Spectral study of very high energy gamma rays from SS 433 with HAWC

TL;DR

This study reports the detection and spectral analysis of very-high-energy gamma-ray emission from the lobes of SS 433 using HAWC data, revealing insights into particle acceleration in astrophysical jets.

Contribution

First resolved TeV gamma-ray emission from SS 433 lobes with detailed spectral and positional analysis using extensive HAWC data.

Findings

Detected gamma-ray emission at 6.6σ and 8.2σ significance in east and west lobes.

Spectral indices are approximately -2.4 and -2.35 for east and west lobes.

Maximum photon energies reach 56 TeV and 123 TeV in the lobes.

Abstract

Very-high-energy (0.1-100 TeV) gamma-ray emission was observed in HAWC data from the lobes of the microquasar SS 433, making them the first set of astrophysical jets that were resolved at TeV energies. In this work, we update the analysis of SS 433 using 2,565 days of data from the High Altitude Water Cherenkov (HAWC) observatory. Our analysis reports the detection of a point-like source in the east lobe at a significance of $6.6\,\sigma$ and in the west lobe at a significance of $8.2\,\sigma$. For each jet lobe, we localize the gamma-ray emission and identify a best-fit position. The locations are close to the X-ray emission sites "e1" and "w1" for the east and west lobes, respectively. We analyze the spectral energy distributions and find that the energy spectra of the lobes are consistent with a simple power-law $\text{d}N/\text{d}E\propto E^{\alpha}$ with $\alpha = -2.44^{+0.13+0.04}_{-0.12-0.04}$ and $\alpha = -2.35^{+0.12+0.03}_{-0.11-0.03}$ for the east and west lobes, respectively. The maximum energy of photons from the east and west lobes reaches 56 TeV and 123 TeV, respectively. We compare our observations to various models and conclude that the very-high-energy gamma-ray emission can be produced by a population of electrons that were efficiently accelerated.