A statistical analysis of the "heartbeat" behaviour of GRS 1915+105

TL;DR

This paper statistically analyzes the heartbeat behavior of GRS 1915+105, revealing bimodal recurrence times, correlations between spectral parameters, and insights into accretion disk and corona dynamics during this state.

Contribution

It provides a comprehensive statistical analysis of heartbeat cycles, uncovering correlations among recurrence time, spectral parameters, and accretion disk properties, advancing understanding of this peculiar state.

Findings

Recurrence time distribution is bimodal, ranging from 20 to 200 seconds.

Minimum count rate increases with recurrence time, maximum remains constant.

Strong correlations found among recurrence time, inner disk radius, and X-ray luminosity.

Abstract

GRS 1915+105 has been active for more than 26 years since it was discovered in 1992. There are hundreds of RXTE pointed observations on this source, and the quasi-regular flares with a slow rise and a sharp decrease (i.e. the "heartbeat" state) were recorded in more than 200 observations. The connections among the disk/corona, jet, and the disk wind at the heartbeat state have been extensively studied. In this work, we firstly perform a statistical analysis of the light curves and the X-ray spectra to investigate this peculiar state. We calculate the parameters for heartbeat cycles, including the recurrence time, the maximum and the minimum count rate, the flare amplitude, and the cumulative radiation for each cycle. The recurrence time has a bimodal distribution ranging from $\sim 20$ to $\sim 200$ s. The minimum count rate increases with increasing recurrence time; while the maximum count rate remains nearly constant around 2 Crab. Fitting the averaged spectrum for each observation, we find the strong correlations among the recurrence time, the apparent inner radius of the accretion disk (or the color correction factor), and the (nonthermal) X-ray luminosity. We suggest that the true inner edge of the accretion disk might always extend to the marginally stable orbit, while the change in corona size should result in the observed correlations.