Sudden disappearance of a small sunspot associated with the 2002 February 20 M2.4 flare

In this Letter, we present the evidence of rapid disappearance of a small sunspot associated with a M2.4 flare, which occurred in NOAA Active Region 9830, at 2106 UT, on 2002 February 20. The sunspot, in the size of about 45 arcsec², completely disappeared in about 60 minutes, coinciding with the onset of the flare. The magnetic flux of this sunspot disappeared in the similar timescale. Furthermore, we found that the disappearing sunspot is located near the edge of the main hard X-ray source observed by RHESSI. This hard X-ray source is located in the magnetic neutral line dividing the disappearing spot and the opposite polarity flux. Two possible explanations are offered: (1) the disappearing sunspot is due to the rapid magnetic reconnection and subsequent submergence; (2) the disappearing sunspot represents impulsive emergence and detachment of a magnetic "bubble".