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Register a new userA single pulse study of PSR J1022+1001
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Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we have recorded 10^5 single pulses from PSR J1022+1001. We studied the polarization properties, their energy distribution and their times of arrival. This is only possible with the high sensitivity available using FAST. There is no indication that PSR~J1022+1001 exhibits giant pulse, nulling or traditional mode changing phenomena. The energy in the leading and trailing components of the integrated profile is shown to be correlated. The degree of both linear and circular polarization increases with the pulse flux density for individual pulses. Our data indicates that pulse jitter leads to an excess noise in the timing residuals of 67 ns when scaled to one hour, which is consistent with Liu et al. (2015). We have unsuccessfully trialled various methods to improve timing precision through the selection of specific single pulses. Our work demonstrates that FAST can detect individual pulses from pulsars that are observed in order to detect and study gravitational waves. This capability enables detailed studies, and parameterisation, of the noise processes that affect the sensitivity of a pulsar timing array.
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Millisecond pulsars (MSPs) are known as highly stable celestial clocks. Nevertheless, recent studies have revealed the unstable nature of their integrated pulse profiles, which may limit the achievable pulsar timing precision. In this paper, we present a case study on the pulse profile variability of PSR J1022+1001. We have detected approximately 14,000 sub-pulses (components of single pulses) in 35-hr long observations, mostly located at the trailing component of the integrated profile. Their flux densities and fractional polarisation suggest that they represent the bright end of the energy distribution in ordinary emission mode and are not giant pulses. The occurrence of sub-pulses from the leading and trailing components of the integrated profile is shown to be correlated. For sub-pulses from the latter, a preferred pulse width of approximately 0.25 ms has been found. Using simultaneous observations from the Effelsberg 100-m telescope and the Westerbork Synthesis Radio Telescope, we have found that the integrated profile varies on a timescale of a few tens of minutes. We show that improper polarisation calibration and diffractive scintillation cannot be the sole reason for the observed instability. In addition, we demonstrate that timing residuals generated from averages of the detected sub-pulses are dominated by phase jitter, and place an upper limit of ~700 ns for jitter noise based on continuous 1-min integrations.
We present radio observation of a millisecond pulsar PSR J0621+1002 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulsar shows periodic pulse intensity modulations for both the first and the third pulse components. The fluctuation spectrum of the first pulse component has one peak of 3.0$pm$0.1 pulse periods, while that of the third pulse component has two diffused peaks of 3.0$pm$0.1 and 200$pm$1 pulse periods. The single pulse timing analysis is carried out for this pulsar and the single pulses can be divided into two classes based on the post-fit timing residuals. We examined the achievable timing precision using only the pulses in one class or bright pulses. However, the timing precision improvement is not achievable.
We have investigated the mode-changing properties of PSR B0329+54 using 31 epochs of simultaneous 13 cm/3 cm single-pulse observations obtained with Shanghai Tian Ma 65 m telescope. The pulsar was found in the abnormal emission mode 17 times, accounting for ~13% of the 41.6 hours total observation time. Single pulse analyses indicate that mode changes took place simultaneously at 13 cm/3 cm within a few rotational periods. We detected occasional bright and narrow pulses whose peak flux densities were 10 times higher than that of the integrated profile in both bands. At 3 cm, about 0.66% and 0.27% of single pulses were bright in the normal mode and abnormal mode respectively, but at 13 cm the occurrence rate was only about 0.007%. We divided the pulsar radiation window into three components (C1, C2 and C3) corresponding to the main peaks of the integrated profile. The bright pulses preferentially occurred at pulse phases corresponding to the peaks of C2 and C3. Fluctuation spectra showed that C2 had excess red noise in the normal mode, but broad quasi-periodic features with central frequencies around 0.12 cycles/period in the abnormal mode. At 3 cm, C3 had a stronger quasi-periodic modulation centered around 0.06 cycles/period in the abnormal mode. Although there were some asymmetries in the two-dimensional fluctuation spectra, we found no clear evidence for systematic subpulse drifting. Consistent with previous low-frequency observations, we found a very low nulling probability for B0329+54 with upper limits of 0.13% and 1.68% at 13 cm/3 cm respectively.
We have carried out a detailed study of single pulse emission from the pulsar B2000+40 (J2002+4050), observed at 1.6 GHz frequencies using the Effelsberg radio telescope. The pulsar has three components which are not well separated, with the central component resembling core emission. We have investigated modulations in single pulse behaviour using the fluctuation spectral analysis which showed presence of two prominent periodicities, around 2.5$P$ and 40$P$, respectively. The shorter periodicity was associated with the phenomenon of subpulse drifting and was seen to be absent in central core component. Drifting showed large phase variations in conal components. Additionally, the periodic modulations had significant evolution with time, varying between very sharp and highly diffuse features. In addition to drifting the pulsar also had presence of nulling in the single pulse sequence. The longer periodic feature in the fluctuation spectra was associated with nulling behaviour. The pulsar joins a select group which shows the presence of phase modulated drifting as well as periodic nulling in the presence of core emission. This provides further evidence for the two phenomena to be distinct from each other with different physical origin.
We report on single-pulse observations of the Galactic Center magnetar PSR J1745$-$2900 that were made using the Parkes 64-m radio telescope with a central frequency of 3.1 GHz at five observing epochs between 2013 July and August. The shape of the integrated pulse profiles was relatively stable across the five observations, indicating that the pulsar was in a stable state between MJDs 56475 and 56514. This extends the known stable state of this pulsar to 6.8 months. Short term pulse shape variations were also detected. It is shown that this pulsar switches between two emission modes frequently and that the typical duration of each mode is about ten minutes. No giant pulses or subpulse drifting were observed. Apparent nulls in the pulse emission were detected on MJD 56500. Although there are many differences between the radio emission of magnetars and normal radio pulsars, they also share some properties. The detection of mode changing and pulse nulling in PSR J1745$-$2900 suggests that the basic radio emission process for magnetars and normal pulsars is the same.
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