# How Dense a CSM is Sufficient to Choke a Jet?

## TL;DR

This study calculates the density of circumstellar medium needed to choke or decelerate jets in supernovae, concluding typical GRB jets are not choked but can be slowed, affecting observed afterglow features.

## Contribution

It provides the first detailed numerical analysis of jet-choking conditions in dense CSM for high-velocity supernovae, clarifying when jets are halted or slowed.

## Key findings

- Typical GRB jets are not choked in the CSM.
- Dense CSM can decelerate jets to Lorentz factor ~10.
- High-mass CSM causes jets to become nonrelativistic and wider.

## Abstract

The progenitor stars of stripped-envelope high-velocity supernovae (Ic-BL SNe) can explode inside a dense circumstellar medium (CSM) that extends out to many times the progenitor radius. This complicates the question of whether all Ic-BL SNe harbor a jet, which can tunnel through the star and be viewed on-axis as a long-duration gamma-ray burst (GRB). More specifically, a sufficiently dense CSM might "choke" the jet, redistributing its energy quasi-spherically. In this study, we numerically calculate the CSM density necessary for jet-choking. For typical GRBs, we determine the jet is not choked in the CSM unless $\rho r^2 > 4 \times 10^{19}$ g/cm; this requires several solar masses of CSM to be situated within $10^{13}$ cm of the progenitor, a much higher density than any CSM observed. We conclude that typical GRB jets are not choked in the CSM. However, in many cases the CSM has sufficient mass to decelerate the jet to a modest Lorentz factor ($\Gamma \sim 10$), which should lead to a long coasting phase for the jet, observable as a long plateau (potentially up to a few days) in the afterglow light curve. For extreme cases of low-energy GRBs in a high-mass CSM, the jet will decelerate to nonrelativistic velocities, causing it to spread modestly to a larger opening angle ($\theta_j \approx 20$ degrees) before breaking out of the CSM. Even in these extreme examples, the jet does not have time to redistribute its energy quasi-spherically in the CSM before breakout.