Introduction

The chspec package includes multiple models for calculating photon spectrum for different temperature distributions that can be loaded in XSPEC spectral fitting package. At present it includes two models:

• chisoth : Emission from isothermal plasma
• chgausdem : Emission from Gaussian distribution of Differential Emission Measure

These models calculate the synthetic photon spectrum from a spectral library, generated by using the atomic database package CHIANTI. The pre-calculated spectra over grid of temperatures is stored in a FITS file.

Step 1: Download the package

• go to → *https://github.com/xastprl/chspec*
• Download the chspec package from this repository by selecting "Code" > "Download ZIP".
• Unzip and place the resulting chspec directory (software folder ) in desired location using

unzip chspec-main.zip

• if you have heasoft in a different environment then go to that env and run →

conda activate xspec

• Now, verify that HEASoft and XSPEC are available: run →.

which xspec
echo $HEADAS

returns:

/home/solararies/softwares/heasoft-6.34/x86_64-pc-linux-gnu-libc2.31

✅ means that HEASoft is already initialized correctly in your current shell session. You're good to go for compiling and using XSPEC models like chspec.

Step 2: Install chspec