A bright flare in the obscured state of GRS 1915+105 as seen by NICER and Swift

TL;DR

This study presents time-resolved X-ray spectroscopy of a bright flare in GRS 1915+105, revealing complex absorption, reflection features, and coupling with jet activity, providing insights into accretion processes during obscured states.

Contribution

First detailed time-resolved spectral analysis of a bright flare in GRS 1915+105 during its obscured state, highlighting stratified absorption and re-illumination phenomena.

Findings

Flare involved increased intrinsic emission and decreased obscuration.

Distinct absorption of neutral and ionized reflection components.

Delayed radio flare indicates coupling between accretion and jet activity.

Abstract

We report time-resolved NICER and Swift X-ray spectroscopy of a bright flare from the black hole X-ray binary GRS 1915+105 during its obscured state, which is characterized by heavy line-of-sight absorption by dense material with complex geometry. In April 2023, an unexpected flare was detected, with the observed X-ray flux increasing by nearly an order of magnitude relative to the typical obscured-state level. The spectra show pronounced variability, including significant evolution of the Fe K emission features. Time-resolved spectral modeling indicates that the main flare is associated with a combination of enhanced intrinsic emission and reduced obscuration. We further find that neutral and ionized reflection components are subject to distinct absorbers, whose evolving visibility implies a stratified absorber-reflector geometry. These properties are consistent with a re-illumination phase following a failed disk wind. A delayed radio flare detected about 2.5 days later suggests a coupling between accretion and jet activity.