The O VII X-Ray Forest Toward Markarian 421: Consistency between XMM-Newton and Chandra

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Recently the first detections of highly ionized gas associated with two Warm-Hot Intergalactic Medium (WHIM) filaments have been reported. The evidence is based on X-ray absorption lines due to O VII and other ions observed by Chandra towards the bright blazar Mrk 421. We investigate the robustness of this detection by a re-analysis of the original Chandra LETGS spectra, the analysis of a large set of XMM-Newton RGS spectra of Mrk 421, and additional Chandra observations. We address the reliability of individual spectral features belonging to the absorption components, and assess the significance of the detection of these components. We ... continued below

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13 pages

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Kaastra, J.S.; Werner, N.; Herder, J.W.A.den; /SRON, Utrecht; Paerels, F.B.S.; /Columbia U., Astron. Astrophys. et al. April 28, 2006.

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Recently the first detections of highly ionized gas associated with two Warm-Hot Intergalactic Medium (WHIM) filaments have been reported. The evidence is based on X-ray absorption lines due to O VII and other ions observed by Chandra towards the bright blazar Mrk 421. We investigate the robustness of this detection by a re-analysis of the original Chandra LETGS spectra, the analysis of a large set of XMM-Newton RGS spectra of Mrk 421, and additional Chandra observations. We address the reliability of individual spectral features belonging to the absorption components, and assess the significance of the detection of these components. We also use Monte Carlo simulations of spectra. We confirm the apparent strength of several features in the Chandra spectra, but demonstrate that they are statistically not significant. This decreased significance is due to the number of redshift trials that are made and that are not taken into account in the original discovery paper. Therefore these features must be attributed to statistical fluctuations. This is confirmed by the RGS spectra, which have a higher signal to noise ratio than the Chandra spectra, but do not show features at the same wavelengths. Finally, we show that the possible association with a Ly{alpha} absorption system also lacks sufficient statistical evidence. We conclude that there is insufficient observational proof for the existence of the two proposed WHIM filaments towards Mrk 421, the brightest X-ray blazar on the sky. Therefore, the highly ionized component of the WHIM still remains to be discovered.

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13 pages

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  • Report No.: SLAC-PUB-11844
  • Grant Number: AC02-76SF00515
  • DOI: 10.2172/881780 | External Link
  • Office of Scientific & Technical Information Report Number: 881780
  • Archival Resource Key: ark:/67531/metadc885703

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  • April 28, 2006

Added to The UNT Digital Library

  • Sept. 21, 2016, 2:29 a.m.

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  • Dec. 6, 2016, 2:23 p.m.

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Kaastra, J.S.; Werner, N.; Herder, J.W.A.den; /SRON, Utrecht; Paerels, F.B.S.; /Columbia U., Astron. Astrophys. et al. The O VII X-Ray Forest Toward Markarian 421: Consistency between XMM-Newton and Chandra, report, April 28, 2006; [Menlo Park, California]. (digital.library.unt.edu/ark:/67531/metadc885703/: accessed August 19, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.