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

We have detected transient X-ray activity from the X-ray burster 4U 0614+091 simultaneously with BATSE/CGRO (20–100 keV) and ASM/RXTE (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 fit 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 ASM/RXTE are a good combination for monitoring X-ray sources over a wide energy band. Subject headings: accretion, accretion disks — stars: individual (4U 0614+091) — stars: neutron — X-rays: stars Columbia University, Department of Physics and Columbia Astrophysics Lab, 538 W. 120th Street, New York, NY 10027 NASA/Marshall Space Flight Center, ES 84, Huntsville, AL 35812 University Space Research Association/ MSFC, ES 84, Huntsville, AL 35812 Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 MIT, Center for Space Science, Room 37-595, Cambridge, MA 02139