Work

Compelling evidence of a link between the lags of the quasi-periodic oscillations and the radio jet in the black-hole X-ray binary GRS 1915+105

Year: 2026

Type: article

Abstract: GRS 1915+105 is one of the most studied black-hole X-ray binaries, known for its extreme variability and rich phenomenology. Previous studies of this source using the Rossi X-ray Timing Explorer reported a transition in the phase lags of type-C quasi-periodic oscillations (QPOs): from soft (where low-energy photons lag the high-energy ones) at QPO frequencies above ∼2 Hz to hard at frequencies below ∼2 Hz. The hard lags of the QPO coincide with episodes of strong radio emission. We analysed NICER observations of GRS 1915+105 obtained between 2018 and 2020, during a period in which the source flux decreased steadily, and performed a detailed spectral-timing study of the detected type-C QPOs. We identify a type-C QPO with frequencies ranging from ∼1.3 − 3.9 Hz that displays soft lags and, contrary to the RXTE observations, shows no evidence of hard phase lags at frequencies below 2 Hz. Quasi-simultaneous AMI-LA radio observations show consistently low radio flux (≲5 mJy) during this period. These results suggest that the hard QPO lags in GRS 1915+105 are linked to the presence of strong radio activity, implying that the relativistic jet may be responsible for the hard phase lags. This supports a scenario in which QPO phase lags trace changes in coronal geometry and accretion–ejection coupling in GRS 1915+105.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202661476