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# Copyright (c) 2017 Weitian LI <liweitianux@live.com>
# MIT license
"""
Chandra ACIS spectrum.
"""
from astropy.io import fits
from .acis import ACIS
class Spectrum:
"""
Chandra ACIS spectrum
"""
def __init__(self, filepath):
self.filepath = filepath
self.fitsobj = fits.open(filepath)
ext_spec = self.fitsobj["SPECTRUM"]
self.header = ext_spec.header
# spectral data
self.channel = ext_spec.data.columns["CHANNEL"].array
self.counts = ext_spec.data.columns["COUNTS"].array
# spectral keywords
self.EXPOSURE = self.header.get("EXPOSURE")
self.BACKSCAL = self.header.get("BACKSCAL")
def calc_pb_flux(self, elow=9500, ehigh=12000):
"""
Calculate the particle background flux:
flux = counts / exposure / area
Parameters
----------
elow, ehigh : float, optional
Lower and upper energy limit for the particle background.
"""
chlow = ACIS.energy2channel(elow)
chhigh = ACIS.energy2channel(ehigh)
counts = self.counts[(chlow-1):chhigh].sum()
flux = counts / self.EXPOSURE / self.BACKSCAL
return flux
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