206 research outputs found
Discovery of X-rays from Mars with Chandra
On 4 July 2001, X-rays from Mars were detected for the first time. The
observation was performed with the ACIS-I detector onboard Chandra and yielded
data of high spatial and temporal resolution, together with spectral
information. Mars is clearly detected as an almost fully illuminated disk, with
an indication of limb brightening at the sunward side, accompanied by some
fading on the opposite side. The morphology and the X-ray luminosity of ~4 MW
are fully consistent with fluorescent scattering of solar X-rays in the upper
Mars atmosphere. The X-ray spectrum is dominated by a single narrow emission
line, which is most likely caused by O-K_alpha fluorescence. No evidence for
temporal variability is found. This is in agreement with the solar X-ray flux,
which was almost constant during the observation. In addition to the X-ray
fluorescence, there is evidence for an additional source of X-ray emission,
indicated by a faint X-ray halo which can be traced to about three Mars radii,
and by an additional component in the X-ray spectrum of Mars, which has a
similar spectral shape as the halo. Within the available limited statistics,
the spectrum of this component can be characterized by 0.2 keV thermal
bremsstrahlung emission. This is indicative of charge exchange interactions
between highly charged heavy ions in the solar wind and exospheric hydrogen and
oxygen around Mars. Although the observation was performed at the onset of a
global dust storm, no evidence for dust-related X-ray emission was found.Comment: 11 pages, 16 figure
Deep XMM-Newton observation of a northern LMC field: I. Selected X-ray sources
First results from a deep XMM-Newton observation of a field in the Large Magellanic Cloud (LMC) near the northern rim of the supergiant shell LMC 4 are presented. Spectral and temporal analyses of a sample of selected X-ray sources yielded two new candidates for supernova remnants, a supersoft X-ray source and a likely high mass X-ray binary (HMXB) pulsar. From the fourteen brightest sources up to ten are active galactic nuclei in the background of the galaxy which can be used as probes for the interstellar medium in the LMC. From the three previously known HMXBs the Be/X-ray binary EXO 053109-6609.2 was the brightest source in the field, allowing a more detailed analysis of its X-ray spectrum and pulse profile. During the pulse EXO 053109-6609.2 shows eclipses of the X-ray emitting areas with increased photo-electric absorption before and after the eclipse. The detection of X-ray pulsations with a period of 69.2 s is confirmed for RX J0529.8-6556 and a possible period of 272 s is discovered from XMMU J053011.2-655122. The results are discussed with respect to individual sources as well as in the view of source population studies in the vicinity of the supergiant shell LMC 4
Multiwavelength appearance of Vela Jr.: Is it up to expectations?
Vela Jr. is one of the youngest and likely nearest among the known galactic
supernova remnants (SNRs). Discovered in 1997 it has been studied since then at
quite a few wavelengths, that spread over almost 20 decades in energy. Here we
present and discuss Vela Jr. properties revealed by these multiwavelength
observations, and confront them with the SNR model expectations. Questions that
remained unanswered at the time of publication of the paper of Iyudin et al.
(2005), e.g. what is the nature of the SNR's proposed central compact source
CXOU J085201.4-461753, and why is the ISM absorption column density apparently
associated with RX J0852.0-4622 much greater than the typical column of the
Vela SNR, can be addressed using the latest radio and X-ray observations of
Vela Jr.. These, and other related questions are addressed in the following.Comment: 8 pages, 7 figures. Accepted for publication in ESA SP-622,
Proceedings of the 6th INTEGRAL Workshop held in Moscow, Russia, July 02-08,
200
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.Comment: 4 pages, LaTex, 4 figures, Accepted for publication in A&A Letter
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