arXiv subjects

B. Aschenbach

Publications and source records attributed to B. Aschenbach.

At least 37 records · Page 2Linked to original sources

arXiv2003

XMM-Newton observation of the brightest X-ray flare detected so far from SgrA*

We report the high S/N observation on October 3, 2002 with XMM-Newton of the brightest X-ray flare detected so far from SgrA* with a duration shorter than one hour (~ 2.7 ks). The light curve is almost symmetrical with respect to the peak flare, and no significant difference between the soft and hard X-ray range is detected. The overall flare spectrum is well represented by an absorbed power-law with a soft photon spectral index of Gamma=2.5+/-0.3, and a peak 2-10 keV luminosity of 3.6 (+0.3-0.4) x 10^35 erg/s, i.e. a factor 160 higher than the Sgr A* quiescent value. No significant spectral change during the flare is observed. This X-ray flare is very different from other bright flares reported so far: it is much brighter and softer. The present accurate determination of the flare characteristics challenge the current interpretation of the physical processes occuring inside the very close environment of SgrA* by bringing very strong constraints for the theoretical flare models.

astro-ph↗

arXiv2003

XMM-Newton observation of SN1993J in M81

In April 2001 SN1993J was observed with both the PN and MOS cameras of the XMM-Newton observatory, resulting in about 7. x 10^4 s of acceptable observation time. Fit results with both the PN and MOS2 camera spectra studying different spectral models are presented. The spectra are best fitted in the energy range between 0.3 and 11 keV by a 2-component thermal model with temperatures of kT_1 = 0.34+-0.04 keV and kT_2 = 6.54+-4 keV, adopting ionization equilibrium. A fit with a shock model also provides acceptable results. Combining the XMM-Newton data with former X-ray observations of the supernova, we discuss the general trend of L_x propto t^{-0.30} and the bump of the X-ray light curve as well as former and recent spectral results in the light of the standard SN model as first proposed by Chevalier in 1982.

astro-ph↗

arXiv2003

X-ray Observations of Neutron Stars and Pulsars: First Results from XMM-Newton

The X-ray Multi-Mirror Mission XMM-Newton is ESA's largest observatory so far; it is dedicated to explore the Universe in the 0.2 - 15 keV X-ray band of the electromagnetic spectrum. Because of its large collecting area very faint sources not accessible before can be observed and it is therefore the long awaited instrument to study young pulsars and neutron stars in supernova remnants, cooling neutron stars and millisecond pulsars at X-ray energies. The high throughput of the instruments, which all are operated simultaneously, provide high resolution spectral, spatial and temporal information from a source during a single observation and make XMM-Newton unique and best suited for pulsar studies. In this article we briefly describe the instrument capabilities useful for pulsar observations and provide information on the timing accuracy on the relative and absolute scale. We further provide scientific results from observations of the Crab-pulsar, PSR J1617-5055 near RCW 103, of young neutron stars in the supernova remnants RX J0852-4622, Puppis-A and RCW 103 including 1E161348-5055.1 which is identified to be the second binary in a supernova remnant. In addition we report on observations of the cooling neutron star PSR B1055-52 and on the millisecond pulsar PSR J0030+0451 which all were observed by XMM-Newton during the first two years of scientific operation.

astro-ph↗

arXiv2002

X-rays from Supernova Remnants

A summary of X-ray observations of supernova remnants is presented including the explosion fragment A of the Vela SNR, Tycho, N132D, RX J0852-4622, the Crab Nebula and the 'bulls eye', and SN 1987A, high-lighting the progress made with Chandra and XMM-Newton and touching upon the questions which arise from these observations and which might inspire future research.

astro-ph↗

arXiv2002

Simultaneous X-ray spectroscopy of YY Gem with Chandra and XMM-Newton

We report on a detailed study of the X-ray spectrum of the nearby eclipsing spectroscopic binary YY Gem. Observations were obtained simultaneously with both large X-ray observatories, XMM-Newton and Chandra. We compare the high-resolution spectra acquired with the Reflection Grating Spectrometer onboard XMM-Newton and with the Low Energy Transmission Grating Spectrometer onboard Chandra, and evidence in direct comparison the good performance of both instruments in terms of wavelength and flux calibration. The strongest lines in the X-ray spectrum of YY Gem are from oxygen. Oxygen line ratios indicate the presence of a low-temperature component (1-4 MK) with density n_e < 2 10^{10} cm^-3. The X-ray lightcurve reveals two flares and a dip corresponding to the secondary eclipse. An increase of the density during phases of high activity is suggested from time-resolved spectroscopy. Time-resolved global fitting of the European Photon Imaging Camera CCD spectrum traces the evolution of temperature and emission measure during the flares. These medium-resolution spectra show that temperatures > 10^7 K are relevant in the corona of YY Gem although not as dominant as the lower temperatures represented by the strongest lines in the high-resolution spectrum. Magnetic loops with length on the order of 10^9 cm, i.e., about 5 % of the radius of each star, are inferred from a comparison with a one-dimensional hydrodynamic model. This suggests that the flares did not erupt in the (presumably more extended) inter-binary magnetosphere but are related to one of the components of the binary.

