Broad-band SEDs of BL Lacertae in August 2008 (blue) and July 1997 (red). The 2008 SED is built with UV and X-ray data from two epochs of Swift observations (Sect. 3), 2008 August 25 and 30, together with simultaneous optical-to-radio data from the GASP-WEBT collaboration, and contemporaneous γ-ray data from Fermi (from Abdo et al. 2010a). The 1997 SED includes EGRET data from Bloom et al. (1997), OSSE data from the HEASARC archive, ASCA+RXTE spectra from Tanihata et al. (2000), while low-frequency data are from the WEBT archive. Solid lines represent model fits; we distinguish the low-energy emission component (dotted lines) from the high-energy one (dashed lines); the contribution by an accretion disc of ~16000 K and 5 × 1044 ergs-1 is marked with a dotted-dashed line. We also show in black the SED corresponding to the XMM-Newton observations of May 2008 (Sect. 4); both the single power law with free absorption and double power law with Galactic absorption fits to the EPIC spectra are displayed.
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