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

Due to the lack of long term pulsed emission in quiescence and the strong timing noise, it is impossible to directly measure the braking index n of a magnetar. Based on the estimated ages of their potentially associated supernova remnants (SNRs), we estimate the values of the mean braking indices of eight magnetars with SNRs, and find that they cluster in a range of 1 ∼42. Five magnetars have smaller mean braking indices of 1 < n < 3, and we interpret them within a combination of magneto-dipole radiation and wind aided braking, while the larger mean braking indices of n > 3 for other three magnetars are attributed to the decay of external braking torque, which might be caused by magnetic field decay. We estimate the possible wind luminosities for the magnetars with 1 < n < 3, and the dipolar magnetic field decay rates for the magnetars with n > 3 within the updated magneto-thermal evolution models. Although the constrained range of the magnetars' braking indices is tentative, due to the uncertainties in the SNR ages, which come from distance uncertainties and the unknown conditions of the expanding shells, our method provides an effective way to constrain the magnetars' braking indices if the measurements of the SNRs' ages are reliable, which can be improved by future observations.

Pulsar positions can be measured with high precision using both pulsar timing methods and very-long-baseline interferometry (VLBI). Pulsar timing positions are referenced to a solar-system ephemeris, whereas VLBI positions are referenced to distant quasars. Here we compare pulsar positions from published VLBI measurements with those obtained from pulsar timing data from c 0000 RAS 2 J.B. Wang et al.the Nanshan and Parkes radio telescopes in order to relate the two reference frames. We find that the timing positions differ significantly from the VLBI positions (and also differ between different ephemerides). A statistically significant change in the obliquity of the ecliptic of 2.16 ± 0.33 mas is found for the JPL ephemeris DE405, but no significant rotation is found in subsequent JPL ephemerides. The accuracy with which we can relate the two frames is limited by the current uncertainties in the VLBI reference source positions and in matching the pulsars to their reference source. Not only do the timing positions depend on the ephemeris used in computing them, but also different segments of the timing data lead to varying position estimates. These variations are mostly common to all ephemerides, but slight changes are seen at the 10µas level between ephemerides.

In this paper, we report on a detailed investigation of the multiwavelength properties of a newly detected γ‐ray pulsar, PSR J2021+4026, in both observational and theoretical aspects. We first identify an X‐ray source in the XMM–Newton serendipitous source catalogue, 2XMM J202131.0+402645, located within the 95 per cent confidence circle of PSR J2021+4026. With an archival Chandra observation, this identification provides an X‐ray position with arcsecond accuracy which is helpful in facilitating further investigations. Searching for the pulsed radio emission at the position of 2XMM J202131.0+402645 with a 25‐m telescope at Urumqi Astronomical Observatory resulted in null detection and places an upper limit of 0.1 mJy for any pulsed signal at 18 cm. Together with the emission properties in X‐ray and γ‐ray, the radio quietness suggests PSR J2021+4026 to be another member of Geminga‐like pulsars. In the radio sky survey data, extended emission features have been identified in the γ‐ray error circle of PSR J2021+4026. We have also re‐analysed the γ‐ray data collected by Fermi's Large Area Telescope. We found that the X‐ray position of 2XMM J202131.0+402645 is consistent with that of the optimal γ‐ray timing solution. We have further modelled the results in the context of the outer gap model, which provides us with constraints for the pulsar emission geometry such as the magnetic inclination angle and the viewing angle. We have also discussed the possibility of whether PSR J2021+4026 has any physical association with the supernova remnant G78.2+2.1 (γ‐Cygni).