AimsMost models identify the X-ray bright North Polar Spur (NPS) with a hot interstellar (IS) bubble in the Sco-Cen star-forming region at ≃130 pc. An opposite view considers the NPS as a distant structure associated with Galactic nuclear outflows. Constraints on the NPS distance can be obtained by comparing the foreground IS gas column inferred from X-ray absorption to the distribution of gas and dust along the line of sight. Absorbing columns towards shadowing molecular clouds simultaneously constrain the CO-H2 conversion factor.MethodsWe derived the columns of X-ray absorbing matter N Habs from spectral fitting of dedicated XMM-Newton observations towards the NPS southern terminus (l II ≃ 29°, b II ≃ +5 to +11°). The distribution of the IS matter was obtained from absorption lines in stellar spectra, 3D dust maps and emission data, including high spatial resolution CO measurements recorded for this purpose.ResultsN Habs varies from ≃ 4.3 to ≃ 1.3 × 1021 cm-2 along the 19 fields. Relationships between X-ray brightness, absorbing column and hardness ratio demonstrate a brightness decrease with latitude governed by increasing absorption. The comparison with absorption data, local and large-scale dust maps rules out a NPS near side closer than 300 pc. The correlation between N Habs and the reddening increases with the sightline length from 300 pc to 4 kpc and is the tightest with Planck τ 353GHz -based reddening, suggesting a much larger distance. N(H)/E(B-V) τ ≃ 4.1 × 1021 cm-2 mag-1, close to Fermi-Planck determinations. N Habs absolute values are compatible with HI-CO clouds at -5 ≤ V LSR ≤ +25 to +45 km s-1 and a NPS potentially far beyond the Local Arm. A shadow cast by a b=+9° molecular cloud constrains X CO in that direction to ≤ 1.0 × 1020 cm-2 K-1 km-1 s. The average X CO over the fields is ≤ 0.75 × 1020 cm-2 K-1 km-1 s.
ContextIn July 2015, the high-mass X-ray binary V0332+53 underwent a giant outburst, a decade after the previous one. V0332+53 hosts a strongly magnetized neutron star. During the 2004-2005 outburst, an anti-correlation between the centroid energy of its fundamental cyclotron resonance scattering features (CRSFs) and the X-ray luminosity was observed.AimsThe long (≈ 100 d) and bright (L x ≈ 1038 erg s-1) 2015 outburst offered the opportunity to study during another outburst the unique properties of the fundamental CRSF and its dependence on the X-ray luminosity.MethodsThe source was observed by the INTEGRAL satellite for ~ 330 ks. We exploit the spectral resolution at high energies of the SPectrometer on INTEGRAL (SPI) and the Joint European X-ray Monitors to characterize its spectral properties, focusing in particular on the CRSF-luminosity dependence. We complement the data of the 2015 outburst with those collected by SPI in 2004-2005 and left unpublished so far.ResultsWe find a highly significant anti-correlation of the centroid energy of the fundamental CRSF and the 3 -100 keV luminosity of E 1 ∝ -0.095(8)L 37 keV. This trend is observed for both outbursts. We confirm the correlation between the width of the fundamental CRSF and the X-ray luminosity previously found in the JEM-X and IBIS dataset of the 2004-2005 outburst. By exploiting the RXTE/ASM and Swift/BAT monitoring data we also report on the detection of a ~ 34 d modulation superimposed on the mean profiles and roughly consistent with the orbital period of the pulsar. We discuss possible interpretations of such variability.
Context:Jets are dynamic, impulsive, well-collimated plasma events that develop at many different scales and in different layers of the solar atmosphere.Aims:Jets are believed to be induced by magnetic reconnection, a process central to many astrophysical phenomena. Within the solar atmosphere, jet-like events develop in many different environments, e.g., in the vicinity of active regions as well as in coronal holes, and at various scales, from small photospheric spicules to large coronal jets. In all these events, signatures of helical structure and/or twisting/rotating motions are regularly observed. The present study aims to establish that a single model can generally reproduce the observed properties of these jet-like events.Methods:In this study, using our state-of-the-art numerical solver ARMS, we present a parametric study of a numerical tridimensional magnetohydrodynamic (MHD) model of solar jet-like events. Within the MHD paradigm, we study the impact of varying the atmospheric plasma β on the generation and properties of solar-like jets.Results:The parametric study validates our model of jets for plasma β ranging from 10-3 to 1, typical of the different layers and magnetic environments of the solar atmosphere. Our model of jets can robustly explain the generation of helical solar jet-like events at various β ≤ 1. This study introduces the new original result that the plasma β modifies the morphology of the helical jet, explaining the different observed shapes of jets at different scales and in different layers of the solar atmosphere.Conclusions:Our results allow us to understand the energisation, triggering, and driving processes of jet-like events. Our model allows us to make predictions of the impulsiveness and energetics of jets as determined by the surrounding environment, as well as the morphological properties of the resulting jets.
The NASA Astrophysics Data System Abstract Service has become a key component of astronomical research. It provides bibliographic information daily, or near daily, to a majority of astronomical researchers worldwide. We describe the history of the development of the system and its current status. Urania (Boyce 1996), and the ADS role in the emerging electronic astronomical data environment are discussed. Astronomy is unique in that it already has a fully functional data resource, where several of the most important data sources exist on-line and inter-operate nearly seamlessly. The ADS and the Strasbourg Data Center (CDS; Genova et al. 2000) form the core of this resource. We show several examples of how to use the ADS, and we show how ADS use has increased as a function of time. Currently it is still increasing exponentially, with a doubling time for number of queries of 17 months. Using the ADS logs we make the first detailed model of how scientific journals are read as a function of time since publication. We find four distinct components. We directly compare the readership rate with the citation rate for scientific articles as a function of age. Citations generally follow reads, but there are some differences. The main journals of astronomy have differences in the ways they are read and cited. We discuss these from a number of different aspects. The impact of the ADS on astronomy can be calculated after making some simple assumptions. We find that the ADS increases the efficiency of astronomical research by 333 Full Time Equivalent (2000 hour) research years per year, and that the value of the early development of the ADS for astronomy, compared with waiting for mature technologies to be adopted, is 2332 FTE research years. A full technical description of the ADS is in three companion articles: Eichhorn et al. (2000), Accomazzi et al. (2000), and Grant et al. (2000). The ADS is available at http://adsabs.harvard.edu/.
We present near-infrared H-band (1.65 micron) surface photometry of 558 galaxies in the Coma Supercluster and in the Virgo cluster. This data set, obtained with the Arcetri NICMOS3 camera ARNICA mounted on the Gornergrat Infrared Telescope, is aimed at complementing, with observations of mostly early-type objects, our NIR survey of spiral galaxies in these regions, presented in previous papers of this series. Magnitudes at the optical radius, total magnitudes, isophotal radii and light concentration indices are derived. We confirm the existence of a positive correlation between the near-infrared concentration index and the galaxy H-band luminosity. (Tables 1 and 2 are only available in electronic form upon request to gavazzi@uni.mi.astro.it)
