REVIEW
Milliarcsecond-scale jet reorientations in GRS 1915+105 pointing towards a warped accretion disc
High Energy Astrophysical Phenomena · Submitted 2 Nov 2026 · 224 references
Pith's verdict: Solid new VLBI measurements of a 57-degree jet reorientation in GRS 1915+105, but the claim that 8-hour PA stability rules out Lense-Thirring precession outruns the data.
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Referee report
The paper
The paper claims
The milliarcsecond jet of GRS 1915+105 swung up to $57^{\circ}\pm 8^{\circ}$ from its pre-obscuration axis in 2019-2021, and the absence of fast intra-epoch motion points to a radiation-driven warped disc rather than Lense-Thirring…
The reading
What carries the argument
The load-bearing measurement is the jet position angle on milliarcsecond scales, obtained by fitting elliptical Gaussian components to VLBA (8.4 GHz) and EVN (4.9 GHz) visibilities and deconvolving intrinsic source sizes from the interstellar scattering sizes measured by Dhawan et al. (2000). The mechanism under test is Lense-Thirring precession, whose predicted period $P_{\rm prec} = \frac{\pi}{3} a_* \frac{GM}{c^3} r_{\rm sph}^3 \left[\frac{1-(r_{\rm in}/r_{\rm sph})^3}{\ln(r_{\rm sph}/r_{\rm in})}\right]$ is evaluated at roughly 27 seconds using the source's mass, spin, and ISCO radius, orders of magnitude shorter than the observed stability timescale. The favoured alternative is the radiation-driven warping instability, in which radiation pressure on the outer disc excites bending eigenmodes; for mass ratios $q \lesssim 0.2$ the single-node mode 1 dominates, and at the system's high inclination it can keep the inner and outer disc on opposite sides of the line of sight, explaining why the obscuration persists regardless of precession phase.
Extended reading notes
Core claim
The paper's central claim is that the jet-launching direction of GRS 1915+105 is not fixed on monthly timescales during the obscured phase: the milliarcsecond jet was measured at $15.3^{\circ}\pm 1.2^{\circ}$ in October 2019, $18.61^{\circ}\pm 0.03^{\circ}$ in October 2020, and $170.9^{\circ}\pm 0.3^{\circ}$ in March 2021, a swing of at least $27.7^{\circ}$ in 126 days and up to $57^{\circ}\pm 8^{\circ}$ from the weighted mean of pre-obscuration milliarcsecond position angles. The absence of position-angle variation within individual 8-hour epochs, together with the $\sim 27$ s period predicted for Lense-Thirring precession given the source's mass, spin, and ISCO radius, leads the authors to rule out rapid inner-disc precession as the direct driver. They conclude that a radiation-driven warped accretion disc, suggested for this source by XRISM spectroscopy and expected in its parameter regime of small mass ratio ($q\sim 0.07$) and long orbital period (33.9 days), is the plausible reorientation mechanism, with a single-node 'mode 1' warp naturally keeping the inner disc hidden behind the outer disc and hence explaining the persistent obscuration.
Load-bearing premise
To rule out rapid Lense-Thirring precession, the paper assumes that a jet whose launch direction swings with a period of tens of seconds would show up as measurable position-angle variation within an 8-hour observation, even though the imaging bins are 5 to 30 minutes long, hundreds of times longer than the predicted about 27 s period, and no time-averaged image of such a fast-precessing jet is modelled.
Editorial extensions
If this is right
- The jet's pointing is tied to the obscured state: the two early epochs share nearly the same large offset from the old axis, and later EA VN measurements show the jet on the opposite side, so the reorientation began with, and tracks, the 2018 obscuration rather than being a transient event.
- Lense-Thirring precession of an inner slim disc is excluded as the direct driver, both because its predicted about 27 s period is incompatible with 8-hour stability at the $\lesssim 5^{\circ}$ level and because XRISM spectroscopy disfavours the required slim-disc geometry.
