EventList¶

class gammapy.data.EventList(table)[source]¶

Bases: object

Event list.

Event list data is stored in table (Table) data member.

The most important reconstructed event parameters are available as the following columns:

TIME - Mission elapsed time (sec)
RA, DEC - ICRS system position (deg)
ENERGY - Energy (usually MeV for Fermi and TeV for IACTs)

Note that TIME is usually sorted, but sometimes it is not. E.g. when simulating data, or processing it in certain ways. So generally any analysis code should assume TIME is not sorted.

Other optional (columns) that are sometimes useful for high level analysis:

GLON, GLAT - Galactic coordinates (deg)
DETX, DETY - Field of view coordinates (deg)

Note that when reading data for analysis you shouldn’t use those values directly, but access them via properties which create objects of the appropriate class:

time for TIME
radec for RA, DEC
energy for ENERGY
galactic for GLON, GLAT

Parameters

tableTable: Event list table

Attributes Summary

`altaz`	ALT / AZ position computed from RA / DEC (`SkyCoord`).
`altaz_frame`	ALT / AZ frame (`AltAz`).
`altaz_from_table`	ALT / AZ position from table (`SkyCoord`).
`energy`	Event energies (`Quantity`).
`galactic`	Event Galactic sky coordinates (`SkyCoord`).
`galactic_median`	Median position in radec
`is_pointed_observation`	Whether observation is pointed
`observation_dead_time_fraction`	Dead-time fraction (float).
`observation_live_time_duration`	Live-time duration in seconds (`Quantity`).
`observation_time_duration`	Observation time duration in seconds (`Quantity`).
`observation_time_start`	Observation start time (`Time`).
`observation_time_stop`	Observation stop time (`Time`).
`observatory_earth_location`	Observatory location (`EarthLocation`).
`offset`	Event offset from the array pointing position (`Angle`).
`offset_from_median`	Event offset from the median position (`Angle`).
`pointing_radec`	Pointing RA / DEC sky coordinates (`SkyCoord`).
`radec`	Event RA / DEC sky coordinates (`SkyCoord`).
`time`	Event times (`Time`).
`time_ref`	Time reference (`Time`).

Methods Summary

`check`([checks])	Run checks.
`from_stack`(event_lists, **kwargs)	Stack (concatenate) list of event lists.
`map_coord`(geom)	Event map coordinates for a given geometry.
`peek`([allsky])	Quick look plots.
`plot_energy`([ax])	Plot counts as a function of energy.
`plot_energy_offset`([ax, center])	Plot counts histogram with energy and offset axes
`plot_image`([allsky])	Quick look counts map sky plot.
`plot_offset2_distribution`([ax, center])	Plot offset^2 distribution of the events.
`plot_time`([ax])	Plots an event rate time curve.
`read`(filename, **kwargs)	Read from FITS file.
`select_energy`(energy_range)	Select events in energy band.
`select_mask`(mask)	Select events inside a mask (`EventList`).
`select_offset`(offset_band)	Select events in offset band.
`select_parameter`(parameter, band)	Select events with respect to a specified parameter.
`select_region`(regions[, wcs])	Select events in given region.
`select_row_subset`(row_specifier)	Select table row subset.
`select_time`(time_interval)	Select events in time interval.
`stack`(other)	Stack with another EventList in place.

Attributes Documentation

altaz¶: ALT / AZ position computed from RA / DEC (SkyCoord).

altaz_frame¶: ALT / AZ frame (AltAz).

altaz_from_table¶: ALT / AZ position from table (SkyCoord).

energy¶: Event energies (Quantity).

galactic¶

Event Galactic sky coordinates (SkyCoord).

Always computed from RA / DEC using Astropy.

galactic_median¶: Median position in radec

is_pointed_observation¶: Whether observation is pointed

observation_dead_time_fraction¶

Dead-time fraction (float).

This is a keyword related to IACTs Defined as dead-time over observation time.

