Multiwavelength Monitoring of the BL Lacertae Object PKS 2155−304 in 1994 May. III. Probing the Inner Jet through Multiwavelength Correlations

Abstract

In May 1994 the BL Lac object PKS 2155-304 was observed continuously for ∼10 days with IUE and EUVE and for 2 days with ASCA, as well as with ROSAT and with ground-based radio, infrared, and optical telescopes. The light curves show a well-defined X-ray flare followed by a broader, lower amplitude extreme ultraviolet (EUV) flare ∼1 day later and a broad, low-amplitude UV flare ∼2 days later. X-ray fluxes obtained at three well separated times the preceding week indicate at least one previous flare of comparable amplitude or perhaps ongoing stochastic X-ray variations, and additional rapid variability was seen at the beginning of the IUE observation, when extremely sharp changes in UV flux occurred. The X-ray flux observed with ASCA flared by a factor of ∼ 2

A ~4.6 h quasi-periodic oscillation in the BL Lacertae PKS 2155-304?

“…Its extreme TeV variability seems to demand an ultra-relativistic flow (bulk Lorentz factor ∼50) in at least portions of the jet that is believed to dominate the emission from this and other BL Lacs and blazars (Ghisellini & Tavecchio 2008). This BL Lac has been the target of several simultaneous multi-wavelength monitoring campaigns (e.g., Urry et al 1993;Brinkmann et al 1994;Edelson et al 1995;Courvoisier et al 1995;Urry et al 1997;Pian et al 1997;Pesce et al 1997;Foschini et al 2007Foschini et al , 2008. PKS 2155−304 is among the few blazars for which claims of an apparent QPO have been made, with UV and optical monitoring (from IUE) over five days possibly having a ∼0.7 d periodicity (Urry et al 1993).…”

Simultaneous Multi-Wavelength Observations of the TeV Blazar Mrk 421 during February–March, 2003: X-Ray and NIR Correlated Variability

“…Edelson et al (1995) have reported correlated emission between X-ray, UV and optical emissions from PKS 2155-304 (an HBL BL Lac object). In another multi-wavelength campaign of PKS 2155-304 from 10 days data, Urry et al 1997 have reported X-ray flare leading EUV flare by one day and UV flare by two days. McComb et al (1995) and Maraschi et al (1999) have reported simultaneous X-ray and γ−ray flares in Mrk 421 in two different campaigns.…”

Multiwavelength Evidence of the Physical Processes in Radio Jets

“…The multi-wavelength spectral energy distributions and variability time scales are used to probe the beaming parameters and the physical properties of the emitting regions, e.g., [48,76,125]. Correlated flares are sometimes measured across wavebands, giving support to the present of a dominant spatial region of emission, e.g., [124,131], but otherwise uncertainties of size scales, geometries, and parameters for the competing processes of energy loss and acceleration, often force the adoption of oversimplified or poorly-constrained models for individual jets.…”