The ablation of gas clouds by blazar jets

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037925 ◽

2020 ◽

Vol 641 ◽

pp. A114

Author(s):

Jonathan Heil ◽

Michael Zacharias

Keyword(s):

Jet Flow ◽

Scale Height ◽

Interstellar Cloud ◽

Emission Region ◽

Ablation Process ◽

Parameter Spaces ◽

Cloud Parameters ◽

Analytical Formulae

Context. Flaring activity in blazars can last for vastly different timescales, and it may be the result of density enhancements in the jet flow that result from the intrusion of an interstellar cloud into the jet. Aims. We investigate the lightcurves expected from the ablation of gas clouds by the blazar jet under various cloud and jet configurations. Methods. We derived the semi-analytical formulae describing the ablation process of a hydrostatic cloud and performed parameter scans of artificial set-ups over both cloud and jet parameter spaces. We then used parameters obtained from measurements of various cloud types to produce lightcurves of these cloud examples. Results. The parameter scans show that a vast zoo of symmetrical lightcurves can be realized. Both cloud and emission region parameters significantly influence the duration and strength of the flare. The scale height of the cloud is one of the most important parameters as it determines the shape of the lightcurve. In turn, important cloud parameters can be deduced from the observed shape of a flare. The example clouds result in significant flares lasting for various timescales.

Download Full-text

Infrared variability due to magnetic pressure-driven jets, dust ejection and quasi-puffed-up inner rims

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa402 ◽

2020 ◽

Vol 493 (3) ◽

pp. 4022-4038 ◽

Cited By ~ 1

Author(s):

Kurt Liffman ◽

Geoffrey Bryan ◽

Mark Hutchison ◽

Sarah T Maddison

Keyword(s):

Accretion Rate ◽

Jet Flow ◽

Flow Speed ◽

Magnetic Pressure ◽

Scale Height ◽

Time Dependent ◽

Gas Flows ◽

Centrifugal Acceleration ◽

The Face ◽

Disc Region

ABSTRACT The interaction between a YSO stellar magnetic field and its protostellar disc can result in stellar accretional flows and outflows from the inner disc rim. Gas flows with a velocity component perpendicular to disc mid-plane subject particles to centrifugal acceleration away from the protostar, resulting in particles being catapulted across the face of the disc. The ejected material can produce a ‘dust fan’, which may be dense enough to mimic the appearance of a ‘puffed-up’ inner disc rim. We derive analytical equations for the time-dependent disc toroidal field, the disc magnetic twist, the size of the stable toroidal disc region, the jet speed, and the disc region of maximal jet flow speed. We show how the observed infrared variability of the pre-transition disc system LRLL 31 can be modelled by a dust ejecta fan from the inner-most regions of the disc whose height is partially dependent on the jet flow speed. The greater the jet flow speed, the higher is the potential dust fan scale height. An increase in mass accretion on to the star tends to increase the height and optical depth of the dust ejection fan, increasing the amount of 1–8 µm radiation. The subsequent shadow reduces the amount of light falling on the outer disc and decreases the 8–40 µm radiation. A decrease in the accretion rate reverses this scenario, thereby producing the observed ‘see-saw’ infrared variability.

Download Full-text

Supernovae and interstellar gas dynamics

Symposium - International Astronomical Union ◽

10.1017/s0074180900100774 ◽

1967 ◽

Vol 31 ◽

pp. 117-119

Author(s):

F. D. Kahn ◽

L. Woltjer

Keyword(s):

Lower Limit ◽

High Velocity ◽

Gas Dynamics ◽

Interstellar Cloud ◽

Interstellar Gas ◽

Random Motions ◽

Relativistic Particles

The efficiency of the transfer of energy from supernovae into interstellar cloud motions is investigated. A lower limit of about 0·002 is obtained, but values near 0·01 are more likely. Taking all uncertainties in the theory and observations into account, the energy per supernova, in the form of relativistic particles or high-velocity matter, needed to maintain the random motions in the interstellar gas is estimated as 1051·4±1ergs.

Download Full-text

Design of a Field-Emission Gun for the Phillips CM20/STEM microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100134090 ◽

1990 ◽

Vol 48 (2) ◽

pp. 100-101

Author(s):

P.M. Mul ◽

B.J.M. Bormans ◽

L. Schaap

Keyword(s):

High Resolution ◽

Field Emission ◽

Analytical Electron Microscopy ◽

Emission Region ◽

Attractive Alternative ◽

Electron Holography ◽

Field Emitter ◽

Field Emitters ◽

Resolution Electron ◽

High Resolution Tem

The first Field Emission Guns (FEG) on TEM/STEM instruments were introduced by Philips in 1977. In the past decade these EM400-series microscopes have been very successful, especially in analytical electron microscopy, where the high currents in small probes are particularly suitable. In High Resolution Electron Holography, the high coherence of the FEG has made it possible to approach atomic resolution.Most of these TEM/STEM systems are based on a cold field emitter (CFE). There are, however, a number of disadvantages to CFE’s, because of their very small emission region: the maximum current is limited (a strong disadvantage for high-resolution TEM imaging) and the emission is unstable, requiring special measures to reduce the strong FEG-induced noise. Thermal field emitters (TFE), i.e. a zirconiated field emitter source operating in the thermal or Schottky mode, have been shown to be a viable and attractive alternative to CFE’s. TFE’s have larger emission regions, providing much higher maximum currents, better stability, and reduced sensitivity to vacuum conditions as well as mechanical and electrical interferences.

Download Full-text