Dead-time is defined as the time during the observation where the detector didn’t record events: http://en.wikipedia.org/wiki/Dead_time https://ui.adsabs.harvard.edu/abs/2004APh….22..285F

The dead-time fraction is used in the live-time computation, which in turn is used in the exposure and flux computation.

observation_live_time_duration¶

Live-time duration in seconds (Quantity).

The dead-time-corrected observation time.

In Fermi-LAT it is automatically provided in the header of the event list.
In IACTs is computed as t_live = t_observation * (1 - f_dead)

where f_dead is the dead-time fraction.

observation_time_duration¶

Observation time duration in seconds (Quantity).

This is a keyword related to IACTs The wall time, including dead-time.

observation_time_start¶: Observation start time (Time).

observation_time_stop¶: Observation stop time (Time).

observatory_earth_location¶: Observatory location (EarthLocation).

offset¶: Event offset from the array pointing position (Angle).

offset_from_median¶: Event offset from the median position (Angle).

pointing_radec¶: Pointing RA / DEC sky coordinates (SkyCoord).

radec¶: Event RA / DEC sky coordinates (SkyCoord).

time¶

Event times (Time).

Notes

Times are automatically converted to 64-bit floats. With 32-bit floats times will be incorrect by a few seconds when e.g. adding them to the reference time.

time_ref¶: Time reference (Time).

Methods Documentation

check(checks='all')[source]¶

Run checks.

This is a generator that yields a list of dicts.

classmethod from_stack(event_lists, **kwargs)[source]¶

Stack (concatenate) list of event lists.

Calls vstack.

Parameters

event_listslist: list of EventList to stack

map_coord(geom)[source]¶

Event map coordinates for a given geometry.

Parameters

geomGeom: Geometry

Returns

coordMapCoord: Coordinates

peek(allsky=False)[source]¶

Quick look plots.

Parameters

allskybool: Whether to look at the events allsky

plot_energy(ax=None, **kwargs)[source]¶

Plot counts as a function of energy.

Parameters

axAxes or None: Axes
**kwargsdict: Keyword arguments passed to hist

Returns

axAxes or None: Axes

plot_energy_offset(ax=None, center=None, **kwargs)[source]¶

Plot counts histogram with energy and offset axes

Parameters

axAxis: Plot axis
centerSkyCoord: Sky coord from which offset is computed
**kwargsdict: Keyword arguments forwarded to pcolormesh

Returns

axAxis: Plot axis

plot_image(allsky=False)[source]¶: Quick look counts map sky plot.

plot_offset2_distribution(ax=None, center=None, **kwargs)[source]¶

Plot offset^2 distribution of the events.

The distribution shown in this plot is for this quantity:

offset = center.separation(events.radec).deg
offset2 = offset ** 2

Note that this method is just for a quicklook plot.

If you want to do computations with the offset or offset^2 values, you can use the line above. As an example, here’s how to compute the 68% event containment radius using numpy.percentile:

import numpy as np
r68 = np.percentile(offset, q=68)

Parameters

axAxes (optional): Axes
centerastropy.coordinates.SkyCoord: Center position for the offset^2 distribution. Default is the observation pointing position.
**kwargs :: Extra keyword arguments are passed to hist.

Returns

axAxes: Axes

Examples

Load an example event list:

>>> from gammapy.data import EventList
>>> from astropy import units as u
>>> import matplotlib.pyplot as plt
>>> events = EventList.read('$GAMMAPY_DATA/hess-dl3-dr1/data/hess_dl3_dr1_obs_id_023523.fits.gz')

Plot the offset^2 distribution wrt. the observation pointing position (this is a commonly used plot to check the background spatial distribution):

>>> plt.cla()
>>> events.plot_offset2_distribution()
<AxesSubplot:xlabel='Offset^2 (deg2)', ylabel='Counts'>

