Kullanıcı:Santos/Deneme4: Revizyonlar arasındaki fark

Vikipedi, özgür ansiklopedi
Sonraki sürümle aradaki fark →
İçerik silindi İçerik eklendi
GörselVikimetin
Santos (mesaj | katkılar)
217 değişiklik
Yeni sayfa: {{GIP bilgi kutusu | ad = GRB 970228 | resim = 200px | altyazı = Hubble Uzay Teleskobu'ndan GRB 970228 | tespit zamanı = 02:58 (UTC)<br>28 Şubat 1997 |...
(Fark yok)

Sayfanın 00.22, 1 Eylül 2010 tarihindeki hâli

GRB 970228
Hubble Uzay Teleskobu'ndan GRB 970228
Tarih02:58 (UTC)
28 Şubat 1997
Süre80 saniye
AraçBeppoSAX
TakımyıldızOrion
Sağ açıklık05s 01d 46.7sn
Dik açıklıkŞablon:DA[1]
Uzaklık8.123×109 lışık yılıs[2]
Kırmızıya kayma0.695[3] (ev sahibi galaksi)
Toplam enerji çıkışı5.2×1044 J
[Vikiveri'de düzenle]



GRB 970228[4] was a gamma-ray burst (GRB) detected on February 28, 1997 at 02:58 UTC. A gamma-ray burst is a highly luminous flash of gamma rays, the most energetic form of electromagnetic radiation. Since 1993, physicists had predicted these bursts to be followed by a longer-lived afterglow at longer wavelengths, such as radio waves, x-rays, and even visible light. Until this event, GRBs had only been observed at gamma wavelengths. This was the first burst for which an afterglow was observed.[5]

The burst had multiple peaks in its light curve and lasted approximately 80 seconds. Peculiarities in the light curve of GRB 970228 suggested that a supernova may have occurred as well. The position of the burst coincided with a galaxy at a redshift of z = 0.695, providing early evidence that GRBs occur well beyond the Milky Way.

Observations

A gamma-ray burst (GRB) is a highly luminous flash of gamma rays, the most energetic form of electromagnetic radiation. GRBs were first detected in 1967 by the Vela satellites, a series of spacecraft designed to detect nuclear explosions in space.[6]

GRB 970228[4] was detected on February 28, 1997 at 02:58 UTC by the Gamma-Ray Burst Monitor (GRBM) and one of the Wide Field Cameras (WFCs) on board BeppoSAX,[7][8] an Italian–Dutch satellite originally designed to study X-rays.[9] Within a few hours, the BeppoSAX team determined the burst's position with an error box—a small area around the specific position to account for the error in the position—of 3 arcminutes.[8] The burst was also detected by the Ulysses space probe.[10]

The burst was located at a right ascension of 05sa 01d 46.7s and a declination of +11° 46′ 53.0″.[1] It lasted around 80 seconds and had multiple peaks in its light curve.[11] Gamma-ray bursts have very diverse time profiles, and it is not fully understood why some bursts have multiple peaks and some have only one. One possible explanation is that multiple peaks are formed when the source of the gamma-ray burst undergoes precession.[12]

Afterglows

In 1993, Bohdan Paczyński and James E. Rhoads published an article arguing that, regardless of the type of explosion that causes GRBs, the extreme energetics of GRBs meant that matter from the host body must be ejected at relativistic speeds during the explosion. They predicted that the interaction between the ejecta and interstellar matter would create a shock front. Should this shock front occur in a magnetic field, accelerated electrons in it would emit long-lasting synchrotron radiation in the radio frequencies, a phenomenon that would later be referred to as a radio afterglow.[13] Jonathan Katz later concluded that this lower-energy emission would not be limited to radio waves, but should range in frequency from radio waves to x-rays, including visible light.[14]

The Narrow Field Instruments on board BeppoSAX began making observations of the GRB 970228's position within eight hours of its detection.[15] A transient x-ray source was detected which faded with a power-law slope in the days following the burst. This x-ray afterglow was the first GRB afterglow ever detected.[8] Power-law decays have since been recognized as a common feature in GRB afterglows, although most afterglows decay at differing rates during different phases of their lifetimes.[16]

