A phase-resolved spectroscopy of quasi-periodic oscillations in the X-ray binary GRS 1915+105 with NICER and NuSTAR
Abstract
Low frequency quasi-periodic oscillations (QPO) with periods between ~10 s and ~0.05 s are often seen in the X-ray flux of accreting stellar-mass black holes. These are often attributed to the Lense-Thirring precession of the inner accretion flow, a General Relativistic effect caused by the spin of the black hole. QPO phase-resolved spectroscopy, (measuring how the X-ray spectrum changes with QPO phase) provides the best test of this model against alternative interpretations, since precession leads to a rocking of the ~6.4 keV iron fluorescence line between Doppler red and blue shift over the course of each QPO cycle. I will present our QPO phase-resolved spectral analysis of the bright black hole X-ray binary system GRS1915+105, utilising simultaneous data from NICER and NuSTAR and implementing a novel method to track changes in the QPO centroid frequency during the course of the observation. The high count rate and broad band X-ray coverage (~0.3-79 keV) provided by the combination of NICER and NuSTAR make this an ideal dataset for our analysis. We find from general relativistic modelling of the phase-resolved iron line profile that an asymmetric, QPO phase dependent disc illumination profile is required to explain the data, consistent with the precession model. However, our fits also return a small inner disc radius which would leave little room for a precessing corona. If this is the case, we must ask "What is precessing?".
- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E1702N