Netherlands Institute for Space Research

About: Netherlands Institute for Space Research is a facility organization based out in Utrecht, Netherlands. It is known for research contribution in the topics: Galaxy & Neutron star. The organization has 737 authors who have published 3026 publications receiving 106632 citations. The organization is also known as: SRON & Space Research Organisation Netherlands.

Suzaku X-Ray Observations of the Accreting NGC 4839 Group of Galaxies and a Radio Relic in the Coma Cluster

Abstract: Based on Suzaku X-ray observations, we study the hot gas around the NGC4839 group of galaxies and the radio relic in the outskirts of the Coma cluster. We find a gradual de cline in the gas temperature from 5 keV around NGC4839 to 3.6 keV at the radio relic, across which there is a further, steeper drop down to 1.5 keV. This drop as well as the observed surface brightness profile are consiste nt with a shock with Mach numberM = 2.2± 0.5 and velocityvs = (1410± 110) km s −1 . A lower limit of B> 0.33� G is derived on the magnetic field strength around the relic from upper limits to inverse Compton X-ray emission. Although this suggests that the non-thermal electrons responsible for the relic are generated by diffusive shock acceleration (DSA), the relation between the measured Mach number and the electron spectrum inferred from radio observations are inconsistent with that expected from the simplest, test-particle theory of DSA. Nevertheless, D SA is still viable if it is initiated by the injection of a pre-existing population of non-thermal electrons. Combined with previous measurements, the temperature profile of Coma in the southwest direction is shallower outside NGC4839 and also slightly shallower in the outermost region. The metal abundance around NGC4839 is confirmed to be higher t han in its vicinity, implying a significant peak in the abundance profile that decreases to 0.2 solar toward th e outskirts. We interpret these facts as due to ram pressure stripping of metal-enriched gas from NGC4839 as it falls into Coma. The relic shock may result from the combined interaction of pre-existing intracluster gas, ga s associated with NGC 4839, and cooler gas flowing in from the large-scale structure filament in the southwest.

Lord of the Rings: A Kinematic Distance to Circinus X-1 from a Giant X-Ray Light Echo

Abstract: Circinus X-1 exhibited a bright X-ray flare in late 2013. Follow-up observations with Chandra and XMM-Newton from 40 to 80 days after the flare reveal a bright X-ray light echo in the form of four well-defined rings with radii from 5 to 13 arcmin, growing in radius with time. The large fluence of the flare and the large column density of interstellar dust toward Circinus X-1 make this the largest and brightest set of rings from an X-ray light echo observed to date. By deconvolving the radial intensity profile of the echo with the MAXI X-ray light curve of the flare we reconstruct the dust distribution toward Circinus X-1 into four distinct dust concentrations. By comparing the peak in scattering intensity with the peak intensity in CO maps of molecular clouds from the Mopra Southern Galactic Plane CO Survey we identify the two innermost rings with clouds at radial velocity and , respectively. We identify a prominent band of foreground photoelectric absorption with a lane of CO gas at . From the association of the rings with individual CO clouds we determine the kinematic distance to Circinus X-1 to be . This distance rules out earlier claims of a distance around , implies that Circinus X-1 is a frequent super-Eddington source, and places a lower limit of on the Lorentz factor and an upper limit of on the jet viewing angle.

Properties of the Intracluster Medium of Abell 3667 Observed with Suzaku XIS

Abstract: We observed the northwest region of the cluster of galaxies A3667 with the Suzaku XIS instrument. The temperature and surface brightness of the intracluster medium were measured up to the virial radius (r200-2.3 Mpc). The radial temperature profile is flatter than the average profile for other clusters until the radius reaches the northwest radio relic. The temperature drops sharply from 5 keV to about 2 keV at the northwest radio relic region. The sharp changes of the temperature can be interpreted as a shock with a Mach number of about 2.5. The entropy slope becomes flatter in the outer region and negative around the radio relic region. In this region, the relaxation timescale of electron-ion Coulomb collisions is longer than the time elapsed after the shock heating and the plasma may be out of equilibrium. Using differential emission measure (DEM) models, we also confirm the multi-temperature structure around the radio relic region, characterized by two peaks at 1 keV and 4 keV. These features suggest that the gas is heated by a shock propagating from the center to outer region.

Efficient calculation of intensity and polarization spectra in vertically inhomogeneous scattering and absorbing atmospheres

Abstract: [1] We present a method for the efficient calculation of moderate- and high-resolution spectra of intensity and polarization in absorption bands. This linear-k method explicitly accounts for the vertical distribution of the absorption optical thickness by using a linear approximation. It can be applied to any radiative transfer model that calculates the intensity (vector) and its derivatives with respect to the absorption optical thickness in different altitude layers of the model atmosphere. For the three spectral windows of the Orbiting Carbon Observatory (OCO), the error on the modeled intensity introduced by the linear-k method is below 0.13% for the O 2 -A band, below 0.06% in the weak CO 2 band, and below 0.12% for the strong CO 2 band, for an aerosol type dominated by coarse mode particles with an aerosol optical thickness (AOT) of 0.3 at the O 2 -A band (the maximum AOT for which OCO retrievals are intended to be performed), and a typical aerosol height distribution with most aerosols located in the boundary layer. For these accuracies the computational effort is reduced by two orders of magnitude compared to line-by-line calculations. A sensitivity study with synthetic OCO measurements shows that the linear-k method introduces a small error of 0.025-0.20 ppm on the retrieved profile weighted mean CO 2 mixing ratio, for a boundary layer dominated aerosol distribution, and 0.050-0.50 ppm for an elevated aerosol layer between 5 and 6 km. In most cases the error is considerably smaller than the retrieval noise.

ExoMol molecular line lists -- XXXVII: spectra of acetylene

Abstract: A new ro-vibrational line list for the ground electronic state of the main isotopologue of acetylene, $^{12}$C$_2$H$_2$, is computed as part of the ExoMol project. The aCeTY line list covers the transition wavenumbers up to 10,000 cm$^{-1}$ ($ \lambda >1$ $\mu$m), with lower and upper energy levels up to 12,000 cm$^{-1}$ and 22,000 cm$^{-1}$ considered, respectively. The calculations are performed up to a maximum value for the vibrational angular momentum, $K_{\rm max}=L_{\rm max}$ = 16, and maximum rotational angular momentum, $J$ = 99. Higher values of $J$ were not within the specified wavenumber window. The aCeTY line list is considered to be complete up to 2200 K, making it suitable for use in characterising high-temperature exoplanet or cool stellar atmospheres. Einstein-A coefficients, which can directly be used to calculate intensities at a particular temperature, are computed for 4.3 billion (4,347,381,911) transitions between 5 million (5,160,803) energy levels. We make comparisons against other available data for $^{12}$C$_2$H$_2$, and demonstrate this to be the most complete line list available. The line list is available in electronic form from the online CDS and ExoMol databases.