# Investigation of the WR 11 field at decimeter wavelengths

## TL;DR

This study conducted low-frequency radio observations of WR11 and surrounding sources to investigate potential non-thermal emission and its relation to gamma-ray detection, finding no direct synchrotron emission from WR11 but identifying a promising candidate source nearby.

## Contribution

It provides the first low-frequency radio catalog of the WR11 field and analyzes a candidate source for high-energy emission, offering insights into the system's radio properties and potential gamma-ray counterparts.

## Key findings

- WR11 shows thermal emission with no detectable non-thermal synchrotron radiation.
- A nearby source, MOST0808-471, exhibits non-thermal spectral index and structure, but its connection to gamma-rays remains uncertain.
- Derived a mass loss rate consistent with models for gamma-ray production in WR11.

## Abstract

The massive binary system WR11 has been recently proposed as the counterpart of a Fermi source. If correct, it would be the second colliding wind binary detected in GeV gamma-rays. However, the reported flux measurements from 1.4 to 8.64GHz fail to establish the presence of non-thermal (synchrotron) emission from this source. Moreover, WR11 is not the only radio source within the Fermi detection box. Other possible counterparts have been identified in archival data, some of which present strong non-thermal radio emission. We conducted "-resolution observations towards WR11 at very low frequencies (150 to 1400~MHz) where the NT emission is expected to dominate, and present a catalog of more than 400 radio-emitters, among which a significant part is detected at more than one frequency, including limited spectral index information. A search for counterparts for this last group pointed at MOST0808-471, a source 2' away from WR11, as a promising candidate for high-energy emission, with resolved structure along 325 - 1390 MHz. For it, we reprocessed archive interferometric data up to 22.3 GHz and obtained a non-thermal radio spectral index of -0.97 +- 0.09. However, multiwavelength observations of this source are required to establish its nature and to assess whether it can produce (part of) the observed gamma-rays. WR11 spectrum follows a spectral index of 0.74 +- 0.03 from 150 to 230 GHz, consistent with thermal emission. We interpret that any putative synchrotron radiation from the colliding-wind region of this relatively short-period system is absorbed in the photospheres of the individual components. Notwithstanding, the new radio data allowed to derive a mass loss rate of 0.000025 Mo/yr, which, according to the latest models for gamma-ray emission in WR 11, would suffice to provide the required kinetic power to feed non-thermal radiation processes.