ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    facet.materialart.
    Unknown
    The CHANDRA HETGS X-ray Grating Spectrum of Eta Carinae (2001)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Eta Carinae may be the most massive and luminous star in the Galaxy and is suspected to be a massive, colliding wind binary system. The CHANDRA X-ray observatory has obtained a calibrated, high-resolution X-ray spectrum of the star uncontaminated by the nearby extended soft X-ray emission. Our 89 ksec CHANDRA observation with the High Energy Transmission Grating Spectrometer (HETGS) shows that the hot gas near the star is non-isothermal. The temperature distribution may represent the emission on either side of the colliding wind bow shock, effectively 'resolving' the shock. If so, the pre-shock wind velocities are approximately 700 and 1800 km/s in our analysis, and these velocities may be interpreted as the terminal velocities of the winds from 71 Carinae and from the hidden companion star. The forbidden-to-intercombination line ratios for the He-like ions of S, Si, and Fe are large, indicating that the line forming region lies far from the stellar photosphere. The iron fluorescent line at 1.93 angstroms, first detected by ASCA, is clearly resolved from the thermal iron line in the CHANDRA grating spectrum. The Fe fluorescent line is weaker in our CHANDRA observation than in any of the ASCA spectra. The CHANDRA observation also provides the first high-time resolution lightcurve of the uncontaminated stellar X-ray emission from 77 Carinae and shows that there is no significant, coherent variability during the CHANDRA observation. The 77 Carinae CHANDRA grating spectrum is unlike recently published X-ray grating spectra of single massive stars in significant ways and is generally consistent with colliding wind emission in a massive binary.
    Keywords: Astronomy
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
  • 2
    facet.materialart.
    Unknown
    Measurement of the small-scale structure of the intergalactic medium using close quasar pairs (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-04-28
    Description: The distribution of diffuse gas in the intergalactic medium (IGM) imprints a series of hydrogen absorption lines on the spectra of distant background quasars known as the Lyman-α forest. Cosmological hydrodynamical simulations predict that IGM density fluctuations are suppressed below a characteristic scale where thermal pressure balances gravity. We measured this pressure-smoothing scale by quantifying absorption correlations in a sample of close quasar pairs. We compared our measurements to hydrodynamical simulations, where pressure smoothing is determined by the integrated thermal history of the IGM. Our findings are consistent with standard models for photoionization heating by the ultraviolet radiation backgrounds that reionized the universe.
    Keywords: Astronomy
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 3
    facet.materialart.
    Unknown
    The ROSAT variable sky (1996)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The spectral and timing characteristics from a sample, of 91 objects, of the variable sources obtained using the Kolmogorov-Smirnov test technique are presented. The data were extracted from the catalog constructed by White, Giommi and Angelini, the WGACAT, based on the pointed observations from the Rosat missions. The application of the test revealed more than 2400 individual variable candidates, with 'sq chi' greater than 12. The sample of these variable sources, mostly unidentified, probably contains many flare stars, a few cataclysmic variables and a possible transient source.
    Keywords: Astronomy
    Type: ; 645-646
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
  • 4
    facet.materialart.
    Unknown
    Iron K Line Variability in the Low-Luminosity AGN NGC 4579 (2000)
    In:  CASI
    Details
    Publication Date: 2009-11-16
    Description: We present results of new ASCA observations of the low-luminosity AGN (LLAGN) NGC 4579 obtained in 1998 December 18 and 28, and we report on detection of variability of an iron K emission line. The X-ray luminosities in the 2-10 keV band for the two observations are nearly identical, L(sub X) approximately = 2 x 10(exp 4l) ergs/s, but they are approximately 35% larger than that measured in 1995 July by Terashima et al. (1998). An Fe K emission line is detected at 6.39 +/- 0.09 keV (source rest frame) which is lower than the line energy 6.73(sup +0.13, sub -0.12) keV in the 1995 observation. If we fit the Fe lines with a blend of two Gaussians centered at 6.4 keV and 6.73 KeV, the intensity of the 6.7 keV line decreased, while the intensity of the 6.4 keV line increased, within an interval of 3.5 years. This variability rules out thermal plasmas in the host galaxy as the origin of the ionized Fe line in this LLAGN. The detection and variability of the 6.4 keV line suggest that an optically thick standard accretion disk is present and subtends a large solid angle viewed from the nucleus at the Eddington ratio of L(sub Bol)/L(sub Eddington) approximately 2 x 10(exp -3) (Ho 1999). A broad disk-line profile is not clearly seen and the structure of the innermost part of accretion disk remains unclear.
