Broad band X-ray properties of GRO J1948+32/KS 1947+300

We present here results obtained from three BeppoSAX observations of the transient X-ray pulsar GRO J1948+32 carried out during the declining phase of its 2000 November–2001 June outburst. Timing analysis of the data clearly shows a 18.7 s pulsation in the X-ray light curves in 0.1–100 keV energy band. The pulse profile of GRO 1948+32 is characterized by a broad peak with a sharp rise followed by a narrow dip. The dip in the pulse profile shows very strong energy dependence. Phase-averaged spectroscopy obtained with three of the BeppoSAX instruments shows that the 0.1–100 keV energy spectrum is described by a Comptonized component, a weak blackbody component (7% of the total emission) for soft X-rays, a narrow and weak iron emission line at 6.7 keV and low column density of material in the line of sight. The results obtained from the analysis are discussed in this paper.     

Solar corona irradiance variability during the 1943–1999 period

We present different aspects of the large-scale distribution of the coronal Fe XIV 530.3 nm emission line brightness (the abbreviation CGL — coronal green line — is used below). Evolution of this line intensity over the solar cycles is demonstrated and the relevance of the solar middle-latitude zones in displaying the coronal activity and variability is underlined.     

Analysis of the nucleus and circumnuclear area of comet Halley with the “I.K.S.” infrared sounder from the “Vega” flyby probes

The “Vega” Soviet flyby probes to comet Halley will carry a French infrared sounder, called “I.K.S.”. In order to assess its observing capabilities, a theoretical model of the comet infrared emission was constructed. We show how the experiment results will be used to derive the nucleus size and radiative properties, and to study the distribution of gas and dust in the inner coma and circumnuclear area. A preliminary discussion is made of the relevance of the data in instances where the cometary phenomena would be more complex than assumed in the model.     

Optical, X-ray and γ-ray observations of compact objects in globular clusters

In the past three years, a new era of study of globular clusters has begun with multiwavelength observations from the current generation of astronomical telescopes in space. We review the recent results obtained from our studies of compact binaries and x-ray sources in globulars with ROSAT and HST as well as our balloon-borne hard x-ray telescope EXITE and ground-based observations (CTIO). With ROSAT, we have obtained the most sensitive high resolution soft x-ray images of clusters which show multiple low luminosity sources in cluster cores that are likely indicative of the long-sought population of cataclysmic variables (CVs). We have obtained deep H images of two clusters with HST and found CV candidates for 3 of the ROSAT sources in the core of NGC 6397. New CTIO imaging and spectroscopy of two ‘dim source’ fields in ω-Cen are also described. With EXITE we carried out the first hard x-ray imaging observations of the cluster 47 Tuc; such studies can ultimately limit the populations of millisecond pulsars and pulsar emission mechanisms. A long ROSAT exposure on 47 Tuc also shows probable cluster diffuse emission, possibly due to hot gas from ablating millisecond pulsars. Multiwavelength studies of globular clusters may provide new constraints on problems as diverse as the origin of CVs and LMXBs and the origin of hot gas in globulars.     

High energy emission from AGN

The recent detection of radio loud quasars with a large high energy γ-ray luminosity is discussed, in the framework of non-thermal synchrotron self Compton models. These observations are strong evidence of relativistic beaming of the radiation, due to the absence of strong photon-photon opacity. If γ-rays are self Compton emission, these sources can be the first observed example of a Compton catastrophe, resulting from the dominance of the radiation over the magnetic energy density. Inhomogeneous and relativistic jet models can in this case explain the observed spectrum from the far infrared to the γ-rays. If, on the other hand, the magnetic energy density is dominant, then the γ-rays must be due to direct synchrotron emission, implying very large particle energies. Pure synchrotron models which take into account electron-positron pair production are then discussed. Multifrequency simultaneous observations are a powerful test of the models.     

High resolution studies of intermediatedrift bursts

We report high resolution observations of the Intermediate Drift (IMD) bursts in decimetric band (ν = 950 – 2650 MHz). With a time resolution of 20 – 50 ms and a frequency resolution of 4 – 10 MHz, we are able to estimate the characteristics of IMD bursts such as the bandwidth and duration of the emission. Frequency drift rate and its dependence on the frequency are derived for individual IMD structures. All IMD bursts analyzed show negative drift rate. The values are of the order of −28 – −274 MHz s⁻¹. The drift rates normalized by the mean frequency are ranged between −0.20 s⁻¹ and −0.02 s⁻¹. Both the frequency drift rate and its frequency dependence provide important clues to the emission mechanisms of IMD. A comparison and a critique of the existing models based on the plasma and the maser emissions with modulation by Alfvén solitons as well as the whistler wave model are presented.     

