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| A deep INTEGRAL hard X-ray survey of the 3C 273/Coma region |
| We present an analysis of the deepest hard X-ray survey to date of about 2500 deg² performed by the IBIS instrument on board INTEGRAL in the 20-60 keV band, with a total exposure time of 4 Ms. We find 34 candidate sources, for which we try to find counterparts at other wavelengths. The ratio of Seyfert 1 to Seyfert 2 is significantly more than the ratio found in the optical. This effect may be explained in the framework of the receding-torus model, but could also be due to absorption columns large enough to affect the 20-60 keV band. None of the predicted Compton-thick objects with 1024 < NH < 1025 cm-2 is detected unambiguously; when taking lower limits on NH into account, the fraction of these objects is found to be lower than 24%. We do not see, but cannot exclude, a relationship between absorption and luminosity similar to what is seen in the 2-10 keV band. Our data suggests the possibility of a lack of objects with 1021 <= NH <= 1022 cm-2, which could be expected if absorption has two origins, for instance a torus-like structure and the host galaxy. We find that the Log N-Log S diagram of our sources is compatible with those obtained in other surveys in hard X-rays. Compared to models of the AGN population selected in the 2-10 keV band, the Log N-Log S diagram is generally in good agreement, but the NH distribution is significantly different, with significantly less unabsorbed sources (NH < 1022 cm-2) at a given flux limit compared to the models. In this survey, we resolve about 2.5% of the cosmic X-ray background in the 20-60 keV band.
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| Publication date: 15 Jul 2008 |
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| ISOC Newsletter #20 |
Contents:
- Foreword
- AO-7 Announcement
- AO-6 Programme
- Science Operations
- Contacting ISOC
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| Publication date: 15 Jul 2008 |
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| First Results from MIRI Verification Model Testing |
| In "Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter", edited by Jacobus M. Oschmann, Jr., Mattheus W. M. de Graauw, Howard A. MacEwen, Proc. of SPIE Vol. 7010, 70103A, (2008), doi: 10.1117/12.789460
The Mid-Infrared Instrument (MIRI) is one of the three scientific instruments to fly on the James Webb Space Telescope (JWST), which is due for launch in 2013. MIRI contains two sub-instruments, an imager, which has low resolution spectroscopy and coronagraphic capabilities in addition to imaging, and a medium resolution IFU spectrometer. A verification model of MIRI was assembled in 2007 and a cold test campaign was conducted between November 2007 and February 2008. This model was the first scientifically representative model, allowing a first assessment to be made of the performance. This paper describes the test facility and testing done. It also reports on the first results from this test campaign. |
| Publication date: 12 Jul 2008 |
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| First tests of the coronagraphic device of MIRI/JWST |
| In "Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter", edited by Jacobus M. Oschmann, Jr., Mattheus W. M. de Graauw, Howard A. MacEwen, Proc. of SPIE Vol. 7010, 70100W, (2008), doi: 10.1117/12.789089
One of the main objectives of the instrument MIRI, the Mid-InfraRed Instrument, of the JWST is the direct detection and characterization of extrasolar giant planets. For that purpose, a coronagraphic device including three Four-Quadrant Phase Masks and a Lyot coronagraph working in mid-infrared, has been developed. We present here the results of the first test campaign of the coronagraphic system in the mid-infrared in the facility developed at the CEA. The performances are compared to the expected ones from the coronagraphic simulations. The accuracy of the centering procedures is also evaluated to validate the choice of the on-board centering algorithm. |
| Publication date: 12 Jul 2008 |
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| MIRI Telescope Simulator |
| In "Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter", edited by Jacobus M. Oschmann, Jr., Mattheus W. M. de Graauw, Howard A. MacEwen. Proc. of SPIE Vol. 7010, 701039, (2008), doi: 10.1117/12.788750
The MTS, MIRI Telescope Simulator, is developed by INTA as the Spanish contribution of MIRI (Mid InfraRed Instrument) on board JWST (James Web Space Telescope). The MTS is considered as optical equipment which is part of Optical Ground Support Equipment for the AIV/Calibration phase of the instrument at Rutherford Appleton Laboratory, UK. It is an optical simulator of the JWST Telescope, which will provide a diffractionlimited test beam, including the obscuration and mask pattern, in all the MIRI FOV and in all defocusing
