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Mkn 841 has been observed simultaneously by XMM and BeppoSAX in January 2001. Due to operational contingency, the 30ks XMM observation was split into two parts, separated by about 15 hours. We first report the presence of a narrow iron line which appears to be rapidly variable between the two pointings, requiring a non-standard interpretation. We then focus on the analysis of the broad band (0.3-200 keV) continuum using the XMM/EPIC, RGS and SAX/PDS data. The Mkn 841 spectrum is well fitted by a comptonization model in a geometry more photon-fed than a simple slab geometry above a passive disk. It presents a relatively large reflection (R>2) which does not agree with an apparently weak iron line. It also show the presence of a strong soft excess wellfitted by a comptonized spectrum in a cool plasma, suggesting the presence of a multi-temperature corona., 4 pages, 5 figures. Proc. of the meeting: "The Restless High-Energy Universe" (Amsterdam, The Netherlands), E.P.J. van den Heuvel, J.J.M. in 't Zand, and R.A.M.J. Wijers Eds

We present broadband optical polarimetry of the classical novae V705 Cas, V4362 Sgr, V2313 Oph and BY Cir in outburst. The data indicate that, in all cases, there is an intrinsic component of polarization and in some cases the variability is very rapid, on a time-scale 1 day. In the case of V705 Cas, we suggest that the origin of the intrinsic component may lie in the clumpiness and/or inhomogeneities of the ejecta, while electron scattering is the most likely cause in V2313 Oph. The wavelength-dependence of polarization in the case of V4362 Sgr suggests scattering by small dust grains, while polarization in resonance lines is the most probable cause of the observed polarization in BY Cir.

We present mid-infrared (2-12 micron) spectra of the microquasar SS 433 obtained with the Infrared Space Observatory (spectroscopic mode of ISOPHOT and ISOCAM). We compare them to the spectra of four Wolf-Rayet stars: WR78, WR134, WR136, and WR147 in the same wavelength range. The mid-infrared spectrum of SS 433 mainly shows HI and HeI emission lines and is very similar to the spectrum of WR147, a WN8(h)+B0.5V binary. The 2-12 micron continuum emission of SS 433 corresponds to optically thin and partially optically thick free-free emission, from which we calculate a mass loss rate of 2-3 x 10^{-4} Msun/yr if the wind is homogeneous and a third of these values if it is clumped. This is consistent with a strong stellar wind from a WN star. However, following recent studies concluding that the mass donor star of SS 433 is not a Wolf-Rayet star, we propose that this strong wind out flows from a geometrically thick envelope of material that surrounds the compact object like a stellar atmosphere, imitating the Wolf-Rayet phenomenon. This wind could also wrap the mass donor star, and at larger distances (~ 40 AU), it might form a dust envelope from which the thermal emission, detected with ISOPHOT at 25 micron and 60 micron, would originate. This wind also probably feeds the material that is ejected in the orbital plane of the binary system and that forms the equatorial outflow detected in radio at distances > 100 AU., 12 pages, 6 figures (3 colour figures), accepted by A&A (in press)

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 high-velocity motion of the pulsar, making PSR B1951+32 a rare pulsar exhibiting both an H alpha bow shock and a shocked X-ray pulsar wind nebula. The distribution of H alpha 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., Comment: To appear in ApJ Letters

We report on the detection of a rapidly variable narrow Fe K$\alpha$ line in Mkn 841. The source has been observed two times by XMM-Newton and simultaneously with BeppoSAX. The two observations, of about 10ks long each, were separated by $\sim$ 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., Comment: Accepted in A&A Letter. 4 pages, 4 figures

We present infrared observations of the supernova remnant G21.5-0.9 with the Very Large Telescope, the Canada-France-Hawaii Telescope and the Spitzer Space Telescope. Using the VLT/ISAAC camera equipped with a narrow-band [FeII] 1.64um filter the entire pulsar wind nebula in SNR G21.5-0.9 was imaged. This led to detection of iron line-emitting material in the shape of a broken ring-like structure following the nebula's edge. The detected emission is limb-brightened. We also detect the compact nebula surrounding PSR J1833-1034, both through imaging with the CFHT/AOB-KIR instrument (K' band) and the IRAC camera (all bands) and also through polarimetric observations performed with VLT/ISAAC (Ks band). The emission from the compact nebula is highly polarised with an average value of the linear polarisation fraction $P_{L}^{avg} \simeq 0.47$, and the swing of the electric vector across the nebula can be observed. The infrared spectrum of the compact nebula can be described as a power law of index $\alpha_{IR} = 0.7 \pm 0.3$, and suggests that the spectrum flattens between the infrared and X-ray bands., Comment: 11 pages, 13 figures, accepted by A&A; more detailed discussion of the reduction and analysis of the narrow-band imaging data added in Sect. 2.4, which results in the change of the structure of Fig.4; uncertainty of the infrared power-law index re-estimated, results in updating Fig.6; minor changes in Sect. 4.2 to estimates of X-ray fluxes and their uncertainties and also to the radio upper limit

