NuSTAR Observations of a Varying-flux Quasar in the Epoch of Reionization

Creators: Marcotulli, Lea¹; Connor, Thomas^{2, 3}; Bañados, Eduardo⁴; Boorman, Peter G.⁵; Migliori, Giulia⁶; Grefenstette, Brian W.⁵; Momjian, Emmanuel⁷; Siemiginowska, Aneta²; Stern, Daniel³; Belladitta, Silvia^{4, 8}; Cheung, C. C.⁹; Fabian, Andrew¹⁰; Khusanova, Yana⁴; Mazzucchelli, Chiara¹¹; Rojas-Ruiz, Sofía¹²; Urry, C. Megan¹

1. Yale University
2. Harvard-Smithsonian Center for Astrophysics
3. Jet Propulsion Lab
4. Max Planck Institute for Astronomy
5. California Institute of Technology
6. Istituto di Radioastronomia di Bologna
7. National Radio Astronomy Observatory
8. Osservatorio di Astrofisica e Scienza dello Spazio di Bologna
9. United States Naval Research Laboratory
10. University of Cambridge
11. Diego Portales University
12. University of California, Los Angeles

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Abstract

With enough X-ray flux to be detected in a 160 s scan by SRG/eROSITA, the z = 6.19 quasar CFHQS J142952+544717 is, by far, the most luminous X-ray source known at z > 6. We present deep (245 ks) NuSTAR observations of this source; with ∼180 net counts in the combined observations, CFHQS J142952+544717 is the most distant object ever observed by the observatory. Fortuitously, this source was independently observed by Chandra ∼110 days earlier, enabling the identification of two nearby (30'' and 45'' away), fainter X-ray sources. We jointly fit both Chandra and NuSTAR observations—self-consistently including interloper sources—and find that, to greater than 90% confidence, the observed 3–7 keV flux varied by a factor of ∼2.6 during that period, corresponding to approximately two weeks in the quasar rest frame. This brightening is one of the most extreme instances of statistically significant X-ray variability seen in the Epoch of Reionization. We discuss possible scenarios that could produce such rapid change, including X-ray emission from jets too faint at radio frequencies to be observed.

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Acknowledgement

We thank the journal anonymous referee for the constructive review. Support for this work was provided by the National Aeronautics and Space Administration through Chandra award numbers GO3-24069X, GO8-19093X, and GO0-21101X issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060.

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). The scientific results reported in this article are based on observations made by the Chandra X-ray Observatory contained in DOI:10.25574/cdc.308. This research has made use of software provided by the Chandra X-ray Center (CXC) in the application package CIAO.

L.M. acknowledges that support for this work was provided by NASA through the NASA Hubble Fellowship grant No. HST-HF2-51486.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. L.M. acknowledges support from NASA contract 80NSSC22K1811. T.C. and A.S. acknowledge support from NASA contract NAS8-03060 to the Chandra X-ray Center. Portions of T.C.'s research were supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, California Institute of Technology, administered by the Universities Space Research Association under contract with NASA. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. G.M. acknowledges financial support from the INAF minigrant "The high-energy view of jets and transients" (Bando Ricerca Fondamentale INAF 2022). C.M. acknowledges support from ANID BASAL project FB210003. Y.K. is thankful for the support of the German Space Agency (DLR) through the program LEGACY 50OR2303. Research at the Naval Research Laboratory is supported by NASA DPR S-15633-Y.

Facilities

NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission, CXO - Chandra X-ray Observatory satellite.

Software References

BXA (J. Buchner et al. 2014), CIAO (A. Fruscione et al. 2006), PyFITS (P. E. Barrett & W. T. Bridgman 1999), XSPEC (K. A. Arnaud 1996).

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