In recent years, it was found that there are several low/hard state of X-ray binaries (XRBs) follow an 'outliers' track of radio-X-ray correlation (L R ∝ L b X and b ∼ 1.4), which is much steeper than the former universal track with b ∼ 0.6. In this work, we compile a sample of bright radio-quiet active galactic nuclei (AGNs) and find that their hard X-ray photon indices and Eddington ratios are positively correlated, which is similar to that of 'outliers' of XRBs, where both bright AGNs and 'outliers' of XRBs have bolometric Eddington ratios 1%L Edd (L Edd is Eddington luminosity). The Eddington-scaled radio-X-ray correlation of these AGNs is also similar to that of 'outliers' of XRBs, which has a form of L 5GHz /L Edd ∝ (L 2−10keV /L Edd ) c with c ≃ 1.59 and 1.53 for AGNs and XRBs respectively. Both the positively correlated X-ray spectral evolution and the steeper radio-X-ray correlation can be regulated by a radiatively efficient accretion flow (e.g., disk-corona). Based on these similarities, we further present a new fundamental plane for 'outliers' of XRBs and bright AGNs in black-hole (BH) mass, radio and X-ray luminosity space: log L R = 1.59 +0.28 −0.22 log L X − 0.22 +0.19 −0.20 log M BH − 28.97 +0.45 −0.45 with a scatter of σ R = 0.51dex. This fundamental plane is suitable for radiatively efficient BH sources, while the former plane proposed by Merloni et al. and Falcke et al. may be most suitable for radiatively inefficient sources.

The hyperluminous X-ray source (HLX-1, the peak X-ray luminosity ∼ 10 42 erg s −1 ) near the spiral galaxy ESO 243-49 is possibly the best candidate for intermediate mass black hole (IMBH), which underwent recurrent outbursts with a period of ∼ 400 days. The physical reason for this quasi-periodic variability is still unclear. We explore the possibility of radiation-pressure instability in accretion disk by modeling the light curve of HLX-1, and find that it can roughly reproduce the duration, period and amplitude of the recurrent outbursts HLX-1 with an IMBH of ∼ 10 5 M ⊙ . Our result provides a possible mechanism to explain the recurrent outbursts in HLX-1. We further find a universal correlation between the outburst duration and the bolometric luminosity for the BH sources with a very broad mass range (e.g., X-ray binaries, XRBs, HLX-1 and active galactic nuclei, AGNs), which is roughly consistent with the prediction of radiation-pressure instability of the accretion disk. These results imply that "heartbeat" oscillations triggered by radiation-pressure instability may appears in different-scale BH systems.

Recently an 'outliers' track of radio-X-ray correlation was found, which is much steeper than the former universal correlation, where dual tracks were speculated to be triggered by different accretion processes. In this work, we test this issue by exploring hard X-ray spectral evolution in four black-hole X-ray binaries (XRBs) with multiple, quasi-simultaneous radio and X-ray observations. Firstly, we find that hard X-ray photon indices, Γ, are anti-and positively correlated to X-ray fluxes when the X-ray flux, F 3−9keV , is below and above a critical flux, F X,crit , which are consistent with prediction of advection dominated accretion flow (ADAF) and disk-corona model respectively. Secondly and most importantly, we find that the radio-X-ray correlations are also clearly different when the X-ray fluxes are higher and lower than the critical flux that defined by X-ray spectral evolution. The data points with F 3−9keV F X,crit have a steeper radio-X-ray correlation (F X ∝ F b R and b ∼ 1.1 − 1.4), which roughly form the 'outliers' track. However, the data points with anti-correlation of Γ − F 3−9keV either stay in the universal track with b ∼ 0.61 or stay in transition track (from the universal to 'outliers' tracks or vice versa). Therefore, our results support that the universal and 'outliers' tracks of radio-X-ray correlations are regulated by radiatively inefficient and radiatively efficient accretion model respectively.

The anti-and positive correlations between X-ray photon index and Eddington-scaled X-ray luminosity were found in decay phase of X-ray binary outbursts and a sample of active galactic nuclei in former works. We further systematically investigate the evolution of X-ray spectral index, along the X-ray flux and Eddington ratio in eight outbursts of four black-hole X-ray binaries, where all selected outbursts have observational data from Rossi X-ray Timing Explorer in both rise and decay phases. In the initial rise phase, the X-ray spectral index is anti-correlated with the flux, and the X-ray spectrum quickly softens when the X-ray flux is approaching the peak value. In the decay phase, the X-ray photon index and the flux follow two different positive correlations, and they become anti-correlated again when the X-ray flux is below a critical value, where the anti-correlation part follow the same trend as that found in the initial rise phase. Compared with other X-ray binaries, GRO J1655-40 has an evident lower critical Eddington ratio for the anti-and positive transition, which suggests that its black-hole mass and distance are not well constrained or its intrinsic physic is different.

Spectra of 76 known dwarf novae from the LAMOST survey were presented. Most of the objects were observed in quiescence, and about 16 systems have typical outburst spectra. 36 of these systems were observed by SDSS, and most of their spectra are similar to the SDSS spectra. Two objects, V367 Peg and V537 Peg, are the first spectra of the object. The spectrum of V367 Peg shows a contribution from an M-type donor and its spectral type could be estimated as M3-5 by combining its orbital period. The signature of a white dwarf spectrum can be seen clearly in four low-accretion-rate WZ Sge stars. Other special spectral features worthy of further observations are also noted and discussed. We present a LAMOST spectral atlas of outbursting dwarf novae. Six objects have their first outburst spectra given here, and the others were also compared with the published outburst spectra. We argue that these data will be useful for further investigation of the accretion disc properties. The He ii λ4686 emission line can be found in the outburst spectra of seven dwarf novae. These objects are excellent candidates for probing the spiral asymmetries of accretion disc.