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Abstract:
We calculate the X-ray signal that should arise due to reflection of the putative collimated X-ray emission of the Galactic supercritical accretor SS 433 on the molecular clouds in its vicinity. The molecular gas distribution in the region of interest has been constructed based on the data of the Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey in 13CO J= 1 → 0 emission line, while the collimated emission was assumed to be aligned with the direction of the relativistic jets, which are continuously launched by the system. We consider all the available Chandraobservations covering the regions possibly containing the reflection signal and put constraints on the apparent face-on luminosity of SS 433 above 4 keV. No signatures of the predicted signal have been found in the analysed regions down to a 4–8 keV surface brightness level of ∼10−11 erg/s/cm2/deg2. This translates into the limit on the apparent face-on 2–10 keV luminosity of SS 433 LX2–10≲ 8 ×1038 erg/s, provided that the considered clouds do fall inside the illumination cone of the collimated emission. This, however, might not be the case due to persisting uncertainty in the line-of-sight distances to SS 433 dSS433 (4.5–5.5 kpc) and to the considered molecular clouds. For the half-opening angle of the collimation cone larger than or comparable to the amplitude of the jets’ precession (≈21°), the stringent upper limit quoted above is most relevant if dSS433 < 5 kpc, provided that the kinematic distances to the considered molecular clouds are sufficiently accurate (within ∼1000 pc of the adopted values). Dropping the last assumption, a more conservative constraint is LX2–10≲ 1040 erg/s for dSS433 = 4.65–4.85 kpc, and yet worse for dSS433 outside this range. We conclude that SS 433 is not likely to belong to the brightest ultraluminous X-ray sources if it could be observed face-on, unless its X-ray emission is highly collimated. However, better X-ray coverage of the molecular clouds in the region of interest is needed to eliminate dependence of this conclusion on incidence of the individual clouds inside the putative X-ray illumination cone of SS 433.
