Multi-wavelength observations of PKS 2155–304 with HESS

Abstract

The High Energy Stereoscopic System (HESS) has observed the high-frequency peaked BL Lac object PKS 2155-304 in 2003 between October 19 and November 26 in Very High Energy (VHE) γ-rays (E≥ 160 GeV for these observations). Observations were carried out simultaneously with the Proportional Counter Array (PCA) on board the Rossi X-ray Timing Explorer satellite (RXTE), the Robotic Optical Transient Search Experiment (ROTSE) and the Nançay decimetric radiotelescope (NRT). Intra-night variability is seen in the VHE band, the source being detected with a high significance on each night it was observed. Variability is also found in the X-ray and optical bands on kilosecond timescales, along with flux-dependent spectral changes in the X-rays. A transient X-ray event with a 1500 s timescale is detected, making this the fastest X-ray flare seen in this object. No correlation can be established between the X-ray and the γ-ray fluxes, or any of the other wavebands, over the small range of observed variability. The average HESS spectrum shows a very soft power law shape with a photon index of 3.37 ± 0.07stat ± 0.10sys. The energy outputs in the 2–10 keV and in the VHE γ-ray range are found to be similar, with the X-rays and the optical fluxes at a level comparable to some of the lowest historical measurements, indicating that PKS 2155-304 was in a low or quiescent state during the observations. Both a leptonic and a hadronic model are used to derive source parameters from these observations. These parameters are found to be sensitive to the model of Extragalactic Background Light (EBL) that attenuates the VHE signal at this source’s redshift (z=0.117).

Astronomy & Astrophysics 442, 895-907 (2005)
ArXiv pre-print

Auxiliary informations

H.E.S.S. data points for Figure 2 (Light curve):

C1: run number
C2: Measurement MJD start
C3: Measurement MJD stop
C4: Integrated flux for E>300 GeV [cm-2 s-1]
C5: Statistical error for this flux [cm-2 s-1]

