Revisiting the Blazar Sequence
Abstract
From observations with EGRET we know that the frequencies at which the low-energy and high-energy components of the spectral energy distributions (SEDs) of blazars peak anti-correlate with their bolometric luminosities. Following the discovery of this anti-correlation, Fossati et al. (1998) and Ghisellini et al. (1998) proposed a simple physical explanation for the anti-correlation in the "blazar sequence", namely that the radiative electron cooling in the more powerful objects accounted for the rather low frequencies of their SED peaks. Except for the most powerful sources, EGRET was only able to make time- and source-averaged statements about the gamma-ray SEDs of blazars. We now re-visit the blazar sequence based on extensive radio (UMRAO, Metsahovi), optical (Tuorla, WIYN, Swift), X-ray (Swift), and gamma-ray (Fermi) observations of 26 blazars in 2008 and 2009. The observations deliver broadband spectral energy distributions with unprecedented signal to noise ratio, and allow us to study how well individual sources fit into the blazar sequence. Furthermore, it becomes possible to study how sources move "along" and "perpendicular" to the blazar sequence as they cycle through quiescent and flaring phases. In this contribution, we scrutinize the time resolved blazar SEDs. Using observational tools as broad band cross-correlation analyses, and theoretical tools like snapshot and time-dependent SED modeling, we discuss the implications of the observations for the physical mechanisms which govern the emission properties.
- Publication:
-
AAS/High Energy Astrophysics Division #11
- Pub Date:
- March 2010
- Bibcode:
- 2010HEAD...11.3319L