Hubble Image of GammaRay Burst Confirms Rice Predictions

first_imgShareCONTACT: Lia Unrau PHONE: (713) 831-4793 [email protected] IMAGE OF GAMMA-RAY BURST CONFIRMS RICE PREDICTIONS It’s ideal for astronomers to have theirpredictions tested in space — which is just what happened for Rice scientistsrecently.When the Hubble Space Telescope tracked the visible-light counterpart of agamma-ray burst just over a week ago, it did more than give astronomers theirfirst close-up look at its fading light — it confirmed a prediction made byRice University scientists that the x-ray and visible light afterglows wouldfade at a certain rate.The find is leading astronomers closer to solving modern astronomy’s greatestmystery, the origin of gamma-ray bursts — the highest-energy radiation in theuniverse.The Rice University scientists predicted that the brightness of the x-ray andvisible-light counterparts would fall as the reciprocal of time. Such a slowdecay is highly unusual in energetic astrophysical phenomena.The burst was detected by several space-based, high-energy astrophysicsobservatories on Feb. 28, and then a fading visible-light source was discoveredby ground-based telescopes. On March 26, this burster was finally imaged byNASA’s Hubble Space Telescope with unprecedented precision.“Researchers have been diligently looking for these fading counterparts fordecades, without success, so this is a real breakthrough for the field,” Riceprofessor Edison Liang says, “and a key confirmation for our model.”In a series of articles written at the end of last year, and to appear in theApril 10 issue of The Astrophysical Journal Letters, the Rice team proposes thata gamma-ray burst fades, not because of explosive expansion as oftenconjectured, but mainly due to radiation cooling, in which the energy of theescaping radiation, or so-called photons, closely mimics the energy of thecooling plasma. This physical model is proposed by Liang together with researchscientist Ian Smith, graduate student Anthony Crider and professor MasaakiKusunose of Japan.“Picture the source as a large ball of very energetic particles whizzingaround,” explains Liang. “A low energy radio or microwave photon injected intothis ionized plasma — most likely created by the plasma itself — bounces offmany particles before it can finally escape. But in the scatterings, theparticles transfer energy to the photons. During the burst, the escaping photonsspan almost the entire electromagnetic spectrum, with most of the energyappearing in the gamma-ray region. As the source slowly cools, gamma rays are nolonger produced, but the source is still visible across the rest of thespectrum, from x-rays to visible-light, as a slowly fading object.”In addition to the inverse-time fading law, the Rice model also predicts thatthe ratio of the burster distance to the size of the source should be around oneto ten trillion. “This relation plus other physical considerations willeventually provide powerful limits to the distance of bursters, which is thesubject of the hottest debate in astronomy today,” comments Liang.Discovered accidentally in the late 1960s by United States nuclear testsurveillance satellites, the origin of gamma-ray bursts has puzzled astronomersfor almost three decades. Results obtained by the Burst and Transient SourceExperiment (BATSE) on board the NASA Compton Observatory, launched in 1991,further deepened the mystery. Currently, astronomers are deeply divided overwhether the bursts originate from an extended halo around our own Milky Way orif they originate in galaxies billions of light years away.###Editors: For a graphic illustrating the Rice predictions in GIF and TIFFformats, see:http://spacsun.rice.edu/~acrider/papers/GRB_DECAY.HTML.Edison Liang, Rice professor of space physics and astronomy, can be reachedat (713) 527-8101, ext. 3524, or [email protected] FacebookTwitterPrintEmailAddThislast_img

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