Discovery of superhumps during a normal outburst of SU Ursae Majoris

TL;DR

This study reports the first detection of superhumps during a normal outburst of SU UMa, indicating the accretion disk reaches the 3:1 resonance even outside superoutbursts.

Contribution

It provides the first observational evidence of superhumps during a normal outburst in SU UMa-type dwarf novae, challenging existing models of disk behavior.

Findings

Superhumps observed during a normal outburst.

Superhump period matches that during superoutbursts.

Accretion disk reaches 3:1 resonance during normal outburst.

Abstract

We report on time-resolved photometry during a 2012 January normaloutburst of SU UMa. The light curve shows hump-like modulations with a period of 0.07903(11) d, which coincides with the known superhump period of SU UMa during superoutbursts. We interpret this as superhump, based on the observed periodicity, profiles of the averaged light curve, and the $g'-I_{\rm c}$ variation during the normal outburst. This is the first case that superhumps are detected during an isolated normal outburst of SU UMa-type dwarf novae. The present result strongly suggests that the radius of the accretion disk already reaches the 3:1 resonance even in the midst of the supercycle.