- If the position-angle changes are due to steady precession, the sky-projected slew rate is bounded between roughly 0.2 degrees per day (from the 126-day shift between EVN E1 and EVN E2) and 15 degrees per day (from intra-epoch stability).
- A radiation-driven warped outer disc can unify two previously separate mysteries: the persistent X-ray obscuration and the measured jet reorientation, with a mode-1 warp keeping the inner disc occulted at all precession phases.
- The EVN E2 two-sided jet components give speed-inclination constraints (ratio $1.28\pm 0.06$ and $1.25\pm 0.02$ for the two component pairs) that, for a jet speed $\beta\sim 0.35$, are consistent with the pre-obscuration inclination of $64^{\circ}\pm 4^{\circ}$, implying that near-edge-on inclinations reported by other authors are not necessarily a stable new geometry.
Reading between the lines
- The exclusion of rapid Lense-Thirring precession rests on an untested averaging assumption: with bins hundreds of times longer than the predicted period, a fast-precessing jet could conceivably average into an apparently stable position angle, so the data as analysed may only exclude precession slower than about 15 degrees per day; a simulation of the time-averaged image would settle this.
- If the warp interpretation is correct, the jet position angle carries information about the warp's precession phase, so dense monitoring should reveal PA changes that correlate in time with variations in the X-ray absorption column and possibly with the roughly 590-day super-orbital modulation previously reported for this source.
- The 40 degree difference between the 6.7 GHz and 43 GHz EA VN position angles in 2023 could be a frequency-dependent core shift along an already bent jet rather than a genuine 20 degrees per day reorientation, so observing at paired frequencies simultaneously would separate the two effects.
- The source sits near the boundary between single-mode and multi-modal warping, so the coherence of future PA monitoring is a discriminator: a steady, repeating precession favours the mode-1 warp, whereas erratic jumps would favour multi-modal warping and predict eventual disc breaking.
Original abstract
The black hole X-ray binary GRS 1915+105 was persistently X-ray bright for over 26 years before entering a prolonged low X-ray flux state in 2018, while remaining bright at radio wavelengths. Multi-wavelength observations suggest this state results from a complex layer of absorbing material of unknown nature. Radio jet observations provide an unobstructed view of the physical changes during this phase, and recent Very Large Array and East Asian VLBI Network observations revealed substantial changes in the jet position angle (PA). We use higher-resolution VLBI observations to investigate the connection between the obscuration event and the jet behaviour close to the launch region. We observed GRS 1915+105 with the Very Long Baseline Array and European VLBI Network at four epochs during the early obscuration phase (2019-2021), sampling a diverse range of jet and accretion behaviours. We study the milliarcsecond jet morphology and PA changes and relate these to the reported X-ray behaviour. Many post-2018 PAs are significantly offset from the pre-obscuration jet axis, which has a weighted mean of $142^\circ \pm 7^\circ$ on milliarcsecond scales. We measure a maximum offset of $57^\circ \pm 8^\circ$, the largest reported for GRS 1915+105 to date. Our epochs reveal a variety of jet behaviour, ranging from a stable, compact source with a large PA offset, to a bright, flaring source with a similar offset, to an extended jet with a PA closer to the pre-obscuration axis, and a non-detection. The lack of measurable PA changes within individual 8-hour epochs rules out rapid Lense-Thirring precession of the inner disc as the direct driver of the jet reorientation. Instead, the timescales involved, the system geometry, and the apparent connection to the X-ray obscuration favour a radiation-driven warped accretion disc, a configuration that could naturally explain the persistent obscuration.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
