beecee Posted January 19, 2018 Share Posted January 19, 2018 https://phys.org/news/2018-01-neutron-star-merger-yields-puzzle-astrophysicists.html Neutron-star merger yields new puzzle for astrophysicists January 18, 2018, McGill University: The afterglow from the distant neutron-star merger detected last August has continued to brighten - much to the surprise of astrophysicists studying the aftermath of the massive collision that took place about 138 million light years away and sent gravitational waves rippling through the universe. New observations from NASA's orbiting Chandra X-ray Observatory, reported in Astrophysical Journal Letters, indicate that the gamma ray burst unleashed by the collision is more complex than scientists initially imagined. "Usually when we see a short gamma-ray burst, the jet emission generated gets bright for a short time as it smashes into the surrounding medium - then fades as the system stops injecting energy into the outflow," says McGill University astrophysicist Daryl Haggard, whose research group led the new study. "This one is different; it's definitely not a simple, plain-Jane narrow jet." Read more at: https://phys.org/news/2018-01-neutron-star-merger-yields-puzzle-astrophysicists.html#jCp ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: the paper:http://iopscience.iop.org/article/10.3847/2041-8213/aaa4f3/meta Brightening X-Ray Emission from GW170817/GRB 170817A: Further Evidence for an Outflow: Abstract The origin of the X-ray emission from neutron star coalescence GW170817/GRB 170817A is a key diagnostic of the unsettled post-merger narrative, and different scenarios predict distinct evolution in its X-ray light curve. Due to its sky proximity to the Sun, sensitive X-ray monitoring of GW170817/GRB 170817A has not been possible since a previous detection at 16 days post-burst. We present new, deep Chandra observations of GW170817/GRB 170817A at 109 days post-burst, immediately after Sun constraints were lifted. The X-ray emission has brightened from a 0.3–8.0 keV flux of erg s−1cm−2 at 16 days to erg s−1 cm−2 at 109 days, at a rate similar to the radio observations. This confirms that the X-ray and radio emission have a common origin. We show that the X-ray light curve is consistent with models of outflow afterglows, in which the outflow can be a cocoon shocked by the jet, dynamical ejecta from the merger, or an off-axis structured jet. Further deep X-ray monitoring can place powerful constraints on the physical parameters of these models, by both timing the passing of a synchrotron cooling break through the X-ray band and detecting the associated steepening of the X-ray photon index. Finally, the X-ray brightening strengthens the argument that simple off-axis top-hat jet models are not consistent with the latest observations of GW170817/GRB 170817A. Link to comment Share on other sites More sharing options...
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