Constraints on gravitational waves from the 2024 Vela pulsar glitch

TL;DR

This paper presents a targeted search for gravitational waves associated with the 2024 Vela pulsar glitch using LVK O4b data, focusing on both short f-mode–driven bursts and long quasi-monochromatic transients up to four months. Employing three unmodeled burst pipelines (cWB, PySTAMPAS, X-pipeline) and four CW-like analyses (CWInPy, transient F-statistic, WPM, HMM), the authors find no significant GW candidates but place the first physically meaningful upper limits that undercut the indirect energy bound derived from the glitch. They interpret the results in the context of specific emission models (Ekman pumping and transient mountains) and demonstrate how joint burst–CW constraints can inform neutron-star mass–radius relations and energy budgets, though current limits are still above some conservative theoretical expectations. The study highlights the potential for future detections as detector sensitivity improves and stresses the value of combining precise radio timing with multi-method GW analyses to probe NS interiors. Data products are released to enable broader use and cross-validation in the community.

Abstract

Among known neutron stars, the Vela pulsar is one of the best targets for gravitational-wave searches. It is also one of the most prolific in terms of glitches, sudden frequency changes in a pulsar's rotation. Such glitches could cause a variety of transient gravitational-wave signals. Here we search for signals associated with a Vela glitch on 29 April 2024 in data of the two LIGO detectors from the fourth LIGO-Virgo-KAGRA observing run. We search both for seconds-scale burst-like emission, primarily from fundamental (f-)mode oscillations, and for longer quasi-monochromatic transients up to four months in duration, primarily from quasi-static quadrupolar deformations. We find no significant detection candidates, but for the first time we set direct observational upper limits on gravitational strain amplitude that are stricter than what can be indirectly inferred from the overall glitch energy scale. We discuss the short- and long-duration observational constraints in the context of specific emission models. These results demonstrate the potential of gravitational-wave probes of glitching pulsars as detector sensitivity continues to improve.

Figures (13)

• Figure 1: Top panel: Vela pulsar radio timing residuals before fitting for the 29 April 2024 glitch. Bottom panel: Timing residuals after fitting for the glitch with the parameters shown in Table \ref{['tab:Vela_glitch']}.
• Figure 2: Top panel: gw detector sensitivities within $T_\mathrm{gl}\pm20$ s around the Vela glitch on 29 April 2024, in terms of their asd (computed with the Welch method in gwpy, gwpy). Bottom left panel: GW data availability over 24 h around the glitch, as used for the burst searches in Section \ref{['sec:burst']}. Bottom right panel: LIGO data availability for the four following months, as used in the long-duration searches in Section \ref{['sec:tcw']}. Virgo data is not used in either type of searches. The glitch time is highlighted in the two bottom panels with a vertical dashed line.
• Figure 3: This schematic summarizes the burst-like transient searches performed for this paper as a function of the duration of anticipated signals and the on-source windows used by each. The on-source window time for X-pipeline is 1$\sigma$ uncertainty around the estimated glitch arrival time using the timing model, the on-source window for cWB is the broadest window in radio observation within which the glitch occurred. The choice for PySTAMPAS is based on analysis requirements and longer duration of the signal.
• Figure 4: $h_{\mathrm{rss}}^{90\%}$ at a detection threshold of $3 \sigma$ (p-value $10^{-3}$) for the three gw burst searches (circle, square and triangle markers), shown against the frequency of damped sinusoids signals. For cWB and X-pipeline, multiple markers at fixed frequencies denote different damping times (see Table \ref{['tab:Bursts_Inj']}), which do not effect the sensitivity drastically. Strains corresponding to the characteristic energy $\Delta E_{\text{c}}$ of the glitch from Equation \ref{['eq:E_characteristic']} are shown as the dashed green line and gw emission would be consistent with it in the shaded region below. The right-hand vertical axis shows the r-mode amplitude $\alpha$ that would correspond to a given $h_{\mathrm{rss}}$ level. See Section \ref{['sec:interpret_bursts']} for interpretation of these results in terms of $\Delta E_{\text{c}}$ and $\alpha$.
• Figure 5: Selected upper limits at 95% confidence from the four cw-like post-glitch searches, in terms of initial strain amplitude (left-hand axis) and ns ellipticity $\epsilon$ (right-hand axis), both defined at the start of signals with exponentially decay parameters $\tau$. The results were chosen to illustrate how upper limits scale with the strictness of prior assumptions built into each search configuration. The CWInPy results have the strictest constraints (fixed frequency evolution and constrained orientation angles), while the three other results are for narrow-band searches, with $\mathcal{F}$-statistic results marginalized over all durations, wpm results for search configurations optimized at each $\tau$ point, and hmm results for $T_\mathrm{coh}=9$ h. For comparison, gw emission at the characteristic energy scale $\Delta E_{\text{c}}$ from Equation \ref{['eq:E_characteristic']} is shown as the magenta shaded band near the top, while the sky blue shaded band further down shows the emission if the gw energy output is suppressed by a factor $Q\approx0.017$, as in the 2007.05893 transient mountain model.