Energy content of accelerated electrons and ions in intense solar flares

The energy content of nonthermal particles in solar flares is shared between accelerated electrons and ions. It isimportant for understanding the particle acceleration mechanism in solar flares. Yohkoh observed a few intense flares which produced both strong gamma-ray lines and electron bremsstrahlung continuum. We analyze energy spectra of X-class solar flares on October 27, 1991(X6.1), November 6, 1997 (X9.4), July 14, 2000 (X5.7) and November 24, 2000 (X2.3). The accelerated electron and proton spectra are derived from a spectral analysis of their high-energy photon emission and the energy contents in >1 MeV electrons and >10 MeV protons are estimated to be 6×l0²⁸ – 4×10³⁰ and 2×10²⁸ – 5×10²⁹ erg, respectively. We study the flare to flare variation in the energy content of >1 MeV electrons and >10 MeV protons for the four Yohkoh gamma-ray flares. Ratios of >1 MeV electron energy content to >10 MeV proton energy content are roughly within an order of magnitude.     

Distinctive spatial configuration of a class ofmicrowave flaring sources

We discuss a class of microwave flares whose source regions exhibit a distinctive spatial configuration; the primaryenergy release in these flares results from the interaction between emerging magnetic flux and an existing overlying region. Such events typically exhibit radio, X-ray and EUV emission at the main flare site (the site of interaction) and in addition radio emission at a remote site up to 1 × 10⁵ km away in another active region. We have identified and studied more than a dozen microwave flares in this class, in order to arrive at some general conclusions on reconnection and energy release in such solar flares. Typically, these flares show a gradual rise showing many subsidiary peaks in both radio and hard X-ray light curves with a quasi-oscillatory nature with periods of 5–6 seconds, a bright compact X-ray & EUV emitting loop in the main flare source, a delay of the radio emission from the remote source relative to the main X-ray-emitting source. The magnetic field in the main flare site changes sharply at the time of the flare, and the remote site appears to be magnetically connected to the main flare site.     

Indicators of black-hole mass and Eddington accretion ratio from QSO X-ray and UV spectra

The evolution of luminous QSOs is linked to the evolution of massive galaxies. We know this because the relic black-holes found locally have masses dependent on the properties of the host galaxy’s bulge. An important way to explore this evolution would be to measure dependences of black-hole masses and Eddington accretion ratios over a range of redshifts, i.e., with cosmological age. For low redshift QSOs (and their lower luminosity Seyfert galaxy counterparts) it has been possible to infer black-hole masses from the luminosities and velocity dispersions of their host-galaxy bulges. These masses agree with those virial black-hole masses calculated from the Doppler widths of the broad Hβ emission lines. The latter method can then be extended to more distant and luminous QSOs, up to redshifts of 0.6 with ground-based optical observations. We discuss ways to extend these explorations to higher redshifts – up to 3 using the widths of QSOs’ broad UV emission lines, and in principle, and to redshifts near 4 from ground-based infrared observations of rest-frame Hβ at 2.5 μm. We discuss the possibility of investigating the accretion history of the higher redshift QSOs using measures of Eddington accretion ratio – the soft X-ray spectral index and the eigenvectors of Principal Components Analyses of QSOs’ UV emission-line spectra.     

Changes in radio emission from PSR J0737–3039B

The double pulsar system, J0737–3039, provides a unique probe of a pulsar magnetosphere due to its edge-on viewing geometry, a tight orbit and a significant rate of advance of the angle of periastron. In this paper, we report on the changes in radio emission from the long period pulsar in this system, J0737–3039B, over a period of 9 months. Observations of this system with Giant Metrewave Radio Telescope (GMRT) show that the duration of the first bright phase of the pulsar centered at 210° orbital longitude from the ascending node is shrinking. These observations will be useful to constrain the proposed models for this system.     