range. The MTS will have to stand an environment similar to the flight conditions (35K) but using a smaller set-up, typically at lab scales. The MTS will be used to verify MIRI instrument-level tests, based on checking the implementation/realisation of the interfaces and performances, as well as the instrument properties not subject to interface control such as overall transmission of various modes of operation. This paper includes a functional description and a summary of the development status. |
| Publication date: 12 Jul 2008 |
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| Microshutter arrays: high contrast programmable field masks for JWST NIRSpec |
| Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter. Edited by Oschmann, Jacobus M., Jr.; de Graauw, Mattheus W.M.; MacEwen, Howard A. Proceedings of the SPIE, Volume 7010, pp. 70103D-70103D-10 (2008)
Microshutter arrays are one of the novel technologies developed for the James Webb Space Telescope (JWST). It will allow Near Infrared Spectrometer (NIRSpec) to acquire spectra of hundreds of objects simultaneously therefore increasing its efficiency tremendously. We have developed these programmable arrays that are based on Micro-Electro Mechanical Structures (MEMS) technology. The arrays are 2D addressable masks that can operate in cryogenic environment of JWST. Since the primary JWST science requires acquisition of spectra of extremely faint objects, it is important to provide very high contrast of the open to closed shutters. This high contrast is necessary to eliminate any possible contamination and confusion in the acquired spectra by unwanted objects. We have developed and built a test system for the microshutter array functional and optical characterization. This system is capable of measuring the contrast of the mciroshutter array both in visible and infrared light of the NIRSpec wavelength range while the arrays are in their working cryogenic environment. We have measured contrast ratio of several microshutter arrays and demonstrated that they satisfy and in many cases far exceed the NIRSpec contrast requirement value of 2000. |
| Publication date: 12 Jul 2008 |
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| The JWST MIRI Double-Prism, Design and Science Drivers |
| In "Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter", edited by Jacobus M. Oschmann, Jr., Mattheus W. M. de Graauw, Howard A. MacEwen, Proc. of SPIE Vol. 7010, 70103K, (2008), doi: 10.1117/12.788672 We present how it is achieved to mount a double prism in the filter wheel of MIRIM - the imager of JWST's Mid Infrared Instrument. In order to cope with the extreme conditions of the prisms' surroundings, the low resolution double prism assembly (LRSDPA) design makes high demands on manufacturing accuracy. The design and the manufacturing of the mechanical parts are presented here, while 'Manufacturing and verification of ZnS and Ge prisms for the JWST MIRI imager' are described in a second paper. We also give insights on the astronomical
possibilities of a sensitive MIR spectrometer. Low resolution prism spectroscopy in the wavelength range from 5-10 microns will allow to spectroscopically determine redshifts of objects close to/at the re-ionization phase of the universe. |
| Publication date: 12 Jul 2008 |
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| The on-ground calibration of the Near Infrared Spectrograph (NIRSpec) instrument on-board the James Webb Space Telescope (JWST) |
| Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter. Edited by Oschmann, J.M., Jr.; de Graauw, Mattheus W.M.; MacEwen, Howard A. Proceedings of the SPIE, Volume 7010, pp. 701035-701035-12 (2008)
The James Webb Space Telescope (JWST) mission is a collaborative project between the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Canadian Space Agency (CSA). JWST is considered the successor to the Hubble Space Telescope (HST) and although its design and science objectives are quite different, JWST is expected to yield equivalently astonishing breakthroughs in infrared space science. Due to be launched in 2013 from the French Guiana, the JWST observatory will be placed in an orbit around the anti- Sun Earth-Sun Lagrangian point, L2, by an Ariane 5 launcher provided by ESA. The payload on board the JWST observatory consists of four main scientific instruments: a near-infrared camera (NIRCam), a mid-infrared camera/spectrograph (MIRI), a near-infrared tunable filter (TFI) and a near-infrared spectrograph (NIRSpec). The instrument suite is completed by a Fine Guidance Sensor (FGS). NIRSpec is a multi-object spectrograph capable of measuring the spectra of about 100 objects simultaneously at low (R~100), medium (R~1000) and high (R~2700) resolutions over the wavelength range between 0.6 micron and 5.0 micron. It features also a classical fix-slits spectroscopy mode as well as a 3D-spectrography mode with spectral resolutions up to 2700. The availability of extensive and accurate calibration data of the NIRSpec instrument is a key element to ensure that the nominal performance of the instrument will be achieved and that high-quality processed data will be made available to the users. In this context, an on-ground calibration is planned at instrument level that will supplement the later in-flight calibration campaign.
