Signature of iron line profile from a Kerr-like wormhole

TL;DR

This study develops a relativistic reflection framework to distinguish Kerr-like wormholes from black holes via iron line profiles in X-ray spectra, highlighting the importance of using self-consistent models for detection.

Contribution

We introduce a new relativistic reflection model incorporating Kerr-like wormhole geometries and demonstrate its effectiveness in identifying wormholes in high-quality X-ray spectra.

Findings

Kerr-like wormholes produce narrower Fe Kα lines with less red wing.

Simple convolution models can mimic wormhole spectra in some cases.

Self-consistent reflection models reveal detectable deviations, unlike approximate methods.

Abstract

Broad, skewed iron K$\alpha$ emission lines in the X-ray spectra of accreting black holes encode key information about the spacetime geometry of the innermost disk. While the Kerr metric is standard for spin measurements, horizonless alternatives like traversable "Kerr-like" wormholes can mimic many black hole signatures, challenging current data interpretations. We develop a relativistic reflection framework incorporating Kerr-like wormhole geometries to predict iron line distortions and assess the feasibility of distinguishing event horizons from wormhole throats.Using a custom ray-tracing subroutine, we implement two \textsc{XSPEC} modules: \texttt{kwline} for $\delta$-function profiles and \texttt{kwconv} for full reflection spectra, parameterized by spin, throat radius, and shape-function coefficients. We compute a dense grid of line profiles and generate synthetic \textit{NuSTAR} spectra with realistic response matrices. By fitting these simulations with canonical Kerr models, we quantify deviations attributable to wormhole geometries.We find that Kerr-like wormholes produce narrower Fe K$\alpha$ lines with suppressed red wings as the throat parameter $\lambda$ increases. In 50 ks \textit{NuSTAR} simulations ($\lambda=0.9, a_*=0.998$), simple convolutional models (\texttt{kerrconv}) can mimic the wormhole spectrum. However, self-consistent models like \texttt{relxillCp} result in statistical failure, yielding structured residuals and unphysical parameter pegging (e.g., emissivity $q_{\rm in} \to 10$). We conclude that large-throat wormholes are detectable in high-quality X-ray spectra if analyzed with fully consistent reflection models rather than post-processing approximations.