Multi-wavelength behaviour of III Zw 2 N.Salvi, M.Page, J.Stevens, K.Mason, K.Wu (University College London)

III Zw 2 is a Seyfert I with a spiral host galaxy. It is classified as a Radio Intermediate Quasar. Superluminal motion of the radio emitting plasma has been observed recently in the source and this is the first detection of its kind in a spiral galaxy. The most enigmatic property of III Zw 2 is its extreme variability from X-ray to radio wavelengths (Fig 1). We find that the X-ray and optical variations are correlated. The infrared variations are concurrent with those in the X-ray and the optical, but the radio lags the other wavelengths by about a year.

We observed III Zw 2 with XMM-Newton in July 2000. The source was weak during the observation. The EPIC spectrum (Fig 2) is well described by a single powerlaw with a photon index 1.7 and a broad Fe K line at 6.4 keV (EW 1.3 keV) in the rest frame of the source. There is no evidence of intrinsic absorption by the source or for a strong soft X-ray excess. Although the X-ray flux has varied considerably during the last decade, the continuum shape in archival X-ray data is consistent with that seen by XMM.

Fig 3. The spectral energy distribution (F ) for III Zw 2. It includes radio to X-ray data taken over the last three decades

Fig 2. The simultaneous powerlaw fit to the high resolution X-ray spectra ( = 1.75 0.01, 2/dof = 764/598) taken with the EPIC detector of the XMM-Newton . The spectra are plotted in the observer frame.

Fig 1. The multi-wavelength light curve of III Zw 2 showing variations in the X-ray, optical, infrared and radio. The radio lags the other wave-lengths by about a year. l

The multi-wavelength spectrum (Fig 3) shows that most of the energy emerges at the infrared/optical frequencies. This is consistent with the bulk of the infrared, optical and radio emission being synchrotron radiation. The X-rays are likely to be a separate component. We deduce from the coordinated optical and X-ray variability that Compton up-scattering by synchrotron electrons could make a significant contribution to the X-ray flux.

DATA SOURCE

X-ray : Schnopper et al. (1978), HEASARC data archive (MSSL/UCL reduced), MSSL/UCL (XMM-Newton consortium)

Optical : Lloyd (1984), Clements et al. (1995), La Palma archives (MSSL/UCL reduced), Neugebauer et al. (1978), Condon et al. (1981), McAlary et al. (1983), Elvis et al. (1994).

Infrared : Neugebauer et al. (1978), Condon et al. (1981), McAlary et al. (1983), Rieke et al. (1978), Elvis et al. (1994), Edelson et al. (1987), Sembay et al. (1987), Hyland et al. (1982), JCMT archive (MSSL/UCL reduced), SAO.

Radio : Brunthaler et al. (2000), Landau et al. (1980), Schnopper et al. (1978), Wright et al. (1977)