Detection of Very Low-Frequency Quasi-Periodic Oscillations in the 2015 Outburst of V404 Cygni

TL;DR

This study reports the detection of very low-frequency quasi-periodic oscillations in the 2015 outburst of V404 Cygni across multiple X-ray instruments, revealing new insights into QPO behavior in black hole X-ray binaries.

Contribution

First comprehensive search for QPOs in V404 Cygni's 2015 outburst using data from six instruments, identifying rare mHz-QPOs and standard Type-C QPOs across different observations.

Findings

Detected 18 mHz QPOs simultaneously in Fermi/GBM and Swift/XRT.

Identified 73 mHz and 1.03 Hz QPOs in Chandra data.

Found a 136 mHz QPO in Swift/XRT data.

Abstract

In June 2015, the black hole X-ray binary (BHXRB) V404 Cygni went into outburst for the first time since 1989. Here, we present a comprehensive search for quasi-periodic oscillations (QPOs) of V404 Cygni during its recent outburst, utilizing data from six instruments on board five different X-ray missions: Swift/XRT, Fermi/GBM, Chandra/ACIS, INTEGRAL's IBIS/ISGRI and JEM-X, and NuSTAR. We report the detection of a QPO at 18 mHz simultaneously with both Fermi/GBM and Swift/XRT, another example of a rare but slowly growing new class of mHz-QPOs in BHXRBs linked to sources with a high orbital inclination. Additionally, we find a duo of QPOs in a Chandra/ACIS observation at 73 mHz and 1.03 Hz, as well as a QPO at 136 mHz in a single Swift/XRT observation that can be interpreted as standard Type-C QPOs. Aside from the detected QPOs, there is significant structure in the broadband power, with a strong feature observable in the Chandra observations between 0.1 and 1 Hz. We discuss our results in the context of current models for QPO formation.