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.

Chemical Enrichment RGS cluster sample (CHEERS): Constraints on turbulence

Abstract: Feedback from AGN, galactic mergers, and sloshing are thought to give rise to turbulence, which may prevent cooling in clusters. We aim to measure the turbulence in clusters of galaxies and compare the measurements to some of their structural and evolutionary properties. It is possible to measure the turbulence of the hot gas in clusters by estimating the velocity widths of their X-ray emission lines. The RGS Spectrometers aboard XMM-Newton are currently the only instruments provided with sufficient effective area and spectral resolution in this energy domain. We benefited from excellent 1.6Ms new data provided by the CHEERS project. The new observations improve the quality of the archival data and allow us to place constraints for some clusters, which were not accessible in previous work. One-half of the sample shows upper limits on turbulence less than 500km/s. For several sources, our data are consistent with relatively strong turbulence with upper limits on the velocity widths that are larger than 1000km/s. The NGC507 group of galaxies shows transonic velocities, which are most likely associated with the merging phenomena and bulk motions occurring in this object. Where both low- and high-ionization emission lines have good enough statistics, we find larger upper limits for the hot gas, which is partly due to the different spatial extents of the hot and cool gas phases. Our upper limits are larger than the Mach numbers required to balance cooling, suggesting that dissipation of turbulence may prevent cooling, although other heating processes could be dominant. The systematics associated with the spatial profile of the source continuum make this technique very challenging, though still powerful, for current instruments. The ASTRO-H and Athena missions will revolutionize the velocity estimates and discriminate between different spatial regions and temperature phases.

Discovery of a New Kind of Explosive X-Ray Transient near M86

Abstract: We present the discovery of a new type of explosive X-ray flash in Chandra images of the old elliptical galaxy M86. This unique event is characterized by the peak luminosity of 6 × 10{sup 42} erg s{sup –1} for the distance of M86, the presence of precursor events, the timescale between the precursors and the main event (∼4000 s), the absence of detectable hard X-ray and γ-ray emission, the total duration of the event, and the detection of a faint associated optical signal. The transient is located close to M86 in the Virgo cluster at the location where gas and stars are seen protruding from the galaxy probably due to an ongoing wet minor merger. We discuss the possible mechanisms for the transient and conclude that the X-ray flash could have been caused by the disruption of a compact white dwarf star by a ∼10{sup 4} M {sub ☉} black hole. Alternative scenarios such that of a foreground neutron star accreting an asteroid or the detection of an off-axis (short) γ-ray burst cannot be excluded at present.

The 9.7 and 18 μm silicate absorption profiles towards diffuse and molecular cloud lines-of-sight

Abstract: Context. Studying the composition of dust in the interstellar medium (ISM) is crucial for understanding the cycle of dust in our galaxy. Aims. The mid-infrared spectral signature of amorphous silicates, the most abundant dust species in the ISM, is studied in different lines-of-sight through the Galactic plane, thus probing different conditions in the ISM. Methods. We have analysed ten spectra from the Spitzer archive, of which six lines-of-sight probe diffuse interstellar medium material and four probe molecular cloud material. The 9.7 μm silicate absorption features in seven of these spectra were studied in terms of their shape and strength. In addition, the shape of the 18 μm silicate absorption features in four of the diffuse sightline spectra were analysed. Results. The 9.7 μm silicate absorption bands in the diffuse sightlines show a strikingly similar band shape. This is also the case for all but one of the 18 μm silicate absorption bands observed in diffuse lines-of-sight. The 9.7 μm bands in the four molecular sightlines show small variations in shape. These modest variations in the band shape are inconsistent with the interpretation of the large variations in τ9.7/E(J − K) between diffuse and molecular sightlines in terms of silicate grain growth. Instead, we suggest that the large changes in τ9.7/E(J − K) must be due to changes in E(J − K).

Unveiling recurrent jets of the ULX Holmberg II X-1: evidence for a massive stellar-mass black hole?

Abstract: We report on the discovery of an apparent triple radio structure hidden inside the radio bubble of the ultraluminous X-ray source Holmberg II X-1. The morphology is consistent with a collimated jet structure, which is observed to emit optically thin synchrotron radiation. The central component has a steep radio spectrum and is brighter than the outer components indicating a renewed radio activity. We estimate a minimum time-averaged jet power of �2 × 10 39 erg s −1 that is associated with a timeaveraged isotropic X-ray luminosity of at least 4 × 10 39 erg s −1 . Our results suggest that Holmberg II X-1 is powered by a black hole of MBH > 25 M⊙, that is inferred to be accreting at a high Eddington rate with intermittent radio activity.

The complex chemistry of outflow cavity walls exposed: the case of low-mass protostars

Abstract: Complex organic molecules are ubiquitous companions of young low-mass protostars. Recent observations suggest that their emission stems, not only from the traditional hot corino, but also from offset positions. In this work, 2D physicochemical modelling of an envelope-cavity system is carried out. Wavelength-dependent radiative transfer calculations are performed and a comprehensive gas-grain chemical network is used to simulate the physical and chemical structure. The morphology of the system delineates three distinct regions: the cavity wall layer with time-dependent and species-variant enhancements; a torus rich in complex organic ices, but not reflected in gas-phase abundances and the remaining outer envelope abundant in simpler solid and gaseous molecules. Strongly irradiated regions, such as the cavity wall layer, are subject to frequent photodissociation in the solid phase. Subsequent recombination of the photoproducts leads to frequent reactive desorption, causing gas-phase enhancements of several orders of magnitude. This mechanism remains to be quantified with laboratory experiments. Direct photodesorption is found to be relatively inefficient. If radicals are not produced directly in the icy mantle, the formation of complex organics is impeded. For efficiency, a sufficient number of FUV photons needs to penetrate the envelope, and elevated cool dust temperatures need to enable grain-surface radical mobility. As a result, a high stellar luminosity and a sufficiently wide cavity favour chemical complexity. Furthermore within this paradigm, complex organics are demonstrated to have unique lifetimes and be grouped into early (formaldehyde, ketene, methanol, formic acid, methyl formate, acetic acid and glycolaldehyde) and late (acetaldehyde, dimethyl ether and ethanol) species.