yields better results in general with slightly more computational cost ($\propto N_{\rm m}^{4/3} \log(N_{\rm s})$) than the supermesh prescription. Our methods can easily be implemented to any grid-based hydrodynamic codes and are well-suited to adaptive mesh refinement methods.'
author:
- |
    Takashi Okamoto$^{1}$[^1], Kohji Yoshikawa$^{1}$, Masayuki Umemura$^{1}$\
    $^{1}$ Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8577 Ibaraki, Japan
date: 'Accepted . Received ; in original form '
title: 'ARGOT: Accelerated radiative transfer on grids using oct-tree'
---

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methods: numerical – radiative transfer.

Introduction
============

Radiative transfer (RT) of photons has fundamental importance for formation of astronomical objects, such as galaxies, stars, and blackholes. Unfortunately, the nature of RT, [in which we have to solve the time evolution of the six-dimensional phase-space information of photons]{} (three spatial dimensions, two angular dimensions, and one frequency dimension; or equivalently three spatial and three momentum dimensions), makes it difficult to solve RT accurately and to couple it with hydrodynamics. To date, various RT schemes has been proposed [@iliev06], some of which are coupled with hydrodynamics [@iliev09]. A wide range of approximation have been used to deal with multi-dimensional nature of the transfer equation and they have their own pros and 