1 files changed, 44 insertions, 0 deletions
diff --git a/acispy/spectrum.py b/acispy/spectrum.py
new file mode 100644
index 0000000..ad38b0d
--- /dev/null
+++ b/acispy/spectrum.py
@@ -0,0 +1,44 @@
+# 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