Fluctuations and symmetry in the speed and direction of the jets of SS433 on different timescales

ABRIDGED We present new results on the variations in speed and direction of the jet bolides in the Galactic microquasar SS433, from high resolution spectra, taken with the ESO 3.6-m New Technology Telescope almost nightly over 0.4 of a precession cycle. We find: (i) These data exhibit multiple ejections within most 24-hour periods and, throughout the duration of the observing campaign, the weighted means of the individual bolides, in both the red jet and the blue jet, clearly exhibit the pronounced nodding known in this system. (ii) We present further evidence for a 13-day periodicity in the jet speed, and show this cannot be dominated by Doppler shifts from orbital motion. (iii) We show the phase of this peak jet speed has shifted by a quarter of a cycle in the last quarter-century. (iv) We show that the two jets ejected by SS433 are highly symmetric on timescales measured thus far. (v) We demonstrate that the anti-correlation between variations in direction and in speed is not an artifact of an assumption of symmetry. (vi) We show that a recently proposed mechanism (Begelman et al 2006) for varying the ejection speed and anti-correlating it with polar angle variations is ruled out. (vii) The speed of expansion of the plasma bolides in the jets is approximately 0.0024c. These novel data carry a clear signature of speed variations. They have a simple and natural interpretation in terms of both angular and speed fluctuations which are identical on average in the two jets. They complement archival optical data and recent radio imaging.Comment: to appear in A&A (8 pages

SS433's jet trace from ALMA imaging and Global Jet Watch spectroscopy: evidence for post-launch particle acceleration

We present a comparison of Doppler-shifted H-alpha line emission observed by the Global Jet Watch from freshly-launched jet ejecta at the nucleus of the Galactic microquasar SS433 with subsequent ALMA imaging at mm-wavelengths of the same jet ejecta. There is a remarkable similarity between the transversely-resolved synchrotron emission and the prediction of the jet trace from optical spectroscopy: this is an a priori prediction not an a posteriori fit, confirming the ballistic nature of the jet propagation. The mm-wavelength of the ALMA polarimetry is sufficiently short that the Faraday rotation is negligible and therefore that the observed E-vector directions are accurately orthogonal to the projected local magnetic field. Close to the nucleus the B-field vectors are perpendicular to the direction of propagation. Further out from the nucleus, the B-field vectors that are coincident with the jet instead become parallel to the ridge line; this occurs at a distance where the jet bolides are expected to expand into one another. X-ray variability has also been observed at this location; this has a natural explanation if shocks from the expanding and colliding bolides cause particle acceleration. In regions distinctly separate from the jet ridge line, the fractional polarisation approaches the theoretical maximum for synchrotron emission.Comment: To appear in ApJ Letter

Interaction of infalling solid bodies with primordial atmospheres of disk-embedded planets

Planets that form early enough to be embedded in the circumstellar gas disk accumulate thick atmospheres of nebular gas. Models of these atmospheres need to specify the surface luminosity (i.e. energy loss rate) of the planet. This luminosity is usually associated with a continuous inflow of solid bodies, where the gravitational energy released from these bodies is the source of energy. However, if these bodies release energy in the atmosphere instead of at the surface, this assumption might not be justified. Our aim is to explore the interactions of infalling planetesimals with primordial atmospheres at an embedded phase of evolution. We investigate effects of atmospheric interaction on the planetesimals (mass loss) and the atmosphere (heating/cooling). We used atmospheric parameters from a snapshot of time-dependent evolution simulations for embedded atmospheres and simulated purely radial, infall events of siliceous planetesimals in a 1D, explicit code. We implemented energy transfer between friction, radiation transfer by the atmosphere and the body and thermal ablation; this gives us the possibility to examine the effects on the planetesimals and the atmosphere. We find that a significant amount of gravitational energy is indeed dissipated into the atmosphere, especially for larger planetary cores, which consequently cannot contribute to the atmospheric planetary luminosity. Furthermore, we examine that planetesimal infall events for cores, $M_\mathrm{C} > 2$M$_{\oplus}$, which actually result in a local cooling of the atmosphere; this is totally in contradiction with the classical model

Jet propulsion of wind ejecta from a major flare in the black hole microquasar SS433

We present direct evidence, from Adaptive-Optics near-infra-red imaging, of the jets in the Galactic microquasar SS433 interacting with enhanced wind-outflow off the accretion disc that surrounds the black hole in this system. Radiant quantities of gas are transported significant distances away from the black hole approximately perpendicular to the accretion disc from which the wind emanates. We suggest that the material that comprised the resulting "bow-tie" structure is associated with a major flare that the system exhibited ten months prior to the observations. During this flare, excess matter was expelled by the accretion disc as an enhanced wind, which in turn is "snow-ploughed", or propelled, out by the much faster jets that move at approximately a quarter of the speed of light. Successive instances of such bow-ties may be responsible for the large-scale X-ray cones observed across the W50 nebula by ROSAT.Comment: Accepted by ApJ Let

What Can Craters Tell Us About a Planet?

In this activity, students examine images of Martian craters and speculate about what caused them. Next, they model the formation of an impact crater by dropping objects into a tray of powder. They examine the effects of each impact and the features each impact creates. Students re-examine the images of the Martian craters to see if their modeling experience gives them additional insights. They create hypotheses to try to explain a feature not seen in their models, a mud-flow-like ejecta blanket. They then write a plan to test one of the hypotheses and carry out their investigation. Finally, students apply their modeling experiences by making several inferences. Educational levels: High school, Middle school

Discovery of a new branch of the Taurid meteoroid stream as a real source of potentially hazardous bodies

Taurid meteor shower produces prolonged but usually low activity every October and November. In some years, however, the activity is significantly enhanced. Previous studies based on long-term activity statistics concluded that the enhancement is caused by a swarm of meteoroids locked in 7:2 resonance with Jupiter. Here we present precise data on 144 Taurid fireballs observed by new digital cameras of the European Fireball Network in the enhanced activity year 2015. Orbits of 113 fireballs show common characteristics and form together a well defined orbital structure, which we call new branch. We found that this branch is characterized by longitudes of perihelia lying between 155.9-160o and latitudes of perihelia between 4.2-5.7o. Semimajor axes are between 2.23-2.28 AU and indeed overlap with the 7:2 resonance. Eccentricities are in wide range 0.80-0.90. The orbits form a concentric ring in the inner solar system. The masses of the observed meteoroids were in a wide range from 0.1 g to more than 1000 kg. We found that all meteoroids larger than 300 g were very fragile, while those smaller than 30 g were much more compact. Based on orbital characteristics, we argue that asteroids 2015 TX24 and 2005 UR, both of diameters 200-300 meters, are direct members of the new branch. It is therefore very likely that the new branch contains also numerous still not discovered objects of decameter or even larger size. Since asteroids of sizes of tens to hundreds meters pose a treat to the ground even if they are intrinsically weak, impact hazard increases significantly when the Earth encounters the Taurid new branch every few years. Further studies leading to better description of this real source of potentially hazardous objects, which can be large enough to cause significant regional or even continental damage on the Earth, are therefore extremely important.Comment: 24 pages, 22 figures, 5 tables. Accepted in Astronomy and Astrophysic