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Register a new userCoupled radio and X-ray emission and evidence for discrete ejecta in the jets of SS 433
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J.C.A. Miller-Jones
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We present five epochs of simultaneous radio (VLA) and X-ray (Chandra) observations of SS 433, to study the relation between the radio and X-ray emission in the arcsecond-scale jets of the source. We detected X-ray emission from the extended jets in only one of the five epochs of observation, indicating that the X-ray reheating mechanism is transient. The reheating does not correlate with the total flux in the core or in the extended radio jets. However, the radio emission in the X-ray reheating regions is enhanced when X-ray emission is present. Deep images of the jets in linear polarization show that outside of the core, the magnetic field in the jets is aligned parallel to the local velocity vector, strengthening the case for the jets to be composed of discrete bullets rather than being continuous flux tubes. We also observed anomalous regions of polarized emission well away from the kinematic trace, confirming the large-scale anisotropy of the magnetic field in the ambient medium surrounding the jets.
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We present the X-ray images of all the available Chandra observations of the galactic jet source SS 433. We have studied the morphology of the X-ray images and inspected the evolution of the arcsec X-ray jets, recently found to be manifestations of in situ reheating of the relativistic gas downstream in the jets. The Chandra images reveal that the arcsec X-ray jets are not steady long term structures; the structure varies, indicating that the reheating processes have no preference for a particular precession phase or distance from the binary core. Three observations made within about five days in May 2001, and a 60 ks observation made in July 2003 show that the variability of the jets can be very rapid, from timescales of days to (possibly) hours. The three May 2001 images show two resolved knots in the east jet getting brighter one after the other, suggesting that a common phenomenon might be at the origin of the sequential reheatings of the knots. We discuss possible scenarios and propose a model to interpret these brightenings in terms of a propagating shock wave, revealing a second, faster outflow in the jet.
The X-ray spectrum of the Galactic microquasar SS 433 contains a rich set of emission lines of highly ionized atoms of heavy elements whose significant Doppler shift leaves no doubt that they are produced in collimated relativistic jets of outflowing material. We have performed a systematic analysis of the high-resolution X-ray spectra obtained by the Chandra observatory to determine the parameters of the jets within the multitemperature model of their emission that self-consistently predicts the sources line and continuum spectrum. The spectrum of SS 433 at energies below 3 keV is shown to be statistically satisfactorily described by the jet emission model, while the introduction of an additional hard component is required above 3 keV. We summarize the jet parameters (bulk velocity, opening angle, kinetic luminosity, base temperature, and relative elemental abundances) derived by fitting the data below 3 keV and describe the revealed degeneracies and systematic effects due to the presence of an additional component. Using the derived parameters, we show that the hard component is compatible with the emission from the hot (up to 40 keV) extension of the visible part of the jets moderately absorbed ($N_H sim 2 times 10^{23}$ cm$^{-2}$) in the cold-wind material. The combined X-ray emission model constructed in this way allows the broadband spectrum of SS 433 to be described self-consistently.
The black hole mass and accretion rate in Ultraluminous X-ray sources (ULXs) in external galaxies, whose X-ray luminosities exceed those of the brightest black holes in our Galaxy by hundreds and thousands of times$^{1,2}$, is an unsolved problem. Here we report that all ULXs ever spectroscopically observed have about the same optical spectra apparently of WNL type (late nitrogen Wolf-Rayet stars) or LBV (luminous blue variables) in their hot state, which are very scarce stellar objects. We show that the spectra do not originate from WNL/LBV type donors but from very hot winds from the accretion discs with nearly normal hydrogen content, which have similar physical conditions as the stellar winds from these stars. The optical spectra are similar to that of SS 433, the only known supercritical accretor in our Galaxy$^{3}$, although the ULX spectra indicate a higher wind temperature. Our results suggest that ULXs with X-ray luminosities of $sim 10^{40}$ erg s$^{-1}$ must constitute a homogeneous class of objects, which most likely have supercritical accretion discs.
We have detected new components in stationary emission lines of SS 433; these are the superbroad components that are low-contrast substrates with a width of 2000--2500 km s-1 in He I $lambda4922$ and H$beta$ and 4000--5000 km s-1 in He II $lambda4686$. Based on 44 spectra taken during four years of observations from 2003 to 2007, we have found that these components in the He II and He I lines are eclipsed by the donor star; their behavior with precessional and orbital phases is regular and similar to the behavior of the optical brightness of SS 433. The same component in H$beta$ shows neither eclipses nor precessional variability. We conclude that the superbroad components in the helium and hydrogen lines are different in origin. Electron scattering is shown to reproduce well the superbroad component of H$beta$ at a gas temperature of 20--35 kK and an optical depth for Thomson scattering $tau approx$ 0.25--0.35. The superbroad components of the helium lines are probably formed in the wind from the supercritical accretion disk. We have computed a wind model based on the concept of Shakura-Sunyaev supercritical disk accretion. The main patterns of the He II line profiles are well reproduced in this model: not only the appearance of the superbroad component but also the evolution of the central two-component part of the profile of this line during its eclipse by the donor star can be explained.
We calculate X-ray signal that should arise due to reflection of the putative collimated X-ray emission of the Galactic supercritical accretor SS 433 on molecular clouds in its vicinity. The molecular gas distribution in the region of interest has been constructed based on the data of the BU-FCRAO GRS in $^{13}$CO $J=1rightarrow0$ 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 $Chandra$ observations 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 $sim 10^{-11}$ erg/s/cm$^2$/deg$^2$. This translates into the limit on the apparent face-on 2-10 keV luminosity of SS 433 $L_{X,2-10}lesssim 8times10^{38}$ 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 $d_{SS433}$ (4.5-5.5 kpc) and to the considered molecular clouds. For half-opening angle of the collimation cone larger than or comparable to the amplitude of the jets precession ($approx21deg$), the stringent upper limit quoted above is most relevant if $d_{SS433}<5$ kpc, provided that the kinematic distances to the considered molecular clouds are sufficiently accurate. Dropping the last assumption, a more conservative constraint is $L_{X,2-10}lesssim10^{40}$ erg/s for $d_{SS433}=4.65-4.85$ kpc (and yet worse 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. (Abridged)
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