AstroSat view of GRS 1915+105 during the soft state: detection of HFQPOs and estimation of mass and spin

Sreehari, H.; Nandi, Anuj; Das, Santabrata; Agrawal, Vivek; Mandal, Samir; Ramadevi, M. C.; Katoch, Tilak

doi:10.1093/mnras/staa3135

Cited by 48 publications

(46 citation statements)

References 67 publications

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“…Finally, considering the present estimates of spin and mass, we conclude that Cygnus X-1 is a maximally rotating, massive black hole binary source. This compact nature echoes to that of the enigmatic galactic black hole source GRS 1915 + 105, which represents a standard template for BH-XRBs (Sreehari et al 2020).…”

Section: Discussionmentioning

confidence: 52%

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AstroSat and MAXI view of Cygnus X-1: Signature of an `extreme' soft nature

Kushwaha,

Agrawal,

Nandi

2021

Preprint

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We present a detailed spectral and timing analysis of Cygnus X-1 with multi-epoch observations, during 2016 to 2019, by SXT and LAXPC on-board AstroSat. We model the spectra in broad energy range of 0.5−70.0 keV to study the evolution of spectral properties while Cygnus X-1 transited from hard state to an extreme soft state via intermediate states in 2017. Simultaneous timing features are also examined by modelling the power density spectra in 3.0−50.0 keV . We find that during high-soft state observations, made by AstroSat on Oct 24, 2017 (MJD 58050), the energy spectrum of the source exhibits an inner disk temperature (kT in ) of 0.46±0.01 keV , a very steep photon index (Γ) of 3.15±0.03 along with a fractional disk flux contribution of ∼ 45%. The power density spectrum in the range of 0.006 − 50.0 Hz is also very steep with a power-law index of 1.12 ±0.04 along with a high RMS value of ∼ 25%. Comparing the spectral softness of high-soft state with those of previously reported, we confirm that AstroSat observed Cygnus X-1 in the 'softest' state. The lowest MAXI spectral hardness ratio of ∼ 0.229 corroborates the softest nature of the source. Moreover, we estimate the spin of the black hole by continuum-fitting method, which indicates that Cygnus X-1 is a maximally rotating 'hole'. Further, Monte Carlo (MC) simulations are performed to estimate the uncertainty in spin parameter, which is constrained as a * > 0.9981 with 3σ confidence interval. Finally, we discuss the implications of our findings.

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Section: Discussionmentioning

confidence: 52%

“…For example, GX 339 − 4 and IGR 17091 − 3624 exhibit a low RMS of ∼ 3% in HSS (Nandi et al 2012;Radhika et al 2018). Recently, Sreehari et al (2020) show in case of HSS of GRS 1915 + 105, a total RMS less than 2%.…”

Section: Discussionmentioning

confidence: 98%

AstroSat and MAXI view of Cygnus X-1: Signature of an `extreme' soft nature

Kushwaha,

Agrawal,

Nandi

2021

Preprint

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“…Gaussian was replaced by diskline model which considers line emission from a relativistic accretion disc (Fabian et al 1989). Residuals corresponding to an absorption edge are seen in the 7 − 9 keV range (see Done et al 2004;Sreehari et al 2020). This is modelled using the smeared edge model, smedge in XSPEC (Ebisawa et al 1994), with index for photoelectric cross-section fixed at -2.67.…”

Section: Spectral Modellingmentioning

confidence: 99%

AstroSat view of IGR J17091-3624 and GRS 1915+105: decoding the 'pulse' in the 'Heartbeat State'

