Detection of Oscillations in a Type I X-Ray Burst of 4U 0614+091 with SVOM/ECLAIRs

TL;DR

This paper reports the detection and analysis of burst oscillations in a Type I X-ray burst from 4U 0614+091, revealing an unusual frequency drift likely caused by orbital motion, implying a very short orbital period.

Contribution

First detection of burst oscillation frequency drift in 4U 0614+091, suggesting a very compact binary system with an orbital period under 20 minutes.

Findings

Detected burst oscillations at 413.674 Hz

Observed a significant downward frequency drift

Inferred a very short orbital period (<20 min)

Abstract

On 2025 January 10, a thermonuclear (Type I) X-ray burst from the neutron star low-mass X-ray binary \textit{4U~0614+091} was detected with the ECLAIRs instrument on board the \textit{SVOM} mission. We present here a time-resolved spectroscopic analysis of the burst, along with the detection of burst oscillations within a 51-second interval during the decay phase. The oscillation frequency is measured to be $\nu = 413.674 \pm 0.002\,\mathrm{Hz}$, consistent with previous reports. However, we detect a significant downward frequency drift over the burst duration, characterized by $\dot{\nu} = (-4.7 \pm 0.3) \times 10^{-3}\,\mathrm{Hz\,s^{-1}}$. This frequency evolution is atypical compared to those observed in similar burst oscillation sources. We tentatively attribute the observed drift to a Doppler shift induced by orbital motion. Under this interpretation, the inferred orbital period must be shorter than 20 minutes, placing \textit{4U~0614+091} among the most compact known low-mass X-ray binaries.