The eruption of Nova V1716 Sco checked by X-rays and gamma rays

Astronomers from China and Taiwan observed the eruption of nova V1716 Sco last year using various X-ray and gamma-ray space observatories. Results of the observation campaign, presented on June 27 on the preprint server arXivprovide basic information regarding the development of this nova.

A nova is a star that experiences a sudden increase in brightness and slowly returns to its original state, a process that can take many months. Such an explosion is the result of an accretion process in a close binary system containing a white dwarf and its companion.

V1716 Sco, also known as Nova Sco 2023, was detected in a magnitude 8.0 flare on April 20, 2023. Subsequent observations of V1716 Sco spectroscopically confirmed that it is a classical (Fe II) nova.

Now, a team of astronomers led by Huihui Wang of Henan University of Science and Technology in Luoyang, China, has examined V1716 Sco in the X-ray and gamma bands. For this purpose, they used NASA’s Swift, NuSTAR, and Fermi spacecraft, as well as the Neutron Star Interior Composition Explorer (NICER) aboard the International Space Station.

“We performed a joint analysis of NuSTAR, Swift, NICER and Fermi-LAT observations of nova V1716 Sco,” the researchers wrote in the paper.

The observations found that the gamma-ray emission began the day after the optical flare of V1716 Sco, with a test statistic (TS) of 70. The duration of this gamma-ray activity with a TS value greater than 4.0 lasted for 40 days. . Additionally, the day after the optical flare, Swift also observed harder X-ray emission.

The finding therefore makes V1716 Sco the first classical nova in which the Swift X-ray detection is concurrent with gamma-ray emission, and the fourth classical nova to show gamma-ray emission concurrent with harder X-ray emission from the NuSTAR data.

By analyzing the X-ray spectrum, the researchers found that the hardness ratio decreased rapidly over time, and the observed emission entered the supersoft source (SSS) phase approximately 40 days after the nova eruption. In addition, the NICER data allowed astronomers to detect quasi-periodic oscillations (QPOs) in the SSS phase with a period of 79.10 seconds.

In an attempt to explain the origin of the detected QPO, the authors of the paper point to the spin modulation of the white dwarf as the most plausible hypothesis. However, they noted that the period of the modulations is not stable over time. This may mean that the hot spot region on the surface of the white dwarf may be shifting over time, or that the periodic modulation may come from another mechanism, such as stellar oscillation.

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