BATSE Detector Responses (gdt.missions.cgro.batse.response)

The BATSE detector response files allow you to compare a theoretical photon spectrum to an observed count spectrum. In short, a single detector response file is only useful for its corresponding detector, for a given source position on the sky, and a given time (or relatively short time span). Essentially, one file contains one or more detector response matrices (DRMs) encoding the energy dispersion and calibration of incoming photons at different energies to recorded energy channels. The matrix also encodes the effective area of the detector as a function of energy for a given source position relative to the detector pointing. This effective area can change dramatically as there is a strong angular-dependence of the response (and the angular-dependence changes with energy!). A file that contains a DRM for a single detector is represented by the BatseRsp class and a file that contains DRMs for multiple detectors is represented by the BatseRspMulti class.

Single-Detector Response Files

Similar to the science data, we can open/read a response file in the following way:

>>> from gdt.core import data_path
>>> from gdt.missions.cgro.batse.response import BatseRsp
>>> filepath = data_path / 'cgro-batse' / 'cont_drm_3_105.fits.gz'
>>> rsp = BatseRsp.open(filepath)
>>> rsp
<BatseRsp: cont_drm_3_105.fits.gz;
 trigger time: 8367.384765717592;
 time range (-0.0013985185178171378, 0.0004503472227952443);
 62 energy bins; 16 channels>

Notice that this returns a single-DRM response object. We can access the DRM directly, which is a ResponseMatrix object:

>>> rsp.drm
<ResponseMatrix: 62 energy bins; 16 channels>

We can fold a photon model through the response matrix to get out a count spectrum. For example, we fold a PowerLaw photon model:

>>> from gdt.core.spectra.functions import PowerLaw
>>> pl = PowerLaw()
>>> # power law with amplitude=0.01, index=-2.0
>>> rsp.fold_spectrum(pl.fit_eval, (0.01, -2.0))
<EnergyBins: 16 bins;
 range (13.140960693359375, 100000.0);
 1 contiguous segments>

This returns an EnergyBins object containing the count spectrum. See Instrument Responses for more information on working with single-DRM responses.

What does a DRM actually look like? We can make a plot of one using the ResponsePlot:

>>> import matplotlib.pyplot as plt
>>> from gdt.core.plot.drm import ResponsePlot
>>> drmplot = ResponsePlot(rsp.drm)
>>> drmplot.xlim = (20.0, 2000.0)
>>> drmplot.ylim = (20.0, 2000.0)
>>> plt.show()

What we see in the plot is a diagonal edge that contains a majority of the effective area. This approximately linear mapping of photon energy to energy channel is called the photopeak. There is also see a bunch of off-diagonal contribution from photons deposited into energy channels lower than the original photon energy. This presence of non-negligible off-diagonal response is one of the reasons that the DRM is not invertible (our lives would be so much easier if was, though).

We can also make a plot of the effective area integrated over photon energies using PhotonEffectiveArea:

>>> from gdt.core.plot.drm import PhotonEffectiveArea
>>> effarea_plot = PhotonEffectiveArea(rsp.drm)
>>> plt.show()

For more details about customizing these plots, see Plotting DRMs and Effective Area.

Multi-Detector Response Files

Some of the response files contain multiple detectors. These are typically identifiable because they do not have a detector number in their filename. You can read these with BatseRspMulti:

>>> from gdt.missions.cgro.batse.response import BatseRspMulti
>>> filepath = data_path / 'cgro-batse' / 'discsc_drm_105.fits.gz'
>>> rsp_multi = BatseRspMulti.open(filepath)
>>> rsp_multi
<BatseRspMulti: 2 detectors>

Note that this contains DRMs for two detectors. We can see which detectors’ DRMs are stored in this file:

>>> rsp_multi.detectors
['LAD3', 'LAD7']

And we can extract one of the DRMs by detector number, name or detector object. For example:

>>> rsp3 = rsp_multi.get_detector('LAD3')
>>> rsp3
<BatseRsp: discsc_drm_3_105.fits.gz;
 trigger time: 8367.384765717592;
 time range (-0.0013985185178171378, 0.0004503472227952443);
 30 energy bins; 4 channels>

This returns a single-detector DRM, and we can perform all the same actions as we did in the previous example.

Reference/API

gdt.missions.cgro.batse.response Module

Classes

BatseRsp()	Class for BATSE single-DRM response files
BatseRspMulti()	BATSE response file for multiple detectors.

Class Inheritance Diagram