Visibility Analysis

The AGILE satellite operated from April 23, 2007 to January 18, 2024 observing thousands of astrophysical sources.

The AGILE spacecraft operated in “pointing mode” from the beginning of the mission to October 15, 2009, completing 101 observation blocks (OBs). The OBs usually consisted of predefined long exposures, drifting about 1 deg per day with respect to the initial boresight direction to obey solar panels constraints.

In November 2009, the attitude control system was reconfigured, and scientific operations were performed “spinning mode” until the end of the mission. AGILE scanned ≈ 80% sky daily (exposure of ≈ 7 · 106 cm2 s) with an angular velocity of about 0.8 deg s-1, performing 200 passes per day on the same sky region.

The visibility of a source thus depend on the off-axis angle with respect to the satellite pointing direction.

Agilepy implements a AGVisibility class that reads the “log files” (AGILE spacecraft files) and extract the Spacecraft Pointing Direction and its time evolution. The quantity can be used to compute the Off-axis angle of a source of interest to check its visibility. If a Fermi Spacecraft file is provided, the same operation can be performed on the file for comparison purposes.

The Visibility Analysis follows these general steps:

1. Prepare a YAML configuration file for AGVisibility. You can do it manually or by using AGVisibility.getConfiguration().

2. Define a AGVisibility object, and read the log files with AGVisibility.computePointingDirection().

3. You can plot the Off-axis angle of a source of interest with AGVisibility.plotVisibility().

4. Additionally, the off-axis angle from Fermi/LAT can be computed with AGVisibility.getFermiPointing().

The AGILE Pointing Direction is taken from the columns TIME, ATTITUDE_RA_Y, ATTITUDE_DEC_Y of the AGILE log files. The Fermi Pointing Direction is taken from the columns START, STOP, RA_SCZ, DEC_SCZ of the Fermi spacecraft files. The results are provided as astropy Table objects, contain the satellites’ pointing coordinates for every given time and the source off-axis angle. They are saved in .csv format by default.

Configuration

We describe here the parameters of the configuration file section by section.

Output

These parameters are common to all agilepy classes.

Option	Type	Default	Required	Description
outdir	string		yes	Output Directory.
filenameprefix	string	ratemters_product	no	Prefix for files.
sourcename	string	rm-source	no	Tag with source name.
username	string	my_name	no	Tag with user name.
verboselvl	int	0	yes	0 for no extra logs, 1 for INFO, 2 for DEBUG.

Input

Option	Type	Default	Required	Description
logfile	string		yes	path to the index file listing relevant AGILE log files to be extracted.
fermiSpacecraftFile	string	null	no	path to the Fermi spacecraft file.

Analysis

Option	Type	Default	Required	Description
timetype	string	tt	no	Format of the Min and Max Times. AGILE seconds can be expressed as tt.
tmin	float	104371200	no	Minimum Time used for visibility estimation. Default is TT=104371200, i.e. 2007-04-23 00:00:00.
tmax	float	632620800	no	Maximum Time used for visibility estimation. Default is TT=632620800, i.e. 2024-01-18 00:00:00.
step	float	1.0	no	time interval in seconds between two consecutive points in the resulting table. Minimum accepted value: 0.1.

Source

Option	Type	Default	Required	Description
frame	string	icrs	no	Reference frame to express the coordinates of the target source.
coord1	float	null	no	1st coordinate of the source. If not provided, the off-axis angle is not computed and only the satellite pointing direction is extracted. It can be set during the analysis.
coord2	float	null	no	2nd coordinate of the source. If not provided, the off-axis angle is not computed and only the satellite pointing direction is extracted. It can be set during the analysis.