The Spreading Layer of GX 9+9

TL;DR

This study investigates the spreading layer on the neutron star GX 9+9, confirming some theoretical predictions about its size and temperature during high accretion states, but also revealing discrepancies at low accretion rates.

Contribution

The paper provides observational evidence of the spreading layer behavior on GX 9+9, validating some models and highlighting areas needing further theoretical development.

Findings

SL-area increases with accretion rate

SL-temperature remains near the Eddington limit during high accretion

Discrepancies at low accretion rates suggest need for further study

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.