AKO 9 is the hottest star (U-B < -0.3) found by (1989) in the error box for X0021.8-7221 on four U frames of 47 Tuc obtained at the 2.2m ESO (La Silla) telescope in 1986 July 26. This star appeared to be invisible on observations obtained in 1989 (Bailyn, 1990) and on excellent images obtained in 1990 at the NTT (Koch and Auriere, 1992) which implies a dimming by at least two magnitudes.

XMM is a third generation X-ray astronomy mission in which the artificial boundary between astronomy and astrophysics disappears. This long lived orbiting observatory brings sensitivity improvements of > 102 over existing missions (EINSTEIN, EXOSAT, ROSAT). It will be capable of finding and studying in detail either the furthest quasars and active galactic nuclei at the edge of the Universe or detecting the coronal emission from the faintest stars within the Galaxy. It is a multi-purpose high-throughput facility (2.4 m2 collecting power at 1 keV) consisting of two arrays of grazing incidence Wolter type 1 telescopes. The first, consisting of 20 telescopes (10 arcsec. on-axis resolution, 1° field of view and energy range up to 5 keV) will be more sensitive than AXAF for the rapid study of many classes of objects. The second array with 7 telescopes (30 arcsec. on-axis resolution, 0.5° field of view but an energy range extending to 10 keV with > 5 × 103 cm2 at 7 keV) will perform tests for spectral evolution in distant active galactic nuclei and studies of line emission with high sensitivity for a wide variety of sources. Both of them will perform spatially resolved high resolution spectroscopy of supernova remnants and clusters of galaxies. An assessment study of this mission is starting in ESA in January 1983.

The Rho Ophiuchi dark cloud region has been the subject of an extensive guest investigation using the Einstein Observatory. The set of observations comprise 14 IPC fields and 3 HRI fields. The densest part of the cloud has been observed 6 times. Forty seven sources were detected at a level > 3.5 σ and twenty more above 2 σ. The majority of these sources have optical, IR, or even radio continuum counterparts; nine are identified with known T Tauri stars, while several others are identified with stars showing H α in emission. All show a high degree of time variability; flux variations reach factors of 5 in a few hours, or 25 in a day. Apparent luminosities are in the range 10(30) – 10(31)(∗) erg.s−1. The possibility that the X-ray variability is due to flares is examined. If this interpretation is correct, one source has been the seat of the largest stellar flare ever recorded in X rays [Lx = 10(32) erg.s−1, Ex ≳10(36) ergs-].

Cosmic ray composition and energy spectra at source have been recently obtained with good precision. The bulk of the observations suggests that cosmic rays originate in unevolved star surface material. Most cosmic rays should be stellar energetic particles first accelerated by flares out of the coronae of F to M stars, that were later reaccelerated to high energy by strong interstellar shockwaves. The limitations of this two-step scenario and of the other plausible stellar and interstellar models are pointed out. The Ne-22 and carbon excesses at cosmic ray source are accounted for if a minor component (2 percent) of cosmic rays are made of He-burning material, plausibly originating in Wolf-Rayet stars. The possible oxygen and Mg-25, Mg-26 excesses could be interpreted in the same context, but not the Si-29, Si-30 excess. 91 references.

The Rho Oph dark cloud region has been the subject of an extensive guest investigation using the Einstein Observatory, using the IPC and HRI instruments, and featuring repeated observations. Up to 70 sources have been discovered, with Lx 1030 erg s-1. On the basis of their spatial distribution, and of many identifications, there seems to be a close connection between these sources and pre-main sequence objects. The sources are highly time-variable, the amplitude of variation reaching a factor of 25 in a day. Several arguments are presented which show that an interpretation in terms of giant stellar flares is consistent with the data.

