Recent observations strongly suggest that the millisecond pulsar binary PSR J1023+0038 has developed an accretion disk since 2013 June. We present a multi-wavelength analysis of PSR J1023+0038, which reveals that (1) its gammarays suddenly brightened within a few days in 2013 June/July and has remained at a high gamma-ray state for several months; (2) both UV and X-ray fluxes have increased by roughly an order of magnitude; and (3) the spectral energy distribution has changed significantly after the gamma-ray sudden flux change. Time variabilities associated with UV and X-rays are on the order of 100-500 s and 50-100 s, respectively. Our model suggests that a newly formed accretion disk, due to the sudden increase of the stellar wind, could explain the changes of all these observed features. The increase of UV is emitted from the disk, and a new component in gamma-rays is produced by inverse Compton scattering between the new UV component and pulsar wind. The increase of X-rays results from the enhancement of injection pulsar wind energy into the intra-binary shock due to the increase of the stellar wind. We also predict that the radio pulses may be blocked by the evaporated winds from the disk, and the pulsar is still powered by rotation.

We have conducted a systematic survey for the X-ray properties of millisecond pulsars (MSPs). Currently, there are 47 MSPs with confirmed X-ray detections. We have also placed the upper limits for the X-ray emission from the other 36 MSPs by using the archival data. We have normalized their X-ray luminosities L x and their effective photon indices Γ into a homogeneous data set, which enable us to carry out a detailed statistical analysis. Based on our censored sample, we report a relation of L x ≃ 10 31.05 Ė /10 35 1.31 erg/s (2-10 keV) for the MSPs. The inferred X-ray conversion efficiency is found to be lower than previously reported estimate that could be affected by selection bias. L x also correlates/anti-correlates with the magnetic field strength at the light cylinder B LC /characteristic age τ . On the other hand, there is no correlation between L x and their surface magnetic field strength B s . We have further divided the sample into four classes: (i) black-widows, (ii) redbacks, (iii) isolated MSPs and (iv) other MSP binaries, and compare the properties among them. We noted that while the rotational parameters and the orbital periods of redbacks and black-widow are similar, L x of redbacks are significantly higher than those of black-widows in the 2-10 keV band. Also the Γ of redbacks are apparently smaller than those of black-widows, which indicates the X-ray emission of redbacks are harder than that of black-widows. This can be explained by the different contribution of intrabinary shocks in the X-ray emission of these two classes.

We use a modified outer-gap model to study the multifrequency phase-resolved spectra of the Crab pulsar. The emissions from both poles contribute to the light curve and the phase-resolved spectra. Using the synchrotron selfCompton mechanism and by considering the incomplete conversion of curvature photons into secondary pairs, the observed phase-averaged spectrum from 100 eV to 10 GeV can be explained very well. The predicted phase-resolved spectra can match the observed data reasonably well, too. We find that the emission from the north pole mainly contributes to leading wing 1. The emissions in the remaining phases are mainly dominated by the south pole. The widening of the azimuthal extension of the outer gap explains trailing wing 2. The complicated phase-resolved spectra for the phases between the two peaks, namely, trailing wing 1, the bridge, and leading wing 2, strongly suggest that there are at least two well-separated emission regions with multiple emission mechanisms-synchrotron radiation, inverse Compton scattering, and curvature radiation. Our best-fit results indicate that there may exist some asymmetry between the south and north poles. Our model predictions can be examined with GLAST.