GRB 241105A: A test case for GRB classification and rapid r-process nucleosynthesis channels

TL;DR

GRB 241105A challenges the traditional short/long GRB classification by exhibiting a hard, brief spike followed by long, weaker emission, with a secure $z=2.681$ host. The study combines multi-wavelength prompt-emission analyses, ML clustering, and detailed afterglow modelling (ISM/wind) plus JWST host characterization to test progenitor scenarios. Results show elements compatible with both collapsar and compact-binary merger origins, though the bright afterglow and star-forming, low-metallicity host favor a collapsar-like environment, while the high redshift keeps merger channels plausible for rapid early Universe enrichment. As a benchmark case at high redshift, GRB 241105A emphasizes the need for nuanced, multi-faceted classification criteria beyond prompt properties alone and informs models of early heavy-element production and galaxy evolution.

Abstract

Gamma-ray bursts (GRBs) offer a powerful window to probe the progenitor systems responsible for the formation of heavy elements through the rapid neutron capture (r-) process, thanks to their exceptional luminosity, which allows them to be observed across vast cosmic distances. GRB 241105A, observed at a redshift of z = 2.681, features a short initial spike (1.5 s) and a prolonged weak emission lasting about 64 s, positioning it as a candidate for a compact binary merger and potentially marking it as the most distant merger-driven GRB observed to date. However, the emerging ambiguity in GRB classification necessitates further investigation into the burst's true nature. Prompt emission analyses, such as hardness ratio, spectral lag, and minimum variability timescales, yield mixed classifications, while machine learning-based clustering places GRB 241105A near both long-duration mergers and collapsar GRBs. We conducted observations using the James Webb Space Telescope (JWST) to search for a potential supernova counterpart. Although no conclusive evidence was found for a supernova, the host galaxy's properties derived from the JWST observations suggest active star formation with low metallicity, and a sub-kpc offset of the afterglow from the host, which appears broadly consistent with a collapsar origin. Nevertheless, a compact binary merger origin cannot be ruled out, as the burst may plausibly arise from a fast progenitor channel. This would have important implications for heavy element enrichment in the early Universe.

Figures (20)

• Figure 1: Light curves of GRB 241105A as detected by Fermi/GBM (left), Swift/BAT (middle), and SVOM/GRM (right) in different energy bands. The red lines are the fitted background. The bottom panel in the GBM plot (left) shows $T_{\rm 90}$ of $69.0$ s overlaid on the combined NaI light curve in the 8-900 keV range.
• Figure 2: Left: A pre-trigger GOTO image of the field taken as part of the all-sky survey at 10:48:54 UT ($T_{0}$-5.29 hr), showing no source at the afterglow position. Right: The GOTO discovery image of the afterglow of GRB 241105A, taken at 16:34:35 UT on 2024-11-05 ($T_{0}$+0.48 hr), shows the transient marked at the burst location.
• Figure 3: VLT/FORS2 optical afterglow spectrum of GRB 241105A at redshift $z=2.681$. Data are in black, the error spectrum is in red, and the horizontal dotted line in grey corresponds to $F_{\lambda}=0$. The green vertical lines correspond to the labeled absorption lines.
• Figure 4: The position of GRB241105A overlaid on a composite JWST NIRCam image combining filters F070W, F115W, and F150W, as described in Section \ref{['sec:offset']}. The disturbed/irregular morphology of the host is clearly visible. One (solid circle, 36 mas) and two (dashed circle, 72 mas) sigma uncertainties on the transient position are shown.
• Figure 5: Lag-luminosity correlation of GRBs using data from Ukwatta2010. GRB 241105A follows the lag-luminosity trend typical of long GRBs, unlike short GRBs.