Addendum: ``Chandra X-Ray Imaging and Spectroscopy of the M87 Jet and Nucleus'' (ApJ, 568, 133 [2002])

Details Addendum: ``Chandra X-Ray Imaging and Spectroscopy of the M87 Jet and Nucleus'' (ApJ, 568, 133 [2002]) Addendum: ``Chandra X-Ray Imaging and Spectroscopy of the M87 Jet and Nucleus'' (ApJ, 568, 133 [2002])

Jul 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004apj...610..624w&link_type=abstract

The Astrophysical Journal, Volume 610, Issue 1, pp. 624-624.

Astronomy and Astrophysics

Astronomy

1

Errata, Addenda

Scientific paper

According to the Chandra Science Center (see ApJ, 568, 133 [2002]), an examination of archived astronomical observations and data acquired from the on-board ACIS calibration source (55Fe) on the Chandra X-ray Observatory shows that there has been a continuous degradation in the ACIS QE since launch. The best interpretation is that this is due to molecular contamination building up on the cold optical blocking filter and/or the CCD chips. This degradation is most severe at energies below 1 keV and becomes negligible above 2 keV.
This contamination was not known when the data reported in our paper on M87 was analyzed. Thus, absorption by these contaminants introduced errors into the X-ray spectra obtained for the nucleus and knots. Eric S. Perlman has rereduced the X-ray spectra using Sherpa, and A. S. W. has rereduced them using XSPEC, both workers taking absorption by the contaminants into account using the ACISABS software. As expected for this effect, the spectra reported in the original paper are too hard. The values of the photon indices, Γ, of the knots (given in col. [5], Table 2) are too small by, on average, 0.15-0.2. The largest error in Γ is ~=0.3.
This problem affects the scientific results in two ways:
(1) In § 3.2, the evidence for photoelectric absorption of soft X-rays from the nucleus in excess of that produced by the Galactic column is weakened, but not totally eliminated. In agreement with the original paper, the column density to all knots is in agreement with the Galactic column [NH(Gal)=2.5×1020 cm-2].
(2) In Figure 4 and § 4.2, we stated that ``in ... knots A, B, and probably D, the X-ray spectrum cannot be reproduced by extending the radio through optical fluxes with a spectrum having a monotonically increasing spectral index with increasing energy. In these cases, the spectrum must turn down above the optical and then flatten out to match the X-ray spectrum.'' This claim and the discussion of how such spectra might result are direct consequences of the too-hard X-ray spectra that we obtained, and are here withdrawn.
A more complete discussion of the Chandra X-ray observations of the jet of M87, and their relation to observations in other wavebands, will be presented elsewhere (E. S. Perlman & A. S. Wilson, in preparation).

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