Defense
Student: Luna Costa Lacerda Espinosa
Program: Astronomia
Title: "Study of Nonthermal Emission in Stellar Bubbles"
Advisor: Profa. Dra. María Victoria del Valle - IAG/USP
Judging Comitee:
- Dra. María Victoria del Valle - Presidente e Orientadora
- Profa. Dra. Vera Jatenco Silva Pereira – IAG
- Prof. Dr. Gustavo Esteban Romero – IAR, Argentina (por videoconferência)
- Prof. Dr. Raniere Maciel de Menezes – CBPF (por videoconferência)
Alternate Members:
- Profa. Dra. Jane Cristina Gregorio-Hetem - IAG
- Prof. Dr. Ciriaco Goddi - IAG
- Prof. Dr. Diego Antonio Falceta Gonçalves - EACH/USP
- Prof. Dr. Claudio Melioli - Universidade de Módena (Itália)
Abstract:
Recently, massive stars have been suggested as possible sources of Galactic cosmic
rays. As their powerful stellar winds expand and interact with the interestellar
medium, strong shock waves are generated. Recent studies indicate that winds
from massive stars play an important role in the galactic production of cosmic rays,
although their expected contribution is smaller than that of supernova remnants. A
useful way to probe particle acceleration in astrophysical environments is through
their non-thermal emission. In 2019, the first detection of non-thermal radio
emission from the stellar bubble G2.4+1.4, associated with the Wolf-Rayet star
WO2, was reported. The observed signal is consistent with synchrotron radiation
produced by relativistic electrons, which are also expected to generate non-thermal
emission at higher energies, particularly in the gamma-ray domain. Assuming that
the particles are accelerated in the shocks produced in the bubble, we developed
two models to estimate the non-thermal emission from electrons and protons: a
homogeneous model and a spatially extended model, based on the classical theory
for stellar bubbles. Our estimates yield maximum energies up to the TeV range for
electrons and around hundred TeVs for protons. From the fitting of the
observational data, a relatively strong magnetic field of 250 µG is required. Both
models predict gamma-ray emission, with non-thermal electrons injected into the
surrounding medium at efficiencies of ~3% ~0.2% in the homogeneous and
extended cases, respectively. Finally, we developed a general model to investigate
the potential of bubbles from O and B-type stars to accelerate particles up to higher
energies. Our findings indicate that the powerful winds of massive stars can
accelerate particles up to hundreds of TeVs, in some cases, producing potentially
observable gamma-ray emission.
Keywords: Particle acceleration, Radiative processes: nonthermal, ISM: stellar bubbles