-sequence companion star cannot have recycled the pulsar to millisecond spin periods, an exotic formation scenario is required. We demonstrate that this extremely wide-orbit binary could have evolved from a triple system that underwent an asymmetric supernova explosion, though find that significant fine-tuning during the explosion is required. Finally, we discuss the implications of the long period orbit on the timing stability of PSR J1024−0719 in light of its inclusion in pulsar timing arrays.
21 year timing of the black-widow pulsar J2051−0827 Shaifullah, G; Verbiest, J. P. W; Freire, P. C. C ...
Monthly notices of the Royal Astronomical Society,
10/2016, Letnik:
462, Številka:
1
Journal Article
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Timing results for the black-widow pulsar J2051−0827 are presented, using a 21 year data set from four European Pulsar Timing Array telescopes and the Parkes radio telescope. This data set, which is ...the longest published to date for a black-widow system, allows for an improved analysis that addresses previously unknown biases. While secular variations, as identified in previous analyses, are recovered, short-term variations are detected for the first time. Concurrently, a significant decrease of ∼ 2.5 × 10− 3 cm− 3 pc in the dispersion measure associated with PSR J2051−0827 is measured for the first time and improvements are also made to estimates of the proper motion. Finally, PSR J2051−0827 is shown to have entered a relatively stable state suggesting the possibility of its eventual inclusion in pulsar timing arrays.
The interferer - victim scenario is described for the case of industrial interference affecting radio astronomical observatories. The sensitivity of radio astronomical receivers and their ...interference limits are outlined. EMC above 30 MHz is a serious problem for Radio Astronomy. Interferer (CISPR) and victim (ITU-R RA 769) standards are not harmonised. The emissions from the interferer and their spectral characteristics are not defined sufficiently well by CISPR standards. The required minimum coupling losses (MCL) between an industrial device and radio astronomical antenna depends on device properties but is shown to exceed 140 dB in most cases. Spatial separation of a few km is insufficient on its own, the terrain must shield > 30-40 dB, additional mitigations such as extra shielding or suppression of high frequency emissions may be necessary. A case by case compatibility analysis and tailored EMC measures are required for individual installations. Aggregation of many weak rfi emitters can become serious problem. If deployment densities are high enough, the emission constraints can even exceed those for a single interferer at a short distance from the radio observatory. Compatibility studies must account not only for the single interferer but also for many widely distributed interference sources.
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