LOFAR 150-MHz observations of SS 433 and W 50

Abstract

We present 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 - 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 ${\chi }^2$ probability of a flat light curve of $8.2\times 10^{-3}$. By comparing the LOFAR flux densities with contemporaneous observations carried out at 4800 MHz with the RATAN-600 telescope, we suggest that an observed $\sim$0.5-1 Jy rise in the 150-MHz flux density may correspond to sustained flaring activity over a period of approximately six 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.

arXiv comment19 pages, 8 figures, 4 tables, accepted for publication in MNRAS

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• Radio activity of supermassive black holes with extremely high accretion rates
• Science with the Murchison Widefield Array: Phase I Results and Phase II Opportunities
• The Large-scale ISM of SS433/W50 Revisited
• Multi-wavelength Emission from Galactic Jets: the Case of the Microquasar SS433
• Continuous Jets and Backflow Models for the Formation of W50/SS433 in Magnetohydrodynamics Simulations
• Axion dark matter-induced echo of supernova remnants
• Detection of a Radio Bubble around the Ultraluminous X-ray Source Holmberg IX X-1
• Axion Echos from the Supernova Graveyard
• A Small-Scale Investigation of Molecular Emission toward the Tip of the Western Lobe of W50/SS433
• Spatially resolved study of the SS 433/W50 west region with Chandra: X-ray structure and spectral variation of non-thermal emission
• An explanation for the peculiar periphery of supernova remnant G309.2-0.6
• W 50 and SS 433
• Molecular clouds at the eastern edge of radio nebula W50
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• Discovery of a radio transient in M81
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• Strong low-frequency radio flaring from Cygnus X-3 observed with LOFAR
• PeV particle acceleration and non-thermal emission in the `minimalist' model of the extended jets in W50/SS433
• Probing extreme black-hole outflows on short timescales via high spectral-resolution X-ray imagers