Plot the offset^2 distribution wrt. the Crab pulsar position (this is commonly used to check both the gamma-ray signal and the background spatial distribution):

>>> import numpy as np
>>> from astropy.coordinates import SkyCoord
>>> center = SkyCoord(83.63307, 22.01449, unit='deg')
>>> bins = np.linspace(start=0, stop=0.3 ** 2, num=30) * u.deg ** 2
>>> plt.cla()
>>> events.plot_offset2_distribution(center=center, bins=bins)
<AxesSubplot:xlabel='Offset^2 (deg2)', ylabel='Counts'>

Note how we passed the bins option of matplotlib.pyplot.hist to control the histogram binning, in this case 30 bins ranging from 0 to (0.3 deg)^2.

plot_time(ax=None, **kwargs)[source]¶

Plots an event rate time curve.

Parameters

axAxes or None: Axes
**kwargsdict: Keyword arguments passed to errorbar

Returns

axAxes: Axes

classmethod read(filename, **kwargs)[source]¶

Read from FITS file.

Format specification: EVENTS

Parameters

filenamepathlib.Path, str: Filename

select_energy(energy_range)[source]¶

Select events in energy band.

Parameters

energy_rangeQuantity: Energy range [energy_min, energy_max)

Returns

event_listEventList: Copy of event list with selection applied.

Examples

>>> from astropy import units as u
>>> from gammapy.data import EventList
>>> event_list = EventList.read('$GAMMAPY_DATA/fermi_3fhl/fermi_3fhl_events_selected.fits.gz')
>>> energy_range =[1, 20] * u.TeV
>>> event_list = event_list.select_energy(energy_range=energy_range)

select_mask(mask)[source]¶

Select events inside a mask (EventList).

Parameters

maskMap: Mask

select_offset(offset_band)[source]¶

Select events in offset band.

Parameters

offset_bandAngle: offset band [offset_min, offset_max)

Returns

event_listEventList: Copy of event list with selection applied.

select_parameter(parameter, band)[source]¶

Select events with respect to a specified parameter.

Parameters

parameterstr: Parameter used for the selection. Must be present in self.table.
bandtuple or astropy.units.Quantity: Min and max value for the parameter to be selected (min <= parameter < max). If parameter is not dimensionless you have to provide a Quantity.

Returns

event_listEventList: Copy of event list with selection applied.

Examples

>>> from astropy import units as u
>>> from gammapy.data import EventList
>>> event_list = EventList.read('$GAMMAPY_DATA/fermi_3fhl/fermi_3fhl_events_selected.fits.gz')
>>> zd = (0, 30) * u.deg
>>> event_list = event_list.select_parameter(parameter='ZENITH_ANGLE', band=zd)

select_region(regions, wcs=None)[source]¶

Select events in given region.

Parameters

regionsstr, Region or list of Region: Region or list of regions (pixel or sky regions accepted). A region can be defined as a string ind DS9 format as well. See http://ds9.si.edu/doc/ref/region.html for details.
wcsWCS: World coordinate system transformation

Returns

event_listEventList: Copy of event list with selection applied.

select_row_subset(row_specifier)[source]¶

Select table row subset.

Parameters

row_specifierslice, int, or array of ints: Specification for rows to select, passed on to self.table[row_specifier].

Returns

event_listEventList: New event list with table row subset selected

Examples

Use a boolean mask as row_specifier:

mask = events.table[‘FOO’] > 42 events2 = events.select_row_subset(mask)

Use row index array as row_specifier:

idx = np.where(events.table[‘FOO’] > 42)[0] events2 = events.select_row_subset(idx)

select_time(time_interval)[source]¶

Select events in time interval.

Parameters

time_intervalastropy.time.Time: Start time (inclusive) and stop time (exclusive) for the selection.

Returns

eventsEventList: Copy of event list with selection applied.

stack(other)[source]¶

Stack with another EventList in place.

Calls vstack.

Parameters

otherEventList: Event list to stack to self