AHELP for CIAO 4.11 Sherpa v1

# bbody

Context: models

## Synopsis

A one-dimensional Blackbody model.

`bbody`

## Description

A model representing the ideal blackbody function. It can be used when the independent axis is in energy or wavelength space.

## Example

```>>> create_model_component("bbody", "mdl")
>>> print(mdl)```

Create a component of the bbody model and display its default parameters. The output is:

```mdl
Param        Type          Value          Min          Max      Units
-----        ----          -----          ---          ---      -----
mdl.space    frozen            0            0            1 0 - energy | 1 - wave
mdl.kT       thawed            1          0.1         1000        keV
mdl.ampl     thawed            1        1e-20        1e+20           ```

### ATTRIBUTES

The attributes for this object are:

### space

Switch to select whether the independent axis is energy or wavelength. This parameter is not fit ( alwaysfrozen is set), and should be set to either 0, when the independent axis is energy with units of keV, or 1 when the axis is wavelength with units of Angstrom.

### kT

The temperature if the blackbody, in keV.

### ampl

The amplitude of the blackbody component.

The blackbody emission is calculated as a function of energy using the expression:

`f(E) = ampl * E^2 / (exp(E / kT) - 1)`

where E is the photon energy, and kT is the blackbody temperature (both in keV). The amplitude, ampl, is related to the ratio of source radius to distance by:

```ampl = (2 * pi / (c^2 * h^3)) (R / d)^2
= 9.884 x 10^31 (R / d)^2```

with Planck's constant (h) specified in keV-s and the speed of light (c) specified in cm/s, and with R and d representing the radius of, and distance to, the source respectively.

There are two conditions when the above equation is not used:

• if E/kt < 10^-4 then f(E) = ampl * E * kT
• if E/kT > 60, f(E) = 0.

## Bugs

See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.