XMM-Newton observations of the TeV BL Lac object PKS 2155--304 in 2006: signature of inverse Compton X-ray emission?

Abstract

This paper reports the first discovery of possible inverse Compoton (IC) X-ray emission below 10 keV in the typical high-energy peaked BL Lac object (HBL) PKS 2155--304. Two XMM-Newton observations performed in 2006 reveal that the 0.6--10 keV X-ray spectra of the source harden ($\Delta \Gamma \sim$ 0.1--0.3) at break energies of about 4 keV. The concave X-ray spectra of the source could be easily interpretated by a mixture of a steep component (i.e., the high energy tail of the synchrotron emission) and a flat one (i.e., the low energy side of the IC emission). However, the steep spectra ($\Gamma \sim$ 2.3) in the hard X-rays indicate that the synchrotron emission still domiantes over the IC one, while the latter is effectively present and perceived as flattening the synchrotron spectrum in this energy range. The quasi-simultaneous optical-UV-X-ray spectral energy distributions (SEDs) obtained with XMM-Newton suggest that the concave X-ray spectra of the source could be the result of down-ward shift of the synchrotron peak frequency to the optical band, incuring the IC emisssion to become more important in the hard ($\sim 4$--10 keV) X-ray band with respective to other cases in which the synchrotron emission peaks in the UV-soft-X-ray range. This discovery provides a new clue for a smooth transition between HBLs and the low-energy peaked BL Lac objects (LBLs).

accepted by ApJ (2008 August 1 issue)

References in corpus (6)

• X-ray spectral evolution of TeV BL Lac objects: eleven years of observations with BeppoSAX, XMM-Newton and SWIFT satellites
• Signatures of synchrotron emission and of electron acceleration in the X-ray spectra of Mrk 421
• Simultaneous X-ray and optical observations of S5 0716+714 after the outburst of March 2004
• X-ray/UV/Optical follow-up of the blazar PKS 2155-304 after the giant TeV flares of July 2006
• XMM-Newton observations of a sample of gamma-ray loud active galactic nuclei
• Disentangling the synchrotron and Inverse Compton variability in the X-ray emission of the intermediate BL Lac object S5 0716+71

Cited by in corpus (12)

• On the origin of the hard X-Ray excess of high-synchrotron-peaked BL Lac object Mrk 421
• X-ray Intraday Variability of the TeV Blazar PKS 2155-304 with Suzaku During 2005-2014
• Signature of Inverse Compton emission from blazars
• The Hard X-ray emission of the blazar PKS 2155--304
• X-Ray Spectral Variability of Thirteen TeV High Energy Peaked Blazars with XMM-Newton
• Convex X-ray Spectra of PKS 2155-304 and Constraints on the Minimum Electron Energy
• NuSTAR View of TeV Blazar Mrk 501
• X-Ray Spectral Variability of the TeV HBL Blazar PG 1553+113 with XMM-Newton
• X-ray Flux and Spectral Variability of Blazar H 2356-309
• X-ray Flux and Spectral Variability of the TeV Blazars Mrk 421 and PKS 2155-304
• 20 years of monitoring: PKS 2155-304 and PKS 1510-089 in the eyes of Swift and Fermi. I. The case of PKS 2155-304
• X-ray Spectral Evolution of High Energy Peaked Blazars