English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

NICER observed two outbursts from the neutron star low-mass X-ray binary4U~1730$-$22 in 2021 and 2022, which showed a similar spectral evolution in thehardness-intensity diagram. Seventeen type I X-ray bursts were identified inboth outbursts. The X-ray burst spectra showed clear deviations from theblackbody model, firstly $\sim10$ s after onset. Adding the enhanced persistentemission due to the Poynting-Robertson drag or the reflection from theaccretion disk both significantly improved the fitting results. We found that12 out of 17 X-ray bursts showed the photospheric radius expansion (PRE)characteristic. Considering the nine PRE bursts out of ten X-ray burstsobserved by Insight-HXMT, 78\% of bursts from 4U~1730--22 exhibited PRE.According to the burst rise time, the duration, the local accretion rate, andthe burst fuel composition estimated from recurrence time, we propose thatthese PRE bursts were powered by pure helium. From the touchdown flux of PREbursts, we estimate the source distance of $ d=7.54\pm{0.46} (X=0)$ kpc for acanonical neutron star with $M_{\rm NS}=1.4M_\odot$ and $R_{\rm NS}=10~{\rmkm}$.

Type I X-ray bursts' spectra and fuel composition from the atoll and transient source 4U 1730$-$22