MS 1603 . 6 + 2600 : an Accretion Disc Corona source ?

We have observed the eclipsing low–mass X–ray binary MS 1603.6+2600 with Chandra for 7 ksec. The X–ray spectrum is well fit with a single absorbed powerlaw with an index of ∼2. We find a clear sinusoidal modulation in the X–ray lightcurve with a period of 1.7±0.2 hours, consistent with the period of 1.85 hours found before. However, no (partial) eclipses were found. We argue that if the X–ray flare observed in earlier X–ray observations was a type I X–ray burst then the source can only be an Accretion Disc Corona source at a distance between ∼11–24 kpc (implying a height above the Galactic disk of ∼8–17 kpc). It has also been proposed in the literature that MS 1603.76+2600 is a dipper at ∼75 kpc. We argue that in this dipper scenario the observed optical properties of MS 1603.6+2600 are difficult to reconcile with the optical properties one would expect on the basis of comparisons with other high inclination low–mass X–ray binaries, unless the X–ray flare was not a type I X–ray burst. In that case the source can be a nearby soft X–ray transient accreting at a quiescent rate as was proposed by Hakala et al. (1998) or a high inclination source at ∼15–20 kpc.