Anticorrelated Hard/Soft X-Ray Emission from the X-Ray Burster 4U 0614+091

Abstract

We have detected transient X-ray activity from the X-ray burster 4U 0614+091 simultaneously with BATSE on board the Compton Gamma Ray Observatory (20-100 keV) and the all-sky monitor (ASM) on board the Rossi X-Ray Timing Explorer (1-12 keV). The peak fluxes reach approximately 40 mcrab in both instruments over a period of about 20 days. The variable emission shows a clear anticorrelation of the hard X-ray flux with the soft X-ray count rate. The observed anticorrelation is another clear counterexample to the notion that only black hole binaries exhibit such correlations. The individual spectra during this period can be fitted by power laws with photon indices 2.2 +/- 0.3 (ASM) and 2.7 +/- 0.4 (BATSE), while the combined spectra can be described by a single power law with index 2.09 +/- 0.08. BATSE and the Rossi X-Ray Timing Explorer ASM are a good combination for monitoring X-ray sources over a wide energy band.