On 7 February 2008, the SOLAR payload was placed onboard the International Space Station. It is composed of three instruments, two spectrometers and a radiometer. The two spectrometers allow us to cover the 16 – 2900 nm spectral range. In this article, we first briefly present the instrumentation, its calibration and its performance in orbit. Second, the solar spectrum measured during the transition between Solar Cycles 23 to 24 at the time of the minimum is shown and compared with other data sets. Its accuracy is estimated as a function of wavelength and the solar atmosphere brightness-temperature is calculated and compared with those derived from two theoretical models.
SOLAR/SOLSPEC: Scientific Objectives, Instrument Performance and Its Absolute Calibration Using a Blackbody as Primary Standard Source
SOLAR is a set of three solar instruments measuring the total and spectral absolute irradiance from 16 nm to 3080 nm for solar, atmospheric and climatology physics. It is an external payload for the COLUMBUS laboratory launched on 7 February 2008. The mission’s primary objective is the measurement of the solar irradiance with the highest possible accuracy, and its variability using the following instruments: SOL-ACES (SOLar Auto-Calibrating EUV/UV Spectrophotometers) consists of four grazing incidence planar gratings measuring from 16 nm to 220 nm; SOLSPEC (SOLar SPECtrum) consists of three double gratings spectrometers, covering the range 165 nm to 3080 nm; and SOVIM (SOlar Variability Irradiance Monitor) is combining two types of absolute radiometers and three-channel filter – radiometers. SOLSPEC and SOL-ACES have been calibrated by primary standard radiation sources of the Physikalisch-Technische Bundesanstalt (PTB). Below we describe SOLSPEC, and its performance.
Analysis of Different Solar Spectral Irradiance Reconstructions and Their Impact on Solar Heating Rates
Proper numerical simulation of the Earth’s climate change requires reliable knowledge of solar irradiance and its variability on different time scales, as well as the wavelength dependence of this variability. As new measurements of the solar spectral irradiance have become available, so too have new reconstructions of historical solar irradiance variations, based on different approaches. However, these various solar spectral irradiance reconstructions have not yet been compared in detail to quantify differences in their absolute values, variability, and implications for climate and atmospheric studies. In this paper we quantitatively compare five different reconstructions of solar spectral irradiance changes during the past four centuries, in order to document and analyze their differences. The impact on atmosphere and climate studies is discussed in terms of the calculation of short wave solar heating rates.
The Solid-state Slit Camera (SSC) is an X-ray camera aboard the MAXI mission of the International Space Station. Two sets of SSC sensors view the X-ray sky using charge-coupled devices (CCDs) in the 0.5–12 keV band. The total area for X-ray detection is about 200 cm2, which is the largest among the missions of X-ray astronomy. The energy resolution at the CCD temperature of −70∘C is 145 eV in full width at the half maximum (FWHM) at 5.9 keV, and the field of view is 1∘.5 (FWHM) × 90∘ for each sensor. The SSC could make a whole-sky image with the energy resolution good enough to resolve line emissions, and monitor the whole-sky at the energy band of < 2 keV for the first time in these decades.
