The First MAXI/GSC Catalog in the High Galactic-Latitude
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PASJ: Publ. Astron. Soc. Japan , 1–??, c 2018. Astronomical Society of Japan. The First MAXI/GSC Catalog in the High Galactic-Latitude Sky Kazuo Hiroi,1 Yoshihiro Ueda,1 Naoki Isobe,1,2 Masaaki Hayashida,1 Satoshi Eguchi,1,3 Mutsumi Sugizaki,4 Nobuyuki Kawai,5 Hiroshi Tsunemi,6 Masaru Matsuoka,4,7 Tatehiro Mihara,4 Kazutaka Yamaoka,8 Masaki Ishikawa,9 Masashi Kimura,6 Hiroki Kitayama,6 Mitsuhiro Kohama,7 Takanori Matsumura,10 Mikio Morii,5 Yujin E. Nakagawa,11 Satoshi Nakahira,4 Motoki Nakajima,12 Hitoshi Negoro,13 Motoko Serino,4 Megumi Shidatsu,1 Tetsuya Sootome,4 Kousuke Sugimori,5 Fumitoshi Suwa,13 Takahiro Toizumi,5 Hiroshi Tomida,7 Yohko Tsuboi,10 Shiro Ueno,7 Ryuichi Usui,5 Takayuki Yamamoto,4 Kyohei Yamazaki,10 Atsumasa Yoshida,8 and the MAXI team 1Department of Astronomy, Kyoto University, Oiwake-cho, Sakyo-ku, Kyoto 606-8502 [email protected] 2Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA) ,3-1-1 Yoshino-dai, Chuo-ku, Sagamihara, Kanagawa 252-5210 3National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka City, Tokyo 181-8588 4MAXI team, Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198 5Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 6Department of Earth and Space Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 7ISS Science Project Office, Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505 8Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258 9School of Physical Science, Space and Astronautical Science, The graduate University for Advanced Studies (Sokendai), Yoshinodai 3-1-1, Chuo-ku, Sagamihara, Kanagawa 252-5210 10Department of Physics, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551 11Research Institute for Science and Engineering, Waseda University, 17 Kikui-cho, Shinjuku-ku, Tokyo 162-0044 12School of Dentistry at Matsudo, Nihon University, 2-870-1 Sakaecho-nishi, Matsudo, Chiba 101-8308 13Department of Physics, Nihon University, 1-8-14 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8308 (Received 2011 June 12; accepted 2011 August 13) Abstract We present the first unbiased source catalog of the Monitor of All-sky X-ray Image (MAXI) mission at high Galactic latitudes ( b > 10◦), produced from the first 7-month data (2009 September 1 to 2010 March 31) of the Gas Slit Camera| | in the 4–10 keV band. We develop an analysis procedure to detect faint sources from the MAXI data, utilizing a maximum likelihood image fitting method, where the image response, background, and detailed observational conditions are taken into account. The catalog consists of 143 X-ray sources above 7 sigma significance level with a limiting sensitivity of 1.5 10−11 ergs cm−2 s−1 (1.2 mCrab) in the 4–10 keV band. Among them, we identify 38 Galactic/LMC/SMC∼ × objects, 48 galaxy clusters, 39 Seyfert galaxies, 12 blazars, and 1 galaxy. Other 4 sources are confused with multiple objects, and one remains unidentified. The log N - log S relation of extragalactic objects is in a good agreement with the HEAO-1 A-2 result, although the list of the brightest AGNs in the entire sky has significantly arXiv:1108.5516v1 [astro-ph.HE] 29 Aug 2011 changed since that in 30 years ago. Key words: catalogs — surveys — galaxies: active — X-rays: galaxies 1. INTRODUCTION a primary product on which many subsequent studies are based. For extragalactic populations, in particular, these All-sky X-ray surveys are powerful tools to investigate results define the “local” sample in the present universe, the whole populations of active and hot phenomena in the end point of their cosmological evolution. Thus, to the universe at the brightest flux end. The strong X- establish the statistical properties of bright X-ray sources ray emitters include Galactic objects such as active stars, using the best quality data over the entire sky has always SNRs, pulsars, CVs, low mass and high mass X-ray bi- been a key issue in high energy astrophysics. naries (with a neutron star or a black hole as the pri- Past all-sky X-ray surveys indeed brought valuable in- mary), and extragalactic objects, mainly active galactic formation on the X-ray source populations. In the soft nuclei (AGNs; Seyfert galaxies and blazars) and clusters X-ray band, the ROSAT mission conducted an all-sky sur- of galaxies. The source catalog consisting of a statistically vey in the 0.1–2.4 keV band, producing the ROSAT All- well-defined sample detected from an unbiased survey