skip to main content

Title: Comparison of time/phase lags in the hard state and plateau state of GRS 1915+105

We investigate the complex behavior of energy- and frequency-dependent time/phase lags in the plateau state and the radio-quiet hard (χ) state of GRS 1915+105. In our timing analysis, we find that when the source is faint in the radio, quasi-periodic oscillations (QPOs) are observed above 2 Hz and typically exhibit soft lags (soft photons lag hard photons), whereas QPOs in the radio-bright plateau state are found below 2.2 Hz and consistently show hard lags. The phase lag at the QPO frequency is strongly anti-correlated with that frequency, changing sign at 2.2 Hz. However, the phase lag at the frequency of the first harmonic is positive and nearly independent of that frequency at ∼0.172 rad, regardless of the radio emission. The lag energy dependence at the first harmonic is also independent of radio flux. However, the lags at the QPO frequency are negative at all energies during the radio-quiet state, but lags at the QPO frequency during the plateau state are positive at all energies and show a 'reflection-type' evolution of the lag energy spectra with respect to the radio-quiet state. The lag energy dependence is roughly logarithmic, but there is some evidence for a break around 4-6 keV. Finally, themore » Fourier-frequency-dependent phase lag spectra are fairly flat during the plateau state, but increase from negative to positive during the radio-quiet state. We discuss the implications of our results in light of some generic models.« less
Authors:
;  [1] ;  [2] ;  [3] ;  [4]
  1. Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai, India (MP) (India)
  2. Boston University, Boston, MA 02215 (United States)
  3. Inter University Center for Astronomy and Astrophysics, Pune (India)
  4. Astronomical Institute, "Anton Pannekoek," University of Amsterdam, Science Park 904, 1098-XH Amsterdam (Netherlands)
Publication Date:
OSTI Identifier:
22341928
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 778; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; BLACK HOLES; COMPARATIVE EVALUATIONS; EMISSION; ENERGY DEPENDENCE; ENERGY SPECTRA; EVOLUTION; FREQUENCY DEPENDENCE; GESELLSCHAFT FUER ANLAGEN- UND REAKTORSICHERHEIT; KEV RANGE; OSCILLATIONS; PERIODICITY; PHOTONS; REFLECTION; VISIBLE RADIATION; X RADIATION