Photospheric Radius Expansion and a double-peaked type-I X-ray burst from GRS 1741.9-2853

Abstract

We present analysis of two type-I X-ray bursts observed by NuSTAR originating from the very faint transient neutron star low-mass X-ray binary GRS 1741.9-2853 during a period of outburst in May 2020. We show that the persistent emission can be modeled as an absorbed, Comptonized blackbody in addition to Fe K$\alpha$ emission which can be attributed to relativistic disk reflection. We measure a persistent bolometric, unabsorbed luminosity of $L_{\mathrm{bol}}=7.03_{-0.05}^{+0.04}\times 10^{36}\mathrm{erg}{\mathrm{s}}^{-1}$, assuming a distance of 7 kpc, corresponding to an Eddington ratio of $4.5\%$. This persistent luminosity combined with light curve analysis leads us to infer that the bursts were the result of pure He burning rather than mixed H/He burning. Time-resolved spectroscopy reveals that the bolometric flux of the first burst exhibits a double-peaked structure, placing the source within a small population of accreting neutron stars which exhibit multiple-peaked type-I X-ray bursts. We find that the second, brighter burst shows evidence for photospheric radius expansion (PRE) and that at its peak, this PRE event had an unabsorbed bolometric flux of $F_{\mathrm{peak}}=2.94_{-0.26}^{+0.28}\times 10^{-8}\mathrm{erg}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$. This yields a new distance estimate of $d=9.0\pm 0.5$ kpc, assuming that this corresponds to the Eddington limit for pure He burning on the surface of a canonical neutron star. Additionally, we performed a detailed timing analysis which failed to find evidence for quasiperiodic oscillations or burst oscillations, and we place an upper limit of $16\%$ on the rms variability around 589 Hz, the frequency at which oscillations have previously been reported.

15 pages, 4 figures, 4 tables, accepted for publication in ApJ

References in corpus (8)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• The role of the reflection fraction in constraining black hole spin
• No Time for Dead Time: Timing analysis of bright black hole binaries with NuSTAR
• Evidence for enhanced persistent emission during sub-Eddington thermonuclear bursts
• Broadband X-ray Imaging and Spectroscopy of the Crab Nebula and Pulsar with NuSTAR
• NuSTAR observation of a Type I X-ray burst from GRS 1741.9-2853
• NuSTAR low energy effective area correction due to thermal blanket tear
• On the illumination of neutron star accretion discs

Cited by in corpus (3)

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• AstroSat observation of rapid Type-I thermonuclear burst from the low mass X-ray binary GX 3+1