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

Shuaitongze Zhao1,2, Honghui Liu2,*, Menglei Zhou2, Swarnim Shashank2,3,1, Cosimo Bambi1,4,†, and Andrea Santangelo2,1

  • *Contact author: honghui.liu@uni-tuebingen.de
  • †Contact author: bambi@fudan.edu.cn
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Phys. Rev. D 114, 063018 – Published 9 September, 2026

DOI: https://doi.org/10.1103/3j4t-pc75

Abstract

We report time-resolved Neutron star Interior Composition Explorer 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 reillumination phase following a failed disk wind. A delayed radio flare detected about 2.5 days later suggests a coupling between accretion and jet activity.

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Phys. Rev. D 114, 063018– Published 9 September, 2026
  • Received 14 April 2026
  • Accepted 19 August 2026
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