X-Ray Spectrum of the Rapid Burster Using the [ITAL]CHANDRA[/ITAL][ITAL]Chandra[/ITAL] HETGS

Abstract

We present observations of the Rapid Burster (RB, also known as MXB 1730-335) using the Chandra High Energy Transmission Grating Spectrometer. The average interval between type II (accretion) bursts was about 40 s. There was one type I (thermonuclear flash) burst and about 20 minibursts that are probably type II bursts whose peak flux is 10%–40% of the average peak flux of the other type II bursts. The time-averaged spectra of the type II bursts are well fitted by a blackbody with a temperature of kT = 1.6 keV, a radius of 8.9 km for a distance of 8.6 kpc, and an interstellar column density of 1.7 × 1022 cm-2. No narrow emission or absorption lines were clearly detected. The 3 σ upper limits to the equivalent widths of any features are less than 10 eV in the 1.1–7.0 keV band and as small as 1.5 eV near 1.7 keV. We suggest that Comptonization destroys absorption features such as the resonance line of Fe XXVI.