TY - GEN
T1 - Variability models of gamma-ray blazars
AU - Levinson, A.
N1 - variability models;gamma-ray blazars;blazar variability;radiation mechanisms;emission region geometry;beaming factors;shock formation;shock dynamics;light travel time;cooling time;particle acceleration;dynamical time;temporal structure;accretion instabilities;jet;
PY - 1999
Y1 - 1999
N2 - Much observational effort has been devoted in recent years to study blazar variability across the electromagnetic spectrum. In addition to spectral and polarization information, variability data can provide stringent constraints on the radiation mechanisms, the geometry of the emission regions, beaming factors, formation and dynamics of shocks, and perhaps the jet's content. In most models the variability pattern is governed by the following timescales: i) the light travel time across the source, ii) the cooling time, iii) the acceleration or injection time of radiating particles, and iv) the dynamical time, which equals roughly the light crossing time in the case of a relativistically expanding source. It is conceivable, however, that the temporal structure observed involves additional, distinct timescales that are associated with completely different physical process, as demonstrated by other transient systems, e.g., radio pulsars, GRB; the overall pulse duration and the duty cycle in the former system reflect the rotation of a neutron star, whereas the temporal substructure (sub-pulses, polarization swings, etc.) is presumably connected with the emission mechanism. A plausible variability scenario for blazars is the formation of a train of shocks during a period of enhanced activity that might be associated with accretion instabilities or with the process responsible for the ejection of the jet. Such a possibility seems to be suggested by some recent observations which reveal, what appears to be rapid flaring during the occurrence of a much longer outburst (Wagner 1998).
AB - Much observational effort has been devoted in recent years to study blazar variability across the electromagnetic spectrum. In addition to spectral and polarization information, variability data can provide stringent constraints on the radiation mechanisms, the geometry of the emission regions, beaming factors, formation and dynamics of shocks, and perhaps the jet's content. In most models the variability pattern is governed by the following timescales: i) the light travel time across the source, ii) the cooling time, iii) the acceleration or injection time of radiating particles, and iv) the dynamical time, which equals roughly the light crossing time in the case of a relativistically expanding source. It is conceivable, however, that the temporal structure observed involves additional, distinct timescales that are associated with completely different physical process, as demonstrated by other transient systems, e.g., radio pulsars, GRB; the overall pulse duration and the duty cycle in the former system reflect the rotation of a neutron star, whereas the temporal substructure (sub-pulses, polarization swings, etc.) is presumably connected with the emission mechanism. A plausible variability scenario for blazars is the formation of a train of shocks during a period of enhanced activity that might be associated with accretion instabilities or with the process responsible for the ejection of the jet. Such a possibility seems to be suggested by some recent observations which reveal, what appears to be rapid flaring during the occurrence of a much longer outburst (Wagner 1998).
KW - astrophysical radiation mechanisms
KW - BL Lac-type objects
KW - gamma-ray sources (astronomical)
KW - quasars
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VL - 159
SP - 471
EP - 474
BT - Astronomical Society of the Pacific Conference Series
CY - USA
ER -