Millisecond X-Ray Pulses from Cygnus X-1

TL;DR

This paper reports the detection of millisecond X-ray pulses from Cyg X-1, indicating rapid variability originating near the black hole's accretion disk, observed across different luminosity states and energy bands.

Contribution

It provides the first evidence of millisecond-scale X-ray pulses in Cyg X-1, linking them to the inner accretion disk region and demonstrating their occurrence in various luminosity states.

Findings

Millisecond X-ray pulses are detected in Cyg X-1.

Pulses originate from the inner accretion disk region.

Pulses occur during different luminosity states.

Abstract

X-ray pulses with millisecond-long FWHM have been detected in RXTE (Rossi X-Ray Timing Explorer) observations of Cyg X-1. Their identity as short-timescale variations in the X-ray luminosity of the source, and not stochastic variability in the X-ray flux, is established by their simultaneous occurrence and similar pulse structure in two independent energy bandpasses. The light-time distance corresponding to the timescale of their FWHM indicates that they originate in the inner region of the accretion disk around the system's black hole component. The fluence in the pulses can equal or exceed the fluence of the system's average continuous flux over the duration of the pulses' FWHM in several different bandpasses between 1 and 73 keV. Millisecond pulses are detected during both high and low luminosity states of Cyg X-1, and during transitions between luminosity states.