It is believed that an isolated pulsar loses its rotational energy mainly through a relativistic wind consisting of electrons, positrons and possibly Poynting flux 1-3 . As it expands, this wind may eventually be terminated by a shock, where particles can be accelerated to energies of X-ray synchrotron emission, and a pulsar wind nebula (PWN) is usually detectable surrounding a young energetic pulsar 1-3 . However, the nature and/or energetics of these physical processes remain very uncertain, largely because they typically cannot be studied in a timeresolved fashion. Here we show that the X-ray PWN around the young pulsar PSR B0540-69 brightens gradually up to 32±8% over the mean previous flux, after a sudden spin-down rate (ν) transition (SRT) by ∼ 36% in December 2011, which has very different properties from a traditional pulsar glitch 4 . No evidence is seen for any change in the pulsed X-ray emission. We conclude that the SRT results from a sudden change in the pulsar magnetosphere that increases the pulsar wind power and hence the PWN X-ray emission. The X-ray light curve of the PWN suggests a mean life time of the particles of 397 ± 374 days, corresponding to a magnetic field strength of 0.78 +4.50 −0.28 mG in the PWN.

The Intermediate Palomar Transient Factory reported the discovery of an unusual type II-P supernova iPTF14hls. Instead of a ∼ 100-day plateau as observed for ordinary type II-P supernovae, the light curve of iPTF14hls has at least five distinct peaks, followed by a steep decline at ∼ 1000 days since discovery. Until 500 days since discovery, the effective temperature of iPTF14hls is roughly constant at 5000-6000 K. In this paper we propose that iPTF14hls is likely powered by intermittent fallback accretion. It is found that the light curve of iPTF14hls can be well fit by the usual t −5/3 accretion law until ∼ 1000 days post discovery when the light curve transitions to a steep decline. To account for this steep decline, we suggest a power-law density profile for the late accreted material, rather than the constant profile as appropriated for the t −5/3 accretion law. Detailed modeling indicates that the total fallback mass is ∼ 0.2M , with an ejecta mass M ej 21M . We find the third peak of the light curve cannot be well fit by the fallback model, indicating that there could be some extra rapid energy injection. We suggest that this extra energy injection may be a result of a magnetic outburst if the central object is a neutron star. These results indicate that the progenitor of iPTF14hls could be a massive red supergiant.

It is well-known that ordinary supernovae (SNe) are powered by 56 Ni cascade decay. Broad-lined type Ic SNe (SNe Ic-BL) are a subclass of SNe that are not all exclusively powered by 56 Ni decay. It was suggested that some SNe Ic-BL are powered by magnetar spin-down. iPTF16asu is a peculiar broad-lined type Ic supernova discovered by the intermediate Palomar Transient Factory. With a rest-frame rise time of only 4 days, iPTF16asu challenges the existing popular models, for example, the radioactive heating ( 56 Ni-only) and the magnetar+ 56 Ni models. Here we show that this rapid rise could be attributed to interaction between the SN ejecta and a preexisting circumstellar medium ejected by the progenitor during its final stages of evolution, while the late-time light curve can be better explained by energy input from a rapidly spinning magnetar. This model is a natural extension to the previous magnetar model. The mass-loss rate of the progenitor and ejecta mass are consistent with a progenitor that experienced a common envelope evolution in a binary. An alternative model for the early rapid rise of the light curve is the cooling of a shock propagating into an extended envelope of the progenitor. It is difficult at this stage to tell which model (interaction+magnetar+ 56 Ni or cooling+magnetar+ 56 Ni) is better for iPTF16asu. However, it is worth noting that the inferred envelope mass in the cooling+magnetar+ 56 Ni is very high.