Launching jets from accretion belts

We propose that sub-Keplerian accretion belts around stars might launch jets. The sub-Keplerian inflow does not form a rotationally supported accretion disk, but it rather reaches the accreting object from a wide solid angle. The basic ingredients of the flow are a turbulent region where the accretion belt interacts with the accreting object via a shear layer, and two avoidance regions on the poles where the accretion rate is very low. A dynamo that is developed in the shear layer amplifies magnetic fields to high values. It is likely that the amplified magnetic fields form polar outflows from the avoidance regions. Our speculative belt-launched jets model has implications on a rich variety of astrophysical objects, from the removal of common envelopes to the explosion of core collapse supernovae by jittering jets.

Electromagnetic-Wave Mechanism of Formation and Propagation of Astrophysical Vortex Jets Generated in the Jumper of a Spiral Galaxy

An explanation of the mechanism of generation and acceleration of jets in outer space is given on the basis of experiments in the physics of electrical discharge. The presence of two arms in the spiral Galaxy gives grounds to assume that they have excess charges of the opposite sign. At the moment when the electric field strength between the tips of the arms becomes sufficient, an electrical breakdown occurs, which is accompanied by the movement of the current-plasma leader in the jumper between the tips of the arms. In the head part of the leader there is a flat electric domain of a strong field, which, during its inception, emits intense transverse electromagnetic waves in a direction perpendicular to the direction of the leader’s motion and to the plane of the accretion disk. The electric domain periodically appears and collapses due to the entry of neutral particles. Transverse electromagnetic waves capture charged particles from the discharge region and accelerate them in the direction of wave propagation. The crossed fields of an electromagnetic wave perform the functions of a multistage accelerator. The acceleration of the particles of the plasma produced in the discharge to relativistic energy values in the region of narrow vortex jets occurs under the action of forces caused by the components of the electromagnetic wave fields and the pressure gradient. The charged particles of a vortex jet acquire a significant rotational moment under the action of the Lorentz force. Explanations of the generation of microwave, bremsstrahlung and optical radiation from the region of the jumper between the arms of the Galaxy in the absence of electrical breakdown are also given.

Modeling the quasi-periodic oscillation of Swift J1644+57

A 200-second X-ray quasi-periodicity in the 2-8 ke V band from Swift J1644+57 was found by Reis et al.From the onset time of quasi-periodic oscillation(QPO),we show that Swift J1644+57 is a plunging event.This QPO may be related to discrete clumps from the accretion disk falling into a supermassive black hole,then the outflow in the jet may be also discontinuous.We estimate the lifetime of clumps to be about several hundreds seconds and the fraction of clumpy ejecta to be about 30% from the QPO.The other possible model involves the interface between the inflow and jet magnetosphere in the magnetically choked accretion flow.Theory and numerical simulations indicate that a magnetic Rayleigh-Taylor and Kelvin-Helmholtz unstable magnetospheric interface can produce a jet-disk QPO mechanism.This event may be the first evidence of jet-disk QPO.From observations,the two models are comparable.

A report on TypeⅡX-ray bursts from SMC X-1

We study RXTE PCA data for the high mass X-ray binary source SMC X-1 between 2003–10 and 2003–12 when the source was in its high states.The source is found to be frequently bursting which can be seen as flares in lightcurves that occur at a rate of one every 800 s, with an average of 4–5 Type Ⅱ X-ray bursts per hour.We note that typically a burst was short, lasting for a few tens of seconds in addition to a few long bursts spanning more than a hundred seconds that were also observed.The flares apparently occupied 2.5% of the total observing time of 225.5 ks.We note a total of 272 flares with mean FWHM of the flare ～21 s.The rms variability and aperiodic variability are independent of flares.As observed, the pulse profiles of the lightcurves do not change their shape, implying that there is no change in the geometry of an accretion disk due to a burst.The hardness ratio and rms variability of lightcurves exhibit no correlation with the flares.The flare fraction shows a positive correlation with the peak-to-peak ratio of the primary and secondary peaks of the pulse profile.The observed hardening or softening of the spectrum cannot be correlated with the flaring rate but may be due to the interstellar absorption of X-rays as evident from the change in hydrogen column density(n_H).It is found that the luminosity of the source increases with the flaring rate.Considering that the viscous timescale is equal to the mean recurrence time of flares, we fixed the viscosity parameter α ～ 0.16.

Broad-band spectral study of LMXB black hole candidate 4U 1957+11 with NuSTAR

We present here the results of broadband spectral analysis of a low-mass X-ray binary and a black hole candidate 4 U 1957+11.The source was observed nine times with the Nuclear Spectroscopic Telescope A rray(NuSTAR)between September 2018 and November 2019.During these observations,the spectral state of 4 U 1957+11 evolved marginally.The disc dominant spectra are described well with a hot,multicolor disc blackbody with disc temperature varying in the range kT_(in)~1.35-1.86 keV and a non-thermal component having a steep slope(Γ=2-3).A broad Fe emission line feature(5-8 keV)was observed in the spectra of all the observations.The relativistic disc model was used to study the effect of distance,inclination and the black hole mass on its spin.Simulations indicate a higher spin for smaller distances and lower black hole masses.At smaller distances and higher masses,spin is maximum and almost independent of the distance.An inverse correlation exists between the spin and the spectral hardening factor for all the cases.The system prefers a moderate spin of about 0.85 for black hole masses between 4-6 M⊙for a 7 kpc distance.

A Multi-parameter Model for Radio Dichotomy of Active Galactic Nuclei and Jets

Based on the coexistence of the Blandford-Znajek and magnetic coupling processes in black hole （BH） accretion disc, a multi-parameter model for jet powers and radio loudnees of active galactic nuclei （AGNs） is studied. It turns out that radio-loudnees of AGNs couM be governed by five parameters： （i） the BH spin, （ii） a power-law index of the variation of the magnetic field on the disc; （iii） a parameter determining the position of the inner edge of the disc, （iv） the ratio of the pressure of the magnetic field on the horizon to the ram pressure of the innermost parts of an accretion flow, and （v） the ratio of the angular velocity of the open field lines to that of the horizon. The observed dichotomy between radio-loud and radio-quiet AGNs is well interpreted by the effects of the above parameters. Furthermore, we discuss the derivative of radio loudness of AGNs with respect to each parameter separately. In addition, the effect of the screw instability on radio loudness of AGNs is discussed.