Isolierte Neutronensterne und ihre sub-stellaren Begleiter

Neben den Radiopulsaren, die die Mehrheit der gegenwärtig beobachteten Neutronensterne ausmachen, gibt es radioleise junge Neutronensterne mit rein thermischer Röntgenstrahlung, die einen direkten Blick auf ihre Oberfläche erlauben. In dieser Arbeit wird untersucht, wie gut die unter Anwendung verschiedener Annahmen simulierte Anzahl von solchen Neutronensternen mit den Beobachtungen übereinstimmt und wieviel mehr Neutronensterne man unter den detektierten, schwachen Röntgenquellen aufgrund dieser Simulationen erwarten kann. Wichtige Fragen sind der Einfluss der Verteilung der Vorgängersterne und der Absorption durch das Interstellare Medium auf die vorhergesagten Neutronensternzahlen. Des weiteren wird nach neuen Kondidaten solcher Neutronensterne gesucht, und zwar in Röntgendaten von ROSAT (RASS, HRI, PSPC pointings) und XMM-Newton, sowie mit Hilfe des SLOAN Quellenkatalogs im sichtbaren Licht. Ein weiteres Projekt ist die Suche nach substellaren Begleitern, also Planeten oder Braunen Zwergen, um junge und nahe Neutronensterne. Zwei Neutronensterne haben eine ausreichend hohe Eigenbewegung, so dass bereits jeweils eine Wiederholungsbeobachtung analysiert werden konnte. Für alle untersuchten 10 Neutronensterne sind obere Grenzen der Helligkeiten im Nahen Infrarot bestimmt worden.Most known neutron stars are radio pulsars, but there are also radio-quiet neutron stars with pure thermal X-ray emission. These radio-quiet neutron stars are of special interest because their thermal X-ray spectra are caused by photospheric emission - allowing a direct view onto the stars' surfaces. This work investigates first the performance of a population synthesis model of neutron stars with thermal X-ray emission. This model is based on several assumptions. Important questions in this work concern the influence of the distribution of the progenitor stars on the observable neutron star number and the role of an inhomogeneous distribution of the X-ray-absorbing interstellar medium. More neutron stars with strong thermal X-ray emission are exprected. This work reports also about a search for new candidates of such neutron stars using data from ROSAT (RASS, PSPC, HRI), XMM-Newton and the sloan Digital Sky Survey. Furthermore we search for substellar companions around young, nearby neutron stars. Two objects are moving fast enough to obtain and analyze the second imaging epoch. For all investigated 10 neutron stars the limits at Near Infrared wavelegths are given

X-ray analysis of the proper motion and pulsar wind nebula for PSR J1741-2054

We obtained six observations of PSR J1741-2054 using the $Chandra$ ACIS-S detector totaling $\sim$300 ks. By registering this new epoch of observations to an archival observation taken 3.2 years earlier using X-ray point sources in the field of view, we have measured the pulsar proper motion at $\mu =109 \pm 10 {\rm mas\ yr}^{-1}$ in a direction consistent with the symmetry axis of the observed H$\alpha$ nebula. We investigated the inferred past trajectory of the pulsar but find no compelling association with OB associations in which the progenitor may have originated. We confirm previous measurements of the pulsar spectrum as an absorbed power law with photon index $\Gamma$=2.68$\pm$0.04, plus a blackbody with an emission radius of (4.5$^{+3.2}_{-2.5})d_{0.38}$ km, for a DM-estimated distance of $0.38d_{0.38}$ kpc and a temperature of $61.7\pm3.0$ eV. Emission from the compact nebula is well described by an absorbed power law model with a photon index of $\Gamma$ = 1.67$\pm$0.06, while the diffuse emission seen as a trail extending northeast of the pulsar shows no evidence of synchrotron cooling. We also applied image deconvolution techniques to search for small-scale structures in the immediate vicinity of the pulsar, but found no conclusive evidence for such structures.Comment: 7 pages, 8 figures, 4 Tables; Accepted by Ap