    Keywords: Astronomy
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
  • 5
    facet.materialart.
    Unknown
    Mapping the X-Ray-Emitting Ejecta in Cassiopeia A with Chandra (2000)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: We present X-ray emission-line equivalent width images of the bright Galactic supernova remnant Cassiopeia A for the elements Si, S, Ar, Ca, and Fe using a 50,000 s observation with the Advanced CCD Imaging Spectrometer on the Chandra X-Ray Observatory. The images essentially map the bulk of detectable ejecta of these elements over a wide range of surface brightnesses and show morphologies distinctly different from that of the broadband X-ray emission and the 4-6 keV continuum emission. The Si, S, Ar, and Ca maps, while different in turn from those of Fe, are similar to the distribution of fast optical ejecta knots in that they clearly delineate the X-ray counterpart of the northeast optical jet. Low surface brightness regions just outside the bright shell in the north and west are also shown to have strong line emission. The strong Fe emission is exterior to that of other elements in the east, as previously noted, but is generally coincident elsewhere. The projected interior has relatively little emission traced by high line equivalent widths.
    Keywords: Astronomy
    Type: The Astrophysical Journal; Volume 537; L119-L122
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
  • 6
    facet.materialart.
    Unknown
    Discovery of a Second High-Frequency Quasi-Periodic Oscillation from the Microquasar GRS 1915+105 (2001)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: We report the discovery in archival Rossi X-Ray Timing Explorer data of a approx. 40 Hz quasi-periodic oscillation QPO) in the hard X-ray flux from the Galactic microquasar GRS 1915+105. The QPO is detected only in the hard X-ray band above approx. 13 keV and was discovered in observations in which the previously known 67 Hz QPO is present. The 40 Hz QPO has a typical rms amplitude of approx. 2% in the 13-27 keV band and a width of approx. 5.5 Hz (FWHM). We show that the 67 and 40 Hz QPOs are detected in the same observations in 1997 July and November. However, the QPO is not detected in observations from 1996 April, May, and June in which the 67 Hz QPO was first discovered. The frequency of the 67 Hz QPO is significantly higher in the 1997 observations by about 5% compared with the 1996 data. The identification of the 40 Hz QPO makes GRS 1915 + 105 the second black hole binary to show a pair of simultaneous high-frequency QPOs (the other being GRO J1655-40). The similarities between the properties of the 67 Hz QPO in GRS 1915+105 and the recently discovered 450 Hz QPO in GRO J1655-40 suggest that the pairs of frequencies in these systems may be produced by the same physical mechanism, with the frequency differences between the two being likely due to different black hole masses in the two systems. We discuss the implications of our result for the mass and spin of GRS 1915+105 as well as for models of X-ray variability in black holes and neutron stars.
    Keywords: Astronomy
    Type: Astronomical Journal; Volume 554; L169-L172
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
  • 7
    facet.materialart.
    Unknown
    Bulk X-ray Doppler Velocities in the Supernova Remnant Cassiopeia A (2002)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: We map the average line-of-sight velocities of the X-ray-emitting mass in the supernova remnant Cassiopeia A using measurements of the centroid of the Si-Healpha blend with the Advanced CCD Imaging Spectrometer on the Chandra X-Ray Observatory. This 4 inch scale map confirms the broad trends noted in previous studies, namely, that the line-of-sight velocity scale is roughly 2000-3000 kilometers per second with relatively more blueshifted material in the southeastern region of the remnant than in the northwest; new details are that the northwestern region consists of two arcs, with the southernmost one representing the most redshifted X-ray-emitting material in Cas A. These results are consistent with contemporaneous results from XMM-Newton. The X-ray patterns resemble the complex velocity patterns measured at optical wavelengths for much denser ejecta, and they support the growing body of evidence that the explosion and subsequent evolution of Cas A were highly asymmetrical.
