Limit on Supernova Emission in the Brightest Gamma-ray Burst, GRB 221009A (2302.03829v2)

Abstract: We present photometric and spectroscopic observations of the extraordinary gamma-ray burst (GRB) 221009A in search of an associated supernova. Some past GRBs have shown bumps in the optical light curve that coincide with the emergence of supernova spectral features, but we do not detect any significant light curve features in GRB~221009A, nor do we detect any clear sign of supernova spectral features. Using two well-studied GRB-associated supernovae (SN~2013dx, $M_{r,max} = -19.54$; SN~2016jca, $M_{r,max} = -19.04$) at a similar redshift as GRB~221009A ($z=0.151$), we modeled how the emergence of a supernova would affect the light curve. If we assume the GRB afterglow to decay at the same rate as the X-ray data, the combination of afterglow and a supernova component is fainter than the observed GRB brightness. For the case where we assume the best-fit power law to the optical data as the GRB afterglow component, a supernova contribution should have created a clear bump in the light curve, assuming only extinction from the Milky Way. If we assume a higher extinction of $E(B-V)$=$1.74$ mag (as has been suggested elsewhere), the supernova contribution would have been hard to detect, with a limit on the associated supernova of $M_{r,max} \approx-$19.54. We do not observe any clear supernova features in our spectra, which were taken around the time of expected maximum light. The lack of a bright supernova associated with GRB~221009A may indicate that the energy from the explosion is mostly concentrated in the jet, leaving a lower energy budget available for the supernova.

• The paper demonstrates that light curve modeling reveals any supernova component is fainter than M₍r₎ ≈ -19.5.
• The study employs combined photometry and spectroscopy to show an absence of characteristic SN Ic-BL spectral features.
• The findings suggest that energy is mainly directed into the GRB jet rather than into a robust supernova outburst.

Analysis of Supernova Emission Limits in GRB 221009A

The paper examines photometric and spectroscopic observations of GRB 221009A, a remarkably luminous gamma-ray burst (GRB), to investigate the presence of an associated supernova (SN). The paper considers the lack of significant light curve anomalies or definitive supernova spectral features.

Observations and Modeling

The authors conducted a comprehensive suite of observations, including photometry and spectroscopy, to detect potential supernova signatures. The photometric observations did not reveal any conspicuous light curve features typically associated with emerging supernovae. Furthermore, with spectroscopic data, the authors report an absence of clear supernova features.

To explore the potential contribution of a supernova, light curves were compared to well-characterized supernovae associated with similar GRBs (SN 2013dx and SN 2016jca) residing at comparable redshifts. The authors applied models assuming baseline values for Galactic extinction $E(B-V) = 1.32$ mag and considered an alternate scenario with elevated extinction $E(B-V) = 1.74$ mag. The spectral analysis attempted to isolate supernova features by modulating the GRB afterglow component based on a power-law spectrum.

Key Findings

1. Light Curve Fitting:
   • Assumptions based on the X-ray afterglow decay rates suggested that any inherent supernova component was dimmer than the observed GRB brightness. The analyses showed that the composite model (afterglow decay plus a potential supernova) could not accommodate the observed data effectively, especially for SN magnitudes above $M_{r} \approx -19.5$.
2. Spectroscopic Data:
   • The authors noted the absence of prototypical SN Ic-BL features (like a broad \ion{Si}{2} absorption) across several spectral observations post-GRB event, further suggesting a lack of significant supernova emission coincident with GRB 221009A.
3. Distance and Energy Distribution:
   • The apparent lack of a substantial supernova may suggest an alternative energy distribution, where the bulk kinetic energy from the event is concentrated in the GRB jet itself rather than a broader supernova outburst.

Implications

The findings identify a critical discrepancy between the expected and observed supernova characteristics in GRB 221009A. This poses intriguing questions regarding the GRB-supernova connection, primarily in scenarios with extreme energy output and minimal supernova luminosity. A potential explanation could involve atypical stellar progenitors or explosive mechanisms where energy is preferentially directed into relativistic jets rather than broader ejecta.

Future Trajectories

Given the rarity and brightness of GRB 221009A, further time-resolved observations could provide more nuanced insights into afterglow behavior and environmental interactions. Additionally, the development of more sophisticated optical and X-ray models accommodating non-standard afterglow and extinction conditions may delineate more accurate GRB-supernova delineations.

This paper represents a significant step in understanding the multifaceted characteristics of GRBs and their potential progenitors, urging a reconsideration of energy dynamics within explosive stellar processes.