A search for signatures of interactions of X-ray binary outflows with their environments with ALMA

¹ ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
e-mail: mdiaztri@eso.org
² Joint ALMA Observatory, Av. Alonso de Cordova 3107, Vitacura, Santiago, Chile
³ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁴ National Radio Astronomy Observatory, Charlottesville, VA, USA
⁵ Academia Sinica Institute of Astronomy and Astrophysics, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan, ROC

Received: 17 December 2020
Accepted: 23 March 2021

Abstract

We observed the X-ray binaries Cir X-1, Sco X-1, GRS 1915+105, GX 13+1, and Cyg X-1 with the Atacama Large Millimeter/submillimeter Array (ALMA). Unresolved continuum emission is found at the positions of all the sources at a frequency of 92 GHz, with flux densities ranging between 0.8 and 10 mJy beam⁻¹. In all cases the emission can be associated with jets that have been extensively observed at lower frequencies. We searched for line emission from Hα recombination, SiO, H₂O, and CH₃OH at the positions of all the sources and, for Cir X-1 and Cyg X-1, also at regions where shocks associated with an interaction between the jet and the interstellar medium had previously been observed. The search did not yield any significant detection, resulting in 3σ upper limits between 0.65 and 3.7 K km s⁻¹ for the existence of line emission in these regions. In contrast, we detected spatially unresolved SiO emission in the field of view of GX 13+1, and we tentatively associate this emission with a SiO maser in a potential young stellar object or evolved star. We also found spatially extended line emission at two additional sites in the field of view of GX 13+1 that we tentatively associate with emission from SO and CH₃OH; we speculate that it may be associated with a star-forming region, but again we cannot rule out alternative origins such as emission from evolved stars.