Flexible Simulated Data with BYOSED

“Build Your Own” SED

The BYOSED framework allows any spectrophotometric model to be used as the underlying template to generate simulated Type Ia light curve data with SNANA. This framework is published in Pierel et al., 2021. By default, this model is the Hsiao+07 model (initfiles/Hsiao07.dat). This can be replaced by any model.

Param File Basics

The only file to set up is the BYOSED.params file. This contains the general aspects of the simulated SN you want to create using BYOSED, and any warping effects you want to add in. This file is separated into the following required and optional sections:

[MAIN]

(Required)

This section contains SED_FILE (name of SED file), as well as MAGSMEAR (magnitude smearing) and MAGOFF (magnitude offsets) definitions to be applied to the base SED defined by sed_file. You may also define CLOBBER and VERBOSE flags here as well. This section may look like the following:

[MAIN]

SED_FILE: Hsiao07.dat
MAGSMEAR: 0.0
MAGOFF: 0.0

[FLAGS]

(Optional)

This section allows you to simply turn warping effects defined in the next section(s) on and off. If this section exists, then it supersedes later sections and defines the warping effects to be used. If it does not exist, all defined warping effects are used. Adding this onto the [MAIN] section, the params file might now look like the following:

[MAIN]

SED_FILE: Hsiao07.dat
MAGSMEAR: 0.0
MAGOFF: 0.0

[FLAGS]

COLOR: True
STRETCH: True
HOST_MASS: False

In this case, a magnitude smearing of 0.1 would be applied to the Hsiao model at all wavelengths, and some color and stretch effects are applied as well based on functions you will define in the next sections.

Warping Effects

The following sections contain all of the various wavelength/phase dependent effects that you want to apply to your SED. In this case, based on the [FLAGS] section, you must have a “COLOR” section and a “STRETCH” section. You can name effects whatever you want with the exception of a “color law” effect, which must be named **”COLOR”, as long as the name of your section and the corresponding name in the [FLAGS] section are identical. Creating a warping effect section requires the following variables in no particular order:

  1. DIST_PEAK
  • The PEAK of an (a)symmetric Gaussian that will define the distribution for the scale parameter
  1. DIST_SIGMA
  • The “low” and “high” standard deviations of the same distribution
  1. DIST_LIMITS
  • The lower and upper cutoff you would like for the same distribution
  1. DIST_FUNCTION
  • A file name to be read that contains a list of phase, wave, value like the following:
#p w v
-20 1000 25.75805
-20 1010 25.64852
-20 1020 25.53899
-20 1030 25.42946
-20 1040 25.31993
-20 1050 25.2104
     ...

You must now define a section for each warping effect, with these variables. For our current example, where I have defined color and stretch effects in my [FLAGS] section, I must define these two sections. If I do not define a [FLAGS] section, then whatever sections that exist apart from the [MAIN] section are assumed to be warping effects. One such section might look like the following:

[COLOR]

WARP_FUNCTION: color_func.dat
DIST_PEAK: 0.0
DIST_SIGMA: 0.07 0.1
DIST_LIMITS: -0.3 0.3

All together, after adding in the stretch section as well, a BYOSED.params file might look something like this:

[MAIN]

SED_FILE: Hsiao07.dat
MAGSMEAR: 0.0
MAGOFF: 0.0

[FLAGS]

COLOR: True
STRETCH: True
HOST_MASS: False

[COLOR]

WARP_FUNCTION: color_func.dat
DIST_PEAK: 0.0
DIST_SIGMA: 0.07 0.1
DIST_LIMITS: -0.3 0.3

[STRETCH]

WARP_FUNCTION: stretch_func.dat
DIST_PEAK: 0.5
DIST_SIGMA: 1.0 0.7
DIST_LIMITS: -2.5 2.5

Or, if you do not define a flags section, color and stretch will automatically be used as warping effects with the following BYOSED.params file:

[MAIN]

SED_FILE: Hsiao07.dat
MAGSMEAR: 0.0
MAGOFF: 0.0

[COLOR]

WARP_FUNCTION: color_func.dat
DIST_PEAK: 0.0
DIST_SIGMA: 0.07 0.1
DIST_LIMITS: -0.3 0.3

[STRETCH]

WARP_FUNCTION: stretch_func.dat
DIST_PEAK: 0.5
DIST_SIGMA: 1.0 0.7
DIST_LIMITS: -2.5 2.5

Final Notes

Now you can replace the Hsiao template with your own template SED, and start adding in warping effects. This warping process is designed so that as many effects as you would like can be included. Anything but a color effect (which should affect the final SED as a function of wavelength and possibly phase) is applied additively, while the color effect is applied multiplicatively. This is similar to the existing SALT2 framework. For the example file above, the final flux would look like this

\[F(\lambda,\phi)=A\Big[H(\lambda,\phi)+S(\lambda,\phi)s\Big]\times10^{-0.4C(\lambda,\phi)c}\]

Where here F is the final flux, H is the Hsiao template, S is the defined stretch function, C is the defined color function, s is the scale parameter pulled from the distribution defined for the stretch function, and c is the scale parameter pulled from the distribution defined for the color function. In principle this could look like the following if you had N such effects:

\[F(\lambda,\phi)=A\Big[H(\lambda,\phi)+X_1(\lambda,\phi)x_1+X_2(\lambda,\phi)x_2+...+X_N(\lambda,\phi)x_N\Big]\times10^{-0.4C(\lambda,\phi)c}\]

Example Files

These are example files that can be used for your sed_file and BYOSED.params. The color and stretch functions are defined by accompanying color and stretch files.