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 ru...
| Main Authors: | , , , , , , , , , |
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| Format: | Journal article |
| Language: | English |
| Published: |
Oxford University Press
2021
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| _version_ | 1797107558030245888 |
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| author | van den Eijnden, J Heywood, I Fender, R Mohamed, S Sivakoff, GR Saikia, P Russell, TD Motta, S Miller-Jones, JCA Woudt, PA |
| author_facet | van den Eijnden, J Heywood, I Fender, R Mohamed, S Sivakoff, GR Saikia, P Russell, TD Motta, S Miller-Jones, JCA Woudt, PA |
| author_sort | van den Eijnden, J |
| collection | OXFORD |
| 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 | 2024-03-07T07:17:50Z |
| format | Journal article |
| id | oxford-uuid:16ed486d-8026-4240-93ce-424c57521f4e |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T07:17:50Z |
| publishDate | 2021 |
| publisher | Oxford University Press |
| record_format | dspace |
| spelling | oxford-uuid:16ed486d-8026-4240-93ce-424c57521f4e2022-09-06T12:04:06ZMeerKAT discovery of radio emission from the Vela X-1 bow shockJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:16ed486d-8026-4240-93ce-424c57521f4eEnglishSymplectic ElementsOxford University Press2021van den Eijnden, JHeywood, IFender, RMohamed, SSivakoff, GRSaikia, PRussell, TDMotta, SMiller-Jones, JCAWoudt, PAVela 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. |
| spellingShingle | van den Eijnden, J Heywood, I Fender, R Mohamed, S Sivakoff, GR Saikia, P Russell, TD Motta, S Miller-Jones, JCA Woudt, PA 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 |
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