The black hole X-ray binary GRS 1915+105 was persistently X-ray bright for over 26 years before entering a prolonged low X-ray flux state in 2018, while remaining bright at radio wavelengths. Multi-wavelength observations suggest this state results from a complex layer of absorbing material of unknown nature. Radio jet observations provide an unobstructed view of the physical changes during this phase, and recent Very Large Array and East Asian VLBI Network observations revealed substantial changes in the jet position angle (PA). We use higher-resolution VLBI observations to investigate the connection between the obscuration event and the jet behaviour close to the launch region. We observed GRS 1915+105 with the Very Long Baseline Array and European VLBI Network at four epochs during the early obscuration phase (2019-2021), sampling a diverse range of jet and accretion behaviours. We study the milliarcsecond jet morphology and PA changes and relate these to the reported X-ray behaviour. Many post-2018 PAs are significantly offset from the pre-obscuration jet axis, which has a weighted mean of $142^\circ \pm 7^\circ$ on milliarcsecond scales. We measure a maximum offset of $57^\circ \pm 8^\circ$, the largest reported for GRS 1915+105 to date. Our epochs reveal a variety of jet behaviour, ranging from a stable, compact source with a large PA offset, to a bright, flaring source with a similar offset, to an extended jet with a PA closer to the pre-obscuration axis, and a non-detection. The lack of measurable PA changes within individual 8-hour epochs rules out rapid Lense-Thirring precession of the inner disc as the direct driver of the jet reorientation. Instead, the timescales involved, the system geometry, and the apparent connection to the X-ray obscuration favour a radiation-driven warped accretion disc, a configuration that could naturally explain the persistent obscuration.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The black hole X-ray binary GRS 1915+105 was persistently X-ray bright for over 26 years before entering a prolonged low X-ray flux state in 2018, while remaining bright at radio wavelengths. | background 1.00 | 0.16 | 0.02 | asserted 1.00 |
| s1 | Multi-wavelength observations suggest this state results from a complex layer of absorbing material of unknown nature. | background 0.82 | 0.10 | 0.02 | hedged possibility 0.99 |
| s2 | Radio jet observations provide an unobstructed view of the physical changes during this phase, and recent Very Large Array and East Asian VLBI Network observations revealed substantial changes in the jet position angle (PA). | background 0.87 | 0.16 | 0.03 | asserted 0.98 |
| s3 | We use higher-resolution VLBI observations to investigate the connection between the obscuration event and the jet behaviour close to the launch region. | contribution 0.88 | 0.56 | 0.02 | asserted 0.61 |
| s4 | We observed GRS 1915+105 with the Very Long Baseline Array and European VLBI Network at four epochs during the early obscuration phase (2019-2021), sampling a diverse range of jet and accretion behaviours. | method 0.98 | 0.97 | 0.02 | asserted 0.99 |
| s5 | We study the milliarcsecond jet morphology and PA changes and relate these to the reported X-ray behaviour. | contribution 0.79 | 0.82 | 0.03 | asserted 0.73 |
| s6 | Many post-2018 PAs are significantly offset from the pre-obscuration jet axis, which has a weighted mean of $142^\circ \pm 7^\circ$ on milliarcsecond scales. | result 1.00 | 0.86 | 0.05 | asserted 1.00 |
| s7 | We measure a maximum offset of $57^\circ \pm 8^\circ$, the largest reported for GRS 1915+105 to date. | result 1.00 | 0.94 | 0.05 | asserted 1.00 |
| s8 | Our epochs reveal a variety of jet behaviour, ranging from a stable, compact source with a large PA offset, to a bright, flaring source with a similar offset, to an extended jet with a PA closer to the pre-obscuration axis, and a non-detection. | result 1.00 | 0.93 | 0.05 | asserted 1.00 |
| s9 | The lack of measurable PA changes within individual 8-hour epochs rules out rapid Lense-Thirring precession of the inner disc as the direct driver of the jet reorientation. | interpretation 0.56 | 0.91 | 0.08 | asserted 1.00 |
| s10 | Instead, the timescales involved, the system geometry, and the apparent connection to the X-ray obscuration favour a radiation-driven warped accretion disc, a configuration that could naturally explain the persistent obscuration. | interpretation 1.00 | 0.72 | 0.92 | hedged possibility 0.89 |
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Figures
Figures reproduced from arXiv:2611.03395 by the authors.
References
Discussion
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