astro-ph↗

arXiv2002

Chandra Observation of SNR G54.1+0.3 -- a Close Cousin of the Crab Nebula

We present a {\it Chandra} ACIS observation of SNR G54.1+0.3. This supernova remnant is resolved into several distinct X-ray emitting components: a central bright point-like source (CXOU J193030.13+185214.1), a surrounding ring, bipolar elongations, plus low surface brightness diffuse emission. The spectra of these components are all well described by power-law models; the spectral index steepens with increasing distance from the point-like source. We find no evidence for any thermal plasma emission that would correspond to shocked interstellar medium or ejecta. The observed morphological and spectral characteristics suggest that G54.1+0.3 is the closest ``cousin'' of the Crab Nebula -- a pulsar wind nebula driven by a combination of equatorial and polar outflows from the putative pulsar represented by the point-like X-ray source.

astro-ph↗

arXiv2001

The XMM-Newton Serendipitous Survey. II. First results from the AXIS high galactic latitude medium sensitivity survey

We present the first results on the identifications of a medium sensitivity survey (X-ray flux limit 2E-14 erg/cm2/s in the 0.5-4.5 keV band) at high galactic latitude (|b|>20 deg) carried out with the XMM-Newton X-ray observatory within the AXIS observing programme. This study is being conducted as part of the XMM-Newton Survey Science Centre activities towards the identification of the sources in the X-ray serendipitous sky survey. The sample contains 29 X-ray sources in a solid angle of 0.26deg2 (source density 113 +/- 21 sources/deg2), out of which 27 (93%) have been identified. The majority of the sources are broad-line AGN (19), followed by narrow emission line X-ray emitting galaxies (6, all of which turn out to be AGN), 1 nearby non-emission line galaxy (NGC 4291) and 1 active coronal star. Among the identified sources we find 2 broad-absorption line QSOs (z~1.8 and z~1.9), which constitute ~10% of the AGN population at this flux level, similar to optically selected samples. Identifications of a further 10 X-ray sources fainter than our survey limit are also presented.

astro-ph↗

arXiv2001

In-orbit performance of the XMM-Newton X-ray telescopes: images and spectra

The performance of the three X-ray telescopes on-board of XMM-Newton is evaluated addressing imaging characteristics and effective collecting area. The agreement with ground calibration data is excellent. The analysis of images and spectra of cosmic X-ray sources, emphazising supernova and supernova remnants, prooves that the telescopes are even better than originally required.

astro-ph↗

arXiv2001

Nonthermal X-Ray Emission from G266.2-1.2 (RX J0852.0-4622)

The newly discovered supernova remnant G266.2-1.2 (RX J0852.0-4622), along the line of sight to the Vela SNR, was observed with ASCA for 120 ks. We find that the X-ray spectrum is featureless, and well described by a power law, extending to three the class of shell-type SNRs dominated by nonthermal X-ray emission. Although the presence of the Vela SNR compromises our ability to accurately determine the column density, the GIS data appear to indicate absorption considerably in excess of that for Vela itself, indicating that G266.2-1.2 may be several times more distant. An unresolved central source may be an associated neutron star, though difficulties with this interpretation persist.

astro-ph↗

arXiv2000

XMM-Newton observation of the Tycho Supernova Remnant

We present the observation of the Tycho supernova remnant obtained with the EPIC and RGS instruments onboard the XMM-Newton satellite. We compare images and azimuthally averaged radial profiles in emission lines from different elements (silicon and iron) and different transition lines of iron (Fe L and Fe K). While the Fe XVII L line and Si XIII K line images are globally spatially coincident, the Fe K emission clearly peaks at a smaller radius, indicating a higher temperature toward the reverse shock. This is qualitatively the profile expected when the reverse shock, after travelling through the outer power-law density profile, has entered the central plateau of the ejecta. The high energy continuum map has an overall smooth distribution, with a similar extent to the radio emission. Its radial profile peaks further out than the lines emission. Brighter and harder continuum regions are observed with a rough bipolar symmetry in the eastern and western edges. The spectral analysis of the southeastern knots supports spatial variations of the relative abundance of silicon and iron, which implies an incomplete mixing of the silicon and iron layers.

