Letter to the Editor

Face changing companion of the redback millisecond pulsar PSR J1048+2339

¹ Institute of Astronomy, National Tsing Hua University, Hsinchu 30013, Taiwan
e-mail: yapyeexuan@gapp.nthu.edu.tw
² Department of Physics, UNIST, Ulsan 44919, Korea
³ School of Physics, Huazhong University of Science and Technology, Wuhan 430074, PR China
⁴ Department of Space Science and Geology, Chungnam National University, Daejeon, Republic of Korea
⁵ Department of Astronomy and Space Science, Chungnam National University, Daejeon, Republic of Korea

Received: 31 October 2018
Accepted: 20 December 2018

Abstract

We present optical observations of the redback millisecond pulsar PSR J1048+2339, which is a 4.66 ms radio pulsar in a compact binary with an orbital period of six hours. We obtained high-quality light curves of PSR J1048+2339 with the Lulin 1 m Telescope. The system shows two distinct six-hour orbital modulations, in which an ellipsoidal modulation changes into a sinusoidal-like profile in less than 14 days. In addition to the change, the brightness of the companion increased by one magnitude, suggesting that the latter type of modulation is caused by the pulsar wind heating of the companion and that the heating became dominant in the system. While the changes are not unexpected, such a timescale is the shortest among similar systems. We performed modeling analysis to extract the properties of the system. We obtained a derived pulsar mass of 2.1 M_⊙ and a companion star mass of 0.4 M_⊙ for the system. The irradiation power increased by a factor of 6 during which the pulsar wind heating dominates. We also report on the two archival Chandra X-ray observations and discuss several possibilities that might cause the varying heating on the companion.