GRBM scientific data

We can classify the GRBM scientific data products in 3 types:

• 1 s ratemeters: the signals detected in each shield between the LLT and the ULT are continuously counted, with a time resolution of 1 s, and recorded by a proper PDS housekeeping, the GRBM ratemeter; another housekeeping counter, the AC ratemeter, records, for each shield, the count rate detected above the PDS Anti Coincidence Threshold (ACT), that is used as a lower level discriminator for any AC signal, adjustable on 8 steps between nominal 100 and 300 keV. This data are transmitted to ground in indirect temporal mode; the dead time is 4 $\mu$s and the number of bits of the counter is 16 (maximum number of counts is 65536);
• GRBM PHA spectra: the counts accumulated every 128 s in the GRBM band (LLT-ULT) are continuously histogrammed on-board in 240 channels spectra by means of PHA analysis (as described above in the PDS section) and transmitted to ground in Spectral Indirect Mode; the real number of PHA channels is 256, but channels from 241 to 256 don't contain scientific data, due to the use of the sliding scale technique. The dead time introduced by the ADC is 14 $\mu$s; the number of bits for each channel is 16;
• High Resolution Time Profiles (HRTP): when the on-board trigger is satisfied, time count profiles are stored independently for each of the four detectors and for any trigger occurring during an orbit and transmitted with the following modality:
  a) 8 s before the trigger time, with a time resolution of 7.8125 ms
  b) 10 s from the trigger time, with a time resolution of 0.488 ms
  c) 88 s starting from 10 s after the trigger time, with a time resolution of 7.8125 ms
  The dead time needed to accumulate and store the data packets for each trigger is about 400 s.. This means that it is not possible to trigger an event occurring before 400 s after the former trigger. The telemetry allocated to the GRBM allows to detect up to 12 events each orbit. These data are transmitted to ground in a specific GRBM Direct Mode.

The first two data sets are used to extrapolate sources flux and spectral properties (see following chapters); both raw and FOT data are reduced using the PDS specific tools contained in the XAS package. The HRTP can be used to perform temporal analysis of GRBs. The relative packets, containing also the trigger time in OBT are present in the orbit per orbit PDS raw data set and are provided to the GRBM hardware team in a specific FOT version. HRTP reduction and trigger time conversion to UT is performed by specific programs developed by the GRBM group. The output of these dedicated programs is a set of ASCII light curves for each of the four LS and for each trigger.

 

 

Energy range 40-700 keV

CsI(Na) thickness 10 mm

Geometrical area 1136 cm² per detecting unit

$$\sim$$ LS1/LS3 On-axis effective area

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$$\sim$$

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$$\pi$$ Field of view (FWHM)

Energy resolution from 43% @40 keV to 15% @600 keV

Maximum time resolution 0.5 ms for HRTP 1 s for GRBM and AC ratemeters 128 s for PHA spectra

Energy spectra 256 channels Minimum channel width

     of energy spectra 2.7 keV

$$\mu$$ ADC dead time

$$\mu$$

Memory allocation 16 bit for each ratemeter bin 16 bit for each PHA spectra channel

  

Figure 1.7: PDS lateral shield view