Garching bei München, Germany
Garching bei München, Germany

Time filter

Source Type

Baumgartner W.H.,NASA | Baumgartner W.H.,University of Maryland Baltimore County | Baumgartner W.H.,Circle Technology | Tueller J.,NASA | And 9 more authors.
Astrophysical Journal, Supplement Series | Year: 2013

We present the catalog of sources detected in 70 months of observations with the Burst Alert Telescope (BAT) hard X-ray detector on the Swift gamma-ray burst observatory. The Swift-BAT 70 month survey has detected 1171 hard X-ray sources (more than twice as many sources as the previous 22 month survey) in the 14-195 keV band down to a significance level of 4.8σ, associated with 1210 counterparts. The 70 month Swift-BAT survey is the most sensitive and uniform hard X-ray all-sky survey and reaches a flux level of 1.03 × 10-11 erg s-1 cm-2 over 50% of the sky and 1.34 × 10-11 erg s-1 cm-2 over 90% of the sky. The majority of new sources in the 70 month survey continue to be active galactic nuclei, with over 700 in the catalog. As part of this new edition of the Swift-BAT catalog, we also make available eight-channel spectra and monthly sampled light curves for each object detected in the survey in the online journal and at the Swift-BAT 70 month Web site. © 2013. The American Astronomical Society. All rights reserved..


Kistler L.M.,University of New Hampshire | Mouikis C.G.,University of New Hampshire | Klecker B.,Max Planck Institute For Extraterrestriche Physik | Dandouras I.,Toulouse 1 University Capitole | Dandouras I.,French National Center for Scientific Research
Journal of Geophysical Research: Space Physics | Year: 2010

We have used the ion composition data from the CIS/CODIF instrument on Cluster to determine how the O+ population in the plasma sheet and the adjacent lobes changes during geomagnetic storms.The Cluster trajectory, which moves over the polar cap, into the lobe, and then into the plasma sheet on each orbit, allows us to track the changes in O+ in these regions for a prestorm orbit, main-phase orbit, and recovery phase orbit.We find that changes in the O+ density and pressure in the plasma sheet are similar to those commonly observed in the ring current during a storm.The O + is low prestorm.It increases by about a factor of 10 just prior to or during the early main phase of the storm, and is reduced, but usually not down to prestorm levels, in the recovery phase.The lobes contain tailward streaming O+ which originates in the "cleft ion fountain".During the storms main phase, this population also increases.A detailed look at the main-phase passes shows that a significant increase in the O+/H+ ratio is observed when this lobe population reaches the plasma sheet, and the tailward streaming O+ is observed continuously as the spacecraft moves from the lobe into the plasma sheet.The enhanced O+ in the lobe and the plasma sheet is observed for many hours during the storm.The inward convection of this population is likely a significant contributor to the storm time ring current.


Arnaud M.,University Paris Diderot | Pratt G.W.,University Paris Diderot | Pratt G.W.,Max Planck Institute For Extraterrestriche Physik | Piffaretti R.,University Paris Diderot | And 3 more authors.
Astronomy and Astrophysics | Year: 2010