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| Publication date: 12 Jul 2008 |
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| Variable winds on Venus mapped in three dimensions |
| We present zonal and meridional wind measurements at three altitude levels within the cloud layers of Venus from cloud tracking using images taken with the VIRTIS instrument on board Venus Express. At low latitudes, zonal winds in the Southern hemisphere are nearly constant with latitude with westward velocities of 105 ms-1 at cloud-tops (altitude ~ 66 km) and 60-70 ms-1 at the cloud-base (altitude ~ 47 km). At high latitudes, zonal wind speeds decrease linearly with latitude with no detectable vertical wind shear (values lower than 15 ms-1), indicating the possibility of a vertically coherent vortex structure. Meridional winds at the cloud-tops are poleward with peak speed of 10 ms-1 at 55° S but below the cloud tops and averaged over the South hemisphere are found to be smaller than 5 ms-1. We also report the detection at subpolar latitudes of wind variability due to the solar tide. |
| Publication date: 10 Jul 2008 |
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| Multi-point observations of the inner boundary of the plasma sheet during geomagnetic disturbances |
| We report on the THEMIS and Double Star TC-1 observations at the geocentric distances of 3 < R < 8 RE during substorms on March 23, 2007. THEMIS crossed the inner boundary of the equatorial dusk-side plasma in the string-of-pearls configuration, allowing the dynamics of particle populations to be traced within time ranges from hours to 10 minutes. Observations show co-existence of the plasma sheet ion population (5 - 30 keV) with the ring current ion population (100 - 1000 keV) at 4 < R < 6 RE . The plasma sheet population was characterized by pronounced "nose"-like dispersion with the spectral density maximum at ~10 keV. The plasma sheet boundary, defined by a sharp decrease of the ~1 keV electron flux, moved inward to R = 4 and outward back to ~8 RE within about 1 hour. Local enhancements of the plasma sheet (1 - 5 keV) electron flux with the characteristic time scale of 2 - 10 min were detected at 5 < R < 6 RE during the substorm. |
| Publication date: 09 Jul 2008 |
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| The ACS Virgo Cluster Survey. XV. The Formation Efficiencies of Globular Clusters in Early-Type Galaxies: The Effects of Mass and Environment |
The fraction of stellar mass contained in globular clusters (GCs), also measured by number as the specific frequency, is a fundamental quantity that reflects both a galaxy's early star formation and its entire merging history. We present specific frequencies, luminosities, and mass fractions for the globular cluster systems of 100 early-type galaxies in the ACS Virgo Cluster Survey, the largest homogeneous catalog of its kind.
[This is an extract of the original abstract.]
