Abstract
Since 1978, when BL Lac objects and violently variable quasars were married to become “blazars”, physical interpretations of the phenomenon have evolved. Remarkably, though, the general picture of relativistic jets beaming their radiation in our direction, proposed that year by Blandford and Rees, remains intact. The main stress on theoretical models has come from observations that reveal ever more extreme variability requiring rampant particle acceleration on time-scales of minutes, often parsecs away from the central black hole. Here the author reviews many of the observations and theoretical ideas that have shaped his studies of blazars over about 40 years. This leads to his preferred scenario that blazar jets contain a helical magnetic field close to the black hole, turbulent plasma on parsecs scales, and both standing and moving shock waves. Particle acceleration can then occur in multiple stages involving the second-order Fermi process, magnetic reconnections, and modest jumps in energy at shock fronts. The most extreme variability, as well as brightness temperatures ~100 times the inverse Compton limit, probably require occasional exceptionally high bulk Lorentz factors. These can result, for example, from supersonic, relativistic turbulence, or ultra-relativistic flows propelled from sites of magnetic reconnection. Future efforts in these and other areas can determine whether these potential solutions are valid.
Highlights
It has been 38 years since the study of rapidly variable extragalactic objects received the focus provided by a name: “blazars”, coined by Ed Spiegel during his post-banquet monologue at the Pittsburgh Conference on BL Lac Objects [1]
When Blandford and Rees [2] applied their radio galaxy jet model to compact radio sources in galactic nuclei, this author expressed some skepticism that a double radio structure would be as prevalent in the jet scenario as it was in the VLBI data
The observation led to the prediction of superluminal of the effects expected in relativistic jets
Summary
It has been 38 years since the study of rapidly variable extragalactic objects received the focus provided by a name: “blazars”, coined by Ed Spiegel during his post-banquet monologue at the Pittsburgh Conference on BL Lac Objects [1]. This is a selective review that omits many important contributions to the field, for which he begs forgiveness He hopes that his reminiscences will help younger researchers gain some perspective that will help in their studies of blazars, the most luminous long-lived objects in the universe. One problem was that the radio spectra were too flat below the self-absorption turnover frequency, a sign of non-uniformity [10]. Another discrepancy was that the peak flux of an outburst at a particular frequency did not follow the dependence on frequency of the expanding blob model [9]. The author proposed a model of a relativistic blast wave propagating through a disk-shaped wind [11,12] that was obsolete within about a year of its publication
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