Revisit of Local X-Ray Luminosity Function of Active Galactic Nuclei with the MAXI Extragalactic Survey
We constructed a new X-ray (2–10 keV) luminosity function of Compton-thin active galactic nuclei (AGNs) in the local universe, using the first MAXI/GSC source catalog surveyed in the 4–10 keV band. The sample consists of 37 non-blazar AGNs at z = 0.002–0.2, whose identification is highly ( > 97%) complete. We confirmed the trend that the fraction of absorbed AGNs with NH > 10 22 cm −2 rapidly decreases against the luminosity ( LX ), from 0.73 ± 0.10 at LX = 10 42−43.5 erg s −1 to 0.12 ± 0.08 at LX = 10 43.5−45.5 erg s −1 . The obtained luminosity function was well-fitted with a smoothly connected double power-law model whose indices are γ1 = 0.84 (fixed) and γ2 = 2.0 ± 0.2 below and above the break luminosity, L∗ = 10 43.3±0.4 erg s −1 , respectively. While the result of the MAXI/GSC agrees well with that of HEAO-1 at LX ≳ 10 43.5 erg s −1 , it gives a larger number density at the lower luminosity range. A comparison between our luminosity function in the 2–10 keV band and that in the 14–195 keV band obtained from the Swift/BAT survey indicates that the averaged broad-band spectra in the 2–200 keV band should depend on the luminosity, approximated by Γ ∼ 1.7 for LX ≲ 10 44 erg s −1 , while Γ ∼ 2.0 for LX ≳ 10 44 erg s −1 . This trend was confirmed by the correlation between the luminosities in the 2–10 keV and 14–195 keV bands in our sample. We argue that there is no contradiction in the luminosity functions between above and below 10 keV once this effect is taken into account.
Long-Term Monitoring of the Black Hole Binary GX 339−4 in the High/Soft State during the 2010 Outburst with MAXI/GSC
We present the results of monitoring the galactic black hole candidate GX 339 − 4 with the Monitor of All-sky X-ray Image (MAXI) / Gas Slit Camera in the high/soft state during an outburst in 2010. All of the spectra throughout the 8-month period were well reproduced with a model consisting of multi-color disk emission and its Comptonization component, whose fraction is ≤ 25% in the total flux. In spite of the flux variability over a factor of 3, the innermost disk radius is constant at Rin = 61 ± 2 km for an inclination angle of i = 46 ∘ and a distance of d = 8 kpc. This Rin value is consistent with those of past measurements with Tenma in the high/soft state. Assuming that the disk extends to the innermost stable circular orbit of a non-spinning black hole, we estimate the black hole mass to be M = 6.8 ± 0.2 M⊙ for i = 46 ∘ and d = 8 kpc, which is consistent with that estimated from the Suzaku observation of the previous low/hard state. Further combined with the mass function, we obtained a mass constraint of 4.3 M⊙ < M < 13.3 M⊙ for the allowed range of d = 6–15 kpc and i < 60 ∘ . We also discuss the spin parameter of the black hole in GX 339 − 4 by applying relativistic accretion disk models to the Swift/XRT data.
Characterization of sensitivity degradation seen from the UV to NIR by RAIDS on the International Space Station
This paper presents an analysis of the sensitivity changes experienced by three of the eight sensors that comprise the Remote Atmospheric and Ionospheric Detection System (RAIDS) after more than a year operating on board the International Space Station (ISS). These sensors are the Extreme Ultraviolet Spectrograph (EUVS) that covers 550-1100 Å, the Middle Ultraviolet (MUV) spectrometer that covers 1900-3100Å, and the Near Infrared Spectrometer (NIRS) that covers 7220-8740 Å. The scientific goal for RAIDS is comprehensive remote sensing of the temperature, composition, and structure of the lower thermosphere and ionosphere from 85-200 km. RAIDS was installed on the ISS Japanese Expansion Module External Facility (JEM-EF) in September of 2009. After initial checkout the sensors began routine operations that are only interrupted for sensor safety by occasional ISS maneuvers as well as a few days per month when the orbit imparts a risk from exposure to the Sun. This history of measurements has been used to evaluate the rate of degradation of the RAIDS sensors exposed to an environment with significant sources of particulate and molecular contamination. The RAIDS EUVS, including both contamination and detector gain sag, has shown an overall signal loss rate of 0.2% per day since the start of the mission, with an upper boundary of 0.13% per day attributed solely to contamination effects. This upper boundary is driven by uncertainty in the change in the emission field due to changing solar conditions, and there is strong evidence that the true loss due to contamination is significantly smaller. The MUV and NIRS have shown stability to within 1% over the first year of operations.
