Simulating X-ray Observations with yt

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Published on February 18, 2014

Author: jzuhone

Source: slideshare.net

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Talk given at the 11th Astro-H Science Working Group Meeting on February 18, 2014, in Matsuyama, Japan.

Simulating X-ray Observations with yt John ZuHone NASA/Goddard Space Flight Center

yt is a Python-based platform for analysis and visualization of astrophysical simulation data Turk et al. 2011, ApJS, 192, 9 Turk & Smith 2011, arXiv:1112.4482

! yt is designed to address physical, not computational, questions

“What is the average mass weighted temperature of the gas within a sphere of radius 100 kpc, centered at the maximum gas density? Oh, and I want it in keV.” from yt.mods import * from yt.utilities.physical_constants import kboltz ! ds = load("IsolatedGalaxy/galaxy0030/galaxy0030") ! sp = ds.h.sphere("max", (100, “kpc”)) ! T = sp.quantities[“WeightedAverageQuantity”](“temperature”, “cell_mass”) ! print (kboltz*T).in_units(“keV”)

Fully-Supported Enzo FLASH Nyx Orion In-Memory MostlySupported In Progress Athena ART Ramses Gadget Hydra Cactus PDKGRAV FITS Images

Formation of a Galaxy Cluster: Sam Skillman

Bolatto et al. 2013, Nature, 499, 450

Method: PHOX • Method developed by Veronica Biffi, Klaus Dolag (http://www.mpa-garching.mpg.de/ ~kdolag/Phox/) • Biffi,V., Dolag, K., Bohringer, H., & Lemson, G. 2012, MNRAS, 420, 3545 • Biffi,V., Dolag, K., Bohringer, H. 2013, MNRAS, 428, 1395

Three Steps: 1. Generate a very large number of photons from an appropriate spectral model for each cell 2. Project photons along a chosen line of sight, Doppler and cosmologically shift their energies. Apply galactic absorption. 3. Convolve photons with instrument models.

Step 1 • First, we define a spectral model. • There are interfaces within the code to use: • PyXspec (https://heasarc.gsfc.nasa.gov/ xanadu/xspec/python/html/) • AtomDB (http://www.atomdb.org) • There is flexibility to include other model sources

Step 1 • In the first step we generate a lot of photons, many more than would be in a typical observation (at least ~10x more) • To make this precise, we specify a very large collecting area and a very long exposure time, along with a source distance • These photons become a Monte-Carlo sample which will be used to make the actual observation • Typically, we will store them to disk, also saving the positions and velocities of the gas they originated from

Three Steps: 1. Generate a very large number of photons from an appropriate spectral model for each cell 2. Project photons along a chosen line of sight, Doppler and cosmologically shift their energies. Apply galactic absorption. Correct for exposure time and effective area. 3. Convolve photons with instrument models.

Step 2 • Using the saved positions, energies, and velocities, we can project them along a line of sight, and use the gas velocities to Doppler-shift them. • We also apply cosmological redshift for distant sources, and galactic foreground absorption (tbabs, wabs, etc.) • Here is where we use the actual effective area (constant or from an ARF) and exposure time of the desired observation

Three Steps: 1. Generate a very large number of photons from an appropriate spectral model for each cell 2. Project photons along a chosen line of sight, Doppler and cosmologically shift their energies. Apply galactic absorption. Correct for exposure time and effective area. 3. Convolve photons with instrument models.

Step 3 • The photon simulator module provides a way to simply convolve with a ARF/RMF pair, to get a quick-and-dirty observation • If you want to accurately simulate a particular detector, you can export the generated events to files that can be read in by instrument simulators

Step 3 • SIMX: http://hea-www.harvard.edu/simx/ • Not a full raytrace, but a predefined set of PSFs, vignetting information, and instrumental responses and outputs to make the simulation. • yt exports SIMPUT files of (x,y,E) that can be read in by SIMX • http://hea-www.harvard.edu/heasarc/formats/ simput-1.1.0.pdf

Advantages • Most expensive step (generating the photons) happens in 3D, and only needs to be done (in most cases) ONCE. • Different projections, different exposure times, different instruments simulated from the same set of photons (computationally cheaper) • It runs in parallel using MPI

A Couple of Examples

Sloshing Cluster Core Athena MHD dataset, T ~ 2.5 keV Density Temperature

Sloshing Cluster Core SXI 100 ks exposure, z = 0.01 (reblocked by 4x) 1 0.1 0.01 normalized counts/s/keV 10 SXS spectrum 0.5 1 2 E (keV) 5

Sloshing Cluster Core

AGN-Blown Bubbles Dataset created from scratch “in memory”: 4 keV β-model cluster with bubbles

AGN-Blown Bubbles SXI 100 ks exposure z = 0.02 (reblocked by 4x)

To Get yt • http://yt-project.org/#getyt • I recommend using the install script: 1. wget http://hg.yt-project.org/yt/raw/yt/ doc/install_script.sh 2. bash install_script.sh 3. source YT_DEST/bin/activate

To Get Help Email Me: jzuhone@milkyway.gsfc.nasa.gov ! Photon Simulator Documentation: http://yt-project.org/doc/analyzing/analysis_modules/ photon_simulator.html ! Website: http://yt-project.org ! Mailing List (yt-users): http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org

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