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تسجيل مستخدم جديدThe binary mass ratio in the black hole transient MAXI J1820+070
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We present intermediate resolution spectroscopy of the optical counterpart to the black hole X-ray transient MAXI J1820+070 (=ASASSN-18ey) obtained with the OSIRIS spectrograph on the 10.4-m Gran Telescopio Canarias. The observations were performed with the source close to the quiescent state and before the onset of renewed activity in August 2019. We make use of these data and K-type dwarf templates taken with the same instrumental configuration to measure the projected rotational velocity of the donor star. We find $v_{rot} sin i = 84 pm 5$ km s$^{-1}$ ($1!-!sigma$), which implies a donor to black-hole mass ratio $q = {M_2}/{M_1} = 0.072 pm 0.012$ for the case of a tidally locked and Roche-lobe filling donor star. The derived dynamical masses for the stellar components are $M_1 = (5.95 pm 0.22)sin ^{-3}i$ $M_odot$ and $M_2 = (0.43 pm 0.08) sin^{-3}i$ $M_odot$. The use of $q$, combined with estimates of the accretion disk size at the time of the optical spectroscopy, allows us to revise our previous orbital inclination constraints to $66^{circ} < i < 81^{circ}$. These values lead to 95% confidence level limits on the masses of $5.73 <M_1(M_odot) < 8.34$ and $0.28 < M_2(M_odot) < 0.77$. Adopting instead the $63 pm 3^{circ}$ orientation angle of the radio jet as the binary inclination leads to $M_1 = 8.48^{+0.79}_{-0.72} M_odot$ and $M_2 = 0.61^{+0.13}_{-0.12} M_odot$ ($1!-!sigma$).
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We study the jet in the hard state of the accreting black-hole binary MAXI J1820+070. From the available radio-to-optical spectral and variability data, we put strong constraints on the jet parameters. We find while it is not possible to uniquely det
ermine the jet Lorentz factor from the spectral and variability properties alone, we can estimate the jet opening angle ($1.5pm 1$ deg), the distance at which the jet starts emitting synchrotron radiation ($sim$3$times10^{10}$cm), the magnetic field strength there ($sim$10$^4$G), and the maximum Lorentz factor of the synchrotron-emitting electrons ($sim$110--150) with relatively low uncertainty, as they depend weakly on the bulk Lorentz factor. We find the breaks in the variability power spectra from radio to sub-mm are consistent with variability damping over the time scale equal to the travel time along the jet at any Lorentz factor. This factor can still be constrained by the electron-positron pair production rate within the jet base, which we calculate based on the observed X-ray/soft gamma-ray spectrum, and the jet power, required to be less than the accretion power. The minimum ($sim$1.5) and maximum ($sim$4.5) Lorentz factors correspond to the dominance of pairs and ions, and the minimum and maximum jet power, respectively. We estimate the magnetic flux threading the black hole and find the jet can be powered by the Blandford-Znajek mechanism in a magnetically-arrested flow accretion flow. We point out the similarity of our derived formalism to that of core shifts, observed in extragalactic radio sources.
MAXI J1820+070 is a newly-discovered black hole X-ray binary, whose dynamical parameters, namely the black hole mass, the inclination angle and the source distance, have been estimated recently. emph{Insight}-HXMT have observed its entire outburst fr
om March 14th, 2018. In this work, we attempted to estimate the spin parameter~$a_*$, using the continuum-fitting method and applying a fully-relativistic thin disk model to the soft-state spectra obtained by emph{Insight}-HXMT. It is well know that $a_*$ is strongly dependent on three dynamical parameters in this method, and we have examined two sets of parameters. Adopting our preferred parameters: $M$ = $8.48^{+0.79}_{-0.72}~M_odot$, $i=63^circpm3^circ$ and $D=2.96pm0.33$ kpc, we found a slowly-spinning black hole of $a_*=0.14 pm 0.09$ ($1sigma$), which give a prograde spin parameter as majority of other systems show. While it is also possible for the black hole to have a retrograde spin (less than 0) if different dynamical parameters are taken.
Using the Very Long Baseline Array and the European Very Long Baseline Interferometry Network we have made a precise measurement of the radio parallax of the black hole X-ray binary MAXI,J1820+070, providing a model-independent distance to the source
. Our parallax measurement of ($0.348pm0.033$) mas for MAXI J1820+070 translates to a distance of ($2.96pm0.33$) kpc. This distance implies that the source reached ($15pm3)%$ of the Eddington luminosity at the peak of its outburst. Further, we use this distance to refine previous estimates of the jet inclination angle, jet velocity and the mass of the black hole in MAXI J1820+070 to be ($63pm3)^{circ}$, ($0.89pm0.09)c$ and ($9.2pm1.3) M_{odot}$, respectively.
Aims. The optical emission of black hole transients increases by several magnitudes during the X-ray outbursts. Whether the extra light arises from the X-ray heated outer disc, from the inner hot accretion flow, or from the jet is currently debated.
Optical polarisation measurements are able to distinguish the relative contributions of these components. Methods. We present the results of BVR polarisation measurements of the black hole X-ray binary MAXI J1820+070 during the period of March-April 2018. Results. We detect small, $sim$0.7%, but statistically significant polarisation, part of which is of interstellar origin. Depending on the interstellar polarisation estimate, the intrinsic polarisation degree of the source is between $sim$0.3% and 0.7%, and the polarisation position angle is between $sim10deg-30deg$. We show that the polarisation increases after MJD 58222 (2018 April 14). The change is of the order of 0.1% and is most pronounced in the R band. The change of the source Stokes parameters occurs simultaneously with the drop of the observed V-band flux and a slow softening of the X-ray spectrum. The Stokes vectors of intrinsic polarisation before and after the drop are parallel, at least in the V and R filters. Conclusions. We suggest that the increased polarisation is due to the decreasing contribution of the non-polarized component, which we associate with the the hot flow or jet emission. The low polarisation can result from the tangled geometry of the magnetic field or from the Faraday rotation in the dense, ionised, and magnetised medium close to the black hole. The polarized optical emission is likely produced by the irradiated disc or by scattering of its radiation in the optically thin outflow.
The observational appearance of black holes in X-ray binary systems depends on their masses, spins, accretion rate and the misalignment angle between the black hole spin and the orbital angular momentum. We used high-precision optical polarimetric ob
servations to constrain the position angle of the orbital axis of the black hole X-ray binary MAXI J1820+070. Together with previously obtained orientation of the relativistic jet and the inclination of the orbit this allowed us to determine a lower limit of 40 degrees on the misalignment angle. Such a large misalignment challenges the models of quasi-periodic oscillations observed in black hole X-ray binaries, puts strong constraints on the black hole formation mechanisms, and has to be accounted for when measuring black hole masses and spins from the X-ray data.
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