Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...419...66m&link_type=abstract
Astrophysical Journal v.419, p.66
Astronomy and Astrophysics
Astronomy
30
X-Rays: Galaxies
Scientific paper
The cluster of galaxies A2256 was observed with BBXRT (Broad Band X-ray Telescope) during the Astro 1 mission with a total exposure of ˜4000 s. Moderate resolution spectra of parts of this cluster of galaxies give information complementary to the high spatial resolution observation of the same cluster by ROSAT. ROSAT spectral images (Briel et al.) have shown evidence of a merger with the northwest clump being cooler than the main cluster body. The BBXRT spectra also show an indication of a lower temperature [kT = 4.6(+0.9, -0.7) keV, 90% confidence errors] in the same general area. The BBXRT data from other regions within 10' from the center show temperatures (T ˜ 7 keV) consistent with the Ginga overall average and constrain the temperature gradient by limiting the polytropic index to γ = 1.10±0.35 (90% confidence errors).
We have detected absorption in excess of the galactic value in several regions of the cluster, similar to that seen in other clusters with the Einstein SSS. One of the observed regions shows an apparent oxygen edge absorption feature at 0.54 ≲ Eedge ≲ 0.62 keV with an edge optical depth of the order of unity. This range of edge energy corresponds to absorption by oxygen with ionization stage between O2+ and O4+. This suggests the existence of about 1012-1013 Msun of warm (T ˜ 0.5-5 × 105 K) absorbing gas. It is unlikely that this component has its origin in the hot intracluster gas, compressed by the shock waves generated in the cluster merging and subsequently cooled, because the cooling timescale of the postshock gas is too large. It may have originated from the cold gas in the subcluster cooling flow heated up by shock waves or ionized by radiation sources.
Using spatially resolved temperature information and absolute fluxes from the BBXRT data, along with core radius and the β-parameter of the modified King profile from the ROSAT PSPC data, we have obtained radial mass profiles of the X-ray emitting gas and the total gravitational mass. At r ˜0.8 h50-1 Mpc, the binding mass range is ˜2.8-3.7 × 1014 Msun for a range of models consistent with the BBXRT spectral data. This gives a total mass within ˜0.8 Mpc of about 5 times the mass of X-ray emitting gas. The total mass and gas fraction of the inner 1 Mpc of the cluster are very similar to those of the Coma Cluster.
Boldt Elihu A.
Holt Stephen S.
Jahoda Keith M.
Kelley Randall
Loewenstein Michael
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