A model for the energy-dependent time-lag and rms of the heartbeat oscillations in GRS 1915+105

Abstract

Energy dependent phase lags reveal crucial information about the causal relation between various spectral components and about the nature of the accretion geometry around the compact objects. The time-lag and the fractional root mean square (rms) spectra of GRS 1915+105 in its heartbeat oscillation class/$\rho$ state show peculiar behaviour at the fundamental and harmonic frequencies where the lags at the fundamental show a turn around at $\sim$ 10 keV while the lags at the harmonic do not show any turn around at least till $\sim$ 20 keV. The magnitude of lags are of the order of few seconds and hence cannot be attributed to the light travel time effects or Comptonization delays. The continuum X-ray spectra can roughly be described by a disk blackbody and a hard X-ray power-law component and from phase resolved spectroscopy it has been shown that the inner disk radius varies during the oscillation. Here, we propose that there is a delayed response of the inner disk radius (DROID) to the accretion rate such that $r_{in}(t)\propto {\dot{m}}^{\beta }(t-{\tau }_d)$. The fluctuating accretion rate drives the oscillations of the inner radius after a time delay ${\tau }_d$ while the power-law component responds immediately. We show that in such a scenario a pure sinusoidal oscillation of the accretion rate can explain not only the shape and magnitude of energy dependent rms and time-lag spectra at the fundamental but also the next harmonic with just four free parameters.

8 pages, 5 figures, 1 table, Accepted for publication in MNRAS

References in corpus (7)

• Spectral and Fourier analyses of X-ray QPO in accreting black holes
• Phase-resolved spectroscopy of low frequency quasi-periodic oscillations in GRS 1915+105
• Energy Dependent Time Delays of kHz Oscillations due to Thermal Comptonization
• Comparison of time/phase lags in the hard state and plateau state of GRS 1915+105
• An imperfect double: probing the physical origin of the low-frequency QPO and its harmonic in black hole binaries
• Alternating lags of QPO harmonics : A Generic model and its application to the 67 millihertz QPO of GRS 1915+105
• Properties of unique hard X-ray dips observed from GRS 1915+105 and IGR J17091-3624 and their implications

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• AstroSat/LAXPC reveals the high energy variability of GRS 1915+105 in the chi class
• On the energy dependence of the QPO phenomenon in the black hole system MAXI J1535-571
• Study of timing evolution from non-variable to structured large-amplitude variability transition in GRS 1915+105 using AstroSat
• Identifying the radiative components responsible for Quasi-Periodic Oscillations of black hole systems
• An Insight-HXMT view of the mHz quasi-regular modulation phenomenon in the black hole X-ray binary 4U 1630-47
• A timing view of the heartbeat state of GRS 1915+105
• The mHz quasi-regular modulations of 4U 1630--47 during its 1998 outburst
• Recurrent Instability in LMXB Accretion Disks: How Strange is GRS 1915+105?