Nothing to hide: An X-ray survey for young stellar objects in the Pipe Nebula

We have previously analyzed sensitive mid-infrared observations to establish that the Pipe Nebula has a very low star-formation efficiency. That study focused on YSOs with excess infrared emission (i.e, protostars and pre-main sequence stars with disks), however, and could have missed a population of more evolved pre-main sequence stars or Class III objects (i.e., young stars with dissipated disks that no longer show excess infrared emission). Evolved pre-main sequence stars are X-ray bright, so we have used ROSAT All-Sky Survey data to search for diskless pre-main sequence stars throughout the Pipe Nebula. We have also analyzed archival XMM-Newton observations of three prominent areas within the Pipe: Barnard 59, containing a known cluster of young stellar objects; Barnard 68, a dense core that has yet to form stars; and the Pipe molecular ring, a high-extinction region in the bowl of the Pipe. We additionally characterize the X-ray properties of YSOs in Barnard 59. The ROSAT and XMM-Newton data provide no indication of a significant population of more evolved pre-main sequence stars within the Pipe, reinforcing our previous measurement of the Pipe's very low star formation efficiency.Comment: Accepted for publication in Ap

Deep Chandra Observations of the Pulsar Wind Nebula Created by PSR B0355+54

We report on Chandra X-ray Observatory (CXO) observations of the pulsar wind nebula (PWN) associated with PSR B0355+54 (eight observations with a 395 ks total exposure, performed over an 8 month period). We investigated the spatial and spectral properties of the emission coincident with the pulsar, compact nebula (CN), and extended tail. We find that the CN morphology can be interpreted in a way that suggests a small angle between the pulsar spin axis and our line-of-sight, as inferred from the radio data. On larger scales, emission from the 7' (2 pc) tail is clearly seen. We also found hints of two faint extensions nearly orthogonal to the direction of the pulsar's proper motion. The spectrum extracted at the pulsar position can be described with an absorbed power-law + blackbody model. The nonthermal component can be attributed to magnetospheric emission, while the thermal component can be attributed to emission from either a hot spot (e.g., a polar cap) or the entire neutron star surface. Surprisingly, the spectrum of the tail shows only a slight hint of cooling with increasing distance from the pulsar. This implies either a low magnetic field with fast flow speed, or particle re-acceleration within the tail. We estimate physical properties of the PWN and compare the morphologies of the CN and the extended tail with those of other bow shock PWNe observed with long CXO exposures.Comment: 11 pages, 8 figure

No Confirmed New Isolated Neutron Stars In The SDSS Data Release 4

We report on follow-up observations of candidate X-ray bright, radio-quiet isolated neutron stars (INSs) identified from correlations of the ROSAT All-Sky Survey (RASS) and the Sloan Digital Sky Survey (SDSS) Data Release 4 in Ag\"ueros et al. (2006). We obtained Chandra X-ray Telescope exposures for 13 candidates in order to pinpoint the source of X-ray emission in optically blank RASS error circles. These observations eliminated 12 targets as good INS candidates. We discuss subsequent observations of the remaining candidate with the XMM-Newton X-ray Observatory, the Gemini North Observatory, and the Apache Point Observatory. We identify this object as a likely extragalactic source with an unusually high log(fX/fopt) ~ 2.4. We also use an updated version of the population synthesis models of Popov et al. (2010) to estimate the number of RASS-detected INSs in the SDSS Data Release 7 footprint. We find that these models predict ~3-4 INSs in the 11,000 square deg imaged by SDSS, which is consistent with the number of known INSs that fall within the survey footprint. In addition, our analysis of the four new INS candidates identified by Turner et al. (2010) in the SDSS footprint implies that they are unlikely to be confirmed as INSs; together, these results suggest that new INSs are not likely to be found from further correlations of the RASS and SDSS.Comment: 11 pages, 2 figures, 3 tables; accepted for publication in A