Investigation of the WR 11 field at decimeter wavelengths

BENAGLIA, P.; DEL PALACIO, S.; ISHWARA-CHANDRA, C. H.; DE BECKER, M.; ISEQUILLA, N. L.; SAPONARA, J.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Año: 2019 vol. 625

0004-6361

The massive binary system WR 11 (γ 2 -Velorum) has been recently proposed as the counterpart of a Fermi source. If this associationis correct, this system would be the second colliding wind binary detected in GeV γ-rays. However, the reported flux measurementsfrom 1.4 to 8.64 GHz fail to establish the presence of non-thermal (synchrotron) emission from this source. Moreover, WR 11 is notthe only radio source within the Fermi detection box. Other possible counterparts have been identified in archival data, some of whichpresent strong non-thermal radio emission.We conducted arcsec-resolution observations towards WR 11 at very low frequencies (150 to 1400 MHz) where the non-thermalemission ?if existent and not absorbed? is expected to dominate, and present a catalog of more than 400 radio-emitters, amongwhich a significant part is detected at more than one frequency, including limited spectral index information. Twenty-one of themare located within the Fermi significant emission. A search for counterparts for this last group pointed at MOST 0808?471, a source2? away from WR 11, as a promising candidate for high-energy emission, with resolved structure along 325 ? 1390 MHz. For it, wereprocessed 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) theobserved γ-rays.WR 11 spectrum follows a spectral index of 0.74±0.03 from 150 MHz to 230 GHz, consistent with thermal emission. We interpret thatany putative synchrotron radiation from the colliding-wind region of this relatively short-period system is absorbed in the photospheresof the individual components. Notwithstanding, the new radio data allowed to derive a mass loss rate of 2.5 × 10 −5 M yr −1 , which,according to the latest models for γ-ray emission in WR 11, would suffice to provide the required kinetic power to feed non-thermalradiation processes.