Jet-dominated quiescent state in black hole X-ray binaries: the cases of A0620--00 and XTE J1118+480

The radiative mechanism of the black hole X-ray transients (BHXTs) in their quiescent states (defined as the 2-10 keV X-ray luminosity $\le 10^{34}{\rm \,erg\,s^{-1}}$) remains unclear. In this work, we investigate the quasi-simultaneous quiescent state spectrum (including radio, infrared, optical, ultraviolet and X-ray) of two BHXTs, A0620--00 and XTE J1118+480. We find that, these two sources can be well described by a coupled accretion -- jet model. More specifically, most of the emission (radio up-to infrared, and the X-ray waveband) comes from the collimated relativistic jet. Emission from hot accretion flow is totally insignificant, and it can only be observed in mid-infrared (the synchrotron peak). Emission from the outer cold disc is only evident in UV band. These results are consistent with our previous investigation on the quiescent state of V404 Cyg, and confirm that the quiescent state is jet-dominated.Comment: 11 pages, 1 figure, accepted for publication in Research in Astronomy and Astrophysic

BCR algorithm and the T(b)T(b) theorem

We show using the Beylkin-Coifman-Rokhlin algorithm in the Haar basis that any singular integral operator can be written as the sum of a bounded operator on $L^p$, $1<p<\infty$, and of a perfect dyadic singular integral operator. This allows to deduce a local $T(b)$ theorem for singular integral operators from the one for perfect dyadic singular integral operators obtained by Hofmann, Muscalu, Thiele, Tao and the first author.Comment: Change of title. New abstract and new introductio

Jet-dominated quiescent states in black hole X-ray binaries: the case of V404 Cyg

The dynamical and radiative properties of the quiescent state (X-ray luminosity $<10^{34}\ {\rm erg s^{-1} cm^{-2}}$) of black hole X-ray transients (BHXTs) remains unclear, mainly because of low-luminosity and poor data quantity. We demonstrate that, the simultaneous multi-wavelength (including radio, optical, ultraviolet and X-ray bands) spectrum of V404 Cyg in its bright quiescent state can be well described by the radiation from the companion star and more importantly, the compact jet. Neither the outer thin disc nor the inner hot accretion flow is important in the total spectrum. Together with several additional recent findings, i.e. the power-law X-ray spectrum and the constant X-ray spectral shape (or constant photon index) in contrast to the dramatic change in the X-ray luminosity, we argue the quiescent state spectrum of BHXTs is actually jet-dominated. Observational features consistent with this jet model are also discussed as supporting evidences.Comment: accepted for the publication in MNRAS Letters, 5 pages, 2 figure