The Magnetic Geometry of Pulsed Astrophysical Jets

Hypersonic, highly collimated, mass outflows ({\it jets}) are a ubiquitousphenomena in astrophysics. While the character of the jets differ, many exhibitsome form of quasi-periodic clumping indicating the jet source is episodic or{\it pulsed}. The presence of pulsed jets in so many astrophysical contextssuggests a common formation mechanism. Such a process seems to have been foundin {\it Magneto-centrifugal launching}, the combination of magnetic andcentrifugal forces that occurs when a magnetized gaseous accretion disk orbitsa central gravitating source. Observations of strong magnetic fields in jetsare, however, rare or indirect. Thus the presence and effects of magneticfields in YSO jets remains an unresolved issue of the highest importance. Inthis letter we focus on what should be expected of the structure of the fieldsin pulsed YSO jets. We show that combining velocity variability with an initialfield configuration consistent with collimated, Magneto-centrifugally launchedjets leads to a clear set of predictions concerning the geometry and relativestrength of the magnetic field components in evolving YSO (and perhaps other)jets.Comment: 8 pages, 3 figures, submitted to the ApJ Letter