The accretion-induced collapse (AIC) of a white dwarf in a binary with a nondegenerate companion can sometimes lead to the formation of a rapidly rotating and highly magnetized neutron star (NS). The spin-down of this NS can drive a powerful pulsar wind (PW) and bring out some detectable multi-wavelength emissions. On the one hand, the PW can evaporate the companion in a few days to form a torus surrounding the NS. Then, due to the blockage of the PW by the torus, a reverse shock can be formed in the wind to generate intense hard X-rays. This emission component disappears in a few weeks' time, after the torus is broken down at its inner boundary and scoured into a very thin disk. On the other hand, the interaction between the PW with an AIC ejecta can lead to a termination shock of the wind, which can produce a long-lasting soft X-ray emission component. In any case, the high-energy emissions from deep inside the system can be detected only after the AIC ejecta becomes transparent for X-rays. Meanwhile, by absorbing the X-rays, the AIC ejecta can be heated effectively and generate a fast-evolving and luminous ultraviolet (UV)/optical transient. Therefore, the predicted hard and soft X-ray emissions, associated by an UV/optical transient, provide a clear observational signature for identifying AIC events in current and future observations (e.g., AT 2018cow).

Super-Chandrasekhar remnants of double white dwarf mergers could sometimes collapse into a rapidly rotating neutron star (NS), accompanying with a mass ejection of a few times 0.01M ⊙ . Bright optical transient emission can be produced by the ejecta due to heating by radioactivities and particularly by energy injection from the NS. Since the merger remnants before collapse resemble a star evolving from the asymptotic giant branch phase to the planetary nebula phase, an intense dusty wind is considered to be driven about several thousand years ago before the collapse and surround the remnant at large radii. Therefore, the optical transient emission can be somewhat absorbed and scattered by the dusty wind, which can suppress the peak emission and cause a scattering plateau in optical light curves. Several years later, as the ejecta finally catches up with the wind material, the shock interaction between them can further give rise to a detectable radio transient emission on a timescale of tens of days. Discovery of and observations to such dust-affected optical transients and shock-driven radio transients can help to explore the nature of super-Chandrasekhar merger remnants and as well as the density and type ratios of double white dwarf systems, which is beneficial in assessing their gravitational wave contributions.

As indicated by the observed X-ray flares, a great amount of energy could be intermediately released from the postburst central engine of gamma-ray bursts (GRBs). As a natural consequence, the GRB external shock could be energized over and over. With such a multiple energy injection model, we explore the unique X-ray afterglow light curve of GRB 050712, which exists four apparent shallow decay plateaus. Together with three early X-ray flares, the central engine of GRB 050712 is supposed to release energy at least seven times after the burst. Furthermore we find that the energy released during four plateaus are all on the same order of magnitude, but the luminosity decreases with time significantly. These results may provide some interesting implications for the GRB central engine.

1FGL J1018.6–5856 is a high mass gamma-ray binary containing a compact object orbiting around a massive star with a period of 16.544 d. If the compact object is a pulsar, non-thermal emissions are likely produced by electrons accelerated at the termination shock, and may also originate from the magnetosphere and the un-shocked wind of the pulsar. In this paper, we investigate the non-thermal emissions from the wind and the shock with different viewing geometries and study the multi-wavelength emissions from 1FGL J1018.6–5856. We present the analysis results of the Fermi/LAT using nearly 10 years of data. The phase-resolved spectra indicate that the GeV emissions comprise a rather steady component that does not vary with orbital motion and a modulated component that shows flux maximum around inferior conjunction. The keV/TeV light curves of 1FGL J1018.6–5856 also exhibit a sharp peak around inferior conjunction, which are attributed to the boosted emission from the shock, while the broad sinusoidal modulations could be originating from the deflected shock tail at a larger distance. The modulations of GeV flux are likely caused by the boosted synchrotron emission from the shock and the IC emission from the un-shocked pulsar wind, while the steady component comes from the outer gap of the pulsar magnetosphere. Finally, we discuss the similarities and differences of 1FGL J1018.6–5856 with other binaries, like LS 5039.

During the in-spiral stage of a compact binary, a wind bubble could be blown into interstellar medium, if the electromagnetic radiation due to the binary orbital motion is strong enough. Therefore, short gamma-ray bursts (SGRBs) due to double neutron star mergers would in principle happen in a wind bubble environment, which can influence the propagation of the SGRB jet and the consequent afterglow emission. By calculating the dynamics and synchrotron radiation of the jet-driven external shock, we reveal that an abrupt jump could appear in the afterglow light curves of SGRBs and the observational time of the jump is dependent on the viewing angle. This light curve jump provides an observational signature to constrain the radius of the wind bubble and then the power of the binary electromagnetic radiation, by combining with gravitational wave detection.