Discovery of IR bursts from Liller I/MXB1730–333

Abstract

THE first detection of IR bursts from the object1 known as Liller I which has been identified2 with the rapid X-ray burster MXB1730–333 is reported here. The rapid burster is the only one of its kind that has been extensively studied in the X-ray region3–5 and some of its known characteristics can be summarised as follows. When it is active it gives several thousand X-ray bursts per day. It operates in two modes: mode I (usually in March and September every year), mode II (usually in April and October every year). In mode I it gives large X-ray bursts with energy in the range 1039–1040 erg and also small bursts with energy in the range of 1038–1039 erg; while in mode II it primarily emits bursts with energy typically close to 1039 erg. These bursts are called type II on the basis of the constant character of their spectrum during the decay phase. The rapid burster occasionally also gives bursts known as type I which are characterised by the softening of the X-ray spectrum during the decay phase. The energy in these bursts is usually in excess of 1039 erg and their frequency is about one every few hours.