We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of the gamma-ray binary system containing the pulsar PSR B1259-63 orbiting around a massive star LS 2883 in an inactive period between the 2017 and 2021 periastron passages. We detected radio continuum emission from the binary system at 97 GHz (Band 3) and 343 GHz (Band 7). Compared with our previous ALMA observations performed soon after the 2017 periastron passage, the fluxes have decreased by an factor of six at 97 GHz and two at 343 GHz. The flux at 343 GHz is large relative to that at 97 GHz and appears to be thermal emission from the circumstellar disk around LS 2883. The decrease of the 343 GHz flux may indicate that the disk has expanded and become partially optically-thin since the disk is no longer affected by pulsar winds. The flux at 97 GHz is consistent with that expected from the pulsed emission from the pulsar, which indicates that the unpulsed emission that had been produced through pulsar-disk or pulsar-stellar wind interaction has disappeared. The image of the system is consistent with a point source and shows no sign of ejecta.

中文翻译：

---

ALMA 在非活动期对 PSR B1259−63/LS 2883 的观测：可变星周盘？

我们报告了阿塔卡马大型毫米/亚毫米阵列 (ALMA) 对包含脉冲星 PSR B1259-63 的伽马射线双星系统的观测结果，该脉冲星 PSR B1259-63 在 2017 年至 2021 年的非活动期间围绕一颗大质量恒星 LS 2883 运行。我们在 97 GHz（频段 3）和 343 GHz（频段 7）下检测到来自双星系统的无线电连续发射。与我们之前在 2017 年近天体通过后不久进行的 ALMA 观测相比，通量在 97 GHz 处减少了六倍，在 343 GHz 处减少了两倍。343 GHz 处的通量相对于 97 GHz 处的通量大，并且似乎是 LS 2883 周围星周盘的热辐射。 343 GHz 通量的减少可能表明该盘自 LS 2883 以来已经膨胀并变得部分光学薄不再受脉冲星风的影响。97 GHz 的通量与脉冲星脉冲发射的预期一致，这表明通过脉冲星盘或脉冲星-恒星风相互作用产生的非脉冲发射已经消失。该系统的图像与点源一致，没有显示出喷射物的迹象。