MeerKAT discovery of radio emission from the Vela X-1 bow shock
Vela X-1 is a runaway X-ray binary system hosting a massive donor star, whose strong stellar wind creates a bow shock as it interacts with the interstellar medium (ISM). This bow shock has previously been detected in H α and infrared, but, similar to all but one bow shock from a massive runaway star...
| Main Authors: | , , , , , , , , , |
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| Format: | Journal Article |
| Language: | English |
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OXFORD UNIV PRESS
2022
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| Subjects: | |
| Online Access: | http://purl.org/au-research/grants/arc/FT140101082 http://hdl.handle.net/20.500.11937/91518 |
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| author | Van Den Eijnden, J. Heywood, I. Fender, R. Mohamed, S. Sivakoff, G.R. Saikia, P. Russell, T.D. Motta, S. Miller-Jones, James Woudt, P.A. |
| author_facet | Van Den Eijnden, J. Heywood, I. Fender, R. Mohamed, S. Sivakoff, G.R. Saikia, P. Russell, T.D. Motta, S. Miller-Jones, James Woudt, P.A. |
| author_sort | Van Den Eijnden, J. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | Vela X-1 is a runaway X-ray binary system hosting a massive donor star, whose strong stellar wind creates a bow shock as it interacts with the interstellar medium (ISM). This bow shock has previously been detected in H α and infrared, but, similar to all but one bow shock from a massive runaway star (BD+43o3654), has escaped detection in other wavebands. We report on the discovery of 1.3 GHz radio emission from the Vela X-1 bow shock with the MeerKAT telescope. The MeerKAT observations reveal how the radio emission closely traces the H α line emission, both in the bow shock and in the larger scale diffuse structures known from existing H α surveys. The Vela X-1 bow shock is the first stellar-wind-driven radio bow shock detected around an X-ray binary. In the absence of a radio spectral index measurement, we explore other avenues to constrain the radio emission mechanism. We find that thermal/free-free emission can account for the radio and H α properties, for a combination of electron temperature and density consistent with earlier estimates of ISM density and the shock enhancement. In this explanation, the presence of a local ISM overdensity is essential for the detection of radio emission. Alternatively, we consider a non-thermal/synchrotron scenario, evaluating the magnetic field and broad-band spectrum of the shock. However, we find that exceptionally high fractions (13 per cent) of the kinetic wind power would need to be injected into the relativistic electron population to explain the radio emission. Assuming lower fractions implies a hybrid scenario, dominated by free-free radio emission. Finally, we speculate about the detectability of radio bow shocks and whether it requires exceptional ISM or stellar wind properties. |
| first_indexed | 2025-11-14T11:36:49Z |
| format | Journal Article |
| id | curtin-20.500.11937-91518 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| language | English |
| last_indexed | 2025-11-14T11:36:49Z |
| publishDate | 2022 |
| publisher | OXFORD UNIV PRESS |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-915182023-05-09T06:23:35Z MeerKAT discovery of radio emission from the Vela X-1 bow shock Van Den Eijnden, J. Heywood, I. Fender, R. Mohamed, S. Sivakoff, G.R. Saikia, P. Russell, T.D. Motta, S. Miller-Jones, James Woudt, P.A. Science & Technology Physical Sciences Astronomy & Astrophysics shock waves stars: early-type stars: individual: HD 77581 radio continuum: general X-rays: binaries X-RAY BINARY MAGNETIC-FIELDS STELLAR WIND COSMIC-RAYS ACCELERATION NEBULA CALIBRATION LIMITS STARS Science & Technology Physical Sciences Astronomy & Astrophysics shock waves stars: early-type stars: individual: HD 77581 radio continuum: general X-rays: binaries X-RAY BINARY PARTICLE-ACCELERATION