JWST/NIRCam Detects Rapid Burster Infrared Counterpart Fading 2.5 Magnitudes in Liller 1

The Rapid Burster has remained optically concealed for decades inside the metal-rich globular cluster Liller 1, where extreme crowding and 11 magnitudes of visual extinction blocked earlier ground-based attempts. Using JWST/NIRCam, Desai and colleagues obtained high-resolution infrared imaging that isolated a variable source whose position and timing align with known X-ray activity, providing the first unambiguous OIR anchor for the system.

The counterpart exhibited rapid infrared fluctuations on minute timescales while fading by approximately 2.5 magnitudes, consistent with changing accretion geometry or disk instabilities near the neutron star. These data directly link the infrared emission to the accretion physics responsible for the object’s unique dual-burst behavior, something no prior X-ray or radio monitoring could resolve.

This detection opens simultaneous multi-wavelength campaigns that can constrain the donor star’s spectral type and test whether Type II bursts arise from disk instabilities or magnetic gating. Future spectroscopy with JWST or ELT-class facilities will be essential to separate the donor continuum from reprocessed accretion light.

A key limitation remains the single-epoch nature of the current JWST data; repeated observations during both quiescent and bursting states are required to establish whether the observed variability pattern is periodic or stochastic.