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| Publication date: 01 Jul 2008 |
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| Reconstruction of the solar spectral UV irradiance for nowcasting of the middle atmosphere state on the basis of LYRA measurements |
| The LYRA instrument onboard ESA PROBA2 satellite will provide 6-hourly solar irradiance at the Lyman-alpha (121.6 nm) and the Herzberg continuum (~200220 nm wavelength range). Because the nowcasting of the neutral and ionic state of the middle atmosphere requires the solar irradiance for the wide spectral area (120680 nm) we have developed the statistical tool for the reconstruction of the full spectrum from the LYRA measurements. The accuracy of the reconstructed irradiance has been evaluated with 1-D transient radiative-convective model with neutral and ion chemistry using the daily solar spectral irradiance measured with SUSIM and SOLSTICE instruments onboard UARS satellite. We compared the results of transient 1-yr long model simulations for 2000 driven by the observed and reconstructed solar irradiance and showed that the reconstruction of the full spectrum using linear regression equation based on the solar irradiance in two LYRA channels can be successfully used for nowcasting of the middle atmosphere. We have also defined some conditions when the proposed approach does not provide reasonable accuracy. |
| Publication date: 30 Jun 2008 |
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| Occurrence of reconnection jets at the dayside magnetopause: Double Star observations |
| We present a statistical study on reconnection occurrence at the dayside magnetopause performed using the Double Star TC1 plasma and magnetic field data. We examined the magnetopause crossings that occurred during the first year of the mission in the 0600-1800 LT interval and we identified plasma flows, at the magnetopause or in the boundary layer, with a different velocity with respect to the adjacent magnetosheath. We used the Walén relation to test which of these flows could be generated by magnetic reconnection. For some event we observed opposite-directed reconnection jets, which could be associated with the passage of the X-line near the satellite. We analyzed the occurrence of the reconnection jets and reconnection jet reversals in relation to the magnetosheath parameters, in particular the local Alfvèn Mach number, the plasma beta, and the magnetic shear angle. We also studied the positions and velocities of the reconnection jets and jet reversals in relation to the magnetosheath magnetic field clock angle. We found that the observations indicate the presence of a reconnection line hinged near the subsolar point and tilted according to the observed magnetosheath clock angle, consistently with the component merging model. |
| Publication date: 27 Jun 2008 |
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| Cluster multispacecraft determination of AKR angular beaming |
| Simultaneous observations of AKR emission using the four-spacecraft Cluster array were used to make the first direct measurements of the angular beaming patterns of individual bursts. By comparing the spacecraft locations and AKR burst locations, the angular beaming pattern was found to be narrowly confined to a plane containing the magnetic field vector at the source and tangent to a circle of constant latitude. Most rays paths are confined within 15° of this tangent plane, consistent with numerical simulations of AKR k-vector orientation at maximum growth rate. The emission is also strongly directed upward in the tangent plane, which we interpret as refraction of the rays as they leave the auroral cavity. The narrow beaming pattern implies that an observer located above the polar cap can detect AKR emission only from a small fraction of the auroral oval at a given location. This has important consequences for interpreting AKR visibility at a given location. It also helps re-interpret previously published Cluster VLBI studies of AKR source locations, which are now seen to be only a subset of all possible source locations. The observations are inconsistent with either filled or hollow cone beaming models. |
| Publication date: 24 Jun 2008 |
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| The wave surveyor technique for fast plasma wave detection in multi-spacecraft data |
| Multi-satellite missions like Cluster allow to study the full spatio-temporal variability of plasma processes in near-Earth space, and both the frequency and the wave vector dependence of dispersion relations can be reconstructed. Existing wave analysis methods include high-resolution beamformers like the wave telescope or k-filtering technique, and the phase differencing approach that combines the correlations measured at pairs of sensors of the spacecraft array. In this paper, we make use of the eigendecomposition of the cross spectral density matrix to construct a direct wave identification method that we choose to call the wave surveyor technique. The analysis scheme extracts only the dominant wave mode but is much faster to apply than existing techniques, hence it is expected to ease survey-type detection of waves in large data sets. The wave surveyor technique is demonstrated by means of synthetic data, and is also applied to Cluster magnetometer measurements. |
| Publication date: 18 Jun 2008 |
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| ST-ECF Newsletter 44 |
Contents: - Hubble Legacy Archive - Data Release One
- The WFC3 Slitless Spectroscopy Simulator aXeSIMweb
- Why Should We Bother to Communicate Astronomy?
