Spectral Analysis of the 2019 and 2022 Outbursts of SAX J1808.4-3658

Abstract

The accreting millisecond pulsar SAX J1808.4-3658 went into outburst from July to November in 2019 and August to October in 2022, which were observed by \textit{NICER} and \textit{NuSTAR}. In this paper, we first present the light curve for both outbursts using \textit{NICER} data. Several thermonuclear bursts occurred during these outbursts. We analyze the evolution of the spectra of two thermonuclear bursts that took place during the 2019 \textit{NuSTAR} observation. We proceed by analyzing the combined broad-band spectrum using \textit{NICER} and \textit{NuSTAR} for the first time for this source. We jointly modeled the combined quiescent spectra of both outbursts with a self-consistent reflection component. In our best-fit model, we find evidence of reflection, consistently constrain the inclination to 72°${}_{-4°}^{+1°}$\, considering this reflection, and identify a 1 keV feature during persistent emission.

References in corpus (10)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• XMM-Newton detects a relativistically broadened iron line in the spectrum of the ms X-ray pulsar SAX J1808.4-3658
• A NICER thermonuclear burst from the millisecond X-ray pulsar SAX J1808.4-3658
• Enhanced optical activity 12 days before X-ray activity, and a 4 day X-ray delay during outburst rise, in a low-mass X-ray binary
• The aperiodic X-ray variability of the accreting millisecond pulsar SAX J1808.4-3658
• Probing jet launching in neutron star X-ray binaries: the variable and polarized jet of SAX J1808.4-3658
• The AstroSat observation of accreting millisecond X-ray pulsar SAX J1808.4-3658 during its 2019 outburst
• Evolution of accretion disc reflection spectra due to a Type I X-ray burst
• The 2019 outburst of AMXP SAX J1808.4-3658 and radio follow up of MAXI J0911-655 and XTE J1701-462
• Hydrogen-triggered X-ray Bursts from SAX J1808.4-3658? The Onset of Nuclear Burning