Comet 9P/Tempel 1 was observed by the Swift X-Ray Telescope (XRT) for a total of 250,024 s. Soft X-ray emission, 0.2-1.0 keV, was seen as a diffuse extended halo with an FWHM of 1.03 x 10 super(5) km ...centered on the comet's nucleus. The X-ray light curve indicates that the comet exhibited a prolonged soft X-ray outburst just after impact of the NASA Deep Impact (DI) spacecraft and enhanced X-ray activity lasted for 12 days. The radial brightness distribution and X-ray spectrum are in excellent agreement with a model of X-ray production in which highly charged minor heavy ion species in the solar wind undergo charge exchange reactions with water group or carbon dioxide group molecules in the neutral coma of the comet. Using this model, we derive a simple expression for the X-ray emission and show that the X-ray flare is, in part, due to an increase in solar wind flux at the comet but is largely due to an enhanced molecule production rate. Assuming that the main outgassing constituent was water, the comet produced (2.9 c 0.4) x 10 super(8) kg over the 12 day period postimpact. The quiescent water production was expected to inject 61.0 x 10 super(8) kg into the coma over the same period so the observed X-ray flux indicates that an additional (1.9 c 0.4) x 10 super(8) kg of water or, alternatively, (3.9 c 0.5) x 10 super(8)kg of carbon dioxide were liberated by the DI impact.
Context. Swift discovered the high redshift ( z =6.29) GRB 050904 with the Burst Alert Telescope (BAT) and began observing with its narrow field instruments 161 s after the burst onset. This ...gamma-ray burst is the most distant cosmic explosion ever observed. Because of its high redshift, the X-ray Telescope (XRT) and BAT simultaneous observations provide 4 orders of magnitude of spectral coverage (0.2-150 keV; 1.4-1090 keV in the source rest frame) at a very early source-frame time (22 s). The X-ray emission was monitored by the XRT up to 10 days after the burst. Aims. We present the analysis of BAT and XRT observations of GRB 050904 and a complete description of its high energy phenomenology. Methods. We performed time resolved spectral analysis and light curve modeling. Results. GRB 050904 was a long, multi-peaked, bright GRB with strong variability during its entire evolution. The light curve observed by the XRT is characterized by the presence of a long flaring activity lasting up to 1-2 h after the burst onset in the burst rest frame, with no evidence of a smooth power-law decay following the prompt emission as seen in other GRBs. However, the BAT tail extrapolated to the XRT band joins the XRT early light curve and the overall behavior resembles that of a very long GRB prompt. The spectral energy distribution softens with time, with the photon index decreasing from-1.2 during the BAT observation to-1.9 at the end of the XRT observation. The dips of the late X-ray flares may be consistent with an underlying X-ray emission arising from the forward shock and with the properties of the optical afterglow reported by Tagliaferri et al. (2005b, A&A, 443, L1). Conclusions. We interpret the BAT and XRT data as a single continuous observation of the prompt emission from a very long GRB. The peculiarities observed in GRB 050904 could be due to its origin within one of the first star-forming regions in the Universe; very low metallicities of the progenitor at these epochs may provide an explanation.
Warfare, whaling, and participation in long distance trade intensified in the Bering Strait region 600–1000 A.D. The development of complex social organization involved the control of resource hot ...spots from coastal promontories and access to iron from distant East Asian centers. Stylistic similarities, recognized as early as the 1920's, provide the basis to recognize peer polity interaction. Despite >800 excavated burials from Point Hope, St. Lawrence Island and East Cape (Siberia), only a variable data base is available for establishing contemporaneity, the extent of interaction, the functioning of societies and the intensity of warfare. Burials do show pronounced internal status differences at Point Hope and Ekven/Uelen at East Cape. Radiocarbon ages reveal a disjunct pattern in settlement histories; Cape Krusenstern settled most densely at 400–650 A.D., Point Hope at 400–900 A.D., while Ekven peaked between 800–1200 A.D. and at NW Cape, St. Lawrence Island, population was greatest between 1000 and 1200 A.D. The relationship of East Cape to Point Hope suggests a close alliance that dominated the Bering Strait region and controlled access to metal and technological innovations from East Asia. Physical evidence of warfare in burials is greater in the NW Cape area, but the extent and contemporaneity of conflict is uncertain. The Birnirk culture controlled only marginal locations, often in very close proximity to Ipiutak sites. The development of whaling is sporadically documented but appears associated with technological innovations in Old Bering Sea and Birnirk polities while the influence of Ipiutak was achieved without a reliance on whaling.