We investigate the regularity of cluster pressure profiles with REXCESS, a representative sample of 33 local (z < 0.2) clusters drawn from the REFLEX catalogue and observed with XMM-Newton. The sample spans a mass range of 10 14 M-{\odot} < M500 < 1015 M-{\odot}, where M500 is the mass corresponding to a density contrast of 500. We derive an average profile from observations scaled by mass and redshift according to the standard self-similar model, and find that the dispersion about the mean is remarkably low, at less than 30 per cent beyond 0.2 R 500, but increases towards the center. Deviations about the mean are related to both the mass and the thermo-dynamical state of the cluster. Morphologically disturbed systems have systematically shallower profiles while cooling core systems are more concentrated. The scaled profiles exhibit a residual mass dependence with a slope of ∼0.12, consistent with that expected from the empirically-derived slope of the M500 - Y X relation; however, the departure from standard scaling decreases with radius and is consistent with zero at R500. The scatter in the core and departure from self-similar mass scaling is smaller compared to that of the entropy profiles, showing that the pressure is the quantity least affected by dynamical history and non-gravitational physics. Comparison with scaled data from several state of the art numerical simulations shows good agreement outside the core. Combining the observational data in the radial range [0.03-1] R 500 with simulation data in the radial range [1-4] R500, we derive a robust measure of the universal pressure profile, that, in an analytical form, defines the physical pressure profile of clusters as a function of mass and redshift up to the cluster "boundary". Using this profile and direct spherical integration of the observed pressure profiles, we estimate the integrated Compton parameter Y and investigate its scaling with M 500 and LX, the soft band X-ray luminosity. We consider both the spherically integrated quantity, Ysph(R), proportional to the gas thermal energy, and the cylindrically integrated quantity, Y cyl(R)=YSZ DA 2, which is directly related to the Sunyaev-Zel'dovich (SZ) effect signal. From the low scatter of the observed Ysph(R500) - YX relation we show that variations in pressure profile shape do not introduce extra scatter into the Ysph(R500) - M500 relation as compared to that from the YX - M500 relation. The Y sph(R500) - M500 and Ysph(R 500) - LX relations derived from the data are in excellent agreement with those expected from the universal profile. This profile is used to derive the expected YSZ - M500 and YSZ - LX relations for any aperture. © 2010 ESO.


Aspin C.,University of Hawaii at Manoa | Reipurth B.,University of Hawaii at Manoa | Herczeg G.J.,Max Planck Institute For Extraterrestriche Physik | Capak P.,California Institute of Technology
Astrophysical Journal Letters | Year: 2010

In early 2008, the young low-mass star EX Lupi, the prototype of the EXor class of eruptive variables, optically brightened by over 5 mag for a period of seven months. The previous time a change of such amplitude had been observed in EX Lup was over 50 years ago. In this Letter, we present new optical and near-IR highresolution spectroscopy of EX Lup during the 2008 outburst. We investigate the physical characteristics of the outburst both soon after it began and some four months later, and consider the observed energetics and kinematics. Emission line strengths, widths, and profiles significantly changed between the two observations. Also, modeling of the 2.2935 μm CO overtone band head emission suggests that an inner gap in the circumstellar gas disk around the star may be present and that it is from the inner edge of the gas disk that the CO overtone emission probably arises. We derive a mass accretion luminosity and rate during the extreme outburst of ∼2 ± 0.5 L⊙ and ∼(2 ± 0.5) × 10-7M⊙ yr-1, respectively, which suggests that this outburst was indeed one of the strongest witnessed in EX Lup, yet not as strong as those observed in FU Orionis stars. © 2010. The American Astronomical Society. All rights reserved.


Alexander T.,Weizmann Institute of Science | Pfuhl O.,Max Planck Institute For Extraterrestriche Physik
Astrophysical Journal | Year: 2014

Massive black holes (MBHs) in galactic nuclei are believed to be surrounded by a high-density stellar cluster, whose mass is mostly in hard-to-detect faint stars and compact remnants. Such dark cusps dominate the dynamics near the MBH: a dark cusp in the Galactic center (GC) of the Milky Way would strongly affect orbital tests of general relativity there; on cosmic scales, dark cusps set the rates of gravitational wave emission events from compact remnants that spiral into MBHs, and they modify the rates of tidal disruption events, to list only some implications. A recently discovered long-period massive young binary (with period P 12 ≲ 1 yr, total mass , and age T 12 ∼ 6 × 106 yr), only ∼0.1 pc from the Galactic MBH, sets a lower bound on the stellar two-body relaxation timescale there, min t rlx∝(P 12/M 12)2/3 T 12 ∼ 107 yr, and, correspondingly, an upper bound on the stellar number density, ( is the rms stellar mass), based on the binary's survival against evaporation by the dark cusp. However, a conservative dynamical estimate, the drain limit, implies . Such massive binaries are thus too short-lived and tightly bound to constrain a dense relaxed dark cusp. We explore here in detail the use of longer-period, less massive, and longer-lived binaries (P 12 ∼ few yr, M 12 ∼ 2-4 M, T 12 ∼ 108-1010 yr), presently just below the detection threshold, for probing the dark cusp and develop the framework for translating their future detections among the giants in the GC into dynamical constraints. © 2014. The American Astronomical Society. All rights reserved.


