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 region^3–5 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.