Recent Progress of the MAXI alert system and the photon event database

Hitoshi Negoro (Nihon University), H. Negoro, H. Ozawa, F. Suwa, M. Asada (Nihon U.), M. S. Serino (RIKEN) and the MAXI Team.


MAXI (Monitor of All-sky X-ray Image) is an all-sky X-ray monitor on the ISS (Matsuoka et al. 2008, PASJ, 61, 999). Now, MAXI plays an important role to provide prompt alert information on transient phenomena in X-rays (for instance, X-ray outbursts, flares, bursts, and state transitions in black hole candidates) through our mailing lists (, the Astronomer's Telegram, and the Gamma-ray Coordinates Network.

We present here recent development on the MAXI alert system and the related photon event database (for more information on earlier results on the system, see Negoro et al., 2010, ADASS XIX, ASP Conf. Ser. 434, 127, [O07.2]). Realtime background subtraction in addition to effective area correction in data processing of the MAXI alert system enables us to detect fainter objects with flux down to about 15 mCrab (a day), and reduces the number of fake events due to the background variations significantly. We then starts to send a prompt E-mail alert automatically to our mailing list members since this July.

Another progress of our system is about the photon-event database. Currently a large number of X-ray events, about more than 1e10 events, are accumulated in our PostgreSQL database. The access time is limited by the seek/search time of the hard disks (RAID drives), a few msec per event on average. As a result, it takes much time to obtain a large number of events from the database. We are investigating much faster access using SSD RAID. We have found that the access time with the SSD RAID is faster than the hard-disk RAID by 10-100 times, as expected, which is compatible to the time for the cluster index table.

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