Ponti G.,Max Planck Institute For Extraterrestriche Physik | Munoz-Darias T.,University of Oxford | Fender R.P.,University of Oxford
Monthly Notices of the Royal Astronomical Society | Year: 2014

High-resolution X-ray spectra of accreting stellar-mass black holes reveal the presence of accretion disc winds, traced by high-ionization Fe K lines. These winds appear to have an equatorial geometry and to be observed only during disc-dominated states in which the radio jet is absent. Accreting neutron star systems also show equatorial high-ionization absorbers. However, the presence of any correlation with the accretion state has not been previously tested. We have studied EXO 0748-676, a transient neutron star system, for which we can reliably determine the accretion state, in order to investigate the Fe K absorption/accretion state/jet connection. Not one of 20 X-ray spectra obtained in the hard state revealed any significant Fe K absorption line. However, intense Fe XXV and Fe XXVI (as well as a rarely observed Fe XXIII line plus S XVI; a blend of S XVI and Ar XVII; CaXX and Ca XIX, possibly produced by the same high-ionization material) absorption lines (EWFe XXIII-XXV = 31 ± 3, EWFe xxvi = 8 ± 3 eV) are clearly detected during the only soft-state observation. This suggests that the connection between Fe K absorption and states (and anticorrelation between the presence of Fe K absorption and jets) is also valid for EXO 0748-676 and therefore it is not a unique property of black hole systems but a more general characteristic of accreting sources. © 2014 The Authors.


Ioppolo S.,Leiden University | Cuppen H.M.,Leiden University | Van Dishoeck E.F.,Leiden University | Van Dishoeck E.F.,Max Planck Institute For Extraterrestriche Physik | Linnartz H.,Leiden University
Monthly Notices of the Royal Astronomical Society | Year: 2011

The production of formic acid (HCOOH) in cold and hot regions of the interstellar medium is not well understood. Recent gas-phase experiments and gas-grain models hint at a solid-state production process at low temperatures. Several surface reaction schemes have been proposed in the past decades, even though experimental evidence for their efficiency was largely lacking. The aim of this work is to give the first experimental evidence for an efficient solid-state reaction scheme providing a way to form HCOOH under astronomical conditions. Several surface reaction channels have been tested under fully controlled experimental conditions by using a state-of-the-art ultrahigh vacuum set-up through co-deposition of H atoms and CO:O2 mixtures with 4:1, 1:1 and 1:4 ratios. During deposition spectral changes in the ice are monitored by means of a Fourier transform infrared (FTIR) spectrometer in reflection absorption infraRed (RAIR) mode. After co-deposition a temperature programmed desorption (TPD) experiment is performed and gas-phase molecules are detected by a quadrupole mass spectrometer (QMS). Formation of HCOOH is observed at low temperatures mainly through hydrogenation of the HO-CO complex, while reactions with the HCO radical as intermediate are found to be inefficient. The HO-CO complex channel, which was previously not considered as an important HCOOH formation route, can explain the presence of HCOOH in dense cold clouds, at the beginning of the warm-up phase of a protostar, and, therefore, is likely to be astrochemically relevant. © 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS.


Ioppolo S.,Leiden University | van Boheemen Y.,Leiden University | Cuppen H.M.,Leiden University | van Dishoeck E.F.,Leiden University | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

