We observed the nearby and relatively understudied ultraluminous X-ray source (ULX) NGC 4190 ULX-1 jointly with Neutron Star Interior Composition Explorer (NICER) and NuSTAR to investigate its broadband spectrum, timing properties, and spectral variation over time. We found NGC 4190 ULX-1 to have a hard spectrum characterized by two thermal components (with temperatures ∼0.25 and ∼1.6 keV) and a high-energy excess typical of the ULX population although the spectrum turns over at an unusually low energy. While no pulsations were detected (with pulsed fraction 3σ upper limits of 16% for NICER and 35% for NuSTAR), the source shows significant stochastic variability, and the covariance spectrum indicates the presence of a high-energy cutoff power-law component, potentially indicative of an accretion column. Additionally, when fitting archival XMM-Newton data with a similar model, we find that the luminosity–temperature evolution of the hot thermal component follows the behavior of a super-Eddington slim disk though the expected spectral broadening for such a disk is not seen, suggesting that the inner accretion disk may be truncated by a magnetic field. Therefore, despite the lack of detected pulsations, there is tantalizing evidence for NGC 4190 ULX-1 being a candidate neutron star accretor although further broadband observations will be required to confirm this behavior.
Return to the Forgotten Ultraluminous X-Ray Source: A Broadband NICER+NuSTAR Study of NGC 4190 ULX-1
Abstract
Copyright and License
© 2024. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
We thank the anonymous referee for useful comments that improved the clarity of this article. H.P.E. acknowledges support under NASA grant 80NSSC21K0123 and NASA contract NNG08FD60C. The majority of this work was performed on the traditional homeland of the Tongva people.
This work made use of data from the NuSTAR and NICER missions, funded by the National Aeronautics and Space Administration. We thank the observing teams for carrying out the coordinated observations. This work has also made use of archival observations by XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA, and the Neil Gehrels Swift Observatory, a NASA science mission.
Facilities
NICER - , NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission, XMM - Newton X-Ray Multimirror Mission satellite, CXO - Chandra X-ray Observatory satellite, HEASARC - , Swift (XRT) -
Software References
astropy (Astropy Collaboration et al. 2013, 2018), HENDRICS (Bachetti 2018), HEASoft (Nasa High Energy Astrophysics Science Archive Research Center (Heasarc), 2014), NICER software, NuSTARDAS, XMM-Newton SAS, Stingray (Bachetti et al. 2022)
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Additional details
- ISSN
- 1538-4357
- National Aeronautics and Space Administration
- 80NSSC21K0123
- National Aeronautics and Space Administration
- NNG08FD60C
- Caltech groups
- Astronomy Department, Space Radiation Laboratory, NuSTAR