- Tiny Tim PSF Simulator - with WFC3 Support
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| Publication date: 15 Jun 2008 |
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| Enceladus - Oasis or Ice Ball? |
| Is it possible for life to exist on Enceladus, the tiny (500 km diameter) icy satellite of Saturn? The Cassini mission found giant gaseous plumes erupting from a tectonically active and warm south polar region. One highly publicized interpretation is that liquid water is present, possibly within tens of meters of the surface, or possibly only at depths of tens of kilometers. An antithetical interpretation is that Enceladus is frigid, stiff, thoroughly solid and composed of ice with interstitial gases to great depths. However, liquid water is just one of the three environmental conditions that are generally thought to be prerequisites for life. There must also be access to the elements out of which complex molecular structures can be constructed--mainly C, H, O, N, S, and--as well as an energy source that can drive metabolism. We examine the range of possible environments on Enceladus that are consistent with the observations in terms of their implications for harboring life. |
| Publication date: 13 Jun 2008 |
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| Iterative inversion of global magnetospheric ion distributions using energetic neutral atom (ENA) images recorded by the NUADU/TC2 instrument |
| A method has been developed for extracting magnetospheric ion distributions from Energetic Neutral Atom (ENA) measurements made by the NUADU instrument on the TC-2 spacecraft. Based on a constrained linear inversion, this iterative technique is suitable for use in the case of an ENA image measurement, featuring a sharply peaked spatial distribution. The method allows for magnetospheric ion distributions to be extracted from a low-count ENA image recorded over a short integration time (5 min). The technique is demonstrated through its application to a set of representative ENA images recorded in energy Channel~2 (hydrogen: 50-81 keV, oxygen: 138-185 keV) of the NUADU instrument during a geomagnetic storm. It is demonstrated that this inversion method provides a useful tool for extracting ion distribution information from ENA data that are characterized by high temporal and spatial resolution. The recovered ENA images obtained from inverted ion fluxes match most effectively the measurements made at maximum ENA intensity. |
| Publication date: 11 Jun 2008 |
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| Observation of three distinct ion populations at the Kelvin-Helmholtz-unstable magnetopause |
| We report Double Star spacecraft observations of the dusk-flank magnetopause and its boundary layer under predominantly northward interplanetary magnetic field (IMF). Under such conditions the flank low-latitude boundary layers (LLBL) of the magnetosphere are known to broaden. The primary candidate processes associated with the transport of solar wind plasma into the LLBL are: (1) local diffusive plasma transport associated with the Kelvin-Helmholtz instability (KHI), (2) local plasma penetration owing to magnetic reconnection in the vicinity of the KHI-driven vortices, and (3) via a pre-existing boundary layer formed through double high-latitude reconnection on the dayside. Previous studies have shown that a cold population of solar wind origin is typically mixed with a hot population of magnetospheric origin in the LLBL. The present observations show the coexistence of three distinct ion populations in the dusk LLBL, during an interval when the magnetopause is unstable to the KHI: (1) a typical hot magnetospheric population, (2) a cold population that shows parallel temperature anisotropy, and (3) a distinct third cold population that shows perpendicular temperature anisotropy. Although no unambiguous conclusion may be drawn from this single event, we discuss the possible mechanisms at work and the origin of each population by envisaging three likely sources: hot magnetospheric plasma sheet, cold magnetosheath of solar wind origin, and cold plasma of ionospheric origin. |
| Publication date: 11 Jun 2008 |
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| The (re-)discovery of G350.1-0.3; a young, luminous supernova remnant and its neutron star |
| We present an XMM-Newton observation of the long-overlooked radio source G350.1-0.3. The X-ray spectrum of G350.1-0.3 can be fit by a shocked plasma with two components: a high-temperature (1.5 keV) region with a low ionization timescale and enhanced abundances, plus a cooler (0.36 keV) component in ionization equilibrium and with solar abundances. The X-ray spectrum and the presence of nonthermal, polarized, radio emission together demonstrate that G350.1-0.3 is a young, luminous supernova remnant (SNR), for which archival H I and 12CO data indicate a distance of 4.5 kpc. The diameter of the source then implies an age of only ~900 years. The SNR's distorted appearance and small size and the presence of 12CO emission along the SNR's eastern edge all indicate that the source is interacting with a complicated distribution of dense ambient material. An unresolved X-ray source, XMMU J172054.5-372652, is detected a few arcminutes west of the brightest SNR emission. The thermal X-ray spectrum and lack of any multiwavelength counterpart suggest that this source is a neutron star associated with G350.1-0.3, most likely a 'central compact object', as seen coincident with other young SNRs such as Cassiopeia A. |
| Publication date: 09 Jun 2008 |
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