Fast Transition between High-soft and Low-soft States in GRS 1915+105: Evidence for a Critically Viscous Accretion Flow

Abstract

We present the results of a detailed analysis of RXTE observations of class $\omega$ which show an unusual state transition between high-soft and low-soft states in the microquasar GRS 1915+105. Out of about 600 pointed RXTE observations, the source was found to exhibit such state transition only on 16 occasions. An examination of the RXTE/ASM data in conjunction with the pointed observations reveals that these events appeared as a series of quasi-regular dips in two stretches of long duration (about 20 days during each occasions) when hard X-ray and radio flux were very low. The X-ray light curve and color-color diagram of the source during these observations are found to be different from any reported so far. The duration of these dips is found to be of the order of a few tens of seconds with a repetition time of a few hundred seconds. The transition between these dips and non-dips which differ in intensity by a factor of ~ 3.5, is observed to be very fast (~ a few seconds). It is observed that the low-frequency narrow QPOs are absent in the power density spectrum (PDS) of the dip and non-dip regions of class $\omega$ and the PDS is a power law in 0.1 - 10 Hz frequency range. There is a remarkable similarity in the spectral and timing properties of the source during the dip and non-dip regions in these set of observations. These properties of the source are distinctly different from those seen in the observations of other classes. This indicates that the basic accretion disk structure during both dip and non-dip regions of class $\omega$ is similar, but differ only in intensity. To explain these observations, we invoke a model in which the viscosity is very close to critical viscosity and the shock wave is weak or absent.

arXiv commentReplaced with correct figures, Jour. of Astrophysics and Astronomy (accepted)

References in corpus (12)

• Spectral Properties of Accretion Disks Around Galactic and Extragalactic Black Holes
• A unified model for the spectral variability in GRS 1915+105
• Grand Unification of Solutions of Accretion and Winds around Black Holes and Neutron Stars
• OSSE and RXTE Observations of GRS 1915+105: Evidence for Non-thermal Comptonization
• Time-Dependent Disk Models for the Microquasar GRS1915+105
• Absorption dips in the light curves of GRO J1655-40 and 4U 1630-47 during outburst
• Rapid Bursts From GRS 1915+105 with RXTE
• A Transition to the Soft State in GRS 1758-258
• The Pattern of Correlated X-ray Timing and Spectral Behavior in GRS 1915+105
• Rapid State Transitions in the Galactic Black Hole Candidate Source GRS 1915+105
• Detection of a Series of X-ray Dips Associated with a Radio Flare in GRS 1915+105
• X-ray properties of the microquasar GRS 1915+105 during a variability class transition

Cited by in corpus (11)

• On the origin of the various types of radio emission in GRS 1915+105
• Exploring the Long-Term Evolution of GRS 1915+105
• Unraveling the foretime of GRS 1915+105 using AstroSat observations: Wide-band spectral and temporal characteristics
• Class Transitions and Two Component Accretion Flow in GRS 1915+105
• Non-linear oscillator models for the X-ray bursting of the microquasar GRS 1915+105
• Evidence of Class Transitions in GRS 1915+105 from IXAE Data
• Evidence of variation of the accretion flow geometry in GRS 1915+105 from IXAE and RXTE data
• A new variability pattern in GRS 1915+105 with NICER and Insight-HXMT observations
• Searching for quantum-gravity footprint around stellar-mass black holes
• Discovery of a new flaring class in GRS 1915+105 using AstroSat
• Spectral signature of mass outflow in Two Component Advective Flow Paradigm