The Spreading Layer of GX 9+9

Abstract

The spreading layer (SL) on neutron star surface of GX 9+9 during the upper banana state was studied using INTEGRAL and RXTE observations. The SL-area becomes larger with increasing accretion rate while the SL-temperature remains close to the critical Eddington value, confirming predictions by Inogamov and Sunyaev (1999) and Suleimanov and Poutanen (2006). However, at low accretion rate the observed temperature is higher and SL-belt shallower than those predicted, requiring confirmation and theoretical explananation.