A Search for Dying Pulse Trains in Cyg X-1 using RXTE

TL;DR

This study searched for dying pulse trains in Cyg X-1 using RXTE data but found no evidence, setting upper limits on their occurrence and supporting the hypothesis of an extreme Kerr black hole with rapid pulse timescales.

Contribution

The paper provides the first X-ray search for dying pulse trains in Cyg X-1 and establishes upper limits on their rate, refining previous UV-based observations.

Findings

No dying pulse trains detected in 10 hours of RXTE data.

Upper limit on DPT rate is less than half of previous UV-based estimate.

Results support the presence of an extreme Kerr black hole with sub-millisecond pulse timescales.

Abstract

Dying pulse trains (DPTs) pulses of radiation with decreasing intensity and decreasing intervals between them are predicted by General Relativity to occur from material spiraling into an event horizon after detaching from the last stable orbit in an accretion disk around a black hole. Two events resembling DPTs were detected in 3 hours observation of Cyg X-1 in the far UV using the High Speed Photometer on the Hubble Space Telescope (Dolan 2001). We observed Cyg X-1, a leading candidate for a black hole, with the proportional counter array on RXTE to seek such events in the low-energy X-ray region. No dying pulse trains with a characteristic timescale between pulses of 1 - 40 ms were detected in 10 hours of observation during Cyg X-1s high luminosity state, low luminosity state, and transitions between states, although individual pulses are clearly detectable in data with 1 ms temporal resolution. The 2 sigma upper limit on the rate of DPTs in the X-ray region is less than half the rate reported by Dolan (2001) in the UV. These negative results are consistent with Cyg X-1 being an extreme Kerr black hole with a characteristic timescale between DPT pulses less than 1 ms.