HETE-2 observation of the evidence of a long acting engine in the extremely soft XRF 040916.

A long and extremely soft X-ray flash was detected and localized by the instruments aboard the HETE-2 at 00:03:30 UT on 2004 Sep. 16. This burst consists of two peaks separated by ∼200 s, with durations of about 110 s and 60 s. We have analyzed the energy spectra of the 1st and 2nd peaks observed with the Wide Field X-Ray Monitor (WXM) and the French Gamma Telescope (FREGATE). We discuss the origin of the 2nd peak in terms of flux variabilities and timescales. We find that it is most likely part of the prompt emission, and is explained by the long-acting engine model. [ABSTRACT FROM AUTHOR]