NuSTAR and Swift observations of the LPT CHIME J1634+44 in a radio-active state.
ATel #17478; Matthew Lundy (Columbia University), Kaya Mori (Columbia University), Shifra Mandel (Columbia University), Tong Bao (INAF-OAB), Ziteng Wang (Curtin University)
on 5 Nov 2025; 19:27 UT
Credential Certification: Matthew Lundy (mwl2145@columbia.edu)
Subjects: Radio, X-ray, Transient, Variables
We report the NuSTAR broadband X-ray observations (E= 3-79 keV) during the elevated
state of CHIME J1634+44 (RA: 16 34 29.96 Dec: +44 50 13.5, J2000). Following
the reports of elevated radio emission (ATels #17434, #17440), approximately 40 ks of NuSTAR observations were collected between 2025-10-28 20:11:11 and 2025-10-29 16:56:12. A preliminary analysis of the data yields a non-detection of excess persistent X-ray emission at the location of CHIME J1634+44 (1.9 σ). Following ATel #17474, we place 3-σ upper limits assuming an absorbed power-law; Γ = 1.7, NH = 0.075 × 1022 cm-2, between 3-79 keV at F < 1.8 × 10-13 erg/s/cm2.
Additionally, observations with Swift were carried out starting at 2025-10-28 15:56:09. These observations totaled an exposure of approximately 5 ks. Using the Swift-XRT PC-mode data, we find no excess X-ray emission at the location of CHIME J1634+44 (0.7 σ). With the same spectral assumptions as above, we find a preliminary 3-σ upper limit between 0.3-10 keV of F < 1 × 10-13 erg/s/cm2.
These non-detections are consistent with the Chandra observations reported in ATel #17474. Detailed work on phase resolved searches and photon clustering are underway and will be presented in a forthcoming publication. We encourage continued multi-wavelength monitoring to complement this campaign.
We are grateful to the NuSTAR and Swift SOC teams for the rapid scheduling of our observations.
