Fast radio bursts (FRBs) are mysterious millisecond-duration radio transients 1, 2. Two possible mechanisms that could generate extremely coherent emission from FRBs invoke neutron star magnetospheres 3-5 or relativistic shocks far from the central energy source 6-8. Detailed polarization observations may help us to understand the emission mechanism. However, the available FRB polarization data have been perplexing, because they show a host of polarimetric properties, including either a constant polarization angle during each burst for some repeaters 9, 10 , or variable polarization angles in some other apparently one-off events 11, 12. Here we report observations of 15 bursts from FRB 180301 and find various polarization

Aims. We intend to study of the nulling and subpulse drifting in PSR J1727−2739 in detail to investigate its radiation properties. Methods. The observations were carried out on 20 March, 2004 using the Parkes 64-m radio telescope with a central frequency of 1518 MHz. A total of 5568 single pulses were analysed.Results. This pulsar shows well-defined nulls with lengths lasting from 6 to 281 pulses and separated by burst phases ranging from 2 to 133 pulses. We estimate a nulling fraction of around 68%. No emission in the average pulse profile integrated over all null pulses is detected with significance above 3σ. Most transitions from nulls to bursts are within a few pulses, whereas the transitions from bursts to nulls exhibit two patterns of decay; these transitions either decrease gradually or rapidly. In the burst phase, we find that there are two distinct subpulse drift modes with vertical spacing between the drift bands of 9.7 ± 1.6 and 5.2 ± 0.9 pulse periods, while sometimes there is a third mode with no subpulse drifting. Some mode transitions occur within a single burst, while others are separated by nulls. Different modes have different average pulse profiles. Possible physical mechanisms are discussed.

We present our piggyback search for fast radio bursts using the Nanshan 26m Radio Telescope and the Kunming 40m Radio Telescope. The observations are performed in the L-band from 1380 MHz to 1700 MHz at Nanshan and S-band from 2170 MHz to 2310 MHz at Kunming. We built the Roach2-based FFT spectrometer and developed the real-time transient search software. We introduce a new radio interference mitigation technique named zero-DM matched filter and give the formula of the signalto-noise ratio loss in the transient search. Though we have no positive detection of bursts in about 1600 and 2400 hours data at Nanshan and Kunming respectively, an intriguing peryton was detected at Nanshan, from which hundreds of bursts were recorded. Perytons are terrestrial radio signals that mimic celestial fast radio bursts. They were first reported at Parkes and identified as microwave oven interferences later. The bursts detected at Nanshan show similar frequency swept emission and have double-peaked profiles. They appeared in different sky regions in about tens of minutes observations and the dispersion measure index is not exactly 2, which indicates the terrestrial origin. The peryton differs drastically from the known perytons detected at Parkes, because it appeared in a precise period of p = 1.71287 ± 0.00004 s. Its origin remains unknown.

By analysing the data acquired from the Parkes 64-m radio telescope at 1369 MHz, we report on the phase-stationary non-drift amplitude modulation observed in PSR J1048−5832. The high-sensitivity observations revealed that the central and trailing components of the pulse profile of this pulsar switch between a strong mode and a weak mode periodically. However, the leading component remains unchanged. Polarization properties of the strong and weak modes are investigated. Considering the similarity to mode changing, we argue that the periodic amplitude modulation in PSR J1048−5832 is periodic mode changing. The fluctuation spectral analysis showed that the modulation period is very short (∼2.1 s or 17P 1 ), where P 1 is the rotation period of the pulsar. We find that this periodic amplitude modulation is hard to explain by existing models that account for the periodic phenomena in pulsars like subpulse drifting.

