Analysis of the BATSE Continuous MER Data

— The CGRO/BATSE database includes many types of data such as the 16-channel continuous background or medium energy resolution burst data (CONT and MER data types). We have calculated some four hundred burst's medium energy resolution spectra and Principal Component Analysis has been applied. We found five components can describe GRBs' spectra. In the process of understanding the internal mechanism of the gamma ray bursts it is of great importance, to classify the events, to find important and less important variables among the observed parameters. Searching for groups and subgroups is still one of the main goals of the GRB research. The BATSE GRB database produced interesting results (e.g. [3, 4, 5, 7, 10] and the references therein). BATSE CONT data are available on the Internet via anonymous ftp from the CGRO Science Support Center site [11]. The CONT data type is trigger independent, has a spectral resolution of 16 channel and a temporal resolution of 2.048 s. Data are organized into 8x16 matrices for each time bin, 8 being the number of detectors and 16 the number of energy channels. These channels are used to approximate the burst's spectrum which is quite variable during the burst (e.g. [6, 8]). We estimated using Principal Component Analysis (PCA) how many parameters are necessary to characterize CONT data. 2. – Data Selection In the CONT database there are ∼ 900 bursts ranging from BATSE trigger number 105 to 3192. The data are background-subtracted and continuous. There is no clear indication where the burst starts or where it ends, so we defined the following criteria: If the count rate exceeds the 4σ level for a given energy channel, the entire bin is included in the summation, where σ is the variation of counts in the given channel. The background c Società Italiana di Fisica