Hard X-Ray Emission Associated with White Dwarfs. IV. Signs of Accretion from Substellar Companions

This research was supported by the NASA grants SAO GO8-9026 (Chandra) and JPL 1319342 (Spitzer). Y.H.C. acknowledges grants MOST 108-2112-M001-045 and MOST 109-2112-M-001-040 from the Ministry of Science and Technology of Taiwan, Republic of China. J.A.T. and M.A.G. are funded by UNAM DGAPA PAPIIT project IA100318. M.A.G. also acknowledges support from grant PGC2018-102184-B-IOO of the Spanish Ministerio de Ciencia, Educacion y Universidades cofunded by FEDER funds. This paper has used observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundacion Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.