# Is Bremsstrahlung A Possible Mechanism to Explain the Thermal Feature in the GRB 130925A X-ray Afterglow?

## TL;DR

This paper explores bremsstrahlung radiation as a potential mechanism for the thermal features observed in the X-ray afterglow of GRB 130925A, offering an alternative to the blackbody model.

## Contribution

It proposes bremsstrahlung radiation as a new explanation for thermal features in GRB afterglows, supported by calculations matching observations.

## Key findings

- Bremsstrahlung can explain the thermal component in GRB 130925A's X-ray afterglow.
- GRBs with bremsstrahlung emission may originate in metal-rich, dusty environments.
- The model fits data from Swift-XRT and NuSTAR observations.

## Abstract

It has been reported that some X-ray spectra of gamma-ray burst (GRB) afterglows cannot be fitted by a simple power law. A blackbody component is added to precisely fit the thermal feature in these spectra. Alternatively, we propose that bremsstrahlung radiation can also be one possible mechanism to explain the thermal component of the GRB X-ray afterglow. In particular, we examine the X-ray afterglow of the ultra-long GRB 130925A in this paper. By our calculation, we find that the X-ray thermal component observed by both Swift-XRT and NuSTAR can be well explained by the bremsstrahlung radiation. Our results indicate that the GRBs with the bremsstrahlung emission in the X-ray afterglow could be born in a metal-rich and dusty environment.