IBIS observing modes

IBIS has several observing modes, for engineering and calibration purposes. However, for scientific use there is only one operating mode, Science Mode.

In Science Mode, ISGRI registers and transmits events on a photon-by-photon basis, i.e., every event is tagged with ( , ) position on the detector plane, event energy (from the pulse height and rise time) and event time.

PICsIT in principle can also operate in photon-by-photon mode. However, the higher background compared to ISGRI would cause telemetry saturation leading to unacceptable data loss. Therefore, the standard mode for PICsIT is histogram. Images and spectra (full spatial resolution, 256 energy channels) are accumulated for about 30 minutes before transmission to ground. There is no time-tagging internal to the histogram, i.e., spectral imaging has time resolution of 30 minutes.

In addition, coarse spectra, without imaging information, are accumulated by PICsIT and transmitted with higher time resolution, but without imaging information. Thus, their usefulness is limited to observations of very strong sources where the source countrate dominates over the background. The time resolution, and the number of energy channels, for this spectral timing data can be commanded from ground. The time resolution can take values between 1 and 500 ms; the current default is 16 ms and eight energy channels. These data are dubbed as ``spectral timing''.

In Table , the properties of all the modes are summarized.

Table: Characteristics of the IBIS Telemetry Formats. Mathematical symbols are not rendered here. Please refer to the PDF version of the document.

	Detector Image	Timing	Spectral
Observing Mode	Resolution	Resolution	Resolution
	(pixels)		(channels)
ISGRI
photon-by-photon	128 128	61.035 s	2048
PICsIT
Photon-by-Photon	64 64	64 s	1024
Spectral-Imaging	64 64	30 min	256
Spectral-Timing	None	1 - 500ms	2 - 8