Probing the Nature of High-Redshift Long GRB 250114A and Its Magnetar Central Engine

TL;DR

This study analyzes GRB 250114A, a high-redshift long GRB at $z=4.732$ with a three-episode prompt emission and a complex X-ray afterglow featuring a flare and plateau. By combining Swift/BAT and XRT data and applying Bayesian methods, the authors identify distinct emission episodes and perform a magnetar-based central-engine fit to the X-ray plateau using a full vacuum-dipole model implemented in Redback, constrained with dynesty sampling. The resulting parameters yield a magnetar with $B_{ m p}\approx13.2\times10^{15}$ G and $P_0\approx14.3$ ms, after a jet-corrected analysis, consistent with a core-collapse Type II progenitor and within the range inferred for other magnetar candidates. The work shows that the magnetar central-engine scenario can account for the sustained engine activity across energy bands and the observed temporal/spectral evolution, while remaining compatible with multiwavelength GRB diagnostics and high-$z$ population trends.

Abstract

GRB 250114A is a long-duration gamma-ray burst (GRB) which triggered the Swift/BAT with a spectroscopic high-redshift at $z = 4.732$. The light curve of the prompt emission is composed of three distinct emission episodes, which are separated by quiescent gaps ranging from tens to hundreds of seconds. While the X-ray light curve exhibits the canonical X-ray emission which is composed of several power-law segments superposition of a giant X-ray flare. More interestingly, there is still significant X-ray emission during the quiescent time in the prompt emission, suggesting a continuously active central engine whose power fluctuates across the $γ$-ray detectability threshold. In this paper, we propose a magnetar as the central engine of GRB 250114A by fitting the X-ray light curve, and infer a magnetic field strength $B_{\rm p}=13.24^{+1.73}_{-5.84} \, \times10^{15}\ \mathrm{G}$ and an initial spin period $P_{0}=14.31^{+0.93}_{-3.16} \, \mathrm{ms}$ of magnetar, with a jet correction, fall within a reasonable range. Furthermore, we also compare the prompt emission, X-ray afterglow, $E_{\mathrm p}$-$E_{γ,\mathrm{iso}}$, and $\varepsilon-$distribution of GBR 250114A with those of other high-$z$ sample-GRBs, and find no significant statistical differences between them.

Figures (7)

• Figure 1: Light curves of prompt emission (black line in top panel) observed by BAT and X-ray emission (blue line in top panel), as well as $E_{\rm p}$ evolution (bottom panel) of GRB 250114A. The red step line is Bayesian block analysis for BAT light curve.
• Figure 2: Left panel: XRT (black) light curve of GRB 250114A. The red solid line represents the total component fitting line. The blue, green, and orange dashed lines are the best fits for the power-law, flare and plateau, respectively. The red, yellow, green and darkred data points are multiband optical data collected from GCN reports. Right panel: corner plots and parameter constraints for the fitting parameters of the XRT light curve of GRB 250114A.
• Figure 3: Comparison of GRB 250114A and Swift sample-GRBs with $z \textgreater 4.5$ in prompt emission.
• Figure 4: Comparison of GRB 250114A and Swift sample-GRBs with $z \textgreater 4.5$ in X-ray afterglow.
• Figure 5: Left panel: $E_{\mathrm p}$ and $E_{\gamma, \mathrm {iso}}$ correlation diagram. Black points and gray diamonds correspond to Type I and Type II GRBs, respectively. The red star is GRB 250114A, and other data are taken from 2009ApJ...703.1696Z. Right panel: 1D and 2D distributions of GRB samples in $T_{\mathrm{90}} - \epsilon$ space. The dashed line indicates $\epsilon = 0.03$, and the data come from 2010ApJ...725.1965L