1. One of main objectives of MAXI, Monitor of All-sky X-ray Image, is to discover X-ray transient objects. By scanning all the sky, MAXI can observe short- and long-term X-ray variabilities. Therefore, MAXI is the best X-ray instrument for the discovery of X-ray transient objects. Observational data are sent to the nova-search system that is a real-time X-ray transient monitor at the Tsukuba Space Center. The system also analyzes time series data at each spherical area. If the system detects large intensity variations above a threshold, the data of the area are sent to the alert system, where adjoining data are put together as one event. If it is admitted that the event is a transient object, the system reports the information soon to MAXI-team members. 45 transient objects or phenomena were reported to Atel and 13 GRBs including soft X-ray flashes were reported to GCN using this system by November in 2010.We present here the outline of the system and improvements newly added to the system,for example a check of shading by a solar paddle, which is necessary from the completely auto-alert system coming soon. MAXI Alert System and Its improvement Fumitoshi Suwa, Hitoshi Negoro, Hiroshi Ozawa (Nihon University), and the MAXI team. suwa@cygnus.phys.cst.nihon-u.ac.jp ●MAXI Nova Alert System DARS MAXI-DB 10 ~ 30s 5m 〜 ●Judgement in the Alert System ●Solar Paddle FWHM(~1.5°) > pixel size(~1°) A true event is expected to split into two or more pixels. →Only such multi-pixels events are selected to suppress a number of background events. However, if a low-flux event occurs at the center of a pixel, X-ray counts in any surrounding pixel might not reach over a threshold. →If data come from the nova search system more than 4 times (in 2 successive scans) in a single pixel close to known objects, the event is detected. A fake event occurs when an object has come out from shading by a solar paddle. July 4 2010 GX339-4 ●Results (preliminary) Magnified image near the Galactic center The nova search system sends data in each pixel area, divided with HEALPix library, to the alert system Go ́rski, K. M. et al., 1997-2007, The HEALPix homepage http://healpix.jpl.nasa.gov HEALPix one pixel OCS JAXA TKSC MAXI operational room Alert System Nova Search RIKEN Flash Reports 7 ~ 8s Alert Mail True event BG events one event One pixel event Nov 21 2010 EXO 2030+375 Earier detection Aug 29 2010 Cir X-1 UT 21:48 UT 05:26 UT 11:08UT 12:41(1pixel) UT 12:41(2pixel) UT 10:35 UT 12:08 UT 13:24 hidden by a solar paddle ●:hidden by a solar paddle ×:no hidden The solar paddle check is possible in about 3 seconds. The below figure shows results on the solar paddle check for events including fake ones occurred on November 23 2010. The number of reports every months Nova alert system detected 57 sources between November, 2009 and November, 2010. Source #b Source #b Source #b 1H 0918-548 1 GS 1826-238 10 RXS J172525.5 1 2S 1417-624 1 GX 1+4 1 RX J1832-33 1 3A 1812-121 1 GX 304-1 2 SAX J1324.5- 6313 1 4U 0513-40 1 GX 339-4 2 SAX J2103.5+4545 1 4U 1137-65 1 H 1145-619 1 SLX 1735-269 1 4U 1210-64 1 H 1608-522 1 SLX 1744-300 1 4U 1538-52 2 H 1624-490 2 SMC X-1 7 4U 1630-472 3 H 1743-322 3 SWIFT J1729.9- 3437 1 4U 1746-37 2 H 1745-203 1 Terzan 2 1 4U 1850-086 2 Her X-1 12 TW Association 7 flare 1 4U 1916-053 1 HETE J1900.1- 2455 3 Vela X-1 23 4U 2206+543 1 HR 1099 1 XB 1832-330 1 A 0535+262 6 II Peg 2 X Per 3 Aql X-1 8 KZ TrA 1 XTE J1701-407 1 AX J1841.0-0536 1 LMC X-4 5 XTE J1709-267 1 BSD 24-491 1 LS V +44 1 XTE J1752-223 1 Cir X-1 6 MAXI J1659- 152 1 XTE J1855-026 1 EX Hya 2 Mkn421 1 EXO 2030+375 4 NGC2110 1 GRO J1008-57 2 RAPID/SLOW Burster 11 1