REM near-IR and optical multiband observations of PKS 2155-304 in 2005

被引：0

作者：

Dolcini, A. ^{[1
]}

Farfanelli, F. ^{[2
]}

Ciprini, S. ^{[2
]}

Treves, A. ^{[1
]}

Covino, S. ^{[3
]}

Tosti, G. ^{[2
]}

Pian, E. ^{[4
]}

Sbarufatti, B. ^{[1
]}

Molinari, E. ^{[3
]}

Chincarini, G. ^{[3
,5
]}

Zerbi, F.M. ^{[3
]}

Malaspina, G. ^{[3
]}

Conconi, P. ^{[3
]}

Nicastro, L. ^{[6
]}

Palazzi, E. ^{[6
]}

Testa, V. ^{[7
]}

Vitali, F. ^{[7
]}

Antonelli, L.A. ^{[7
]}

Danziger, J. ^{[4
]}

Tagliaferri, G. ^{[3
]}

Meurs, E. ^{[8
]}

Vergani, S. ^{[8
]}

Fernandez-Soto, A. ^{[9
]}

Distefano, E. ^{[10
]}

Cutispoto, G. ^{[10
]}

D'Alessio, F. ^{[7
]}

机构：

[1] Università degli Studi dell'Insubria, Dipartimento di Fisica e Matematica, via Valleggio 11, 22100 Como, Italy

[2] Dipartimento di Fisica e Osservatorio Astronomico, Università di Perugia, via. A. Pascoli, 06123 Perugia, Italy

[3] INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy

[4] INAF, Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34143 Trieste, Italy

[5] Università degli Studi di Milano-Bicocca, Dipartimento di Fisica, Piazza delle Scienze, 3, 20126 Milan, Italy

[6] INAF/IASF Bologna, via Gobetti 101, 40129 Bologna, Italy

[7] INAF, Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy

[8] Dunsink Observatory, Castleknock, Dublin 15, Ireland

[9] Observatori Astronomic, Universitat de Valencia, Aptdo. Correos 22085, Valencia 46071, Spain

[10] INAF, Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy

来源：

Astronomy and Astrophysics | 2007年 / 469卷 / 02期

关键词：

Context. Spectral variability is the main tool for constraining emission models of BL Lac objects. Aims. By means of systematic observations of the BL Lac prototype PKS 2155-304 in the infrared-optical band; we explore variability on scales of months; days; and hours. Methods. We made our observations with the robotic 60 cm telescope REM located at La Silla; Chile; and VRIJHK filters were used. Results. 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 lasting 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; in contrast to the general pattern observed in the UV-X-ray bands. On five nights in November we had nearly continuous monitoring for 2-3 h. A variability episode on a time scale of τ 24 h is well-documented; and a much more rapid flare with τ = 1-2 h; is also apparent; but is supported by relatively few points. Conclusions. The overall spectral energy distribution of PKS 2155-304 is commonly described by a synchrotron-self-Compton model. The optical infrared emission is in excess of the expectation of the model in its original formulation. This can be explained by a variation in the frequency of the synchrotron peak; which is not unprecedented in BL Lacs. © ESO 2007;

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页码：503 / 510

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