ASTROPHYSICAL PARAMETERS OF LS 2883 AND IMPLICATIONS FOR THE PSR B1259-63 GAMMA-RAY BINARY

作者：Negueruela Ignacio^*; Ribo Marc; Herrero Artemio; Lorenzo Javier; Khangulyan Dmitry; Aharonian Felix A

来源：Astrophysical Journal Letters, 2011, 732(1): L11.

DOI：10.1088/2041-8205/732/1/L11

• binaries: close
• gamma rays: stars
• pulsars: individual (PSR B1259-63)
• stars: emission-line, Be
• stars: individual (LS 2883)
• X-rays: binaries

Only a few binary systems with compact objects display TeV emission. The physical properties of the companion stars represent basic input for understanding the physical mechanisms behind the particle acceleration, emission, and absorption processes in these so-called gamma-ray binaries. Here we present high-resolution and high signal-to-noise optical spectra of LS 2883, the Be star forming a gamma-ray binary with the young non-accreting pulsar PSR B1259-63, showing it to rotate faster and be significantly earlier and more luminous than previously thought. Analysis of the interstellar lines suggests that the system is located at the same distance as (and thus is likely a member of) Cen OB1. Taking the distance to the association, d = 2.3 kpc, and a color excess of E(B - V) = 0.85 for LS 2883 results in M-V approximate to -4.4. Because of fast rotation, LS 2883 is oblate (R-eq similar or equal to 9.7 R-circle dot and R-pole similar or equal to 8.1 R-circle dot) and presents a temperature gradient (T-eq approximate to 27,500 K, log g(eq) = 3.7; T-pole approximate to 34,000 K, log g(pole) = 4.1). If the star did not rotate, it would have parameters corresponding to a late O-type star. We estimate its luminosity at log(L-L-circle dot) similar or equal to 4.79 and its mass at M-* approximate to 30 M-circle dot. The mass function then implies an inclination of the binary system i(orb) approximate to 23 degrees, slightly smaller than previous estimates. We discuss the implications of these new astrophysical parameters of LS 2883 for the production of high-energy and very high-energy gamma rays in the PSR B1259-63/LS 2883 gamma-ray binary system. In particular, the stellar properties are very important for prediction of the line-like bulk Comptonization component from the unshocked ultrarelativistic pulsar wind.

• 出版日期2011-5-1