The X-ray-faint early-type galaxy NGC 4697

Abstract

We analyze archival ROSAT HRI, ROSAT PSPC, and ASCA data of the X-ray-faint early-type galaxy NGC 4697. The joint ROSAT PSPC + ASCA spectrum is fitted by a two-component thermal model, a MEKAL model with kT(MEKAL) = 0.26(-0.03)(+0.04) keV with low metallicity and a bremsstrahlung model with kT(BREM) = 5.2(-1.6)(+3.0) keV. A similar model was found to fit the spectra of another faint early-type galaxy (NGC 4382) and the bulge of M31. We interpret this soft emission as a combination of emission from a soft component of low-mass X-ray binaries (LMXBs) and from a low-temperature interstellar medium, although the relative contributions of the two components could not be determined. Twelve point sources were identified within 4 ' of NGC 4697, of which 11 are most likely LMXBs associated with the galaxy. The soft X-ray colors of four of the LMXBs in NGC 4697 support the claim that LMXBs possess a soft spectral component. Finally, we present a simulation of what we believe the Chandra data of NGC 4697 will look like.