Main-Cluster XIS0XIS1XIS3 Weighted mean Chandra Figure 2 : XIS spectra of the main-cluster XIS keV Main-Cluster Sub-Cluster Search for Bulk Motion in A2256 with Suzaku and ASTRO-H UEDA Shutaro HAYASHIDA Kiyoshi, NAGAI Masaaki, and TAWA Noriaki (Osaka University) UEDA Shutaro HAYASHIDA Kiyoshi, NAGAI Masaaki, and TAWA Noriaki (Osaka University) 3. Bulk Motion of the Hot Gas 4. ASTRO-H Simulation 1. Introduction Merging process plays a key role in evolution of clusters of galaxies. The nearby rich cluster A2256 is a well-studied example of merging clusters, showing 1) distinctive two peaks in the X-ray image 1), 2) two (or three) components in the radial velocity distribution of galaxies 2), 3) a cold front in the gas temperature map 3). If the merging event in A2256 is at its early stage, as was suggested by authors, the hot gas in the main-cluster and that in the sub-cluster may have different velocities by their bulk motions. We aim to measure those velocities from X-ray spectra observed with Suzaku XIS. A2256 is also known as one of the clusters in which non-thermal hard X-ray emission was detected with Beppo-SAX and RXTE 4),5). Furthermore, radio relic was observed in this cluster. These might be related to the merging event, in which non-thermal electrons are produced. Search for non-thermal emission with Suzaku XIS/HXD is also the purpose of our observation SXS Measurement of Turbulent Flow 2. Observation & Analysis Suzaku AO-1 observation of A2256 was performed on Nov , Exposure time was 96ks for the XIS and 97ks for the HXD. Unfortunately, since the observation was just after the XIS2 trouble on Nov 9, XIS2 was not available and the SCI was off for other three sensors during the observation. We re-processed the XIS data with the latest CALDB at , as the energy scale error is crucial for our analysis. We estimated Non-X-ray and Cosmic X-ray Background by utilizing the method we developed 6). MWH LHB CXB ICM Main-Cluster Weighted mean XIS0XIS1XIS3 Chandra Sub-Cluster 5. Summary Velocity Difference of km/s is detected between the X-ray emitting hot gas at the main-cluster and that at the sub-cluster. It supports the idea that A2256 is in the early stage of a merging event of (at least) two clusters. SXS simulations indicates the redshifts will be measured as accurate as a few tens km/s when we the turbulent velocity dispersion is 100km/s or less. If the turbulent velocity is as large as 10eV(~450km/s), the uncertainty in the bulk velocity gets larger but small enough for positive detection. The velocity dispersion itself will be measured with an accuracy of about 100km/s. As shown in Fig. 1, we extracted two circular regions (main-cluster, sub-cluster), each with 2.5’ radius. The spectra were fitted with APEC model for the ICM component, with particular focus on the redshifts determined in the fits. Although detailed examinations on the systematic errors will be reported in our upcoming paper, we confirmed that the results are consistent with/without additional corrections to the CCD energy scale. Statistically significant difference of the redshifts in the main and the sub is found, and its direction is consistent with that measured for optical galaxies. References 1)Briel, U.G. et al. 1991, A&A, 246, L10 2)Berrington, R.C., Lugger, P., & Cohn, H.N. 2002, AJ, 123, )Sun, M. et al. 2002, ApJ, 565, 867 4)Fusco-Femiano, R., Landi, R., & Orkandini, M., 2005 ApJ, L69 5)Rephaeli, Y., & Gruber, D.E. 2003, ApJ, 595, 137 6)Tawa, N. et al. 2008, PASJ, 60 S11-S SXS Simulation of Bulk Motion in A2256 Optical galaxies (Berrington et al., 2002) Redshift Difference of x10 -2 (Velocity Difference of km/s )is detected between the hot gas in the main-cluster and that in the sub-cluster. (Errors are 90%CL. We have not yet corrected for the PSF leakage between the two regions.) APEC model kT= keV Z= Sub-Cluster MWH LHB CXB ICM APEC model kT= keV Z= SXS Simulation (APEC model) We performed SXS simulation by utilizing response file(SXS baseline design, FWHM is 7eV) that is distributed with ASTRO-H official website. The exposure time is set as 78ks. We normalized the count rate of SXS by referring the spectral fits with XIS; the count rate of SXS is ~0.4 cts/s for the entire energy band and 2.2x10 -3 cts/s in the iron lines. This simulation indicates the redshfits are determined with accuracy of a few tens km/s, enough for our pourpose. Note, however, that the extract region of the SXS (3’x3’) is much smaller than the regions for the XIS shown in Fig.1.. We further consider the spectral model in which turbulent motion of the gas is not negligible. Specifically, we convolve the APEC model with gsmooth model. It is found that the SXS can measure the velocity dispersions with an accuracy of a few eV, i.e., 100km/s. Even with the turbulent velocity of 10eV(~450km/s), the redshift difference between the main and the sub clusters will be detected significantly. Optical galaxies Chandra results from Sun et al., 2002 Chandra results from Sun et al., 2002 Turbulent flow:2eV(~90km/s)Turbulent flow:10eV(~450km/s) SXS Simulation (APEC convolved with gsmooth) He-like Iron line ~2.6x10 -3 cts/s He-like Iron line ~3.0x10 -3 cts/s Figure1 : XIS image of A2256 Figure 3 : XIS spectra of the sub-cluster Figure 4 : Redshift Difference between main and sub clusters SXS Simulation Suzaku XIS Fig 5 : XIS spectrum in 6-8keV Fig 6 : SXS spectrum in among 6- 8keV Table 1: Redshifts obtained with XIS and SXS Figure 7 : SXS simulations in which turbulent flow is taken into account Redshift [ x10 -2 ] mainsub XIS SXS Velocity Difference [km/s] XIS SXS He-like Iron line ~2.2x10 -3 cts/s Fig 8 : Redshift obtained in SXS simulations Fig 9 : Turbulent velocity obtained in SXS simulations Velocity Difference [km/s] XIS SXS(0eV) SXS(2eV) SXS(10eV) Table 2: Redshifts obtained with SXS simulation