Anticorrelated Hard X‐Ray Time Lag in GRS 1915+105: Evidence for a Truncated Accretion Disk (original) (raw)
Related papers
2004
Multi-wavelength observations of Galactic black hole candidate sources indicate a close connection between the accretion disk emission and the jet emission. The recent discovery of an anti-correlated time lag between the soft and hard X-rays in Cygnus X-3 (Choudhury & Rao 2004) constrains the geometric picture of the diskjet connection into a truncated accretion disk, the truncation radius being quite close to the black hole. Here we report the detection of similar anti-correlated time lag in the superluminal jet source GRS 1915+105. We show the existence of the pivoting in the X-ray spectrum during the delayed anti-correlation and we also find that the QPO parameters change along with the spectral pivoting. We explore theoretical models to understand this phenomenon.
Time Lag in Transient Galactic and Extragalactic Accreting Sources
Proceedings of Accretion Processes in Cosmic Sources – II — PoS(APCS2018), 2019
X-ray binaries are cauldrons of fundamental physical processes which appear along practically the whole electromagnetic spectrum. The sub-class of X-ray transient sources show multifrequency behaviour which deserve particular attention in order to understand the causing physics. These binary systems consist of a compact star and an optical star, therefore there is a mutual influence between these two stars that drive the low energy (LE) (i.e. radio, IR, optical) and high energy (HE) (i.e. UV, X-ray, γ-ray) processes. The LE processes are produced mostly on the optical star and the HE processes mostly on the compact star, typically a neutron star. Thus it appears evident that through the study of LE processes it is possible to understand also the HE processes and vice versa. In this paper we will discuss this problem starting from the experimental evidence of a delay between LE and HE processes detected for the first time in the X-ray/Be system A0535+26/HDE245770 (e.g. Giovannelli & Sabau-Graziati, 2011; Giovannelli, Bisnovatyi-Kogan & Klepnev, 2013 (here after GBK13); Giovannelli et al., 2015b). This delay is common in cataclysmic variables (CVs) and other binary systems with either a neutron star or a black hole. Since a delay between LE processes and HE processes has been experimentally observed in several active galactic nuclei (AGNs), we will discuss also the tidal disruption of stars by massive BHs, following the original idea of Rees (1998): stars in galactic nuclei can be captured or tidally disrupted by a central black hole. Some debris would be ejected at high speed, the remainder would be swallowed by the hole, causing a bright flare lasting at most a few years.
On the Role of the Accretion Disk in Black Hole Disk-Jet Connections
The Astrophysical Journal, 2012
Models of jet production in black hole systems suggest that the properties of the accretion disk-such as its mass accretion rate, inner radius, and emergent magnetic field-should drive and modulate the production of relativistic jets. Stellar-mass black holes in the "low/hard" state are an excellent laboratory in which to study disk-jet connections, but few coordinated observations are made using spectrometers that can incisively probe the inner disk. We report on a series of 20 Suzaku observations of Cygnus X-1 made in the jet-producing low/hard state. Contemporaneous radio monitoring was done using the Arcminute MicroKelvin Array radio telescope. Two important and simple results are obtained: (1) the jet (as traced by radio flux) does not appear to be modulated by changes in the inner radius of the accretion disk and (2) the jet is sensitive to disk properties, including its flux, temperature, and ionization. Some more complex results may reveal aspects of a coupled disk-corona-jet system. A positive correlation between the reflected X-ray flux and radio flux may represent specific support for a plasma ejection model of the corona, wherein the base of a jet produces hard X-ray emission. Within the framework of the plasma ejection model, the spectra suggest a jet base with v/c 0.3 or the escape velocity for a vertical height of z 20 GM/c 2 above the black hole. The detailed results of X-ray disk continuum and reflection modeling also suggest a height of z 20 GM/c 2 for hard X-ray production above a black hole, with a spin in the range 0.6 a 0.99. This height agrees with X-ray time lags recently found in Cygnus X-1. The overall picture that emerges from this study is broadly consistent with some jet-focused models for black hole spectral energy distributions in which a relativistic plasma is accelerated at z = 10-100 GM/c 2 . We discuss these results in the context of disk-jet connections across the black hole mass scale.