astro-ph↗

arXiv2000

The first broad-band X-ray images and spectra of the 30 Doradus region in the LMC

We present the XMM-Newton first light image, taken in January 2000 with the EPIC pn camera during the instrument's commissioning phase, when XMM-Newton was pointing towards the Large Magellanic Cloud (LMC). The field is rich in different kinds of X-ray sources: point sources, supernova remnants (SNRs) and diffuse X-ray emission from LMC interstellar gas. The observations are of unprecedented sensitivity, reaching a few 10^32 erg/s for point sources in the LMC. We describe how these data sets were analysed and discuss some of the spectroscopic results. For the SNR N157B the power law spectrum is clearly steeper than previously determined from ROSAT and ASCA data. The existence of a significant thermal component is evident and suggests that N157B is not a Crab-like but a composite SNR. Most puzzling is the spectrum of the LMC hot interstellar medium, which indicates a significant overabundance of Ne and Mg of a few times solar.

astro-ph↗

arXiv2000

AGN in the XMM-Newton first-light image as probes for the interstellar medium in the LMC

The XMM-Newton first-light image revealed X-ray point sources which show heavily absorbed power-law spectra. The spectral indices and the probable identification of a radio counterpart for the brightest source suggest AGN shining through the interstellar gas of the Large Magellanic Cloud (LMC). The column densities derived from the X-ray spectra in combination with HI measurements will allow to draw conclusions on HI to H_2 ratios in the LMC and compare these with values found for the galactic plane.

astro-ph↗

arXiv2000

Cassiopeia A: on the origin of the hard X-ray continuum and the implication of the observed O VIII Ly-alpha/Ly-beta distribution

We present the first results on the hard X-ray continuum image (up to 15 keV) of the supernova remnant Cas A measured with the EPIC cameras onboard XMM-Newton. The data indicate that the hard X-ray tail, observed previously, that extends to energies above 100 keV does not originate in localised regions, like the bright X-ray knots and filaments or the primary blast wave, but is spread over the whole remnant with a rather flat hardness ratio of the 8-10 and 10-15 keV energy bands. This result does not support an interpretation of the hard X-radiation as synchrotron emission produced in the primary shock, in which case a limb brightened shell of hard X-ray emission close to the primary shock front is expected. In fact a weak rim of emission near the primary shock front is discernable in the hardest X-ray image but it contains only a few percent of the hard X-ray emissivity. The equivalent width of the Fe-K line blend varies by more than an order of magnitude over the remnant, it is hard to explain this as Fe-emission from the reverse shock heated ejecta given the ejecta temperature and the age of the remnant. The uniquely high wavelength-dispersive RGS-spectrometer has allowed, for the first time, to extract monochromatic images in several highly ionised element species with high spectral resolution. We present here a preliminary result on the measurement of the O VIII Ly-alpha and Ly-beta brightness distribution and brightness ratios. The large observed decrease of the Ly-alpha/Ly-beta ratio going from the N to the SE can be explained by small-scale (10 arcsec) variations in the N_H column over the remnant and the potential presence of resonance scattering of the O VIII Ly-alpha photons in the limb brightened shell.

astro-ph↗

arXiv2000

The X-ray Spectrum and Light Curve of Supernova 1995N

We report on multi-epoch X-ray observations of the Type IIn (narrow emission line) supernova SN 1995N with the ROSAT and ASCA satellites. The January 1998 ASCA X-ray spectrum is well fitted by a thermal bremsstrahlung (kT~10 keV, N_H~6e20 cm^-2) or power-law (alpha~1.7, N_H~1e21 cm^-2) model. The X-ray light curve shows evidence for significant flux evolution between August 1996 and January 1998: the count rate from the source decreased by 30% between our August 1996 and August 1997 ROSAT observations, and the X-ray luminosity most likely increased by a factor of ~2 between our August 1997 ROSAT and January 1998 ASCA observations, although evolution of the spectral shape over this interval is not ruled out. The high X-ray luminosity, L_X~1e41 erg/sec, places SN 1995N in a small group of Type IIn supernovae with strong circumstellar interaction, and the evolving X-ray luminosity suggests that the circumstellar medium is distributed inhomogeneously.

