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A continuous transition from Type-C Quasi Periodic Oscillations to the Heartbeat state in the Black hole X-ray binary 4U 1630-47

Chintan Patel, Sayantan Bhattacharya, Karan Akbari, Sudip Bhattacharyya, Manojendu Choudhury

TL;DR

This study analyzes AstroSat/LAXPC observations of 4U 1630-47 during its 2023 outburst to capture a rare, rapid transition from a Type-C QPO state at $f_0 \approx 3.7$–$5.7$ Hz to a Heartbeat state with a low-frequency modulation near $40$ s ($\sim$ $25$–$28$ mHz). Using PDS, HID, PCD, and HRD analyses, the authors track a continuous evolution through a transition phase within less than a day, culminating in the disappearance of the QPO in the Heartbeat state. The findings support a picture where a hard inner flow, modulated by Lense–Thirring precession, softens and then undergoes a radiation-pressure–driven limit cycle as the disk approaches the inner regions, producing rapid, large-amplitude heartbeats. This work establishes 4U 1630–47 as a second system to GRS 1915+105 that exhibits a continuous QPO-to-Heartbeat transition and highlights the importance of uninterrupted monitoring to understand the coupling between inner-disk dynamics and variability states in BHXRBs.

Abstract

We present a timing analysis of the black hole X-ray binary (BHXRB) 4U 1630-47 using AstroSat observations from 10-19 March 2023, for the first time capturing a rare and rapid transition in variability properties. Within less than a day, the source evolved from a type-C quasi-periodic oscillation (QPO) state, with centroid frequencies between 3-5 Hz, to the Heartbeat state, characterized by a broad peak in the power density spectrum at ~25 mHz, corresponding to a ~40 s modulation period. As the source evolved, it passed through a transition track where the QPO features weakened and ultimately disappeared in the Heartbeat state. In the hardness-intensity Diagram, the QPOs occur at higher hardness and lower intensity, followed by a brightening phase as the source moved towards the soft intermediate state, and finally reached the Heartbeat state through a transition towards lower hardness. In the power-color diagram, this transition is marked by a clear shift to a distinct region of power color space, separate from the range occupied by other observed states. This work establishes 4U 1630-47 as another system, apart from GRS 1915+105, where a continuous transition from QPO to Heartbeat state has been observed. Notably, 4U 1630-47 is the only system where the QPO is absent during the heartbeat state. This provides us with another probe to understand the physical mechanism governing this transition and the overall accretion mechanism in BHXRBs.

A continuous transition from Type-C Quasi Periodic Oscillations to the Heartbeat state in the Black hole X-ray binary 4U 1630-47

TL;DR

This study analyzes AstroSat/LAXPC observations of 4U 1630-47 during its 2023 outburst to capture a rare, rapid transition from a Type-C QPO state at – Hz to a Heartbeat state with a low-frequency modulation near s ( – mHz). Using PDS, HID, PCD, and HRD analyses, the authors track a continuous evolution through a transition phase within less than a day, culminating in the disappearance of the QPO in the Heartbeat state. The findings support a picture where a hard inner flow, modulated by Lense–Thirring precession, softens and then undergoes a radiation-pressure–driven limit cycle as the disk approaches the inner regions, producing rapid, large-amplitude heartbeats. This work establishes 4U 1630–47 as a second system to GRS 1915+105 that exhibits a continuous QPO-to-Heartbeat transition and highlights the importance of uninterrupted monitoring to understand the coupling between inner-disk dynamics and variability states in BHXRBs.

Abstract

We present a timing analysis of the black hole X-ray binary (BHXRB) 4U 1630-47 using AstroSat observations from 10-19 March 2023, for the first time capturing a rare and rapid transition in variability properties. Within less than a day, the source evolved from a type-C quasi-periodic oscillation (QPO) state, with centroid frequencies between 3-5 Hz, to the Heartbeat state, characterized by a broad peak in the power density spectrum at ~25 mHz, corresponding to a ~40 s modulation period. As the source evolved, it passed through a transition track where the QPO features weakened and ultimately disappeared in the Heartbeat state. In the hardness-intensity Diagram, the QPOs occur at higher hardness and lower intensity, followed by a brightening phase as the source moved towards the soft intermediate state, and finally reached the Heartbeat state through a transition towards lower hardness. In the power-color diagram, this transition is marked by a clear shift to a distinct region of power color space, separate from the range occupied by other observed states. This work establishes 4U 1630-47 as another system, apart from GRS 1915+105, where a continuous transition from QPO to Heartbeat state has been observed. Notably, 4U 1630-47 is the only system where the QPO is absent during the heartbeat state. This provides us with another probe to understand the physical mechanism governing this transition and the overall accretion mechanism in BHXRBs.

Paper Structure

This paper contains 9 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Observation & Data Analysis
  3. Results
  4. Discussion
  5. Type-C QPOs
  6. Heartbeat state
  7. The rapid transition of 4U 1630--47
  8. Conclusion
  9. acknowledgments

Figures (3)

  • Figure 1: Top row: Overall summary of variability evolution in 4U 1630–47 as observed on 15 March 2023 (left) and 16 March 2023 (right) observed with AstroSat LAXPC. The zero of the time-axis corresponds to MJD 60018.0284 and ends at MJD 60019.1891. Middle and bottom row: representational segments of 1000s of the LAXPC light curves (middle) from each variability state and corresponding power density spectra (bottom row) for three distinct states — Left: Type-C QPO, Middle: transition state, and Right: Heartbeat state.
  • Figure 2: The HID of LAXPC observations of 4U 1630--47 from 10–19 March 2023. The hardness is defined as the ratio of count rates in the 7–40 keV and 3–7 keV bands. Observations are color coded as per the day of observation with different color and marker for the temporally instable states. The blue diamond represents the QPOs which occur on 15 March, and the red star corresponds to the Heartbeat state which occurs on 15 and 16 March (5 on 15 March and 3 on 16 March, as shown in Figure \ref{['fig1']}, top panel). The solid black arrow represents the transition from SIMS to HIMS and the dotted black line represents jump from 12 to 15 March (no observations on 13 & 14 March). The purple arrow shows the reverse transition.
  • Figure 3: The PCD 10.1093/mnras/stv191 where the PDS is divided into three frequency bands: band1 (0.0024–0.1 Hz), band2 (0.1–1 Hz), and band3 (1–10 Hz). PC1 is the ratio of the variance band1/band2, and PC2 is band3/band2.