The complex behaviour of the microquasar GRS 1915+105 in the rho class observed with BeppoSAX. I: Timing analysis

TL;DR

This study analyzes the timing behavior of the microquasar GRS 1915+105 in the rho class using BeppoSAX data, revealing energy-dependent variability modes, burst structure components, and correlations between recurrence time and count rate.

Contribution

It provides a detailed timing analysis distinguishing regular and irregular variability modes and identifies the energy-dependent components of the burst structure in GRS 1915+105.

Findings

Recurrence time varies from 45 to 75 seconds and correlates with count rate.

Two components identified: slow leading trail and pulse, with different energy dependencies.

Regular and irregular modes are distinguished by power distribution in Fourier and wavelet spectra.

Abstract

GRS 1915+105 was observed by BeppoSAX for about 10 days in October 2000. For about 80% of the time, the source was in the variability class $\rho$, characterised by a series of recurrent bursts. We describe the results of the timing analysis performed on the MECS (1.6--10 keV) and PDS (15--100 keV) data. The X-ray count rate from \grss showed an increasing trend with different characteristics in the various energy bands. Fourier and wavelet analyses detect a variation in the recurrence time of the bursts, from 45--50 s to about 75 s, which appear well correlated with the count rate. From the power distribution of peaks in Fourier periodograms and wavelet spectra, we distinguished between the {\it regular} and {\it irregular} variability modes of the $\rho$ class, which are related to variations in the count rate in the 3--10 keV range. We identified two components in the burst structure: the slow leading trail, and the pulse, superimposed on a rather stable level. We found that the change in the recurrence time of the regular mode is caused by the slow leading trails, while the duration of the pulse phase remains far more stable. The evolution in the mean count rates shows that the time behaviour of both the leading trail and the baseline level are very similar to those observed in the 1.6--3 and 15--100 keV ranges, while that of the pulse follows the peak number. These differences in the time behaviour and count rates at different energies indicate that the process responsible for the pulses must produce the strongest emission between 3 and 10 keV, while that associated with both the leading trail and the baseline dominates at lower and higher energies