An X-ray spectroscopic search for dark matter in the Perseus cluster with Suzaku

We present the results from deep Suzaku observations of the central region of the Perseus cluster. Bulbul et al. (2014, ApJ, 789, 13) reported the detection by XMM-Newton instruments of an unidentified X-ray emission line at an energy around 3.5 keV in spectra for the Perseus and other clusters. They argued for a possibility of the decay of sterile neutrino, a dark matter candidate. We examine Suzaku X-ray Imaging Spectrometer (XIS) spectra of the Perseus cluster for evidence in the 3.5 keV line and other possible dark matter features in the 2-6 keV energy band. In order to search for and constrain a weak line feature with the XIS, observations of the Crab Nebula are used to evaluate the system's effective area. We found no line feature at the claimed position with a systematic line flux upper limit at a half (1.5 eV in line equivalent width) of the claimed best-fitting value by Bulbul et al. (2014). We discuss this inconsistency in terms of instrumental calibration errors and modeling of continuum emission. Future prospects for high-energy resolution spectroscopy with ASTRO-H are presented.