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GK Persei

GK Persei, or Nova Persei 1901, was a famous classical nova that nearly reached magnitude 0 in the first year of the last century.  It took GK Per several years to return to its faint state, but even now its quiescence is remarkably unquiet.  Within a few decades of outburst GK Per showed evidence of outbursts, and by the 1960s it was clear that GK Per was showing dwarf nova-like outbursts, brightenings of 2-3 magnitudes every few years, each lasting for 100 days or so.  Unlike classical nova outbursts which are thermonuclear runaway events on the surfaces of the white dwarf, dwarf nova outbursts come from state transitions in the accretion disk around the white dwarf when the disk suddenly becomes hot and opaque and shines very brightly.  These outbursts had exhibited a strange decline in intensity in recent years, but the outburst in early 2010 bucked the trend.  GK Per reached magnitude 9.5 -- four magnitudes above quiescence -- in an outburst lasting about 200 days.

In addition to showing these outbursts, GK Per also shows high-energy emission indicating that it has a magnetic white dwarf primary star, and is known as an intermediate polar.

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