This paper describes a multiplex image coding system designed to be associated with a non-imaging spectrometer (Si(Li) or thermal spectrometer). The resulting instrument, an imaging spectrometer, could be used as a focal instrument for an astronomical grazing incidence telescope. The coding system consists in a movable mask with pseudo randomly distributed holes, located in the telescope focal plane. The pixel size lies in the range 100-200 microns. The close association of the coder with a Si(Li) spectrometer or with an X-ray bolometer gives an imaging spectrometer combining the good efficiency ( >50% between 0.1 and 10 keV) and energy resolution ( ΔE~100 eV for Si(Li),~ 10 eV (expected) for a bolometer) of these energy dispersive devices, with the spatial resolution of the mask.

Silica aerogels have been produced in large and transparent blocks for space astrophysics experiments since the beginning of the 1970’s.

Recently the Saclay-Copenhagen spectrometer on board the satellite HEAO 3 has provided extremely accurate data on the elemental composition and energy spectra of cosmic ray nuclei from Be to Zn in the energy range 0.7 to 25 GeV/n. These data have been interpreted in the framework of galactic diffusion model, either homogeneous or with a halo. The data tend to favor a rather flat halo, ~ 1 kpc thick. The mean escape pathlength from the Galaxy is found to decrease with the magnetic rigidity of the particles R as R-0.6. The momentum spectra at the source for the main primary elements between C and Fe are well fitted by a single power law with an exponent γ = -2.41 ± 0.05. Implications for cosmic ray sources and confinement of recent results on high energy cosmic nuclei, electrons and gamma rays are reviewed.

We present new data on the X-ray source lying in the core of 47 Tuc that is the brightest of the dim globular cluster X-ray sources. From the recalibrated IPC Einstein satellite data the X-ray spectrum was obtained [thermal bremsstrahlung with kT = 2 -1 +4 keV and no intrinsic absorption]. X-ray variability is present at time scales of days, hours and tens of minutes. In addition we have discovered transient periodic pulsations at period 120.200 s. Rapid periodic pulsations at period 4.580 s are also marginally present.

The X-ray properties of the supernova remnant G 29.7 – 0.3 are discussed based on spectral data from the EXOSAT satellite. In the 2 to 10 keV range a featureless power-law spectrum is obtained, the best-fit parameters being: energy spectral index α -0.77, hydrogen column density on the line of sight NH= 2.3.1022 cm-2. The incident X-ray flux from the source is (3.6 ± 0.1) 10-11 erg cm-2 s-1 in the 2 to 10 keV range corresponding to an intrinsic luminosity of about 2.1036 erg s-1 for a distance of 19 kpc. The source was not seen with the imaging instrument thus constraining the hydrogen column density to be NH = (3.3 ± 0.3) 1022 cm-2 and the energy spectral index α = 1.0±0.15. This new observation is consistent with emission by a synchroton nebula presumably fed by an active pulsar. An upper limit of ~ 1.5% for the pulsed fraction in the range of periods 32ms to 104 s has been obtained.

The end of the 1970 decade has provided exciting new results in cosmic ray astrophysics both in theory and observations. To mention only two of the many results: (i) the discovery of large isotopic anomalies in cosmic ray neon and possibly Mg and Si compositions as compared to the solar system matter (Fisher et al., 1976; Garcia-Munoz et al., 1979; Mewalt et al., 1980; Wiedenbeck et al., 1981) has provided for the first time a direct proof that a specific component of cosmic rays is accelerated near active sites of nucleosynthesis; (ii) the great advances made in understanding shock wave acceleration have given a great impetus to the problem of the origin of cosmic rays in allowing a direct comparison between theory and observations in a wide variety of physical conditions (Axford 1981). Yet as exciting and astrophysically rewarding as these results may be, they fall short of achieving the full potential of cosmic ray astrophysics in the study of sources and propagation of cosmic rays in the Galaxy. This information can best be obtained at relativistic energies, where composition changes due to solar modulation and ionization losses are negligible and where secondary cosmic ray production in the interstellar medium is minimized, with nuclear interaction cross sections being constant or varying only slowly with energy. However at relativistic energies, where the results are simpler to interpret, the mass measurements are more difficult to perform. In order to achieve these aims a radical improvement in satellite instrumentation was necessary, namely the transition from the small solid state telescope working beautifully in the lower energy range (~ 100 MeV/n) to the very large Cerenkov telescope providing high resolution and high statistics in the relativistic energy range.