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.

Further Constraints on Thermal Quiescent X-Ray Emission from SAX J1808.4-3658

Abstract: We observed SAX J1808.4-3658 (1808), the first accreting millisecond pulsar, in deep quiescence with XMM-Newton and (near simultaneously) Gemini-South. The X-ray spectrum of 1808 is similar to that observed in quiescence in 2001 and 2006, describable by an absorbed power law with photon index 1.74 ± 0.11 and unabsorbed X-ray luminosity LX = 7.9 ± 0.7 × 1031 ergs s–1, for NH = 1.3 × 1021 cm–2. Fitting all the quiescent XMM-Newton X-ray spectra with a power law, we constrain any thermally emitting neutron star (NS) with a hydrogen atmosphere to have a temperature less than 30 eV and L NS (0.01-10 keV) <6.2 × 1030 ergs s–1. A thermal plasma model also gives an acceptable fit to the continuum. Adding an NS component to the plasma model produces less stringent constraints on the NS; a temperature of 36+4 –8 eV and L NS (0.01-10 keV) = 1.3+0.6 –0.8 × 1031 ergs s–1. In the framework of the current theory of NS heating and cooling, the constraints on the thermal luminosity of 1808 and 1H 1905+000 require strongly enhanced cooling in the cores of these NSs. We compile data from the literature on the mass transfer rates and quiescent thermal flux of the largest possible sample of transient NS low-mass X-ray binaries. We identify a thermal component in the quiescent spectrum of the accreting millisecond pulsar IGR J00291+5934, which is consistent with the standard cooling model. The contrast between the cooling rates of IGR J00291+5934 and 1808 suggests that 1808 may have a significantly larger mass. This can be interpreted as arising from differences in the binary evolution history or initial NS mass in these otherwise similar systems.

Black hole masses of tidal disruption event host galaxies

Abstract: The mass of the central black hole in a galaxy that hosted a tidal disruption event (TDE) is an important parameter in understanding its energetics and dynamics. We present the first homogeneously measured black hole masses of a complete sample of 12 optically/UV-selected TDE host galaxies (down to ghost ≤ 22 mag and z = 0.37) in the Northern sky. The mass estimates are based on velocity dispersion measurements, performed on late time optical spectroscopic observations. We find black hole masses in the range of 3 × 10^5 M_⊙ ≤ M_(BH) ≤ 2 × 10^7 M_⊙. The TDE host galaxy sample is dominated by low-mass black holes (∼ 10^6 M_⊙), as expected from theoretical predictions. The blackbody peak luminosity of TDEs with M_(BH) ≤ 10^(7.1) M_⊙ is consistent with the Eddington limit of the supermassive black hole (SMBH), whereas the two TDEs with M_(BH) ≥ 10^(7.1) M_⊙ have peak luminosities below their SMBH Eddington luminosity, in line with the theoretical expectation that the fallback rate for M_(BH) ≥ 10^(7.1) M_⊙ is sub-Eddington. In addition, our observations suggest that TDEs around lower mass black holes evolve faster. These findings corroborate the standard TDE picture in 10^6 M_⊙ black holes. Our results imply an increased tension between observational and theoretical TDE rates. By comparing the blackbody emission radius with theoretical predictions, we conclude that the optical/UV emission is produced in a region consistent with the stream self-intersection radius of shallow encounters, ruling out a compact accretion disc as the direct origin of the blackbody radiation at peak brightness.

The x-ray spectral evolution of galactic black hole x-ray binaries toward quiescence

Abstract: Most transient black hole X-ray binaries (BHXBs) spend the bulk of their time in a quiescent state, where they accrete matter from their companion star at highly sub-Eddington luminosities (we define quiescence here as a normalized Eddington ratio lx = L 0.5-10 keV/L Edd < 10–5). Here, we present Chandra X-ray imaging spectroscopy for three BHXB systems (H 1743–322, MAXI J1659–152, and XTE J1752–223) as they fade into quiescence following an outburst. Multiple X-ray observations were taken within one month of each other, allowing us to track each individual system's X-ray spectral evolution during its decay. We compare these three systems to other BHXB systems. We confirm that quiescent BHXBs have softer X-ray spectra than low-hard-state BHXBs, and that quiescent BHXB spectral properties show no dependence on the binary system's orbital parameters. However, the observed anti-correlation between X-ray photon index (Γ) and lx in the low-hard state does not continue once a BHXB enters quiescence. Instead, Γ plateaus to an average Γ = 2.08 ± 0.07 by the time lx reaches ~10–5. lx ~ 10–5 is thus an observationally motivated upper limit for the beginning of the quiescent spectral state. Our results are discussed in the context of different accretion flow models and across the black hole mass scale.

Hot organic molecules toward a young low-mass star: a look at inner disk chemistry

Abstract: Spitzer Space Telescopespectra of the low-mass young stellar object (YSO) IRS 46 ( ) in Ophiuchus L ≈ 0.6 L bol , reveal strong vibration-rotation absorption bands of gaseous C 2H2, HCN, and CO2. This is the only source out of a sample of ∼100 YSOs that shows these features, and this is the first time that they are seen in the spectrum of a solar-mass YSO. Analysis of the Spitzer data combined with Keck L- and M-band spectra reveals excitation temperatures of 350 K and abundances of 10 6 to 10 5 with respect to H2, orders of magnitude higher than those found in cold clouds. In spite of this high abundance, the HCN line is barely detected with the J p 4–3 James Clerk Maxwell Telescope (JCMT), indicating a source diameter less than 13 AU. The (sub)millimeter continuum emission and the absence of scattered light in near-infrared images limit the mass and temperature of any remnant collapsing envelope to less than 0.01 M, and 100 K, respectively. This excludes a hot-core–type region as found in high-mass YSOs. The most plausible origin of this hot gas rich in organic molecules is in the inner (!6 AU radius) region of the disk around IRS 46, either the disk itself or a disk wind. A nearly edgeon two-dimensional disk model fits the spectral energy distribution (SED) and gives a column of dense warm gas along the line of sight that is consistent with the absorption data. These data illustrate the unique potential of high-resolution infrared spectroscopy to probe the organic chemistry, gas temperatures, and gas kinematics in the planet-forming zones close to a young star. Subject headings: infrared: ISM — ISM: individual (IRS 46) — ISM: jets and outflows — ISM: molecules — planetary systems: protoplanetary disks — stars: formation

The outburst decay of the low magnetic field magnetar sgr 0418+5729

Abstract: N.R. is supported by a Ramon y Cajal Research Fellowship, and by grants AYA2009-07391, AYA2012-39303, SGR2009-811, TW2010005, and iLINK 2011-0303. J.A.P. and D.V. acknowledge support from the grants AYA 2010-21097-C03-02 and Prometeo/2009/103. R.T. and S.M. are partially funded through an INAF 2011 PRIN grant. A.P. is supported by a JAE-Doc CSIC fellowship co-funded with the European Social Fund under the program “Junta para la Ampliacion de Estudios,” by the Spanish MICINN grant AYA2011-30228-C03-02 (co-funded with FEDER funds), and by the AGAUR grant 2009SGR1172 (Catalonia).