Does Low‐Frequency X‐Ray QPO Behavior in GRS 1915+105 Influence Subsequent X‐Ray and Infrared Evolution?

Abstract

Using observations with the Rossi X-Ray Timing Explorer, we examine the behavior of 2-10 Hz quasi-periodic oscillations (QPOs) during spectrally hard dips in the X-ray light curve of GRS 1915+105 that are accompanied by infrared flares. Of the 12 light curves examined, 9 are β class and three are α class, following the scheme of Belloni et al. In most cases, the QPO frequency is most strongly correlated to the power-law flux, which partially contradicts some earlier claims that the strongest correlation is between QPO frequency and blackbody flux. Seven β-class curves are highly correlated to blackbody features. In several cases, the QPO evolution appears to decouple from the spectral evolution. We find that β-class light curves with strong correlations can be distinguished from those without by their spike morphology. We also show that the origin and strength of the subsequent infrared flare may be causally linked to the variations in QPO frequency evolution and not solely tied to the onset of soft X-ray flaring behavior. We divide the 12 α- and β-class light curves into three groups based on the evolution of the QPO, the morphology of the trigger spike, and the infrared flare strength. An apparent crossover case leads us to conclude that these groups are not unique modes but represent part of a continuum of accretion behaviors. We believe the QPO behavior at the initiation of the hard dip can ultimately be used to determine the terminating X-ray behavior and the following infrared flaring behavior.