Accretion Flow Properties of Swift J1727.8-1613 and Estimation of the BH Mass

Dipak Debnath; Hsiang-Kuang Chang; Sujoy Kumar Nath; Lev Titarchuk

paper

Accretion Flow Properties of Swift J1727.8-1613 and Estimation of the BH Mass

arXiv:2504.16391

Abstract

The rising phase of the 2023-24 outburst of the recently discovered bright transient black hole candidate Swift J1727.8-1613 was monitored by {\it Insight}-HXMT. We study the evolution of hard ( $4$ -150 $k e V) an d so f t ($ 2 $-$ 4 $k e V) ban d p h o t o n co u n t r a t es, t h e ha r d n essr a t i o (H R), QP O f r e q u e n c i es, an d s p ec t r a l f e a t u r es u s in g d ai l y o b ser v a t i o n s f r o m t h eH X M T / L E, M E, an d H E in s t r u m e n t s b e tw ee n A ug u s t 25 an d O c t o b er 5, 2023. T h e QP O f r e q u e n cy i s f o u n d t o b es t r o n g l y cor r e l a t e d w i t h t h eso f t - ban d X - r a y co u n t r a t es, an d s p ec t r a l p h o t o nin d i ces . I n co n t r a s t, a s t r o n g an t i - cor r e l a t i o ni so b ser v e d b e tw ee n H R an d QP O f r e q u e n cy, a s w e l l a s b e tw ee n H R an d p h o t o nin d e x . B a se d o n t h ee v o l u t i o n o f t h e t e m p or a l an d s p ec t r a l p r o p er t i es, t h er i s in g p ha seo f t h eo u t b u r s t i ss u b d i v i d e d in t os i x p a r t s . T h ee v o l u t i o n o f t h e QP O s in p a r t s 1 - 5 i s f i tt e d w i t h t h e p r o p a g a t in g osc i l l a t or y s h oc k (P O S) so l u t i o n t o u n d er s t an d t h e na t u r eo f t h ee v o l u t i o n f r o ma p h y s i c a l p er s p ec t i v e . A nin w a r d - p r o p a g a t in g s h oc k w i t h w e ak e nin g s t r e n g t h (e x ce pt in p a r t 4) i so b ser v e dd u r in g t h e p er i o d o f o u r s t u d y . T h e p r o bab l e ma sso f t h eso u r ce i ses t ima t e d t o b e$ 13.5 \pm 1.9~M_\odot $u s in g t h e QP O f r e q u e n cy ($ ν $) - p h o t o nin d e x ($ Γ$) scaling method.

15 Pages, 6 Figures, 2 Tables (Accepted for publication in ApJ)