Katoch,

Baby,

Nandi

et al. 2020

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IGR J17091-3624 is a transient galactic black hole which has a distinct quasi-periodic variability known as 'heartbeat', similar to the one observed in GRS 1915+105. In this paper, we report the results of ∼ 125 ks AstroSat observations of this source during the 2016 outburst. For the first time a double peaked QPO (DPQ) is detected in a few time segments of this source with a difference of δf ∼ 12 mHz between the two peaks. The nature of the DPQ was studied based on hardness ratios and using the static as well as the dynamic power spectrum. Additionally, a low frequency (25-48 mHz) 'heartbeat' single peak QPO (SPQ) was observed at different intervals of time along with harmonics (50 − 95 mHz). Broadband spectra in the range 0.7 − 23 keV, obtained with SXT and LAXPC, could be fitted well with combination of a thermal Comptonisation and a multicolour disc component model. During AstroSat observation, the source was in the Soft-Intermediate State (SIMS) as observed with Swift/XRT. We present a comparative study of the 'heartbeat' state variability in IGR J17091-3624 with GRS 1915+105. Significant difference in the timing properties is observed although spectral parameters (Γ ∼ 2.1 − 2.4 and T max ∼ 0.6 − 0.8 keV) in the broad energy band remain similar. Spectral properties of segments exhibiting SPQ and DPQ are further studied using simple phase resolved spectroscopy which does not show a significant difference. Based on the model parameters, we obtain the maximum ratio of mass accretion rate in GRS 1915+105 to that in IGR J17091-3624 as ∼ 25 : 1. We discuss the implications of our findings and comment on the physical origin of these exotic variabilities.

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“…variability studies in the hard energy band. For example, AstroSat data has been used to study the spectraltiming properties of several black hole X-ray binaries, including Cygnus X-1 (Misra et al 2017;Maqbool et al 2019), Cygnus X-3 (Pahari et al 2017), MAXI J1535-571 (Bhargava et al 2019;Sreehari et al 2019), Swift J1658.2-4242 (Jithesh et al 2019), GRS 1915+105 (Rawat et al 2019;Belloni et al 2019;Misra et al 2020;Sreehari et al 2020), MAXI J1820+070 (Mudambi et al 2020) and 4U 1630-472 (Baby et al 2020). The soft X-ray (< 4 keV) rapid timing properties of black hole X-ray binaries (BHXRBs) were largely unknown, which is now being explored using the X-ray Timing Instrument (XTI) onboard the Neutron star Interior Composition Explorer (NICER).…”

Section: Introductionmentioning

confidence: 99%

Broadband Spectral and Timing Properties of MAXI J1348-630 using AstroSat and NICER Observations

Jithesh,

Misra,

Maqbool

et al. 2021

Preprint

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We present broadband X-ray spectral-timing analysis of the new Galactic X-ray transient MAXI J1348-630 using five simultaneous AstroSat and NICER observations. Spectral analysis using AstroSat data identify the source to be in the soft state for the first three observations and in a faint and bright hard state for the next two. Quasiperiodic oscillations at ∼ 0.9 and ∼ 6.9 Hz, belonging to the type-C and type-A class are detected. In the soft state, the power density spectra are substantially lower (by a factor > 5) for the NICER (0.5-12 keV) band compared to the AstroSat/LAXPC (3-80 keV) one, confirming that the disk is significantly less variable than the Comptonization component. For the first time, energy-dependent fractional rms and time lag in the 0.5-80 keV energy band was measured at different Fourier frequencies, using the bright hard state observation. Hard time lag is detected for the bright hard state, while the faint one shows evidence for soft lag. A single-zone propagation model fits the LAXPC results in the energy band 3-80 keV with parameters similar to those obtained for Cygnus X-1 and MAXI J1820+070. Extending the model to lower energies, reveals qualitative similarities but having quantitative differences with the NICER results. These discrepancies could be because the NICER and AstroSat data are not strictly simultaneous and because the simple propagation model does not take into account disk emission. The results highlight the need for more joint coordinated observations of such systems by NICER and AstroSat.

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AstroSat view of GRS 1915+105 during the soft state: detection of HFQPOs and estimation of mass and spin

Cited by 48 publications

References 67 publications

AstroSat and MAXI view of Cygnus X-1: Signature of an `extreme' soft nature

AstroSat and MAXI view of Cygnus X-1: Signature of an `extreme' soft nature

AstroSat view of IGR J17091-3624 and GRS 1915+105: decoding the 'pulse' in the 'Heartbeat State'

Broadband Spectral and Timing Properties of MAXI J1348-630 using AstroSat and NICER Observations

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