The complex behaviour of the microquasar GRS 1915+105 in the ρ class observed with BeppoSAX

III. The hard X-ray delay and limit cycle mapping^⋆

¹ INFN, Sezione Roma 1, Piazzale A. Moro 2, 00185 Roma, Italy
² Dipartimento di Fisica, Università La Sapienza, Piazzale A. Moro 2, 00185 Roma, Italy
³ INAF, IASF, Sez. di Palermo, via U. La Malfa 153, 90146 Palermo, Italy
e-mail: mineo@iasf-palermo.inaf.it
⁴ Dipartimento di Fisica, Università di Palermo, via Archirafi 36, 90123 Palermo, Italy
⁵ INAF, IAPS, Sez. di Roma, via Fosso del Cavaliere 100, 00113 Roma, Italy
⁶ INAF, Osservatorio Astronomico di Roma, 23807 Monte Porzio Catone, Italy
⁷ INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy

Received: 29 October 2012
Accepted: 25 April 2013

Abstract

Context. The microquasar GRS1915+105 was observed by BeppoSAX in October 2000 for about ten days while the source was in ρ mode, which is characterized by a quasi-regular type I bursting activity.

Aims. This paper presents a systematic analysis of the delay of the hard and soft X-ray emission at the burst peaks. The lag, also apparent from the comparison of the [1.7–3.4] keV light curves with those in the [6.8–10.2] keV range, is evaluated and studied as a function of time, spectral parameters, and flux.

Methods. We apply the limit cycle mapping technique, using as independent variables the count rate and the mean photon rate. The results using this technique were also cross-checked using a more standard approach with the cross-correlation methods. Data are organized in runs, each relative to a continuous observation interval.

Results. The detected hard-soft delay changes in the course of the pointing from ~3 s to ~10 s and presents a clear correlation with the baseline count rate.