Investigation of a likely orbital periodicity of Nova Hercules 2021 in X-rays and gamma-rays

TL;DR

This study detects a 0.153-day orbital period in Nova Hercules 2021 across X-ray and gamma-ray observations, revealing potential high-inclination geometry and short-lived gamma-ray emission, advancing understanding of nova emissions.

Contribution

It provides the first detection of a consistent orbital period in X-rays and gamma-rays for Nova Hercules 2021, highlighting the multi-wavelength behavior of the nova.

Findings

X-ray period matches optical orbital period

Gamma-ray emission detected near optical peak

Gamma-ray emission lasted less than 1 day

Abstract

We report a detection of a 0.153 days period in the classical nova V1674 Her using the NICER observations taken within a month since the outburst (i.e., about MJD 59405). The X-ray period is consistent with the orbital period previously found in the optical band, strongly suggesting the NICER signal as the X-ray orbital periodicity of the system. A seemingly double-humped profile was obtained by folding the detrended X-ray light curve with the period after removing the rotational X-ray pulsations of the nova. The profile may be caused by occultation by the companion or the accretion disk, possibly indicating a high inclination of the system. The gamma-ray emission of V1674 Her with a significance level > 5 sigma was detected by Fermi-LAT close to its optical peak and the emission faded away within 1 day, which is the shortest duration known for a gamma-ray nova. Folded on 0.153days, a marginal gamma-ray variability can be also seen in the LAT light curve, but without the double-hump feature observed in X-rays. If the gamma-ray modulation is real, its origin is probably different from that observed in the X-ray and optical bands.