The surface formation of CO2 at low temperatures through the reaction CO + OH and direct dissociation of the resulting HO-CO complex is shown by hydrogenation of a CO:O2 ice mixture. Such a binary ice is not fully representative for an interstellar ice, but the hydrogenation of O2 ice produces OH radicals, which allows the investigation of the interstellar relevant CO + OH solid state reaction under fully controlled laboratory conditions. Similar recent astrophysical ice studies have focused on the investigation of isolated surface reaction schemes, starting from the hydrogenation of pure ices, like solid CO or O2. For such ices, no CO2 formation is observed upon H-atom exposure. The hydrogenation of binary ice mixtures presented here allows to investigate for the first time the influence of the presence of other species in the ice on the pure ice reaction shemes. Mixtures of CO:O2 are deposited on a substrate in an ultra high vacuum setup at low temperatures (15 and 20K) and subsequently hydrogenated. The ice is monitored by means of Reflection Absorption InfraRed Spectroscopy (RAIRS). Results show that solid CO2 is formed in all studied CO:O2 mixtures under our laboratory conditions. Within the experimental uncertainties no dependency on ice temperature or composition is observed. The laboratory results show a correlation between the formation of CO2 and H2O, which is consistent with the astronomical observation of solid CO2 in water-rich environments. The results also show that the contemporary presence of CO and O2 molecules in the ice influences the final product yields of the separate CO + H (H2CO, CH3OH) and O2+ H (H2O2 and H2O) channels, even though the formation rates are not significantly affected. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Ioppolo S.,Leiden University | Cuppen H.M.,Leiden University | Romanzin C.,Leiden University | Van Dishoeck E.F.,Leiden University | And 2 more authors.
Physical Chemistry Chemical Physics | Year: 2010

Water is the main component of interstellar ice mantles, is abundant in the solar system and is a crucial ingredient for life. The formation of this molecule in the interstellar medium cannot be explained by gas-phase chemistry only and its surface hydrogenation formation routes at low temperatures (O, O2, O3 channels) are still unclear and most likely incomplete. In a previous paper we discussed an unexpected zeroth-order H 2O production behavior in O2 ice hydrogenation experiments compared to the first-order H2CO and CH3OH production behavior found in former studies on hydrogenation of CO ice. In this paper we experimentally investigate in detail how the structure of O2 ice leads to this rare behavior in reaction order and production yield. In our experiments H atoms are added to a thick O2 ice under fully controlled conditions, while the changes are followed by means of reflection absorption infrared spectroscopy (RAIRS). The H-atom penetration mechanism is systematically studied by varying the temperature, thickness and structure of the O2 ice. We conclude that the competition between reaction and diffusion of the H atoms into the O2 ice explains the unexpected H2O and H2O2 formation behavior. In addition, we show that the proposed O2 hydrogenation scheme is incomplete, suggesting that additional surface reactions should be considered. Indeed, the detection of newly formed O3 in the ice upon H-atom exposure proves that the O2 channel is not an isolated route. Furthermore, the addition of H2 molecules is found not to have a measurable effect on the O2 reaction channel. © 2010 the Owner Societies.


Mortier A.,University of Porto | Mortier A.,Leiden University | Oliveira I.,Leiden University | van Dishoeck E.F.,Leiden University | van Dishoeck E.F.,Max Planck Institute For Extraterrestriche Physik
Monthly Notices of the Royal Astronomical Society | Year: 2011

The results of an optical spectroscopic survey of a sample of young stellar objects and pre-main-sequence stars in the Lupus clouds are presented. 92 objects were observed with the Very Large Telescope/Fibre Large Array Multi Element Spectrograph. All of those objects show infrared excess as discovered by the Spitzer Legacy Program 'From Molecular Cores to Planet-Forming Disks' (c2d). After reduction, 54 spectra with good signal-to-noise ratio are spectrally classified. Effective temperatures and luminosities are derived for these objects, and used to construct Hertzsprung-Russell diagrams for the population. The sample consists of mostly M-type stars, with 10percent K-type stars. Individual ages and masses are inferred for the objects according to theoretical evolutionary models. The mean population age is found to be between 3.6 and 4.4Myr, depending on the model, while the mean mass is found to be ∼0.3M ⊙ for either model. Together with literature data, the distribution of spectral types is found to be similar to that in Chamaeleon I and IC 348. The Hα line in emission, found in 49percent of the sample, is used to distinguish between classical and weak-line T Tauri stars. 56percent of the objects show Hα in emission and are accreting T Tauri stars. Mass accretion rates between 10 -8 and 10 -11 M ⊙yr -1 are determined from the full width at 10percent of the Hα peak intensity. These mass accretion rates are, within a large scatter, consistent with the relation found in the literature. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Loading Max Planck Institute For Extraterrestriche Physik collaborators
Loading Max Planck Institute For Extraterrestriche Physik collaborators