Light curves and polarizations of gravitationally lensed kilonovae

Kilonovae are generally believed to originate from the ejecta of binary neutron stars (NSs) or black hole and NS mergers. Free neutrons might be retained in the outermost layer of the ejecta to produce a precursor via $\beta$-decay. During the propagation of kilonovae to observers, a small percentage of them might be gravitationally lensed by foreground objects. In this paper, three lens models, i.e., the point-mass model, the singular isothermal sphere (SIS) model, and the Chang-Refsdal model, were taken into consideration to explore the light curves and polarizations of gravitationally lensed kilonovae. We found that if the time delay between two images exceeds the ejecta heating timescale for the lens mass $\sim 10^{10}~M_\odot$ in the SIS model, a tiny bump-like signal will be generated in the light curve, and the total luminosity will be magnified in all cases. The polarization of lensed kilonovae is significantly enhanced in most cases. Future detections of lensed kilonovae will impose constraints on the morphology of the ejecta and aid in the determination of the nature of compact object mergers and the search for strong gravitational lenses.
Comment: 11 pages, 4 figures, accepted for publication in ApJ