is Sky Survey (RASS) Bright Source Catalog (BSC; Voges 2 K. Hiroi et al. [Vol. , et al. 1999) and Faint Source Catalog (FSC; Voges et al. relations. Section 5 gives the conclusion. The analysis of 2000), which contain 18,811 and 105,924 sources, respec- the local luminosity function of Seyfert galaxies based on tively. Because of its large sample size, only a part of the this catalog is reported in an accompanying paper (Ueda RASS sources has been optically identified (e.g., Schwope et al. 2011, submitted to PASJ). et al. 2000). Hard X-rays above 2 keV are more effective to detect obscured objects, such as “type 2” AGNs, due 2. DATA REDUCTION to its strong penetrating power against photoelectric ab- sorption. In the late 1970s, HEAO-1 A-2 performed an For the catalog production, we use the MAXI/GSC all-sky X-ray survey at b > 20◦ in the 2–10 keV band data taken between 2009 September 1 and 2010 March down to a limiting sensitivity| | of 3.1 10−11 ergs cm−2 31, when all the GSC counters were operated with a high s−1, detecting 61 extragalactic sources∼ including× 29 AGNs voltage of 1650 V. Only the data in the 4–10 keV band (Piccinotti et al. 1982). Rossi X-ray Timing Explorer are utilized in this paper, because in this energy band (1) (RXTE) also carried out an all-sky survey using “slew” the energy and position responses are best calibrated at mode data of the Proportional Counter Array (PCA) in present, and (2) a high signal-to-noise ratio is achieved the 3–8 keV and 8–20 keV bands, and achieved the sensi- thanks to high detection efficiency of the counters and to tivity similar to, and an order of magnitude higher than relatively low background rate (Sugizaki et al. 2011). those of HEAO-1 A-1 and A-4, respectively (Revnivtsev et Starting from the event files with processing version 0.3 al. 2004). The RXTE/PCA survey detected 294 sources provided by the MAXI team, we apply the following data including 100 AGNs, although the identification is not screening to obtain clean data used in the image analysis complete (80%). Recently, the Swift and INTEGRAL described in section 3. The processed event files contain satellites have performed all-sky surveys in the hard X-ray columns of the arrival time (TIME), energy (PI), and sky band above 10 keV (Swift: Tueller et al. 2008; Tueller et position (R.A. and Dec. ) for each photon as essential al. 2010; Cusumano et al. 2010; Baumgartner et al. 2010, information. We utilize the data of all the twelve GSC INTEGRAL: Bird et al. 2007; Beckmann et al. 2006, counters from 2009 September 1 to 22, while those of only 2009; Krivonos et al. 2007; Bird et al. 2010). These cata- eight counters (GSC 0, 1, 2, 3, 4, 5, 7, and 8) are included logs contain heavily obscured AGNs with absorption col- in the later epoch since the operation of the rest four coun- umn densities larger than 1024 cm−2. Total 628 AGNs ters were stopped due to a hardware trouble. The photon have been detected in the Palermo Swift/BAT 54-month events detected by the carbon anodes #1 and #2 in all catalog (Cusumano et al. 2010). the counters are excluded because of the response problem Monitor of All-sky X-ray Image (MAXI; Matsuoka et al. in the current calibration. To discard the data suffering 2009) is the first scientific mission operated on the inter- from high background rates, we only utilize the data taken national space station (ISS). It carries two types of X-ray when the ISS latitude is between 40◦ and 40◦, and those cameras: Gas Slit Camera (GSC; Sugizaki et al. 2011; detected at the central part of each− counter with the pho- Mihara et al. 2011) and Solid-state Slit Camera (SSC; ton incident angle φ < 38◦ (φ; for definition, see Mihara Tsunemi et al. 2010; Tomida et al. 2011), covering the et al. 2011). | | energy bands of 2–30 keV and 0.5–12 keV, respectively. Figure 1 displays the effective exposure map in the MAXI/GSC observes nearly the whole sky every 92 min- Galactic coordinates for the MAXI/GSC 7-month data, utes with two instantaneous fields of view of 160◦ 3◦. where the net exposure corrected for the detection effi- One of the main goals of the MAXI mission is to× pro- ciency, multiplied by the projected area of the slit ( vide a new all-sky X-ray source catalog, including both cosφ), is given in units of s cm2 at each sky position.∝ transient and persistent objects. By integrating the data This is obtained from the simulation utilizing the MAXI over a long period, MAXI/GSC is expected to achieve so simulator maxisim (Eguchi et al.