   C1    C2      C3      C4          C5
   16111 931.901 931.92  1.92432e-07 5.87125e-08
   16112 931.922 931.942 1.48235e-07 8.70025e-08
   16113 931.944 931.963 2.65835e-07 1.76985e-07
   16114 931.965 931.985 4.11136e-07 3.9243e-07
   16133 932.773 932.792 1.85062e-07 2.95384e-08
   16134 932.794 932.814 1.14295e-07 2.71888e-08
   16135 932.816 932.835 1.06131e-07 2.86047e-08
   16136 932.837 932.857 1.66545e-07 3.49137e-08
   16137 932.862 932.871 1.67701e-07 5.87609e-08
   16138 932.878 932.898 2.00983e-07 5.25281e-08
   16139 932.9   932.92  2.7011e-07 6.33879e-08
   16177 933.801 933.821 9.94945e-08 2.62985e-08
   16178 933.824 933.843 1.63161e-07 3.14128e-08
   16179 933.845 933.865 1.19585e-07 3.63449e-08
   16180 933.869 933.882 1.12786e-07 4.94397e-08
   16181 933.887 933.907 2.00023e-08 4.93208e-08
   16182 933.909 933.928 7.4317e-09 7.02726e-08
   16183 933.93  933.95  -4.99824e-08 1.21754e-07
   16184 933.952 933.971 2.46012e-07 2.73064e-07
   16239 934.847 934.867 2.35682e-07 3.9681e-08
   16244 934.879 934.899 2.39819e-07 4.98043e-08
   16245 934.901 934.92  3.05315e-07 7.41217e-08
   16246 934.922 934.942 1.14048e-07 1.20817e-07
   16247 934.945 934.965 9.90168e-08 2.25107e-07
   16304 935.839 935.858 1.02939e-07 2.23819e-08
   16305 935.86  935.88  1.38776e-07 2.88508e-08
   16306 935.882 935.901 1.4419e-07 3.24099e-08
   16307 935.904 935.923 9.96062e-08 4.51357e-08
   16335 936.792 936.798 1.56728e-07 3.27861e-08
   16336 936.801 936.809 2.09341e-07 3.09797e-08
   16337 936.812 936.831 1.85725e-07 2.10327e-08
   16338 936.837 936.857 2.74454e-07 2.73391e-08
   16339 936.86  936.88  2.14695e-07 4.3451e-08
   16341 936.887 936.906 3.00293e-07 6.52136e-08
   16342 936.908 936.928 4.96421e-08 9.45738e-08
   16344 936.931 936.951 1.01076e-07 1.73787e-07
   16345 936.952 936.972 -1.96149e-07 3.89745e-07
   16385 937.789 937.808 1.45725e-07 1.99012e-08
   16386 937.811 937.83  8.82509e-08 2.06825e-08
   16387 937.833 937.84  1.36426e-07 4.13985e-08
   16388 937.843 937.863 1.96682e-07 3.85466e-08
   16390 937.867 937.886 1.00268e-07 4.69874e-08
   16395 937.938 937.957 3.93707e-07 2.51487e-07
   16422 938.771 938.79  1.94495e-07 2.70708e-08
   16423 938.798 938.818 1.70572e-07 2.02592e-08
   16424 938.82  938.84  1.42619e-07 2.15689e-08
   16426 938.85  938.868 1.92898e-07 4.02886e-08
   16428 938.889 938.9   -2.02254e-08 6.44156e-08
   16467 939.841 939.86  1.91814e-07 2.74359e-08
   16469 939.866 939.885 1.39981e-07 5.02034e-08
   16470 939.887 939.907 4.85761e-08 6.28993e-08
   16471 939.909 939.929 2.14581e-07 7.30034e-08
   16472 939.931 939.943 1.90551e-07 1.56459e-07
   16784 957.797 957.817 2.12983e-07 3.1073e-08
   16785 957.819 957.838 1.7122e-07 3.74294e-08
   16787 957.844 957.863 1.93908e-07 5.36236e-08
   16789 957.869 957.888 2.17583e-07 9.42977e-08
   16799 958.798 958.818 1.77164e-07 3.12006e-08
   16800 958.82  958.839 1.68557e-07 3.73929e-08
   16801 958.842 958.861 2.60936e-07 5.78739e-08
   16802 958.864 958.883 2.83561e-07 8.88488e-08
   16805 958.911 958.926 -1.04248e-06 1.41141e-06
   16814 959.78  959.799 2.72642e-07 2.92071e-08
   16815 959.802 959.821 2.21276e-07 3.30156e-08
   16816 959.823 959.843 1.97274e-07 3.94553e-08
   16821 959.879 959.898 2.25702e-07 1.66921e-07
   16918 965.808 965.822 1.91565e-08 4.33076e-08
   16919 965.824 965.838 -3.0305e-08 6.40689e-08
   16920 965.84  965.854 3.04849e-07 1.0175e-07
   16921 965.856 965.876 5.63698e-08 1.58193e-07
   16949 966.787 966.807 1.86063e-07 5.31771e-08
   16956 966.841 966.86  8.62889e-08 9.62763e-08
   16958 966.863 966.883 3.70432e-07 2.58749e-07
   16978 967.784 967.803 1.76316e-07 3.60811e-08
   16980 967.808 967.828 1.95159e-07 5.24548e-08
   16981 967.83  967.85  1.43306e-07 7.55906e-08
   16982 967.852 967.871 1.74333e-07 1.79266e-07
   16983 967.874 967.893 -2.73285e-07 5.27112e-07
   17012 968.822 968.841 2.35602e-07 6.84422e-08
   17013 968.843 968.863 1.09761e-07 1.21769e-07
   17051 969.857 969.876 -3.22406e-07 2.43507e-07

H.E.S.S. data points for Fig.5 (spectrum)

The upper limits are at the 90% confidence level by the method of Helene.

   C1: bin
   C2: Centre of bin (TeV)
   C3: dN/dE (photons cm-2 s-1 TeV-1)
   C4: bin half-width (TeV)
   C5: significance (sigma)
   C6: Statistical error on dN/dE (photons cm-2 s-1 TeV-1)
   
   C1 C2    C3          C4     C5      C6
   0 0.2335 3.72483e-06 0.0335 9.50982 4.22005e-07
   1 0.3115 1.32259e-06 0.0445 11.5537 1.27338e-07
   2 0.415  6.79133e-07 0.059  15.6574 5.19765e-08
   3 0.5535 2.17833e-07 0.0795 12.3588 1.98759e-08
   4 0.7385 6.79127e-08 0.1055 8.59417 8.40514e-09
   5 0.9845 3.19339e-08 0.1405 7.9274  4.24743e-09
   6 1.3125 9.79563e-09 0.1875 5.02736 1.98795e-09
   7 1.75   4.82813e-09 0.25   4.81984 1.01936e-09
   8 2.3335 1.5674e-09  0.3335 2.55188 6.17228e-10
   9 3.112  9.10236e-10 0.445 2.36961  3.85811e-10

   The upper limits are:
   For Energy (TeV): 4.05538 The Upper Limit is 3.22974e-10
   For Energy (TeV): 5.4083 The Upper Limit is 1.7786e-10
   For Energy (TeV): 7.21163 The Upper Limit is 1.39623e-10
   For Energy (TeV): 9.61655 The Upper Limit is 5.6051e-11
   For Energy (TeV): 12.8241 The Upper Limit is 5.60408e-11
   For Energy (TeV): 17.0997 The Upper Limit is 1.3069e-11

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