Suzaku broad-band spectroscopy of RX J1347.5–1145: constraints on the extremely hot gas and non-thermal emission

¹ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany e-mail: ota@mpe.mpg.de
² Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan
³ Saitama University, Shimo-Okubo 255, Sakura, Saitama 338-8570, Japan
⁴ Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan
⁵ The University of Texas at Austin, 2511 Speedway, RLM 15.306, Austin, TX 78712, USA
⁶ Tohoku University, Aramaki, Aoba, Sendai 980-8578, Japan
⁷ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁸ Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano 384-1805, Japan
⁹ The University of Tokyo, Tokyo 113-0033, Japan
¹⁰ Center for Computational Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan

Received: 5 May 2008
Accepted: 28 August 2008

Abstract

Context. We present the results of our analysis of long Suzaku observations (149 ks and 122 ks for XIS and HXD, respectively) of the most X-ray luminous galaxy cluster, RX J1347.5–1145, at .

Aims. To understand the gas physics of a violent, cluster merger, we study physical properties of the hot (~20 keV) gas clump in the south-east (SE) region discovered previously by Sunyaev–Zel'dovich (SZ) effect observations. Using hard X-ray data, a signature of non-thermal emission is also explored.

Methods. We perform single as well as multi-temperature fits to the Suzaku XIS spectra. The Suzaku XIS and HXD, and the Chandra ACIS-I data are then combined to examine the properties of the hot gas component in the SE region. We finally look for non-thermal emission in the Suzaku HXD data.

Results. The single-temperature model fails to reproduce the 0.5–10 keV continuum emission and Fe-K lines measured by XIS simultaneously. A two-temperature model with a very hot component improves the fit, although the XIS data can only provide a lower limit to the temperature of the hot component. In the Suzaku HXD data, we detect hard X-ray emission above the background in the 12–40 keV band at the 9σ level; however, the significance becomes marginal when the systematic error in the background estimation is included. With the joint analysis of the Suzaku and Chandra data, we determine the temperature of the hot gas in the SE region to be (statistical; 90% confidence level) (systematic; 90% confidence level) keV, which is in an excellent agreement with the previous joint analysis of the SZ effect in radio and the Chandra X-ray data. This is the first time that the X-ray analysis alone provides a good measurement of the hot component temperature in the SE region, which is possible because of Suzaku's unprecedented sensitivity over the wide X-ray band. These results indicate strongly that RX J1347.5–1145 has undergone a recent, violent merger. The spectral analysis shows that the SE component is consistent with being thermal. We measure the 3σ upper limit to the non-thermal flux, in the 12–60 keV band, which provides a limit on the inverse Compton scattering of relativistic electrons off the CMB photons. Combining this limit with the discovery of a radio mini halo in this cluster at 1.4 GHz, which measures the synchrotron radiation, we find a lower limit to the strength of the intracluster magnetic field, such that .