Numerical simulations of the radiance from the comet 46P/Wirtanen in the various configurations of the measurements during “Rosetta” mission

The work we present deals with the spectrometric measurements of VIRTIS instrument of the Comet P/Wirtanen planned for the Rosetta mission. This spectrometer can monitor (VIRTIS M channel: 0.250μm – 0.980μm; Δκ=20cm⁻¹; 0.980 – 5.0 μm; Δκ = 5cm⁻¹; VIRTIS H channel: 2.0 μm – 5.0 μm; Δκ=2cm⁻¹) the nucleus and the coma in order to provide a general picture of coma's composition, the production of gas and dust, the relationship of coma production to surface composition and the structure and variation of mineralogy of the nucleus surface. During the mission the observation conditions of the spectroscopic investigation change due to different relative positions spacecraft/comet, and to the different illumination conditions of the surface at various distances of the comet to the Sun. The nucleus surface is continuously modified by the ice sublimation accompanied by gas and dust emission. Consequently the surface also its spectrophotometric properties changes and their monitoring can give a new insight. The important role of simulations is to predict the results of measurements in various experimental condition what, in the future, can help in interpretation of the measured data.

In this paper the first results of our simulation the radiance from the comet in the 0.25–5.0μm spectral range at two distances from the Sun (1AU and 3AU) are shown. The distance between the Rosetta orbiter and the nucleus surface as well as the sun zenith angles are taken into account according to the Rosetta mission phases. In fact the surface and coma properties vary along the comet orbit, and should be taken into account in our calculations. The optical parameters of the dust on the surface (e.g. reflectance) and in the coma (e.g. Q_ext) were calculated from optical constants of possible comet analogues. The thermodynamic parameters of the comet are taken from the models of comet evolution. Through this kind of modelling it is possible to identify the surface characteristics in spectra of the radiation from the surface of nucleus transmitted through the coma loaded with dust and gases.

Even if the “Rosetta mission” is postponed, with the consequence of a target change, we think that our idea and the method used for the simulations can be useful also for the new Rosetta target - the comet 67P/Churyumov Gerasimenko.     

Sunspot numbers during 1736–1739 revisited

Some periods in the sunspot number reconstruction composed by Hoyt and Schatten [Hoyt, D.V., Schatten, K.H. Group Sunspot Numbers: a new solar activity reconstruction. Sol. Phys. 179, 189–219, 1998. Reprinted with figures in Sol. Phys. 181, 491–512, 1998], are based on very few records. For example, there are only a few solar observations during the years 1736–1739. In this paper we intend to improve the reliability of the sunspot numbers reconstruction developed by Hoyt and Schatten for this 4-years period based on information about solar activity published in three journals of that epoch: “Philosophical Transactions”, “Histoire de l’Académie Royale des Sciences”, and “Nova Acta Eruditorum”. We were able to identify 42 papers with solar observations, including 30 with relevant information on sunspots. Based upon this new outlook, a reconstruction of the monthly solar activity for these years is proposed.     

Measuring the matter distribution within z = 0.2 cluster lenses with XMM-Newton

We present an analysis of seven clusters observed by XMM-Newton as part of our survey of 17 most X-ray luminous clusters of galaxies at z  0.2 selected for a comprehensive and unbiased study of the mass distribution in massive clusters. Using the public software FTOOLS and XMMSAS we have set up an automated pipeline to reduce the EPIC MOS and pn spectro-imaging data, optimized for extended sources analysis. We also developped a code to perform intensive spectral and imaging analysis particularly focussing on proper background estimate and removal. XMM-Newton deep spectro-imaging of these clusters allowed us to fit a standard β-model to their gas emission profiles as well as a standard MEKAL emission model to their extracted spectra, and test their inferred characteristics against already calibrated relations.     

X-ray broad line emission in Seyfert galaxies: Mrk 766 and NGC 4051

Long (>100 ks) observations of the bright Seyfert galaxies Mrk 766 and NGC 4051 have been obtained using XMM-Newton. The RGS 5–38 Å spectra reveal evidence of broad features. These can be modelled with relativistic emission lines coming from the immediate vicinity of a massive rotating black hole. Lines of OVIII, NVII and CVI are required to reproduce the spectrum of Mrk 766, whereas the spectrum of NGC 4051 can be modelled using a single, even broader OVIII line. Both Seyferts also exhibit broad iron line emission in the 2–8 keV range, and the data available thus far suggest that the strength of the low-energy emission lines and the strength of the iron line may be correlated.     

