Unveiling the origin of HESS J1809−193^⋆

¹ Instituto de Astronomía y Física del Espacio (IAFE), UBA-CONICET, CC 67, Suc. 28, 1428 Buenos Aires, Argentina
e-mail: gcastell@iafe.uba.ar
² FADU, University of Buenos Aires, 1053 Buenos Aires, Argentina
³ CBC, University of Buenos Aires, 1053 Buenos Aires, Argentina

Received: 16 October 2015
Accepted: 29 December 2015

Abstract

Aims. The main goal of this paper is to provide new insights on the origin of the observable flux of γ rays from HESS J1809−193 using new high-quality observations in the radio domain.

Methods. We used the Expanded Very Large Array (now known as the Karl G. Jansky Very large Array, JVLA) to produce a deep full-synthesis imaging at 1.4 GHz of the vicinity of PSR J1809−1917. These data were used in conjunction with ¹²CO observations from the James Clerk Maxwell Telescope in the transition line J = 3−2 and atomic hydrogen data from the Southern Galactic Plane Survey to investigate the properties of the interstellar medium in the direction of the source HESS J1809−193.

Results. The new radio continuum image, obtained with a synthesized beam of 8′′ × 4′′ and a sensitivity of 0.17 mJy beam^-1, reveals with unprecedented detail all the intensity structures in the field. No radio counterpart to the observed X-ray emission supposed to be a pulsar wind nebula powered by PSR J1809−1917 is seen in the new JVLA image. We discovered a system of molecular clouds on the edge of the supernova remnant (SNR) G11.0−0.0 shock front, which is positionally coincident with the brightest part of the TeV source HESS J1809−193. We determine, on the basis of kinematic and morphological evidences, a physical link of the SNR with the clouds for which we estimated a total (molecular plus atomic) mass of ~3 × 10³M_⊙ and a total proton density in the range 2–3 × 10³ cm^-3.

Conclusions. We propose as the most likely origin of the very high-energy γ-ray radiation from HESS J1809−193 a hadronic mechanism through collisions of ions accelerated at the SNR G11.0−0.0 shock with the molecular matter in the vicinity of the remnant.