SOXS Overview

This section provides a general overview of the capabilities of SOXS. SOXS has three main components:

  1. Tools to generate simple models of astrophysical sources
  2. I/O interface to SIMPUT files
  3. An instrument simulator for X-ray telescopes

These are outlined in detail below. Figure 1 shows a flowchart of how one transforms models of astrophysical sources to event lists using SOXS.


Figure 1: Flowchart depicting how source models are written to SIMPUT files which then can be used to simulate X-ray observations using SOXS and compare them with the outputs of other tools.

Generating Simplified Models of Sources

SOXS provides tools to build simplified models of sources on the sky. These consist of Spectrum and SpatialModel objects. The first creates models of spectra of a number of different types and a number of different sources. Methods are also provided to

To find out more about Spectrum objects, visit one of the following links:

To learn about SpatialModel objects, visit one of the following links:

The purpose of these methods is to generate statistically representative samples of photons which can be written to SIMPUT files, described next.


For storage and representation of source models, SOXS uses the SIMPUT file format. SIMPUT stands for “SIMulated inPUT”, and was developed at the University of Erlangen-Nuremberg for use with the SIXTE mock X-ray observation package. However, other similar packages, such as SIMX and MARX use SIMPUT as a possible input format for source models, making it possible to used models produced in or for SOXS with these packages to compare the expected performance of X-ray Surveyor with other instruments.

SOXS currently provides facilities for both input and output of SIMPUT catalogs with photon lists. Photon lists are FITS tables of RA, Dec, and energy from the simulated source, generated assuming a large exposure time and a large collecting area so that the sample is large enough that the instrument simulator is able to “observe” a representative subset. The SIMPUT outputs can be used to compare simulations made with SOXS to simulations of other X-ray instruments past, current, and future, and likewise SIMPUT catalogs with photon lists not created with SOXS can be used as inputs to SOXS’s instrument simulator.

For more information, visit Working with SIMPUT Catalogs.

The Instrument Simulator

The instrument simulator in SOXS takes unconvolved events in the form of a SIMPUT file and performs the following operations:

  1. Uses the effective area curve from an ARF to determine which events will actually be detected.
  2. Projects these events onto the detector plane and perform PSF blurring and dithering of their positions.
  3. Add particle/instrumental and astrophysical background events.
  4. Convolves the event energies with the response matrix from an RMF to produce channels.
  5. Writes everything to an event file.

The instrument simulator is called using either the instrument_simulator() Python function or the instrument_simulator command-line script.

Currently, the instrument simulator can simulate “default” instrument configurations for Lynx, Athena, Chandra, and Hitomi, but one can also supply a modified instrument configuration for use with the instrument simulator, which is laid out in more detail in Instrument Simulation in SOXS.

Working with Other Tools

SOXS is designed so that the SIMPUT files it produces may be used in other X-ray simulation tools, and other tools which produce SIMPUT files may then be read in by SOXS. Here we list a few of the tools and software that you may have interest in using:



MARX is a set of programs developed to provide a detailed ray-tracing simulation of the on-orbit performance of Chandra. The SIMPUT files produced by SOXS can be used as inputs to MARX to simulate Chandra observations to compare with those made by SOXS.



SIMX simulates a photon-counting detector’s response to an input source, including a simplified model of any telescope. SIMX is a “convolution tool” that uses standard descriptions of telescope PSF and the detector response to model how sources will appear. The SIMPUT files produced by SOXS can be used as inputs to SIMX, and may be useful for simulating observations using other instruments, such as Athena, Hitomi, etc.



SIXTE is a software package for X-ray telescope observation simulations developed at the Erlangen Centre for Astroparticle Physics (ECAP) under the leadership of Christian Schmid. It allows to undertake instrument performance analyses and to produce simulated event files for mission and analysis studies. Its primary goal is to produce simulated Athena observations, but it can produce observations of several other missions as well. The SIMPUT files produced by SOXS can be used as inputs to SIXTE.



pyXSIM is a Python package for simulating X-ray observations from 3-D models of astrophysical sources. pyXSIM makes it possible to generate synthetic X-ray observations of these sources from a wide variety of models, whether from grid-based simulation codes such as FLASH, Enzo, and Athena, to particle-based codes such as Gadget and AREPO, and even from datasets that have been created “by hand”, such as from NumPy arrays. pyXSIM can be used to produce SIMPUT files which can be ingested by SOXS for making simulated observations.