NICER observation list: Target ID 663301

Although the WD mass limit is believed to be universal, recent several theoretical studies claimed that the mass limit can vary. For example, WD's strong internal magnetic field should affect the mass limit. To investigate this effect, we have to measure both of mass and radius of the magnetic WDs. Here, we propose a new technique to measure the WD radius which utilizes a fact that a cap blackbody radiation zone on the WD sends significant flux to observers because of the WD curvature even when the normal vector of the center of the radiation zone is normal to the line of sight. We will demonstrate our new technique with four 15 ks NICER observations (60 ks in total) of a magnetic WD binary V405 Aur. We prefer to divide the observation time to see fluctuation of the background.