Hard X-rays and QPO in <i>Swift</i> J1727.8−1613: the rise and plateau of the 2023 outburst
I. A. Mereminskiy, A. Lutovinov, S. Molkov, Roman Krivonos, A. Semena, S. Sazonov, A. Tkachenko, R. Sunyaev
Abstract
ABSTRACT We report on the detection of type-C quasi-periodic oscillations during the initial stages of the outburst of Swift J1727.8–1613 in 2023. Using data of the INTEGRAL observatory along with the data of the Mikhail PavlinskyART-XC telescope on board Spektr-RG and X-ray Telescope (XRT) of the Neil Gehrels Swift observatory the fast growth of the quasi-periodic oscillations (QPO) frequency was traced. We present a hard X-ray light curve that covers the initial stages of the 2023 outburst – the fast rise and plateau – and demonstrate that the QPO frequency was stable during the plateau. The switching from type-C to type-B QPO was detected with the beginning of the source flaring activity. We have constructed a broad-band spectrum of Swift J1727.8−1613 and found an additional hard cutoff power-law spectral component extending at least up to 250 keV. Finally, we have obtained an upper limit on the hard X-ray flux at the beginning of the optical outburst and estimated the delay of the hard X-ray outburst with respect to the optical one.