[Paper Review] What did we learn from the extremely bright gamma ray bursts 990123 and 080319B?

S. Dado, Arnon Dar|ArXiv.org|Dec 17, 2008

Gamma-ray bursts and supernovae5 references4 citations

TL;DR

This paper demonstrates that the cannonball (CB) model—using inverse Compton scattering (ICS) and synchrotron radiation (SR) in a high-density wind environment—successfully explains the multiwavelength lightcurves of the two brightest GRBs, 990123 and 080319B, without requiring new physics. The model accounts for their prompt emission, afterglow, spectral evolution, and observed delays in optical peaks, offering a simpler and more consistent description than the fireball model.

ABSTRACT

The two brightest and so far the best studied gamma ray bursts (GRBs), 990123 and 080319B, were ordinary, highly collimated GRBs produced in a core collapse supernova explosion within a high-density wind environment and observed from a very near-axis viewing angle. Inverse Compton scattering (ICS) and synchrotron radiation (SR), the two dominant radiation mechanisms in the cannonball (CB) model of GRBs, together with the burst environment, provide a very simple and sufficiently accurate description of the multiwavelength lightcurves of their prompt and afterglow emissions.

Motivation & Objective

• To evaluate whether the cannonball model can consistently explain the extreme brightness and multiwavelength lightcurves of GRBs 990123 and 080319B.
• To challenge the prevailing fireball model by showing its inability to explain key observational features such as spectral-timing decoupling and chromatic breaks.
• To demonstrate that the cannonball model’s predictions, derived from first principles, accurately reproduce the observed prompt and afterglow emissions of these two GRBs.
• To highlight the model’s success in explaining the lack of correlation between hard X-ray/γ-ray and optical peaks, and the observed polarization trends.

Proposed method

• The cannonball model is applied using inverse Compton scattering (ICS) and synchrotron radiation (SR) as the dominant radiation mechanisms.
• The model assumes a highly collimated jet from a core-collapse supernova in a high-density wind environment, with the burst observed from a near-axis viewing angle.
• The time-dependent peak energy of the ICS spectrum is modeled as $ E_p(t) \approx E_p(0) t_p^2 / (t_p^2 + t^2) $, which governs the spectral evolution.
• The model incorporates the burst environment—specifically, a wind blown into a constant-density interstellar medium (ISM)—to explain spectral and temporal variations.
• The lightcurve shapes are derived from the combined effects of ICS and SR emission, with the break frequency dependent on density variations along the jet trajectory.
• Theoretical predictions are compared directly with multiwavelength data from BATSE, BeppoSAX, Swift, and ground-based telescopes for both GRBs.

Experimental results

Research questions

• RQ1 Can the cannonball model explain the prompt and afterglow emission lightcurves of the two brightest GRBs, 990123 and 080319B, without invoking new physics?
• RQ2 Why is the prompt optical emission in these GRBs delayed relative to the hard X-ray and γ-ray emission, contrary to fireball model predictions?
• RQ3 Does the cannonball model account for the observed chromatic behavior and lack of jet breaks in the afterglow lightcurves?
• RQ4 Why is the polarization of the prompt emission in these bursts expected to be low, contrary to predictions for ordinary GRBs?
• RQ5 Can the cannonball model predict detectable high-energy photon fluxes from collisions in the wind environment?

Key findings

• The cannonball model successfully reproduces the multiwavelength lightcurves of GRB 990123 and 080319B using only ICS and SR, without requiring adjustable parameters or new physics.
• The observed delay between the hard X-ray/γ-ray and optical peaks is naturally explained by the model, contradicting fireball model expectations of correlated peaks.
• The model accounts for the chromatic nature of the afterglow lightcurves, which deviate from standard fireball model predictions of achromatic jet breaks.
• The spectral evolution, including the transition from $ \beta_O(0) \sim 0.5 $ to $ \beta_O(t) \sim 1.1 $ at late times, is well reproduced by the model.
• The model predicts low polarization in the prompt X-ray and γ-ray emission for these near-axis bursts, consistent with observations, unlike the high polarization predicted for off-axis GRBs.
• The model predicts detectable fluxes of sub-GeV photons from ICS of glory light by electrons swept into the cannonballs, and sub-TeV photons and marginal neutrino fluxes from hadronic collisions, offering testable predictions for future observations.