1. NuSTAR observations of a varying-flux quasar in the Epoch of Reionization
- Author
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Marcotulli, Lea, Connor, Thomas, Bañados, Eduardo, Boorman, Peter G., Migliori, Giulia, Grefenstette, Brian W., Momjian, Emmanuel, Siemiginowska, Aneta, Stern, Daniel, Belladitta, Silvia, Cheung, C. C., Fabian, Andrew, Khusanova, Yana, Mazzucchelli, Chiara, Rojas-Ruiz, Sofía, and Urry, C. Megan
- Subjects
Astrophysics - High Energy Astrophysical Phenomena - Abstract
With enough X-ray flux to be detected in a 160s 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 $\sim180$ 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 $\sim110$ 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 $\sim2.6$ during that period, corresponding to approximately two weeks in the quasar rest-frame. This brightening is one 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., Comment: 16 pages, 7 Figures, 3 Tables; accepted for publication in the Astrophysical Journal Letters (ApJL)
- Published
- 2025