Cooling of Magnetars with Exotic Matter

Nobutoshi Yasutake1, Tsuneo Noda2, Kotaro Fujisawa3, Kei Kotake4,5, Toshikazu Shigeyama6 1Department of Physics, Chiba Institute of Technology, Shibazono 2-1-1, Narashino, Chiba, 275-0023, Japan 2Kurume Institute of Technology, 2228-66 Kamitsu-machi, Kurume, Fukuoka 830-0052, Japan 3Advanced research Institute for Science and Engineering, Waseda University, Okubo 3-4-1, Shinjuku, Tokyo, 169-8555, Japan 4Department of Applied Physics, Faculty of Science, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka, 814-0180, Japan 5Division of Theoretical Astronomy, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, 181-8588, Japan 6Research Center for the Early Universe (RESCEU), School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan E-mail: [email protected] (Received August 29, 2016)

Thermal evolutions of magnetars are studied concerned with effects of exotic matter. All results are shown in two spatial dimensions for comparison with observational results by NuSTAR, NICER etc. in near future. Thermal conduction of envelope/crust in magnetars is affected by the strong magnetic field, and it could be an origin of hot/cold spots, which are expressed well with the two black body fitting. This study also stresses effects of the equation of state, on which the cooling processes, the thermal conductivity, and the heat capacity strongly depend. Exotic matter changes thermal evolutions of magnetars drastically, hence the effects could be detected in observations. KEYWORDS: dense matter, stars: neutron, stars: evolution

1. Introduction

The thermal evolution of neutron stars (NSs) is a key issue to know the properties of superdense matter, e.g. thermal conductivities, heat capacities, the equation of state (EOS), and cooling processes. At such a high density region, there is a possibility of the quark-hadron phase transition, but it is difficult to reveal the behaviors of such matter only by theoretical ways. We, hence, need to compare theoretical indications of the phase transition with observations and/or experiments. As a matter of fact, the observations of the NS mass by Demorest et al. and Antniadis et al. constrain the EOS strongly [1, 2]. Thanks to recent progresses of X-ray observations, the magnetic field also helps our understand- ing of superdense matter through the observed properties of magnetars (see Ref. [3] as a review). The observations suggest that some magnetars do not have uniform surface temperature, and we need to introduce two-blackbody temperature at least to explain them. In this study we focus on the thermal evolution calculations of magnetars with the quark-hadron phase transition, and the results support the two-blackbody temperature on the surface.

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