SIMULTANEOUS OBSERVATIONS OF PKS 2155-304 WITH HESS, FERMI, RXTE, AND ATOM: SPECTRAL ENERGY DISTRIBUTIONS AND VARIABILITY IN A LOW STATE

Journal Article · Sun May 10 00:00:00 EDT 2009 · Astrophysical Journal (Online)

DOI:https://doi.org/10.1088/0004-637X/696/2/L150; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21300639

Aharonian, F; Bernloehr, K; Bochow, A; Buehler, R ^[1]; Akhperjanian, A G ^[2]; Anton, G; Brucker, J ^[3]; Barres de Almeida, U; Chadwick, P M ^[4]; Bazer-Bachi, A R; Borrel, V ^[5]; Becherini, Y ^[6]; Behera, B ^[7]; Boisson, C ^[8]; Brion, E; Brun, P ^[9]; Bulik, T ^[10]; Buesching, I ^[11]; Boutelier, T ^[12]

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1. Max-Planck-Institut fuer Kernphysik, P.O. Box 103980, D-69029 Heidelberg (Germany)
2. Yerevan Physics Institute, 2 Alikhanian Brothers Street, 375036 Yerevan (Armenia)
3. Universitaet Erlangen-Nuernberg, Physikalisches Institut, Erwin-Rommel-Str. 1, D-91058 Erlangen (Germany)
4. University of Durham, Department of Physics, South Road, Durham DH1 3LE (United Kingdom)
5. Centre d'Etude Spatiale des Rayonnements, CNRS/UPS, BP 44346, F-31028 Toulouse Cedex 4 (France)
6. Astroparticule et Cosmologie (APC), CNRS, Universite Paris 7 Denis Diderot, 10, rue Alice Domon et Leonie Duquet, F-75205 Paris Cedex 13 (France)
7. Landessternwarte, Universitaet Heidelberg, Koenigstuhl, D-69117 Heidelberg (Germany)
8. LUTH, Observatoire de Paris, CNRS, Universite Paris Diderot, 5 Place Jules Janssen, 92190 Meudon (France)
9. IRFU/DSM/CEA, CE Saclay, F-91191 Gif-sur-Yvette, Cedex (France)
10. Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw (Poland)
11. Unit for Space Physics, Northwest University, Potchefstroom 2520 (South Africa)
12. Laboratoire d'Astrophysique de Grenoble, INSU/CNRS, Universite Joseph Fourier, BP 53, F-38041 Grenoble Cedex 9 (France)

We report on the first simultaneous observations that cover the optical, X-ray, and high-energy gamma-ray bands of the BL Lac object PKS 2155-304. The gamma-ray bands were observed for 11 days, between 2008 August 25 and 2008 September 6 (MJD 54704-54715), jointly with the Fermi Gamma-ray Space Telescope and the HESS atmospheric Cherenkov array, providing the first simultaneous MeV-TeV spectral energy distribution (SED) with the new generation of {gamma}-ray telescopes. The ATOM telescope and the RXTE and Swift observatories provided optical and X-ray coverage of the low-energy component over the same time period. The object was close to the lowest archival X-ray and very high energy (VHE; >100 GeV) state, whereas the optical flux was much higher. The light curves show relatively little ({approx}30%) variability overall when compared to past flaring episodes, but we find a clear optical/VHE correlation and evidence for a correlation of the X-rays with the high-energy spectral index. Contrary to previous observations in the flaring state, we do not find any correlation between the X-ray and VHE components. Although synchrotron self-Compton models are often invoked to explain the SEDs of BL Lac objects, the most common versions of these models are at odds with the correlated variability we find in the various bands for PKS 2155-304.

• OSTI ID: 21300639
• Journal Information: Astrophysical Journal (Online), Vol. 696, Issue 2; Other Information: DOI: 10.1088/0004-637X/696/2/L150; Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-4357
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
BL LACERTAE OBJECTS
ENERGY SPECTRA
FLARING
GALAXIES
GAMMA RADIATION
GEV RANGE
MEV RANGE
TELESCOPES
TEV RANGE
X RADIATION