GECAM detection of a bright type-I X-ray burst from 4U 0614+09: confirmation its spin frequency at 413 Hz

TL;DR

This paper reports the detection of a bright thermonuclear X-ray burst from 4U 0614+09 by GECAM, confirming its spin frequency at 413 Hz and revealing a multi-peak burst oscillation profile for the first time in a nonpulsating source.

Contribution

The study provides the first detection of a multi-peak burst oscillation profile in a nonpulsating source, confirming the spin frequency and characterizing the burst's properties with GECAM.

Findings

Confirmed the spin frequency at 413 Hz for 4U 0614+09.

Detected the brightest burst (excluding superbursts) from the source.

Observed a multi-peak structure in the burst oscillation profile.

Abstract

One month after launching Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM), a bright thermonuclear X-ray burst from 4U~0614+09, was observed on January 24, 2021. We report the time-resolved spectroscopy of the burst and a burst oscillation detection at 413 Hz with a fractional amplitude 3.4\% (rms). This coincides with the burst oscillation previously discovered with \textit{Swift}/BAT \citep{Strohmayer2008}, and therefore confirms the spin frequency of this source. This burst is the brightest one in the normal bursts (except the superburst) ever detected from 4U~0614+09, which leads to an upper limit of distance estimation as 3.1 kpc. The folded light curve during the burst oscillation shows a multi-peak structure, which is the first case observed during a single burst oscillation in nonpulsating sources. The multi-peak profile could be due to additional harmonics of the burst oscillation, which is corresponding to several brighter/fainter spots at the stellar surface.