A jet model for Galactic black-hole X-ray sources: some constraining correlations
Astronomy and Astrophysics, 2008
Context. Some recent observational results impose significant constraints on all the models that have been proposed to explain the Galactic black-hole X-ray sources in the hard state. In particular, it has been found that during the hard state of Cyg X-1 the power-law photon number spectral index, Γ, is correlated with the average time lag, < t lag >, between hard and soft X-rays. Furthermore, the peak frequencies of the four Lorentzians that fit the observed power spectra are correlated with both Γ and < t lag >. Aims. We have investigated whether our jet model can reproduce these correlations. Methods. We performed Monte Carlo simulations of Compton upscattering of soft, accretion-disk photons in the jet and computed the time lag between hard and soft photons and the power-law index Γ of the resulting photon number spectra. Results. We demonstrate that our jet model naturally explains the above correlations, with no additional requirements and no additional parameters.
Nature Astronomy, 2017
Relativistic plasma jets are observed in many accreting black holes. According to theory, coiled magnetic fields close to the black hole accelerate and collimate the plasma, leading to a jet being launched 1-3. Isolating emission from this acceleration and collimation zone is key to measuring its size and understanding jet formation physics. But this is challenging because emission from the jet base cannot be easily disentangled from other accreting components. Here, we show that rapid optical flux variations from a Galactic black-hole binary are delayed with respect to X-rays radiated from close to the black hole by ~0.1 seconds, and that this delayed signal appears together with a brightening radio jet. The origin of these sub-second optical variations has hitherto been controversial 4-8. Not only does our work strongly support a jet origin for the optical variations, it also sets a characteristic elevation of ≲10 3 Schwarzschild radii for the main inner optical emission zone above the black hole 9 , constraining both internal shock 10 and magnetohydrodynamic 11 models. Similarities with blazars 12,13 suggest that jet structure and launching physics could potentially be unified under mass-invariant models. Two of the best-studied jetted black hole binaries show very similar optical lags 8,14,15 , so this size scale may be a defining feature of such systems. In June 2015, the Galactic X-ray binary V404 Cygni underwent the brightest outburst of an Xray binary so far this century. We coordinated simultaneous optical observations from the William Herschel Telescope with X-ray observations from the NuSTAR space observatory on the morning of June 25. These were high frame-rate optical observations taken by the ULTRACAM instrument, sampling timescales down to 35.94 milliseconds (ms). Both optical and X-ray light curves show variability on a broad range of timescales characteristic of this source 15,16 (Fig. 1). The AMI telescope provided contiguous radio coverage throughout this period. Details of the observations may be found in Methods. These coordinated observations occurred on June 25, the day preceding the peak of the 2015 outburst. When the optical observations began, the X-ray intensity was two orders of magnitude below peak, and the spectrum was dominated by low-energy X-rays (i.e., it was in a state characterised as being relatively 'soft'). Steady, compact jet activity is not expected in such a state, and consistent with this, the radio spectral index is negative, as is typical of emission from discrete optically-thin ejecta. NuSTAR observations were interrupted about 2000 seconds later due to a period of Earth occultation, which separates the two halves (hereafter, 'epochs') of the sequence under consideration. At some point during this occultation, the source underwent a dramatic and very rapid change in its X-ray spectral state. When NuSTAR emerged from Earth occultation, the spectrum was
2004
The wide-band X-ray spectra of the high mass X-ray binary Cygnus X-3 exhibits a pivoting behavior in the ‘low ’ (as well as ‘hard’) state, correlated to the radio emission. The time scale of the soft and hard X-rays ’ anti-correlation, which gave rise to the pivoting feature, was found to be less than a day from the monitoring observations by RXTE–ASM and CGRO–BATSE. In this Letter we report the detection of a lag of � 1000s in the anti-correlation of the hard X-ray emission (20–50 keV) to that of the soft X-ray emission (2–7 keV), which may be attributed to the viscous time scale of flow of matter in the accretion disk. This suggests the geometrical picture of a truncated accretion disc with a Compton cloud inside the disc, the relative sizes of which determine the spectral shape. Any change in the disc structure will take place in a viscous time scale, with corresponding anti-correlated change in the Compton cloud. We also report the pivoting in the spectra in one span of a pointe...
