NICER observation list: Target ID 771301

We propose to observe thermonuclear X-ray bursts from 4U 1820-30 in its low-hard state using NuSTAR and NICER. The goal of this study is to understand the nature of the so-called persistent emission and how it responds to X-ray bursts. We aim to investigate the timing and spectral properties of the bursts, including their recurrence time. Using various spectral models, our study will be crucial in examining how photospheric radius expansion bursts affect the geometry of the accretion flow, such as the inner disk and corona. In previous studies, NICER has detected a persistent count rate of about 1200 c/s from the source in a low-hard state. The peak of thermonuclear X-ray bursts reaches up to a NICER count rate of 20000 c/s.