139 research outputs found

    Testing two-component jet models of GRBs with orphan afterglows

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    In the \swift era, two-component jet models were introduced to explain the complex temporal profiles and the diversity of early afterglows. In this paper, we concentrate on the two-component jet model; first component is the conventional afterglow and second is the emission due to the late internal dissipation such as the late-prompt emission. We suggest herein that the two-component jet model can be probed by the existence of two optical peaks for orphan GRB afterglows. Each peak is caused by its respective jet as its relativistic beaming cone widens to encompass the off-axis line of sight. Typically, the first peak appears at 104βˆ’10510^4-10^5 s and the second at 105βˆ’10610^5-10^6 s. Furthermore, we expect to observe a single, bright X-ray peak at the same time as the first optical peak. Because orphan afterglows do not have prompt emission, it is necessary to monitor the entire sky every 10410^4 s in the X-ray regime. We can test the model with orphan afterglows through the X-ray all-sky survey collaboration and by using ground-based optical telescopes.Comment: 6 pages, 4 figures, accepted for publication in PAS

    Universal transition diagram from dormant to actively accreting supermassive black holes

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    The vast majority of supermassive black holes (SMBHs) in the local universe exhibit levels of activity much lower than those expected from gas supplying rates onto the galactic nuclei, and only a small fraction of silent SMBHs can turn into active galactic nuclei. Revisiting observational data of very nearby SMBHs whose gravitational spheres of influence are spatially reached by the Chandra X-ray satellite, we find that the level of BH activity drastically increases from the quiescent phase when the inflow rate outside of the BH influence radius is higher than 0.1% of the Eddington accretion rate. We also show that the relation between the nuclear luminosity and gas accretion rate from the BH influence radius measured from X-ray observations is well described by the universal state transition of accreting SMBHs, as predicted by recent hydrodynamical simulations with radiative cooling and BH feedback. After the state transition, young massive stars should form naturally in the nucleus, as observed in the case of the nearest SMBH, Sagittarius Aβˆ—^\ast, which is currently quiescent but was recently active.Comment: 9 pages (main text), 2 figures, 1 table, accepted for publication in Ap
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