    Keywords: Astronomy
    Type: The American Astrophysical Society; Volume 560; L175-L179
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
  • 8
    facet.materialart.
    Unknown
    Pulsar Polar Cap Heating and Surface Thermal X-ray Emission (2002)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: We investigate the effect of pulsar polar cap (PC) heating produced by positrons returning from the upper pair formation front. Our calculations are based on a self-consistent treatment of the pair dynamics and the effect of electric field screening by the returning positrons. We calculate the resultant X-ray luminosities and discuss the dependence of the PC heating efficiencies on pulsar parameters, such as characteristic spin-down age, spin period, and surface magnetic field strength. In this study we concentrate on the regime where the pairs are produced in a magnetic field by curvature photons emitted by accelerating electrons. Our theoretical results are not in conflict with the available observational x-ray data and suggest that the effect of PC heating should significantly contribute to the thermal x-ray fluxes from middle-aged and old pulsars. The implications for current and future x-ray observations of pulsars are briefly outlined.
    Keywords: Astronomy
    Type: The Astrophysical Journal; Volume 556; 987-1001
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
  • 9
    facet.materialart.
    Unknown
    The High Throughput X-ray Spectroscopy (HTXS) Mission (1997)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: The HTXS mission concept combines large effective area (approximately 15,000 sq cm at 1 keV), high spectral resolution (E/Delta(E) approximately 300-3000), and broad energy bandpass (0.25-40 keV and possibly up to 100 keV) by using replicated optics together with a complement of spectroscopic instrumentation including reflection gratings readout by charge-coupled device detectors (CCDs), quantum micro-calorimeters, and cadmium zinc telluride (CZT) or comparable high energy detectors. An essential feature of this concept involves minimization of cost (approximately $350M for development and approximately $500-600M including launches) and risk by building six identical modest satellites to achieve the large area. Current mission and technology studies are targeted towards a new start in the 2002 timeframe, with first launch around 2005-2006. The HTXS mission represents a major advance, providing as much as a factor of 100 increase in sensitivity over currently planned high resolution X ray spectroscopy missions. HTXS will mark the start of a new era when high quality X ray spectra will be obtained for all classes of X ray sources, over a wide range of luminosity and distance. With its increased capabilities, HTXS will address many fundamental astrophysics questions such as the origin and distribution of the elements from carbon to zinc, the formation and evolution of clusters of galaxies, the validity of general relativity in the strong gravity limit, the evolution of supermassive black holes in active galactic nuclei, the details of supernova explosions and their aftermath, and the mechanisms involved in the heating of stellar coronae and driving of stellar winds.
    Keywords: Astronomy
    Type: The Next Generation of X-Ray Observatories; 173-189; XRA97/02
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
  • 10
    facet.materialart.
    Unknown
    X-Ray Probes of Cosmic Star-Formation History (2001)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: In a previous paper we point out that the X-ray luminosity L(sub x) of a galaxy is driven by the evolution of its X-ray binary population and that the profile of L(sub x) with redshift can both serve as a diagnostic probe of the Star Formation Rate (SFR) profile and constrain evolutionary models for X-ray binaries. We update our previous work using a suite of more recently developed SFR profiles that span the currently plausible range. The first Chandra deep imaging results on L(sub x)-evolution are beginning to probe the SFR profile of bright spirals and the early results are consistent with predictions based on current SFR models. Using these new SFR profiles the resolution of the "birthrate problem" of lowmass X-ray binaries (LMXBs) and recycled, millisecond pulsars in terms of an evolving global SFR is more complete. We also discuss the possible impact of the variations in the SFR profile of individual galaxies.
    Keywords: Astronomy
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...