# Swift J1644+57 as an off-axis Jet

**Authors:** Paz Beniamini, Tsvi Piran, Tatsuya Matsumoto  
**arXiv:** [2305.06370](https://arxiv.org/abs/2305.06370)  
**Date:** 2023-05-10  
**Summary page:** https://www.summarizepaper.com/en/paper/2305.06370v1/

## Key points

- The discovery of Swift J1644+57 is the first jetted tidal disruption event (TDE)
- There has been a puzzle regarding the constant increase in its jet energy as observed through radio observations
- Recent research suggests that this phenomenon can be explained by viewing the jet slightly off-axis
- In such a scenario, the apparent increase in energy is due to the slowing down of the jet and broadening of its beaming cone
- Using equipartition analysis, they have inferred an increasing jet energy as a larger region of the jet is observed
- Their simple off-axis model accounts for multi-wavelength radio observations and resolves this long-standing puzzle
- They were able to estimate the beaming angle of the jet to be approximately 21 degrees which implies super Eddington luminosity during Swift J1644+57's prompt phase
- Beniamini et al.'s research presents a closure relation between spectral and temporal flux for off-axis jets that can be used to test whether other radio transients are off-axis or not.
- This provides valuable insights into understanding TDEs and offers new tools for future research in astrophysics.

## Summary

The discovery of Swift J1644+57, the first jetted tidal disruption event (TDE), has presented a long-standing puzzle regarding the constant increase in its jet energy as observed through radio observations. Recent research by Paz Beniamini, Tsvi Piran and Tatsuya Matsumoto suggests that this phenomenon can be explained by viewing the jet slightly off-axis. In such a scenario, the apparent increase in energy is due to the slowing down of the jet and broadening of its beaming cone. Using equipartition analysis, they have inferred an increasing jet energy as a larger region of the jet is observed. Their simple off-axis model accounts for multi-wavelength radio observations and resolves this long-standing puzzle. Furthermore, their model allows for self-consistent evolution of synchrotron signatures from an off-axis jet as a function of time. For the first time, they were also able to estimate the beaming angle of the jet to be approximately 21 degrees which implies super Eddington luminosity during Swift J1644+57's prompt phase. In addition to resolving this puzzle surrounding Swift J1644+57's constant increase in energy, Beniamini et al. 's research presents a closure relation between spectral and temporal flux for off-axis jets that can be used to test whether other radio transients are off-axis or not. This provides valuable insights into understanding TDEs and offers new tools for future research in astrophysics.