We report detailed investigation of nulling and drifting behavior of two pulsars PSRs J1741−0840 and J1840−0840 observed from the Giant Meterwave Radio Telescope at 625 MHz. PSR J1741−0840 was found to show nulling fraction (NF) of around 30±5% while PSR J1840−0840 was shown to have NF of around 50±6%. We measured drifting behavior from different profile components in PSR J1840−0840 for the first time with the leading component showing drifting with 13.5±0.7 periods while the weak trailing component showed drifting of around 18±1 periods. Large nulling do hamper accuracy of these quantities derived using standard Fourier techniques. A more accurate comparison was drawn from driftband slopes, measured after sub-pulse modeling. These measurements revealed interesting sporadic and irregular drifting behavior in both pulsars. We conclude that the previously reported different drifting periodicities in the trailing component of PSR J1741−0840 is likely due to the spread in these driftband slopes. We also find that both components of PSR J1840−0840 show similar driftband slopes within the uncertainties. Unique nulling-drifting interaction is identified in PSR J1840−0840 where, in most occasions, the pulsar tends to start nulling after what appears to be an end of a driftband. Similarly, when the pulsar switches back to an emission phase, in most occasions it starts at the beginning of a new driftband in both components. Such behaviors have not been detected in any other pulsars to our knowledge. We also found that PSR J1741−0840 seems to have no memory of its previous burst phase while PSR J1840−0840 clearly exhibits memory of its previous state even after longer nulls for both components. We discuss possible explanations for these intriguing nulling-drifting interactions seen in both pulsars based on various pulsar nulling models.

Glitches correspond to sudden jumps of rotation frequency (ν) and its derivative ( ) of pulsars, the origin of which remains not well understood yet, partly because the jump processes of most glitches are not well time-resolved. There are three large glitches of the Crab pulsar, detected in 1989, 1996, and 2017, which were found to have delayed spin-up processes before the normal recovery processes. Here we report two additional glitches of this pulsar that occurred in 2004 and 2011 for which we discovered delayed spin-up processes, and present refined parameters of the largest glitch, which occurred in 2017. The initial rising time of the glitch is determined as <0.48 hr. The two glitches that occurred in 2004 and 2011 had delayed spin-up time scales (τ 1) of 1.7 ± 0.8 days and 1.6 ± 0.4 days, respectively. We also carried out a statistical study of these five glitches with observed spin-up processes. We find that the Δν versus relation of these five glitches is similar to those with no detected delayed spin-up process, indicating that they are similar to the others in nature except that they have larger amplitudes. For these five glitches, the amplitudes of the delayed spin-up process ( ) and recovery process (Δν d2), their time scales (τ 1, τ 2), and permanent changes in spin frequency (Δν p) and total frequency step (Δν g) have positive correlations. From these correlations, we suggest that the delayed spin-up processes are common for all glitches, but are too short and thus difficult to be detected for most glitches.

PSR J1825−0935 (PSR B1822−09) switches between radio-quiet (Q-mode) and radiobright (B-mode) modes. The Q-mode is known to have a periodic fluctuation that modulates both the interpulse and the main pulse with the same period. Earlier investigators argued that the periodic Q-mode modulation is associated with drifting subpulses. We report on single-pulse observations of PSR J1825−0935 that were made using the Parkes 64-m radio telescope with a central frequency of 1369 MHz. The high-sensitivity observations revealed that the periodic Q-mode modulation is in fact a periodic longitude-stationary intensity modulation occurring in the interpulse and the main pulse. The fluctuation spectral analysis showed that the modulation period is about 43P 1 , where P 1 is the rotation period of the pulsar. Furthermore, we confirm that the modulation patterns in the interpulse and the main pulse are phase-locked. Specifically, the intensities of the interpulse and the immediately following main pulse are more highly correlated than for the main pulse and interpulse at any other lag. Polarization properties of the strong and weak Q-mode states are different, even for the trailing part of the main pulse which does not show the periodic intensity modulation.

We report on a detailed study on the mode switching in pulsar J1326−6700 by analysis the data acquired from the Parkes 64-m radio telescope at 1369 MHz. During the abnormal mode, the emission at the central and trailing components becomes extremely weak. Meanwhile, the leading emission shifts towards earlier by almost 2 degrees, and remains in this position for typically less than a minute. The mean flux density of the normal mode is almost five times that of the abnormal mode. Our data show that 85% of the time for PSR J1326−6700 was in the normal mode and 15% was in the abnormal mode. The intrinsic distributions of mode timescales can be well described by Weibull distributions, which presents a certain amount of memory in mode switching. Furthermore, a quasi-periodicity has been identified in the mode switching in pulsar J1326−6700. The estimated delay emission heights based on the kinematical effects indicate that the abnormal mode may be originated from higher altitude than the normal mode.