Discovery of the binary pulsar PSR B1259-63 in very-high-energy gamma rays around periastron with HESS

F. Aharonian et al. (H.E.S.S. Collaboration)
Astronomy & Astrophysics 442, 1-10 (2005)
2005

Abstract

We report the discovery of very-high-energy (VHE) γ-ray emission of the binary system PSR B1259-63/SS 2883 of a radio pulsar orbiting a massive, luminous Be star in a highly eccentric orbit. The observations around the 2004 periastron passage of the pulsar were performed with the four 13 m Cherenkov telescopes of the HESS experiment, recently installed in Namibia and in full operation since December 2003. Between February and June 2004, a γ-ray signal from the binary system was detected with a total significance above 13σ. The flux was found to vary significantly on timescales of days which makes PSR B1259-63 the first variable galactic source of VHE γ-rays observed so far. Strong emission signals were observed in pre- and post-periastron phases with a flux minimum around periastron, followed by a gradual flux decrease in the months after. The measured time-averaged energy spectrum above a mean threshold energy of 380 GeV can be fitted by a simple power law F₀(E/1 TeV)^-Γ with a photon index Γ = 2.7±0.2_stat±0.2_sys and flux normalisation F₀ = (1.3 ± 0.1_stat ± 0.3_sys) × 10^-12 TeV^-1 cm^-2 s^-1. This detection of VHE γ-rays provides unambiguous evidence for particle acceleration to multi-TeV energies in the binary system. In combination with coeval observations of the X-ray synchrotron emission by the RXTE and INTEGRAL instruments, and assuming the VHE γ-ray emission to be produced by the inverse Compton mechanism, the magnetic field strength can be directly estimated to be of the order of 1 G.

Astronomy & Astrophysics 442, 1-10 (2005)

ArXiv pre-print

Auxiliary informations

H.E.S.S. data points for Figure 3

Energy interval     Mean energy     Flux         Flux Error
[TeV]               [TeV]           [/TeV cm^2 s]

0.375   0.5         0.456451        1.25048e-11  4.57791e-12
0.5     0.667       0.572835        6.01352e-12  1.04343e-12
0.667   0.889       0.759971        2.38419e-12  4.66954e-13
0.889   1.186       1.02389         1.37417e-12  2.49253e-13
1.186   1.581       1.35537         6.31734e-13  1.3359e-13 
1.581   2.108       1.81369         2.89455e-13  7.80193e-14
2.108   2.812       2.46419         7.24055e-14  4.43537e-14

Remarks: Statistical errors only. Systematic error on flux scale estimated to 30%. See paper for details.

H.E.S.S. data points for Figure 4

Energy interval     Mean energy     Flux         Flux Error
[TeV]               [TeV]           [/TeV cm^2 s]
February 2004
0.341   0.5         0.461281        2.58176e-11  1.01972e-11
0.5     0.734       0.594261        9.24443e-12  1.96584e-12
0.734   1.077       0.882449        2.42391e-12  7.18455e-13
1.077   1.581       1.27151         1.02396e-12  3.2237e-13 
1.581   2.321       1.86542         5.00384e-13  1.66636e-13
2.321   3.406       2.8986          9.44283e-14  7.08636e-14
March 2004
0.375   0.5         0.461278        1.47721e-11  8.50051e-12
0.5     0.667       0.581347        5.39957e-12  1.68189e-12
0.667   0.889       0.767602        2.0203e-12   7.30113e-13
0.889   1.186       1.01761         6.25928e-13  3.52138e-13
1.186   1.581       1.34859         5.63274e-13  2.01795e-13
1.581   2.108       1.84364         1.61648e-13  1.12214e-13
April 2004
0.5     0.734       0.624378        6.78596e-12  2.30883e-12
0.734   1.077       0.912952        2.45165e-12  8.69895e-13
1.077   1.581       1.31953         9.90971e-13  4.05391e-13
1.581   2.321       1.89604         2.78799e-13  1.80601e-13
2.321   3.406       2.75055         1.53499e-13  9.79989e-14