Continued monitoring of PMN J1603-4904: further MeerKAT, NuSTAR, and H.E.S.S. epochs

ATel #17410; G. Bruni (INAF-IAPS), M. Brienza (INAF-IRA), J. Rodi (INAF-IAPS), G. Migliori, M. Giroletti, E. Liuzzo (INAF-IRA), E. Bronzini (U. Bologna & INAF-OAS), M. Kadler (U. Wuerzburg), L. Hernandez-Garcia (U. Valparaiso), F. Panessa, E. Torresi, P. Da Vela (INAF-OAS), M. Cerruti (U. Paris Cite), , C. Reynolds (CSIRO), P. Goswami (LSW, U. Heidelberg) and Stefan J. Wagner, for the H. E.S. S. collaboration
on 22 Sep 2025; 10:50 UT
Credential Certification: Gabriele Bruni (gabriele.bruni@inaf.it)

Tweet

We report on further observations of the flaring CSO PMN J1603-4904 performed with MeerKAT, NuSTAR, and H.E.S.S.. MeerKAT carried out a third and a fourth epoch on July 29 and August 29, 2025, respectively. As in the previous epochs, MeerKAT observed the target for approximately 15 minutes at 3 GHz (S4 band). Phase referencing was applied, and data were processed using the SARAO Science Data Processor (SDP) continuum pipeline. The final images have an angular resolution of 4.09" x 3.61", P.A. -62.8 deg, and RMS 36 uJy/beam (Jul 29), while 4.17" x 3.49", P.A. -57.2 deg, and RMS 43 uJy/beam (Aug 29). The measured flux density is 1.40+/-0.07 Jy (Jul 29), and 1.39+/-0.07 Jy (Aug 29). These values are consistent within uncertainties with the previous measurements, indicating no significant radio variability to date.

The High Energy Stereoscopic System (H.E.S.S.) conducted a second follow-up observation of the source at very-high energies (VHE; E>100 GeV) in coordination with MeerKAT on the night of 29 July 2025, roughly a month after the initial follow-up (ATel #17307). The offline analysis of about 1.8 h of livetime revealed no significant excess (detection significance < 1 sigma), indicating that the source is no longer active in the VHE band. No further coordinated observations were taken, as the H.E.S.S. visibility is limited after July due to high zenith constraints.

NuSTAR (Nuclear Spectroscopic Telescope Array) performed DDT observations from 27 August 6:15:07 to 28 August 1:20:00 2025 UTC, quasi-contemporaneously with MeerKAT. Spectral analysis in the 3-20 keV energy range found the data are well described by an absorbed powerlaw model with an intrinsic NH = (5.3+/-1.6) x 10^22 /cm^2, Gamma = 3.1+/-0.1 with chi^2/dof = 74.96/73 = 1.03 assuming a galactic absorption of NH = 6.32 x 10^21 /cm^2 and a redshift of 0.18 (Mueller et al., 2015). The unabsorbed flux in the 2-10 keV band is about 2.4 x 10^-12 erg/cm^2/s.

The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation. H.E.S.S. is an array of five imaging atmospheric Cherenkov telescopes to study very-high-energy gamma-ray sources and is located in the Khomas Highlands in Namibia. It was constructed and is operated by researchers from Armenia, Australia, Austria, Denmark, France, Germany, Ireland, Japan, the Netherlands, Poland, South Africa, UK, and the host country, Namibia. This research has made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. Data analysis was performed using the NuSTAR Data Analysis Software (NuSTARDAS), jointly developed by the ASI Science Data Center (SSDC, Italy) and the California Institute of Technology (USA).