LOFAR 150-MHz observations of SS 433 and W 50

Journal article

We present Low-Frequency Array (LOFAR) high-band data over the frequency range 115–189 MHz for the X-ray binary SS 433, obtained in an observing campaign from 2013 February to 2014 May. Our results include a deep, wide-field map, allowing a detailed view of the surrounding supernova remnant W 50 at low radio frequencies, as well as a light curve for SS 433 determined from shorter monitoring runs. The complex morphology of W 50 is in excellent agreement with previously published higher frequency maps; we find additional evidence for a spectral turnover in the eastern wing, potentially due to foreground free–free absorption. Furthermore, SS 433 is tentatively variable at 150 MHz, with both a debiased modulation index of 11 per cent and a χ2 probability of a flat light curve of 8.2 × 10−3. By comparing the LOFAR flux densities with contemporaneous observations carried out at 4800 MHz with the RATAN-600 telescope, we suggest that an observed ∼0.5–1 Jy rise in the 150-MHz flux density may correspond to sustained flaring activity over a period of approximately 6 months at 4800 MHz. However, the increase is too large to be explained with a standard synchrotron bubble model. We also detect a wealth of structure along the nearby Galactic plane, including the most complete detection to date of the radio shell of the candidate supernova remnant G 38.7−1.4. This further demonstrates the potential of supernova remnant studies with the current generation of low-frequency radio telescopes.

Authors: Broderick, JW; Fender, RP; Miller-Jones, JCA; Trushkin, SA; Stewart, AJ

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 475
• Issue: 4
• Pages: 5360–5377
• Publication date: 2018-01-12
• Acceptance date: 2017-12-21
• DOI: 10.1093/mnras/sty081
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: ISM; supernova remnants; stars; individual: SS 433; ISM; jets and outflows; radio continuum; stars; radio continuum; ISM; ISM; individual objects: W50