Introduction

Most X-ray binaries (XRBs) exhibit spectral state transitions during their outburst phases. When these sources awaken from quiescence, their brightness increases dramatically, and they trace out a characteristic q-shaped pattern in the hardness-intensity diagram as they evolve from the hard to the soft state and eventually back to the hard state [Belloni, 2010].

Typically, the transition begins in the hard state, where the spectrum is dominated by a power-law-like spectrum with a high-energy cutoff, produced by Compton up-scattering of seed photons in a hot corona [Thorne and Price, 1975, Sunyaev and Truemper, 1979]. In this state, reflection signatures also emerge as coronal photons irradiate and are reprocessed by the accretion disk [Matt et al., 1991]. As the outburst progresses, the system enters the disk-dominated soft state, characterized by a multi-temperature blackbody spectrum from the accretion disk [Novikov and Thorne, 1973]. During the transition from the hard state to the soft state, sources often pass through an intermediate state, in which quasi-periodic oscillations (QPOs) are frequently observed [Ingram and Motta, 2019]. The presence of different types of QPOs further allows this intermediate state to be subdivided into the hard-intermediate state (HIMS) and the soft-intermediate state (SIMS).

The model DAO focuses on X-ray reflection, which is generally observed in the hard state [Liu et al., 2023]. It computes the reprocessed radiation from disk–corona systems, similar to well-known reflection models such as reflionx [Ross and Fabian, 2005] and xillver [García and Kallman, 2010, García et al., 2013, García et al., 2014]. The main goal of DAO is to provide an accurate, flexible, and community-accessible reflection code that enables researchers to perform studies tailored to their specific scientific needs.

In this document, I aim to include all relevant information about the model—such as its usage, approximations, and underlying physics—and to continuously update this user guide. Please feel free to contact me if you encounter any questions or issues.

After you have installed, we recommend the following steps to get started with DAO:

  1. Consult the Quick Start for a basic execution tutorial.

  2. Review the Model Input Parameters and Output Files sections for detailed specifications.

  3. Utilize Python scripts to manage your workflow and see Example for more details practices.

  4. For a detailed description of the physics and mathematics behind DAO, please refer to the Theory section.

The paper is available now by arxiv: DAO: A New and Public Non-Relativistic Reflection Model