Discovery of one new class in the light curve of GRS 1915+105

TL;DR

This paper reports the discovery of a new variability class, called epsilon, in the X-ray light curve of GRS 1915+105, revealing insights into accretion rate changes and state transitions in this black hole binary system.

Contribution

The study identifies and characterizes a novel epsilon class of variability in GRS 1915+105, linking spectral states and accretion processes during state transitions.

Findings

Discovery of a new epsilon variability class in GRS 1915+105.

Spectral analysis shows state transition characteristics.

Higher RMS amplitude observed at high energies during high count rates.

Abstract

From the study of X-ray light curve and color-color diagram of the low mass X-ray binary GRS 1915+105, observed by on board proportional counter array (PCA) of Rossi X-ray Timing Explorer (RXTE), we discover a new class of variability, which we name $\epsilon$ class. We have studied observations between MJD 51200 and 51450. The class shows unusual periodic-like variation in count rate during rise time of two x-ray bursts. The class take place when the source is in radio quiet state. The huge expansion in color-intensity diagram indicates the class to be an adjusting stage of increasing accretion rate. Spectral analysis shows that during lower count rate, the spectrum is hard power-law dominating, indicating similarity towards hard intermediate state, and during higher count rate, the spectrum is thermal disk blackbody component dominating, indicating similarity towards high soft state. Hence, this class is important in understanding the way of state transition leads to change in accretion rate. No signature of any low frequency quasi periodic oscillation was seen in this class. We also find that when the class was showing higher counts, the average RMS amplitude is significantly high for high energy band (14-60 keV) compared to low energy band (2-8 keV).