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تسجيل مستخدم جديدA Strong Jet Signature in the Late-Time Lightcurve of GW170817
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K. P. Mooley
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We present new 0.6-10 GHz observations of the binary neutron star merger GW170817 covering the period up to 300 days post-merger, taken with the Karl G. Jansky Very Large Array, the Australia Telescope Compact Array, the Giant Metrewave Radio Telescope and the MeerKAT telescope. We use these data to precisely characterize the decay phase of the late-time radio light curve. We find that the temporal decay is consistent with a power-law slope of t^-2.2, and that the transition between the power-law rise and decay is relatively sharp. Such a slope cannot be produced by a quasi-isotropic (cocoon-dominated) outflow, but is instead the classic signature of a relativistic jet. This provides strong observational evidence that GW170817 produced a successful jet, and directly demonstrates the link between binary neutron star mergers and short-hard GRBs. Using simple analytical arguments, we derive constraints on the geometry and the jet opening angle of GW170817. These results are consistent with those from our companion Very Long Baseline Interferometry (VLBI) paper, reporting superluminal motion in GW170817.
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The binary neutron star (BNS) merger GW170817 was the first astrophysical source detected in gravitational waves and multi-wavelength electromagnetic radiation. The almost simultaneous observation of a pulse of gamma-rays proved that BNS mergers are
associated with at least some short gamma-ray bursts (GRBs). However, the gamma-ray pulse was faint, casting doubts on the association of BNS mergers with the luminous, highly relativistic outflows of canonical short GRBs. Here we show that structured jets with a relativistic, energetic core surrounded by slower and less energetic wings produce afterglow emission that brightens characteristically with time, as recently seen in the afterglow of GW170817. Initially, we only see the relatively slow material moving towards us. As time passes, larger and larger sections of the outflow become visible, increasing the luminosity of the afterglow. The late appearance and increasing brightness of the multi-wavelength afterglow of GW170817 allow us to constrain the geometry of its ejecta and thus reveal the presence of an off-axis jet pointing about 30 degrees away from Earth. Our results confirm a single origin for BNS mergers and short GRBs: GW170817 produced a structured outflow with a highly relativistic core and a canonical short GRB. We did not see the bright burst because it was beamed away from Earth. However, approximately one in 20 mergers detected in gravitational waves will be accompanied by a bright, canonical short GRB.
The binary neutron star merger GW170817 was accompanied by radiation across the electromagnetic spectrum and localized to the galaxy NGC 4993 at a distance of 41+/-3 Mpc. The radio and X-ray afterglows of GW170817 exhibited delayed onset, a gradual r
ise in the emission with time as t^0.8, a peak at about 150 days post-merger, followed by a relatively rapid decline. To date, various models have been proposed to explain the afterglow emission, including a choked-jet cocoon and a successful-jet cocoon (a.k.a. structured jet). However, the observational data have remained inconclusive as to whether GW170817 launched a successful relativistic jet. Here we show, through Very Long Baseline Interferometry, that the compact radio source associated with GW170817 exhibits superluminal motion between two epochs at 75 and 230 days post-merger. This measurement breaks the degeneracy between the models and indicates that, while the early-time radio emission was powered by a wider-angle outflow (cocoon), the late-time emission was most likely dominated by an energetic and narrowly-collimated jet, with an opening angle of <5 degrees, and observed from a viewing angle of about 20 degrees. The imaging of a collimated relativistic outflow emerging from GW170817 adds substantial weight to the growing evidence linking binary neutron star mergers and short gamma-ray bursts.
GW170817 is the first gravitational wave detection of a binary neutron star merger. It was accompanied by radiation across the electromagnetic spectrum and localized to the galaxy NGC 4993 at a distance of 40 Mpc. It has been proposed that the observ
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We present our broadband study of GW170817 from radio to hard X-rays, including NuSTAR and Chandra observations up to 165 days after the merger, and a multi-messenger analysis including LIGO constraints. The data are compared with predictions from a
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