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#!/usr/bin/env python3
#
# Calculate the *background surface brightness (SB)* level from the
# *corrected background spectrum*.
# The calculated background SB value is used to provide constraint for
# surface brightness profile (SBP) fitting, and is also adopted to
# subtract the background contribution before carrying out the SBP
# deprojection.
#
# Weitian LI
# Created: 2016-06-10
# Updated: 2016-06-10
#
import argparse
import subprocess
import tempfile
import json
from collections import OrderedDict
import numpy as np
from astropy.io import fits
def energy2channel(energy):
"""
Convert energy (eV) to Chandra ACIS channel number.
Reference: http://cxc.harvard.edu/ciao/dictionary/pi.html
"""
return int((energy / 14.6) + 1)
def parse_erange(erange):
"""
Parse the given erange string, and return the lower and upper energies.
"""
e_low, e_high = map(float, erange.split(":"))
return (e_low, e_high)
def calc_exp(expmap, regfile):
"""
Calculate the area of the background spectrum extraction region,
and the mean exposure (un-normalized w.r.t exposure time) of that region.
"""
tf = tempfile.NamedTemporaryFile()
cmd_args = [
"dmextract",
"infile=%s[bin sky=region(%s)]" % (expmap, regfile),
"outfile=%s" % tf.name,
"opt=generic", "clobber=yes"
]
subprocess.run(["punlearn", "dmextract"])
subprocess.run(args=cmd_args)
with fits.open(tf.name) as hist_fits:
total_exp = hist_fits["HISTOGRAM"].data["COUNTS"][0]
total_exp_err = hist_fits["HISTOGRAM"].data["ERR_COUNTS"][0]
area = hist_fits["HISTOGRAM"].data["AREA"][0]
mean_exp = hist_fits["HISTOGRAM"].data["SUR_BRI"][0]
mean_exp_err = hist_fits["HISTOGRAM"].data["SUR_BRI_ERR"][0]
tf.close()
return {
"total_exp": total_exp,
"total_exp_err": total_exp_err,
"area": area,
"mean_exp": mean_exp,
"mean_exp_err": mean_exp_err,
}
def calc_spec_counts(spec, erange):
"""
Calculate the spectrum total counts within the specified energy range.
Also extract the EXPOSURE and BACKSCAL information.
"""
specfits = fits.open(spec)
channel = specfits["SPECTRUM"].data["CHANNEL"]
counts = specfits["SPECTRUM"].data["COUNTS"]
channel_low, channel_high = map(energy2channel, erange)
chan_idx = np.where(np.logical_and(channel >= channel_low,
channel <= channel_high))
total_counts = np.sum(counts[chan_idx])
return {
"energy_low": erange[0],
"energy_high": erange[1],
"channel_low": channel_low,
"channel_high": channel_high,
"counts": int(total_counts),
"exposure": specfits["SPECTRUM"].header["EXPOSURE"],
"backscal": specfits["SPECTRUM"].header["BACKSCAL"],
}
def main():
parser = argparse.ArgumentParser(
description="Calculate the background surface brightness")
parser.add_argument("-b", "--orig-bkg", dest="orig_bkg", required=True,
help="original/uncorrected local background " +
"spectrum (e.g., lbkg.pi), from which to get the " +
"original/source EXPOSURE and BACKSCAL, etc.")
parser.add_argument("-B", "--corr-bkg", dest="corr_bkg", required=True,
help="corrected background spectrum for the " +
"Galactic and cosmic background radiations " +
"(e.g., bkgcorr_blanksky_lbkg.pi)")
parser.add_argument("-r", "--bkg-region", dest="bkg_region", required=True,
help="region used to extract the background " +
"spectrum (e.g., lbkg.reg")
parser.add_argument("-e", "--expmap", dest="expmap", required=True,
help="exposure map w.r.t the spectrum")
parser.add_argument("-E", "--erange", dest="erange", required=True,
help="energy range used for the exposure map " +
"(e.g., 700:7000)")
parser.add_argument("-o", "--outfile", dest="outfile",
required=False, default="sb_bkg.json",
help="json file to save the background SB results")
args = parser.parse_args()
e_low, e_high = parse_erange(args.erange)
orig_bkg_results = calc_spec_counts(args.orig_bkg, erange=(e_low, e_high))
corr_bkg_results = calc_spec_counts(args.corr_bkg, erange=(e_low, e_high))
exp_results = calc_exp(args.expmap, regfile=args.bkg_region)
corr_counts = corr_bkg_results["counts"]
corr_exposure = corr_bkg_results["exposure"]
corr_backscal = corr_bkg_results["backscal"]
orig_exposure = orig_bkg_results["exposure"]
orig_backscal = orig_bkg_results["backscal"]
area = exp_results["area"]
mean_exp = exp_results["mean_exp"]
bkg_sb = corr_counts / corr_exposure / (mean_exp / orig_exposure) \
/ (area * corr_backscal / orig_backscal)
results = OrderedDict([
("energy_low", e_low),
("energy_high", e_high),
("channel_low", corr_bkg_results["channel_low"]),
("channel_high", corr_bkg_results["channel_high"]),
("counts", corr_counts),
("exposure", orig_exposure),
("exposure_bkg", corr_exposure),
("backscal", corr_backscal),
("total_exp", exp_results["total_exp"]),
("total_exp_err", exp_results["total_exp_err"]),
("area", exp_results["area"]),
("mean_exp", exp_results["mean_exp"]),
("mean_exp_err", exp_results["mean_exp_err"]),
("bkg_sb", bkg_sb),
])
results_json = json.dumps(results, indent=2)
print(results_json)
open(args.outfile, "w").write(results_json+"\n")
if __name__ == "__main__":
main()
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