Low-Intensity States in the Neutron Star X-ray Binary Aql X-1
  Aql X-1 was observed in a Low Intensity State (LIS), a state that is usually characterized by high optical but low X-ray flux. Our daily monitoring of the source using the 1.3m telescope in Cerro Tololo Inter-America Observatory operated by the Small and Moderate Aperture Research Telescope System (SMARTS) was used to trigger a series of target-of-opportunity (ToO) observations of the source using the Rossi X-ray Timing Explorer satellite (RXTE). The X-ray colors and temporal variability studies suggest that the source was in a powerlaw dominated state featuring high rms variability in the lightcurve and dominance of hard photons during this LIS. The ToO observations were continued until the source made a transition to the canonical thermal dominated or high/soft state. 
Dipankar Maitra and Charles D. Bailyn