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Abstract. We report on the detection of a rapidly variable narrow Fe Kα line in Mkn 841. The source has been observed two times by XMM-Newton and simultaneously with BeppoSAX. The two observations, of about 10 ks long each, were separated by ∼15 hours. The line flux reaches a maximum during the first observation and is significantly reduced in the second one. The continuum shape and flux, instead, keep roughly constant between the two pointings. Such rapid variability of a narrow (unresolved by the XMM-pn instrument) line has never been reported in the past. These results are not easily explained in the standard cold reflection model where the narrow line component is supposed to be produced far from the primary X-ray source (e.g. from the torus) and is thus not expected to vary rapidly. Different interpretations are discussed.

Periodic UV modulation of X1850-087: a double degenerate binary in the globular cluster NGC 6712? Homer, L.; Charles, P.A.; Naylor, T.; van Paradijs, J.A.; Auriere, M.; Koch-Miramond, L.

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The radio pulsar B1951+32 and the supernova remnant CTB 80 provide a rich laboratory for the study of neutron stars and supernova remnants. Here, we present ground-based optical and near-infrared observations of them, along with X-ray observations with Chandra and a re-analysis of archival data obtained with the Hubble Space Telescope. The X-ray observations reveal a cometary pulsar wind nebula which appears to be confined by a bow shock produced by highvelocity motion of the pulsar, making PSR B1951+32 a rare pulsar exhibiting both an Hα bow shock and a shocked X-ray pulsar wind nebula. The distribution of Hα and radio continuum emission is indicative of a contact discontinuity of the shocked pulsar winds and shocked ambient medium at ∼0.05 pc. On the other hand, the optical synchrotron knot of PSR B1951+32 likely has a flat spectrum in the optical and near-infrared wavebands, and our astrometry is consistent with only one of the two reported optical counterpart candidates for the pulsar.