astro-ph↗

arXiv2000

Imaging Performance of the XMM-Newton X-ray telescopes

The in-orbit imaging performance of the three X-ray telescopes on board of the X-ray astronomy observatory XMM-Newton is presented and compared with the performance measured on ground at the MPE PANTER test facility. The comparison shows an excellent agreement between the on ground and in-orbit performance.

astro-ph↗

arXiv2000

X-ray observations of supernova remnant G54.1+0.3: X-ray spectrum and the discovery of an X-ray jet

We present in this paper analyses of the $ROSAT$ PSPC and $ASCA$ SIS and GIS observations of the Crab-like supernova remnant (SNR) G54.1+0.3. Its spectrum obtained by $ROSAT$ PSPC favors a power law model with a photon index of -0.8$^{+0.8}_{-2.0}$, absorbed energy flux in 0.1-2.4 keV of 1.0$\times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$, and absorption column density of 12.3$^{+8.0}_{-3.2}\times 10^{21}$ cm$^{-2}$. $ASCA$ SIS observation shows that its spectrum can also be best fitted with power law model. The fitted parameters are, photon index -1.9$^{+0.1}_{-0.2}$, absorbed energy flux in 0.7-2.1 keV 6.5$\times10^{-13}$ erg cm$^{-2}$ s$^{-1}$, and column density 17.9$^{+2.8}_{-2.5}\times 10^{21}$ cm$^{-2}$. The high absorption column density indicates a distance similar to the radius of the galaxy. The 0.1-2.4 keV X-ray luminosity of G54.1+0.3 is 3.2$\times10^{33}$$d_{10}^2$ erg s$^{-1}$, where $d_{10}$ is the distance in 10 kpc. With an image restoration method we have obtained high spatial resolution X-ray image of the remnant, which clearly shows an X-ray jet pointing to the northeast with a length about 40$\arcsec$ from the center of the nebula. Its X-ray luminosity in 0.1-2.4 keV is about 5.1$\times10^{32}$$d_{10}^2$ erg s$^{-1}$. The X-ray jet is consistent with the radio extension to the northeast in both direction and position. We propose that the X-ray jet is connected with the pulsar assumed to exist in the remnant.

astro-ph↗

arXiv1999

The Compact Central Object in Cas A: A Neutron Star with Hot Polar Caps or a Black Hole?

The central pointlike X-ray source of the Cas A supernova remnant was discovered in the Chandra First Light Observation and found later in the archival ROSAT and Einstein images. The analysis of these data does not show statistically significant variability of the source. The power-law fit yields the photon index 2.6-4.1, and luminosity (2-60)e34 erg/s, for d=3.4 kpc. The power-law index is higher, and the luminosity lower, than those observed fromvery young pulsars. One can fit the spectrum equally well with a blackbody model with T=6-8 MK, R=0.2-0.5 km, L=(1.4-1.9)e33 erg/s. The inferred radii are too small, and the temperatures too high, for the radiationcould be interpreted as emitted from the whole surface of a uniformly heated neutron star. Fits with the neutron star atmosphere models increase the radius and reduce the temperature, but these parameters are still substantially different from those expected for a young neutron star. One cannot exclude, however, that the observed emission originates from hot spots on a cooler neutron star surface. Because of strong interstellar absorption, the possible low-temperature component gives a small contribution to the observed spectrum; an upper limit on the (gravitationally redshifted) surface temperature is < 1.9-2.3 MK. Amongst several possible interpretations, we favor a model of a strongly magnetized neutron star with magnetically confined hydrogen or helium polar caps on a cooler iron surface. Alternatively, the observed radiation may be interpreted as emitted by a compact object (more likely, a black hole) accreting from a fossil disk or from a late-type dwarf in a close binary.

astro-ph↗

arXiv1999

Spectroscopic Study of the Vela-Shrapnel

Several shrapnels have been detected in the vicinity of Vela SNR by the ROSAT all-sky survey. We present here the spectral properties of shrapnel `A' observed with the ASCA satellite. A prominent Si-K emission line with relatively weak emission lines from other elements have been detected, revealing that the relative abundance of Si is a few ten-times higher than those of other elements. Combining with the ROSAT PSPC results, we obtained the electron temperature, $kT_{\rm e}$, to be $0.33 \pm 0.01$ keV. The total mass of shrapnel `A' is estimated to be $\sim 0.01 M_\odot$. If it is an ejecta of a supernova explosion, the interstellar matter (ISM) would be swept up in the leading edge while the ejecta material would be peeled off in the trailing edge, which should be confirmed by future observations.

astro-ph↗