2020/11/04 by D. J. K. Buisson, A. C. Fabian, P. Gandhi +8
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics #Gamma-ray bursts and supernovae #Lag #Nanotechnology #Physics #Pulsars and Gravitational Waves Research #Soft materials #astro-ph.HE
paper · pdf · doi:10.1093/mnras/staa3510
MNRAS, resubmitted after minor revision. 12 pages, 10 figures, 1 table
arxiv created 2020/11/04 · openalex created_date 2020/11/09 · openalex publication_date 2020/11/11 · arxiv updated 2020/11/18 · openalex updated_date 2026/08/05
ABSTRACT We continue the analysis of NuSTAR data from the recent discovery outburst of MAXI J1820+070 (optical counterpart ASASSN-18ey), focussing on an observation including unusual flaring behaviour during the hard to soft state transition, which is a short phase of outbursts and so comparatively rarely observed. Two plateaus in flux are separated by a variable interval lasting ∼10 ks, which shows dipping then flaring stages. The variability is strongest (with fractional variability up to F\rm Var∼ 10 \rm per cent) at high energies and reduces as the contribution from disc emission becomes stronger. Flux-resolved spectra show that the variability is primarily due to the power-law flux changing. We also find a long soft lag of the thermal behind the power-law emission, which is 20-1.2+1.6 s during the flaring phase. The lag during the dipping stage has a different lag–energy spectrum, which may be due to a wave passing outwards through the disc. Time-resolved spectral fitting suggests that the lag during the flaring stage may be due to the disc re-filling after being disrupted to produce the power-law flare, perhaps related to the system settling after the jet ejection which occurred around 1 d before. The time-scales of these phenomena imply a low viscosity parameter, α ∼ 10−3, for the inner region of the disc.