NICER, NuSTAR, and Insight-HXMT Views to the Newly Discovered Black Hole X-Ray Binary Swift J1727.8-1613

Abstract

Abstract Swift J1727.8–1613 is a black hole X-ray binary newly discovered in 2023. We perform spectral analysis with simultaneous Insight-HXMT, NICER, and NuSTAR observations when the source was approaching the hard intermediate state. Such a joint view reveals an additional hard component apart from the normally observed hard component with reflection in the spectrum, to be distinguished from the usual black hole X-ray binary systems. By including this extra component in the spectrum, we have measured a high spin of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.98</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.07</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.02</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> and an inclination of around <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>40</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.2</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> °, which is consistent with NICER results reported before. However, we find that the additional spectral component cannot be exclusively determined due to the model degeneracy. Accordingly, a possible jet/corona configuration is adjusted to account for the spectral fitting with different model trials. The extra component may originate either from a relativistic jet or a jet base/corona underneath a slow jet.