Rossi X-Ray Timing Explorer Spectrum of A2319

Details Rossi X-Ray Timing Explorer Spectrum of A2319 Rossi X-Ray Timing Explorer Spectrum of A2319

Feb 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002apj...565..877g&link_type=abstract

The Astrophysical Journal, Volume 565, Issue 2, pp. 877-882.

Astronomy and Astrophysics

Astronomy

25

Galaxies: Clusters: General, Galaxies: Clusters: Individual (A2319), Galaxies: Magnetic Fields, Radiation Mechanisms: Nonthermal

Scientific paper

The cluster of galaxies A2319 was observed in 1999 for ~160 ks by the PCA and HEXTE instruments aboard the Rossi X-Ray Timing Explorer (RXTE) satellite. No noticeable variability is seen in the emission measured by either instrument over the ~8 week observation. The quality of the data allows, for the first time, a meaningful search for emission whose spectral properties are distinct from those of the primary thermal emission with (previously measured) mean temperature in the range 8-10 keV. Fitting the RXTE data by a single thermal component, we obtain kT=8.6+/-0.1 (all errors are 90% confidence limits), a low iron abundance ZFe~0.16+/-0.02, and large positive residuals below 6 keV and between 15 to 30 keV. The quality of the fit is drastically improved if a second component is added. A two-temperature model yields kT1~=10.1+/-0.6, kT2~=2.8+/-0.6, and of ZFe~0.23+/-0.03, which is consistent with previously measured values. An equally good fit is obtained by a combination of a primary thermal and a secondary nonthermal component with kT~=8.9+/-0.6 and a power-law (photon) index α~=2.4+/-0.3. We have repeated the analysis by performing joint fits to both these RXTE measurements and archival ASCA data. At most, 25% of the RXTE secondary component could be present in the ASCA data. Allowing for this difference, very similar results were obtained with only somewhat different values for the temperature (kT=9.2+/-0.5) and power-law index (α~=2.5+/-0.3) in the latter model. The deduced value of α is consistent with the measured spectrum of extended radio emission in A2319. Identifying the power-law emission as Compton scattering of the radio-emitting electrons by the cosmic microwave background (CMB), we obtain B~0.1-0.3 μG for the volume-averaged magnetic field, and ~4×10-14(R/2Mpc)-3 ergs cm-3 for the mean energy density of the emitting electrons in the central region (radius R) of A2319.

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