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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Brightest gamma-ray burst ever observed reveals new mysteries of cosmic   
   explosions    
      
     Date:   
         March 28, 2023   
     Source:   
         Harvard-Smithsonian Center for Astrophysics   
     Summary:   
         Scientists believe the gamma-ray emission, which lasted over 300   
         seconds, is the birth cry of a black hole, formed as the core of   
         a massive and rapidly spinning star collapses under its own weight.   
      
      
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   FULL STORY   
   ==========================================================================   
   On October 9, 2022, an intense pulse of gamma-ray radiation swept through   
   our solar system, overwhelming gamma-ray detectors on numerous orbiting   
   satellites, and sending astronomers on a chase to study the event using   
   the most powerful telescopes in the world.   
      
      
   ==========================================================================   
   The new source, dubbed GRB 221009A for its discovery date, turned out   
   to be the brightest gamma-ray burst (GRB) ever recorded.   
      
   In a new study that appears today in the Astrophysical Journal Letters,   
   observations of GRB 221009A spanning from radio waves to gamma-rays,   
   including critical millimeter-wave observations with the Center for   
   Astrophysics | Harvard & Smithsonian's Submillimeter Array (SMA)   
   in Hawaii, shed new light on the decades-long quest to understand the   
   origin of these extreme cosmic explosions.   
      
   The gamma-ray emission from GRB 221009A lasted over 300   
   seconds. Astronomers think that such "long-duration" GRBs are the birth   
   cry of a black hole, formed as the core of a massive and rapidly spinning   
   star collapses under its own weight. The newborn black hole launches   
   powerful jets of plasma at near the speed of light, which pierce through   
   the collapsing star and shine in gamma- rays.   
      
   With GRB 221009A being the brightest burst ever recorded, a real mystery   
   lay in what would come after the initial burst of gamma-rays. "As the   
   jets slam into gas surrounding the dying star, they produce a bright   
   `afterglow' of light across the entire spectrum," says Tanmoy Laskar,   
   assistant professor of physics and astronomy at the University of Utah,   
   and lead author of the study. "The afterglow fades quite rapidly, which   
   means we have to be quick and nimble in capturing the light before it   
   disappears, taking its secrets with it."  As part of a campaign to use   
   the world's best radio and millimeter telescopes to study the afterglow   
   of GRB 221009A, astronomers Edo Berger and Yvette Cendes of the Center   
   for Astrophysics (CfA) rapidly gathered data with the SMA.   
      
   "This burst, being so bright, provided a unique opportunity to explore   
   the detailed behavior and evolution of an afterglow with unprecedented   
   detail -- we did not want to miss it!" says Edo Berger, professor of   
   astronomy at Harvard University and the CfA. "I have been studying these   
   events for more than twenty years, and this one was as exciting as the   
   first GRB I ever observed."  "Thanks to its rapid-response capability,   
   we were able to quickly turn the SMA to the location of GRB 221009A,"   
   says SMA project scientist and CfA researcher Garrett Keating. "The team   
   was excited to see just how bright the afterglow of this GRB was, which   
   we were able to continue to monitor for more than 10 days as it faded."   
   After analyzing and combining the data from the SMA and other telescopes   
   all over the world, the astronomers were flummoxed: the millimeter and   
   radio wave measurements were much brighter than expected based on the   
   visible and X-ray light.   
      
   "This is one of the most detailed datasets we have ever collected,   
   and it is clear that the millimeter and radio data just don't behave   
   as expected," says CfA research associate Yvette Cendes. "A few GRBs   
   in the past have shown a brief excess of millimeter and radio emission   
   that is thought to be the signature of a shockwave in the jet itself,   
   but in GRB 221009A the excess emission behaves quite differently than   
   in these past cases."  She adds, "It is likely that we have discovered a   
   completely new mechanism to produce excess millimeter and radio waves."   
   One possibility, says Cendes, is that the powerful jet produced by   
   GRB 221009A is more complex than in most GRBs. "It is possible that the   
   visible and X-ray light are produced by one portion of the jet, while the   
   early millimeter and radio waves are produced by a different component."   
   "Luckily, this afterglow is so bright that we will continue to study its   
   radio emission for months and maybe years to come," adds Berger. "With   
   this much longer time span we hope to decipher the mysterious origin   
   of the early excess emission."  Independent of the exact details of   
   this particular GRB, the ability to respond rapidly to GRBs and similar   
   events with millimeter-wave telescopes is an essential new capability   
   for astronomers.   
      
   "A key lesson from this GRB is that without fast-acting radio and   
   millimeter telescopes, such as the SMA, we would miss out on potential   
   discoveries about the most extreme explosions in the universe," says   
   Berger. "We never know in advance when such events will occur, so we   
   have to be as responsive as possible if we're going to take advantage   
   of these gifts from the cosmos."   
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Cosmic_Rays # Black_Holes # Space_Telescopes # Astronomy   
                   # Space_Exploration # Astrophysics # Stars # Cosmology   
       * RELATED_TERMS   
             o Gamma_ray_burst o Supernova o Blue_supergiant_star   
             o Spitzer_space_telescope o Black_hole o   
             Compton_Gamma_Ray_Observatory o Quasar o Holographic_Universe   
      
   ==========================================================================   
   Story Source: Materials provided by   
   Harvard-Smithsonian_Center_for_Astrophysics. Note: Content may be edited   
   for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Tanmoy Laskar, Kate D. Alexander, Raffaella Margutti, Tarraneh   
      Eftekhari,   
         Ryan Chornock, Edo Berger, Yvette Cendes, Anne Duerr, Daniel   
         A. Perley, Maria Edvige Ravasio, Ryo Yamazaki, Eliot H. Ayache,   
         Thomas Barclay, Rodolfo Barniol Duran, Shivani Bhandari, Daniel   
         Brethauer, Collin T.   
      
         Christy, Deanne L. Coppejans, Paul Duffell, Wen-fai Fong, Andreja   
         Gomboc, Cristiano Guidorzi, Jamie A. Kennea, Shiho Kobayashi,   
         Andrew Levan, Andrei P. Lobanov, Brian D. Metzger, Eduardo Ros,   
         Genevieve Schroeder, P.   
      
         K. G. Williams. The Radio to GeV Afterglow of GRB 221009A. The   
         Astrophysical Journal Letters, 2023; 946 (1): L23 DOI:   
         10.3847/2041-8213/ acbfad   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/03/230328145539.htm   
      
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