Probing the Structure of Accreting Compact Sources through X‐Ray Time Lags and Spectra
The Astrophysical Journal, 1999
We exhibit, by compiling all data sets we can acquire, that the Fourier frequency dependent hard X-ray lags, first observed in the analysis of aperiodic variability of the light curves of the black hole candidate Cygnus X-1, appear to be a property shared by several other accreting black hole candidate sources and also by the different spectral states of this source. We then present both analytic and numerical models of these time lags resulting by the process of Comptonization in a variety of hot electron configurations. We argue that Subject headings: accretion-black hole physics-radiation mechanisms: Compton and inverse Compton-stars: neutron-X-rays Hz, with the PSD slope being flatter than the value corresponding to simple exponential
Detection of an anticorrelated hard X-ray time lag in cygnus X-3
The Astrophysical Journal Letters, 2004
The wide-band X-ray spectra of the high mass X-ray binary Cygnus X-3 exhibits a pivoting behavior in the 'low' (as well as 'hard') state, correlated to the radio emission. The time scale of the soft and hard X-rays' anti-correlation, which gave rise to the pivoting feature, was found to be less than a day from the monitoring observations by RXTE-ASM and CGRO-BATSE. In this Letter we report the detection of a lag of 1000s in the anti-correlation of the hard X-ray emission (20-50 keV) to that of the soft X-ray emission (2-7 keV), which may be attributed to the viscous time scale of flow of matter in the accretion disk. This suggests the geometrical picture of a truncated accretion disc with a Compton cloud inside the disc, the relative sizes of which determine the spectral shape. Any change in the disc structure will take place in a viscous time scale, with corresponding anti-correlated change in the Compton cloud. We also report the pivoting in the spectra in one span of a pointed observation when an episode of the rearranging of the accretion system is serendipitously observed. This is the first such observation of hard X-ray delay seen in the persistent Galactic microquasars, within the precincts of the hard state.
Monthly Notices of the Royal Astronomical Society, 2009
We present results from modeling of quasi-simultaneous broad band (radio through Xray) observations of the galactic stellar black hole (BH) transient X-ray binary (XRB) systems XTE J1118+480 and GX 339−4 using an irradiated disc + compact jet model. In addition to quantifying the physical properties of the jet, we have developed a new irradiated disc model which also constrains the geometry and temperature of the outer accretion disc by assuming a disc heated by viscous energy release and X-ray irradiation from the inner regions. For the source XTE J1118+480, which has better spectral coverage of the two in optical and near-IR (OIR) wavelengths, we show that the entire broad band continuum can be well described by an outflow-dominated model + an irradiated disc. The best-fit radius of the outer edge of the disc is consistent with the Roche lobe geometry of the system, and the temperature of the outer edge of the accretion disc is similar to those found for other XRBs. Irradiation of the disc by the jet is found to be negligible for this source. For GX 339−4, the entire continuum is well described by the jet-dominated model only, with no disc component required. For the two XRBs, which have very different physical and orbital parameters and were in different accretion states during the observations, the sizes of the jet base are similar and both seem to prefer a high fraction of non-thermal electrons in the acceleration/shock region and a magnetically dominated plasma in the jet. These results, along with recent similar results from modeling other galactic XRBs and AGNs, may suggest an inherent unity in diversity in the geometric and radiative properties of compact jets from accreting black holes.
Time-delays between the soft and hard X-ray bands in GRS 1915 + 105
Monthly Notices of the Royal Astronomical Society, 2005
The hard X-ray lightcurves exhibit delays of ∼ 1 s with respect to the soft X-ray lightcurves when the microquasar GRS 1915+105 is in the state of frequent, regular outbursts (states ρ and κ of . Such outbursts are supposed to be driven by the radiation pressure instability of the inner disc parts. The hard X-ray delays are then caused by the time needed for the adjustment of the corona to changing conditions in the underlying disc. We support this claim by the computation of the time evolution of the disc, including a non-stationary evaporation of the disc and mass exchange with the corona.