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We report on simultaneous optical and X-ray observations of the dwarf nova SSCyg with Tomo-e Gozen/1.05 m Kiso Schmidt and Neutron star Interior CompositionExploreR (it NICER) / International Space Station (ISS). A total of fourobservations were carried out in the quiescent state and highly correlatedlight variations between the two wavelengths were detected. We have extractedlocal brightness peaks in the light curves with a binning interval of 1 sec,called `shots', and have evaluated time lags between the optical and X-rayvariations by using a cross-correlation function. Some shots exhibitsignificant optical lags to X-ray variations and most of them are positiveranging from $+$0.26 to 3.11 sec, which have never been detected.  They may be ascribable to X-ray reprocessing in the accretion disk and/or thesecondary star. This analysis is possible thanks to the high timing accuracyand the high throughput of NICER and the matching capability of Tomo-e Gozen.Also, it is confirmed that the correlation between the optical and X-rayvariations changed in the middle of one of our observation windows and theX-ray spectrum softer than 2 keV varied in accordance with the correlation.

Detection of highly correlated optical and X-ray variations in SS Cygni with Tomo-e Gozen and NICER