Introduction

The WAM is the lateral BGO (= Bi$_3$Ge$_4$O$_{12}$ crystal) anti-coincidence shield of the Hard X-ray Detector (HXD). It consists of 4 identical walls (referred as WAM 0, 1, 2 and 3), which are further composed of 5 anti-counter units for each wall. The primary role of the WAM is a background rejection for the HXD-PIN and GSO, but the WAM can observe bright gamma-ray transients such as gamma-ray bursts (GRBs) and soft gamma repeaters (SGRs) in the range of 50-5000 keV.

The WAM data consists of two types of data: Gamma burst (BST) and Transient (TRN) data (Table 1.1). The BST data are available only when the onboard GRB trigger occurs. They have time history (TH) data with a fine time resolution (1/32 or 1/64 sec) in the four energy ranges and the 55 channel pulse height (PH) histogram data with coarse time resolution (1/2 or 1 sec) during the finite time intervals (64 sec or 128 sec). On the other hand, the TRN data cover all the time with 1-sec time resolution for monitoring the background. They have 55 channel pulse-height histogram data.

Details of the WAM instrumentation are described in K. Yamaoka et al. 2009 PASJ vol. 61 S35. The spectral cross-calibration among Swift/BAT and Konus/Wind are in T. Sakamoto et al. 2011, PASJ vol. 63, 215.

Table 1.1: Characteristics of the WAM data (TRN data and BST data).

Data	Energy	Epoch	Time resolution	Time coverage
BST	4 channels	2005 Aug. 22 - 2006 Mar. 20	1/32 s (TH)	128 s (16 s before and
	55 channels		1 s (PH)	112 s after the trigger)
	4 channels	2006 Mar. 20 - present	1/64 s (TH)	64 s (8 s before and
	55 channels		0.5 s (PH)	56 s after the trigger)
TRN	55 channels	2005 Aug. 22 - present	1 s (PH)	Always transferred to the
				telemetry every 1 s