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تسجيل مستخدم جديدFRB 200428: an Impact between an Asteroid and a Magnetar
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A fast radio burst (FRB) was recently detected to be associated with a hard X-ray burst from the Galactic magnetar SGR 1935+2154. Scenarios involving magnetars for FRBs are hence highly favored. In this work, we suggest that the impact between an asteroid and a magnetar could explain such a detection. According to our calculations, an asteroid of mass $10^{20}$ g will be disrupted at a distance of $7 times 10^9$ cm when approaching the magnetar. The accreted material will flow along the magnetic field lines from the Alfven radius $sim 10^7$ cm. After falling onto the magnetars surface, an instant accretion column will be formed, producing a Comptonized X-ray burst and an FRB in the magnetosphere. We show that all the observational features of FRB 200428 could be interpreted self-consistently in this scenario. We predict quasi-periodic oscillations in this specific X-ray burst, which can serve as an independent observational test.
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Very recently, an extremely bright fast radio burst (FRB) 200428 with two sub-millisecond pulses was discovered to come from the direction of the Galactic magnetar SGR 1935+2154, and an X-ray burst (XRB) counterpart was detected simultaneously. These
observations favor magnetar-based interior-driven models. In this Letter, we propose a different model for FRB 200428 associated with an XRB from SGR 1935+2154, in which a magnetar with high proper velocity encounters an asteroid of mass $sim10^{20},$g. This infalling asteroid in the stellar gravitational field is first possibly disrupted tidally into a great number of fragments at radius $sim {rm a,,few}$ times $10^{10},$cm, and then slowed around the Alfv$acute{rm e}$n radius by an ultra-strong magnetic field and in the meantime two major fragments of mass $sim 10^{17},$g that cross magnetic field lines produce two pulses of FRB 200428. The whole asteroid is eventually accreted onto the poles along magnetic field lines, impacting the stellar surface, creating a photon-e$^pm$ pair fireball trapped initially in the stellar magnetosphere, and further leading to an XRB. We show that this gravitationally-powered model can interpret all of the observed features self-consistently.
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however, no FRB-like events had been detected in association any magnetar burst, including one giant flare. Recently, a pair of FRB-like bursts (FRB 200428 hereafter) separated by milliseconds (ms) were detected from the general direction of the Galactic magnetar SGR J1935+2154. Here we report the detection of a non-thermal X-ray burst in the 1-250 keV energy band with the Insight-HXMT satellite, which we identify as emitted from SGR J1935+2154. The burst showed two hard peaks with a separation of 34 ms, broadly consistent with that of the two bursts in FRB 200428. The delay time between the double radio and X-ray peaks is about 8.57 s, fully consistent with the dispersion delay of FRB 200428. We thus identify the non-thermal X-ray burst is associated with FRB 200428 whose high energy counterpart is the two hard peaks in X-ray. Our results suggest that the non-thermal X-ray burst and FRB 200428 share the same physical origin in an explosive event from SGR J1935+2154.
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