Collimated radiation in SS 433

Abstract

Context. The microquasar SS 433 is well known for its precessing, relativistic, and highly collimated baryonic jets, which manifest in its optical spectrum as pairs of hydrogen and helium emission lines moving with large Doppler shifts. Depending on their heating mechanism, the optical jet bullets may serve as a probe of the collimated radiation coming from the inner region close to the compact object, and which is not directly visible to observers on Earth. Aims. We aim to better understand the baryonic jet phenomenon in SS 433, in particular the properties of the optical bullets and their interaction with the ionizing collimated radiation. Methods. The optical interferometer VLTI/GRAVITY has allowed us to spatially resolve the optical jets in SS 433 for the first time. We present here the second such observation taken over three nights in July 2017. In addition, we used the X-shooter spectrograph at VLT to study the optical bullets in SS 433 in detail. Over the full wavelength range 0.3−2.5 μm, we identified up to twenty pairs of jet lines observed simultaneously, which we modeled with the spectral synthesis code Cloudy. Results. GRAVITY reveals elongated exponential-like radial spatial profiles for the optical jets on scales ≲1−10 mas, suggestive of a heating mechanism acting throughout a long portion of the jet and naturally explained by photoionization by the collimated radiation. We also spatially resolve the movement of the optical bullets for the first time, detecting more extended jet components corresponding to previous ejections. Cloudy photoionization models can explain the spatial intensity profiles measured with GRAVITY and the emission line ratios from X-shooter, and constrain the properties of the optical bullets and the ionizing radiation. We find that the latter must peak in the UV with an isotropic luminosity (as inferred by a face-on observer) ∼1041 erg s−1. Provided that the X-ray spectral energy distribution is sufficiently hard, the collimated X-ray luminosity could still be high enough so that the face-on observer would see SS 433 as ultraluminous X-ray source and it would still be compatible with the H/He/He+ ionization balance of the optical bullets. The kinetic power in the optical jets is constrained to 2−20 × 1038 erg s−1, and the extinction in the optical jets to AV = 6.7 ± 0.1. We suggest there may be substantial AV ≳ 1 and structured circumstellar extinction in SS 433, likely arising from dust formed in equatorial outflows.

Super-Keplerian equatorial outflows in SS 433

“…The model fits were done for all the components simultaneously, but here we show only the visibility model for the stationary line for clarity (full model is shown in the Appendix). For the jet model and results, we refer to the companion paper on the jets (Waisberg et al 2018).…”

“…Figure 4 shows the relevant part of the K band spectrum for Epoch 2, with velocities centered on the Brγ line. For the complete K band spectra, we refer to the companion paper on the jets (Waisberg et al 2018).…”

“…Moreover, because of the blending with Paα emission lines from the receding jet, which also produces differential visibility signatures, it is necessary to perform simultaneous fits for the Brγ line and the jets. For the model and results for the jets we refer to the companion paper (Waisberg et al 2018).…”

“…solid lines show the models without the blended jet emission lines, whereas the dashed lines show the full combined model (as the fits are done). For the jet models and results, we refer to the companion paper on the jets (Waisberg et al 2018). The projected length and position angle of each baseline is indicated.…”

An optical spectroscopic and polarimetric study of the microquasar binary system SS 433

“…Using only S2 and S5 and interpolating the Serkowski 1 For details about the EMMI dataset see Blundell et al (2011) while the XSHOOTER data set corresponds to the ESO Program Id: 0101.D-0696 and P.I. : Waisberg, Idel (the dataset is published, in part, in Waisberg et al 2019 = 2.79 ± 0.26, which is significantly lower than the value given by SCal. Moreover, the PA changes drastically.…”