MAGNETIC-FIELDS STELLAR WIND COSMIC-RAYS NEBULA CALIBRATION LIMITS STARS astro-ph.HE astro-ph.HE Vela X-1 is a runaway X-ray binary system hosting a massive donor star, whose strong stellar wind creates a bow shock as it interacts with the interstellar medium (ISM). This bow shock has previously been detected in H α and infrared, but, similar to all but one bow shock from a massive runaway star (BD+43o3654), has escaped detection in other wavebands. We report on the discovery of 1.3 GHz radio emission from the Vela X-1 bow shock with the MeerKAT telescope. The MeerKAT observations reveal how the radio emission closely traces the H α line emission, both in the bow shock and in the larger scale diffuse structures known from existing H α surveys. The Vela X-1 bow shock is the first stellar-wind-driven radio bow shock detected around an X-ray binary. In the absence of a radio spectral index measurement, we explore other avenues to constrain the radio emission mechanism. We find that thermal/free-free emission can account for the radio and H α properties, for a combination of electron temperature and density consistent with earlier estimates of ISM density and the shock enhancement. In this explanation, the presence of a local ISM overdensity is essential for the detection of radio emission. Alternatively, we consider a non-thermal/synchrotron scenario, evaluating the magnetic field and broad-band spectrum of the shock. However, we find that exceptionally high fractions (13 per cent) of the kinetic wind power would need to be injected into the relativistic electron population to explain the radio emission. Assuming lower fractions implies a hybrid scenario, dominated by free-free radio emission. Finally, we speculate about the detectability of radio bow shocks and whether it requires exceptional ISM or stellar wind properties. 2022 Journal Article http://hdl.handle.net/20.500.11937/91518 10.1093/mnras/stab3395 English http://purl.org/au-research/grants/arc/FT140101082 OXFORD UNIV PRESS fulltext |
| spellingShingle | Science & Technology Physical Sciences Astronomy & Astrophysics shock waves stars: early-type stars: individual: HD 77581 radio continuum: general X-rays: binaries X-RAY BINARY MAGNETIC-FIELDS STELLAR WIND COSMIC-RAYS ACCELERATION NEBULA CALIBRATION LIMITS STARS Science & Technology Physical Sciences Astronomy & Astrophysics shock waves stars: early-type stars: individual: HD 77581 radio continuum: general X-rays: binaries X-RAY BINARY PARTICLE-ACCELERATION MAGNETIC-FIELDS STELLAR WIND COSMIC-RAYS NEBULA CALIBRATION LIMITS STARS astro-ph.HE astro-ph.HE Van Den Eijnden, J. Heywood, I. Fender, R. Mohamed, S. Sivakoff, G.R. Saikia, P. Russell, T.D. Motta, S. Miller-Jones, James Woudt, P.A. MeerKAT discovery of radio emission from the Vela X-1 bow shock |
| title | MeerKAT discovery of radio emission from the Vela X-1 bow shock |
| title_full | MeerKAT discovery of radio emission from the Vela X-1 bow shock |
| title_fullStr | MeerKAT discovery of radio emission from the Vela X-1 bow shock |
| title_full_unstemmed | MeerKAT discovery of radio emission from the Vela X-1 bow shock |
| title_short | MeerKAT discovery of radio emission from the Vela X-1 bow shock |
| title_sort | meerkat discovery of radio emission from the vela x-1 bow shock |
| topic | Science & Technology Physical Sciences Astronomy & Astrophysics shock waves stars: early-type stars: individual: HD 77581 radio continuum: general X-rays: binaries X-RAY BINARY MAGNETIC-FIELDS STELLAR WIND COSMIC-RAYS ACCELERATION NEBULA CALIBRATION LIMITS STARS Science & Technology Physical Sciences Astronomy & Astrophysics shock waves stars: early-type stars: individual: HD 77581 radio continuum: general X-rays: binaries X-RAY BINARY PARTICLE-ACCELERATION MAGNETIC-FIELDS STELLAR WIND COSMIC-RAYS NEBULA CALIBRATION LIMITS STARS astro-ph.HE astro-ph.HE |
| url | http://purl.org/au-research/grants/arc/FT140101082 http://hdl.handle.net/20.500.11937/91518 |