REM near-IR and optical multiband observations of PKS2155-304 in 2005

Abstract

Spectral variability is the main tool for constraining emission models of BL Lac objects. By means of systematic observations of the BL Lac prototype PKS 2155-304 in the infrared-optical band, we explore variability on the scales of months, days and hours. We made our observations with the robotic 60 cm telescope REM located at La Silla, Chile. VRIJHK filters were used. PKS 2155-304 was observed from May to December 2005. The wavelength interval explored, the total number of photometric points and the short integration time render our photometry substantially superior to previous ones for this source. On the basis of the intensity and colour we distinguish three different states of the source, each of duration of months, which include all those described in the literature. In particular, we report the highest state ever detected in the H band. The source varied by a factor of 4 in this band, much more than in the V band (a factor ~2). The source softened with increasing intensity, contrary to the general pattern observed in the UV-X-ray bands. On five nights of November we had nearly continuous monitoring for 2-3 hours. A variability episode with a time scale of ~24 h is well documented, a much more rapid flare with t=1-2 h, is also apparent, but is supported by relatively few points.

This paper is the corrected version of the paper published in A&A 469 503. It contains the material in the "Errata Corrrige", in press in A&A

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Cited by in corpus (12)

• An Optical View of BL Lacertae Objects
• Simultaneous multiwavelength observations of the second exceptional gamma-ray flare of PKS 2155-304 in July 2006
• A ~4.6 h quasi-periodic oscillation in the BL Lacertae PKS 2155-304?
• Detection of Intra-day Variability Timescales of Four High Energy Peaked Blazars with XMM-Newton
• A multiwavelength view of the flaring state of PKS 2155-304 in 2006
• Long and short term variability of seven blazars in six near-infrared/optical bands
• Optical quasi-periodic oscillation and color behavior of blazar PKS 2155-304
• Infrared to X-ray observations of PKS 2155-304 in a low state
• Spectral energy distributions of the BL Lac PKS 2155-304 from XMM-Newton
• Flux and spectral variability of the blazar PKS 2155-304 with XMM-Newton: Evidence of Particle Acceleration and Synchrotron Cooling
• AGILE observation of a gamma-ray flare from the blazar 3C 279
• New Multiwavelength Observations of PKS 2155-304 and Implications for the Coordinated Variability Patterns of Blazars