We present the results of the deepest optically identified X-ray survey yet made. The X-ray survey was obtained with the ROSAT position-sensitive proportional counter (PSPC) and reaches a flux limit ...of 1.6 × 10−15 erg cm−2 s−1 (0.5−2.0 keV). Above a flux limit of 2 × 10−15 erg cm−2 s−1 we define a complete sample of 70 sources, of which 59 are identified. For a further five sources we have tentative identifications and for a further four the X-ray error boxes are blank to R=23 mag. At brighter fluxes (≥10−14 erg cm−2 s−1) we confirm the results of previous less deep X-ray surveys, with 84 per cent of our sources being QSOs. However, at the faint flux limit the survey is dominated by a population of galaxies with narrow emission lines (NELGs). In addition, at intermediate fluxes we find a small number of groups and clusters of galaxies at redshifts generally > 0.3. Most of these groups are poor systems of low X-ray luminosity and the number that we find is consistent with a zero evolutionary scenario, unlike the situation for high-luminosity clusters at the same redshift. To a flux limit of 2 × 10−15 erg cm−2 s−1, QSOs contribute > 31 per cent of the cosmic soft X-ray background (XRB), groups/clusters contribute ~ 10 per cent and NELGs contribute ~ 8 per cent. However, the QSO differential source count slope below 10−14 erg cm−2 s−1 is ~ −1.4, severely sub-Euclidean, as is the (poorly defined) group/cluster slope, whereas the differential NELG slope is close to Euclidean ( ~ − 2.4). If the NELG source counts continue to rise at that slope, all of the remaining cosmic soft XRB will be explained by a flux limit of ~ 1−2 × 10~16 erg cm−2 s−1, with NELGs contributing about one quarter of the XRB. The average NELG X-ray spectrum is harder than that of the QSOs, and similar to that of the remaining unresolved cosmic XRB, suggesting that NELGs will also be substantial contributors to the XRB at higher energies. The observed NELGs lie in the redshift range 0.1−0.6 and have MR= − 20 to − 23, approximately 3 mag more luminous than typical field galaxies. They have predominantly blue colours, and some are definitely spirals, but the presence of some ellipticals cannot yet be ruled out. Many are in interacting or disturbed systems. The NELGs have optical spectra similar to those of the majority of the field galaxy population at a similar redshift and may simply be the more luminous members of the emission-line field galaxy population. Based on optical line ratios and X-ray/optical flux ratios, the NELGs, both as a sample and within individual galaxies, appear to be a mixture of starburst galaxies and true active galactic nuclei (AGN).
XMM-Newton RGS spectroscopy of LMC X-3 Page, M. J.; Soria, R.; Wu, K. ...
Monthly notices of the Royal Astronomical Society,
10/2003, Letnik:
345, Številka:
2
Journal Article
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We present soft X-ray spectroscopy of the black hole binary LMC X-3 from the XMM–Newton Reflection Grating Spectrometer. The observations span the full range of spectral states seen in LMC X-3. The ...spectra are completely dominated by continuum emission, and the neutral absorbing column measured from the Oi edge (NH= 3.8+0.8−0.7× 1020 cm−2) is consistent with the Galactic interstellar column density towards LMC X-3. We find no evidence for variability of the neutral absorbing column. We also constrain the ionized column density using the upper limits to the equivalent width of the Oii–Oviii K-shell resonance lines: we find that the equivalent hydrogen column density of gas in which O is partially ionized is < 8× 1020 cm−2. From this upper limit we can rule out a line-driven stellar wind as the power source for the X-ray emission of LMC X-3 except when it is faint. At wavelengths longward of the peak emission the spectral shape is well described by a multitemperature disc–blackbody spectrum; the power-law component, which dominates at shorter wavelengths, does not continue longward of the disc–blackbody peak. This implies that the multitemperature disc–blackbody component supplies the seed photons that are Compton upscattered in the hot corona, consistent with the standard paradigm for black hole X-ray binary spectral states.
Aims. X-ray sources at intermediate fluxes (a few times 10 super(-14) erg cm super(-2) s super(-1)) with a sky density of similar to 100 deg super(-2) are responsible for a significant fraction of ...the cosmic X-ray background at various energies below 10 keV. The aim of this paper is to provide an unbiased and quantitative description of the X-ray source population at these fluxes and in various X-ray energy bands. Methods. We present the XMM- Newton Medium sensitivity Survey (XMS), including a total of 318 X-ray sources found among the serendipitous content of 25 XMM-Newton target fields. The XMS comprises four largely overlapping source samples selected at soft (0.5-2 keV), intermediate (0.5-4.5 keV), hard (2-10 keV) and ultra-hard (4.5- 7.5 keV) bands, the first three of them being flux-limited. Results. We report on the optical identification of the XMS samples, complete to 85-95%. At the flux levels sampled by the XMS we find that the X-ray sky is largely dominated by Active Galactic Nuclei. The fraction of stars in soft X-ray selected samples is below 10%, and only a few per cent for hard selected samples. We find that the fraction of optically obscured objects in the AGN population stays constant at around 15-20% for soft and intermediate band selected X-ray sources, over 2 decades of flux. The fraction of obscured objects amongst the AGN population is larger ( similar to 35-45%) in the hard or ultra- hard selected samples, and constant across a similarly wide flux range. The distribution in X-ray-to-optical flux ratio is a strong function of the selection band, with a larger fraction of sources with high values in hard selected samples. Sources with X-ray-to-optical flux ratios in excess of 10 are dominated by obscured AGN, but with a significant contribution from unobscured AGN.
ABSTRACT
We present XMM–Newton observations of the eclipsing polar EP Dra that cover nearly three binary orbital cycles. The X‐ray and ultraviolet data show evidence for a prominent dip before the ...eclipse, which is due to the accretion stream obscuring the accretion region. The dip ingress is rapid in hard X‐rays, suggesting that there is a highly collimated core of absorption. We find that a different level of absorption column density is required to match the observed count rates in different energy bands. We propose that this is due to the fact that different absorption components should be used to model the reprocessed X‐rays, the shocked X‐ray component and the ultraviolet emission, and we explore the effect that this has on the resulting fits to the spectrum. Further, there is evidence that absorption starts to obscure the softer X‐rays shortly after the onset of the bright phase. This suggests that material is threaded by an unusually wide range of magnetic field lines, consistent with the recent suggestion of Bridge et al. We find that the period is slightly greater than that determined some years ago by Schwope & Mengel.
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