X-Ray and Radio Variabilities of PSR J2032+4127 near Periastron

We present X-ray and radio monitoring observations of the gamma-ray binary PSR J2032+4127/MT91 213 during its periastron passage in late 2017. Dedicated Chandra, XMM-Newton, NuSTAR X-ray observations, and Very Large Array radio observations of this long orbit (50 yr), 143 ms pulsar/Be star system clearly revealed flux and spectral variability during the passage. The X-ray spectrum hardened near periastron, with a significant decrease in the power-law (PL) photon index from Γ ≈ 2 to 1.2 and evidence of an increased absorption column density. We identified a possible spectral break at a few keV in the spectrum that suggests synchrotron cooling. A coincident radio and X-ray flare occurred one week after periastron, which is possibly the result of the pulsar wind interacting with the Be stellar disk and generating synchrotron radiation. However, a multiwavelength comparison indicates that the X-ray and radio spectra cannot be simply connected by a single PL component. Hence, the emission in these two energy bands must originate from different particle populations.