We present the first published measurement of an altitude profile of the O II 61.7 nm emission, a dayglow feature that can be used to monitor photoionization of O in the lower thermosphere. This photoionization process also results in the O II 83.4 nm emission that, unlike 61.7 nm, is resonantly scattered by ionospheric O+. Although ionospheric characteristics can be inferred from the shape and intensity of 83.4 nm altitude profiles, the interpretation can result in nonunique ion density profiles if the intensity of this source of photons that illuminates the ionosphere from below is unknown. The 61.7 nm emission provides a means to test the accuracy of current models used to calculate the intensity of that source. The data presented here were collected by the Remote Atmospheric and Ionospheric Detection System from the International Space Station on 29 October 2009. The measured 61.7 nm profiles show a steeper drop in intensity below 260 km, where the emission peaks, compared to our model calculations. While the current analysis cannot resolve if the discrepancy is caused by inaccuracies in our model thermospheric composition, photoabsorption cross sections, or both, a 15%–20% increase in the effective O2 photoabsorption at 61.7 nm produces the best qualitative match to the measured profile. Ostensibly, 61.7 nm measurements could replace these model calculations as a more direct measure of the intensity of the 83.4 nm photon source region. In either case, accurate specification of local thermospheric neutral species remains an important component of daytime ionospheric remote sensing.
HCl and ClO profiles inside the Antarctic vortex as observed by SMILES in November 2009: comparisons with MLS and ACE-FTS instruments
We present vertical profiles of hydrogen chloride (HCl) and chlorine monoxide (ClO) as observed by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the International Space Station (ISS) inside the Antarctic vortex on 19–24 November 2009. The SMILES HCl value reveals 2.8–3.1 ppbv between 450 K and 500 K levels in potential temperature (PT). The high value of HCl is highlighted since it is suggested that HCl is a main component of the total inorganic chlorine (Cly), defined as Cly ≃ HCl + ClO + chlorine nitrate (ClONO2), inside the Antarctic vortex in spring, owing to low ozone values. To confirm the quality of two SMILES level 2 (L2) data products provided by the Japan Aerospace Exploration Agency (JAXA) and Japan's National Institute of Information and Communications Technology (NICT), vis-à-vis the partitioning of Cly, comparisons are made using other satellite data from the Aura Microwave Limb Sounder (MLS) and Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). HCl values from the SMILES NICT L2 product agree to within 10% (0.3 ppbv) with the MLS HCl data between 450 and 575 K levels in PT and with the ACE-FTS HCl data between 425 and 575 K. The SMILES JAXA L2 product is 10 to 20% (0.2–0.5 ppbv) lower than that from MLS between 400 and 700 K and from ACE-FTS between 500 and 700 K. For ClO in daytime, the difference between SMILES (JAXA and NICT) and MLS is less than ±0.05 ppbv (100 %) between 500 K and 650 K with the ClO values less than 0.2 ppbv. ClONO2 values as measured by ACE-FTS also reveal 0.2 ppbv at 475–500 K level, resulting in the HCl / Cly ratios of 0.91–0.95. The HCl / Cly ratios derived from each retrieval agree to within −5 to 8 % with regard to their averages. The high HCl values and HCl / Cly ratios observed by the three instruments in the lower stratospheric Antarctic vortex are consistent with previous observations in late Austral spring.
Overview of the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) and Sensitivity to Chlorine Monoxide, ClO
The Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) has made observations in the Earth's atmosphere from the Japanese Experiment Module (JEM) since October of 2009 to April of 2010, with the aid of 4-K mechanical cooler and super-conductive mixer for the submillimeter limb-emission sounding. The outline of SMILES instrument and its operation on board, as well as sensitivity of SMILES to the chlorine monoxide, ClO, are described. Theoretical ClO detection capability of SMILES at upper stratosphere (25-45 km) is verified by using observed data, and limitations of ClO detection below 25 km and above 45 km are discussed.