1E 1740.7-2942 revisited: Confirmation of its identification with the core of a double sided radio jet structure

After more than two years of successful in-orbit operations, the γ-ray coded aperture SIGMA telescope has accumulated 800 hours of live-time observations of the Galactic Center region, including the remarkable hard source identified with the X-ray source 1E 1740.7–2942. The long-term behavior of the soft γ-ray emission of 1E 1740.7–2942, as determined from the SIGMA survey, supplemented with previously available soft γ-ray data, leads to its identification with a singular radio source, which consists of a double sided radio jet emanating from a compact variable core whose variability is correlated with that of the soft γ-ray source. The compact radio core, which lies well inside the improved soft γ-ray (40–150 keV) error circle (27″ radius) derived from the high-resolution SIGMA survey, is also inside the ROSAT and TTM error circle derived respectively in the soft and hard X-ray bands.     

A preliminary look at the dust in comet Halley

Highlights of infrared observations of the dust are discussed and compared with first results from the space probes. An emission feature was detected at 3.4 μm; the 10 and 20 μm silicate features were well-observed; and far-infrared data out to 160 μm were obtained. Organic material seems to be abundant in grains and may explain the 3.4 μm emission. Calculations are presented for one example of organic material. A component of the grains may volatize at temperatures around 300 K.     

Energetic ion emission for active spacecraft control

Future space missions aiming at the accurate measurement of cold plasmas and DC to very low frequency electric fields will require that the potential of their conductive surfaces be actively controlled to be near the ambient plasma potential. In the near-Earth space these spacecraft are usually solar-cell powered; consequently, parts of their surface are most of the time exposed to solar photons. Outside the plasmasphere, a positive surface potential due the dominance of surface-emitted photoelectrons over ambient plasma electrons is to be expected. Photo- and ambient electrons largely determine the potential and positive values between a few Volts up to 100 V have been observed. Active ion emission is the obvious solution of this problem. A liquid metal ion emitter and a saddle field ion emitter are nearing the stage of flight unit fabrication. We will attempt to clamp the spacecraft potential to values close to the plasma potential. We present first results from vacuum chamber tests and describe the emission behaviour and characteristics of emitters producing, respectively, In⁺ and N₂⁺ beams with an energy of ≥ 5 keV.     

Near infrared studies of the massive X-ray binary 2S 0114+65

We present near-infrared spectroscopy of the massive X-ray binary 2S 0114+650. These observations covering the spectral range 1.08–2.35 μm span the region where Paschen and Brackett series recombination lines of hydrogen are expected to be seen, namely, Paβ , Brγ and Br 10–17 lines. The absence of any of these lines in emission supports earlier inferences that the optical component in 2S 0114+650 is unlikely to be a Be star but rather a B type supergiant. Near-IR photometry gives J = 8.78, H = 8.53 and K = 7.96; these values show marginal variations from earlier reported measurements.     

X-ray, γ-emission and energetic particles in near-Earth space as measured by CORONAS-F satellite: From maximum to minimum of the last solar cycle

The Russian solar observatory CORONAS-F was launched into a circular orbit on July 31, 2001 and operated until December 12, 2005. Two main aims of this experiment were: (1) simultaneous study of solar hard X-ray and γ-ray emission and charged solar energetic particles, (2) detailed investigation of how solar energetic particles influence the near-Earth space environment. The CORONAS-F satellite orbit allows one to measure both solar energetic particle dynamics and variations of the solar particle boundary penetration as well as relativistic electrons of the Earth’s outer radiation belt during and after magnetic storms. We have found that significant enhancements of relativistic electron flux in the outer radiation belt were observed not only during strong magnetic storms near solar maximum but also after weak storms caused by high speed solar wind streams. Relativistic electrons of the Earth’s outer radiation belt cause volumetric ionization in the microcircuits of spacecraft causing them to malfunction, and solar energetic particles form an important source of radiation damage in near-Earth space. Therefore, the present results and future research in relativistic electron flux dynamics are very important.     

Hard X-ray source profiles as determined by RHESSI

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has been recording rotationally-modulated X-rays from solar flares since its launch on February 5, 2002. Its 9 grid pairs time-modulate the detected photon flux giving RHESSI spatial information on hard X-rays at 9 logarithmically-spaced angular scales ranging from 2.3 to 183 arcsec. Using the calibrated modulation profiles for a variety of flares, we present new information on the spatial profiles of the hard X-ray structures in flares. We find that the FWHM of cores of single-component flares range from 3 to 11″ in size. Most of the flares in this set show extended emission out to 2 to 3 times the radii of the cores, and these ‘halos’ contain up to 25% of the total flux.