Optical images were taken of GRB 970228's position on March 1 and March 8 using the William Herschel Telescope and the Isaac Newton Telescope. Comparison of the images revealed an object which had decreased in luminosity in both visible light and infrared light.[1] This was the burst's optical afterglow. The predicted radio afterglow was never observed for this burst.[3] At the time of this burst's discovery, GRBs were believed to emit radiation isotropically. The afterglows from this burst and several others—such as GRB 970508 and GRB 971214—provided early evidence that GRBs emit radiation in collimated jets, a characteristic which lowers the total energy output of a burst by several orders of magnitude.[17]

Supernova relation

From top left to right, a blue sphere grows larger and gains more layers. At far right, the sphere explodes. From bottom right to left, the exploded sphere flattens out to a swirling disk with two bright beams of light coming out of the axis of rotation.
Artist's illustration showing the life of a massive star as it goes supernova, collapses into a black hole, and emits a gamma-ray burst along its axis of rotation Credit: Nicolle Rager Fuller/NSF

Daniel Reichart of the University of Chicago and Titus Galama of the University of Amsterdam independently analyzed GRB 970228's optical light curve, both concluding that the host object may have undergone a supernova explosion several weeks before the gamma-ray burst occurred.[18][19]

Galama analyzed the light curve of the burst and found that its luminosity decayed at different rates at different times. The luminosity decayed more slowly between March 6 and April 7 than it did before and after these dates. Galama concluded that the earlier light curve had been dominated by the burst itself, whereas the later light curve was produced by the underlying Type Ic supernova.[20] Reichart noted that the late afterglow was redder than the early afterglow, an observation which conflicted with the then-preferred relativistic fireball model for the gamma-ray burst emission mechanism. He also observed that the only GRB with a similar temporal profile was GRB 980326,[19] for which a supernova relation had already been proposed by Joshua Bloom.[21]

An alternative explanation for the light curves of GRB 970228 and GRB 980326 was the concept of dust echoes. Although GRB 980236 did not provide enough information to definitively rule out this explanation, Reichart showed that the light curve of GRB 970228 could only have been caused by a supernova.[22] Definitive evidence linking gamma-ray bursts and supernovae was eventually found in the spectrum of GRB 020813[23] and the afterglow of GRB 030329.[24] However, supernova-like features only become apparent in the weeks following a burst, leaving the possibility that very early luminosity variations could be explained by dust echoes.[25]

Host galaxy

During the night between March 12 and 13, Jorge Melnick made observations of the region with the New Technology Telescope. He discovered a faint nebular patch at the burst's position, almost certainly a distant galaxy. Although there was a remote chance that the burst and this galaxy were unrelated, their positional coincidence provided strong evidence that GRBs occur in distant galaxies rather than within the Milky Way.[26] This conclusion was later supported by observations of GRB 970508, the first burst to have its redshift determined.[27]

The position of the burst's afterglow was measurably offset from the centroid of the host galaxy, effectively ruling out the possibility that the burst originated in an active galactic nucleus. The redshift of the galaxy was later determined to be z = 0.695,[3] which corresponds to a distance of approximately 8.123×109 lightyears.[2] At this distance, the burst would have released a total of 5.2×1044 J assuming isotropic emission.[28]

Notes

  1. ^ a b c Groot 1997
  2. ^ a b Comoving distance calculated using the following online conversion system:
    Wright, Edward L. (9 May 2008). "Ned Wright's Javascript Cosmology Calculator". UCLA Division of Astronomy & Astrophysics. Erişim tarihi: 2010-06-11. 
  3. ^ a b c Bloom 2001
  4. ^ a b "GRB" indicates that the event was a gamma-ray burst, and the numbers follow a YYMMDD format corresponding to the date on which the burst occurred: February 28, 1997
  5. ^ Schilling 2002, p. 101
  6. ^ Schilling 2002, pp. 12–16
  7. ^ Varendoff 2001, p. 381
  8. ^ a b c Costa 1997b
  9. ^ Schilling 2002, pp. 58–60
  10. ^ Hurley 1997
  11. ^ Costa 1997a
  12. ^ Zwart 2001
  13. ^ Paczyński 1993
  14. ^ Katz 1994
  15. ^ Costa 1997a
  16. ^ Panaitescu 2007, §2
  17. ^ Huang 2002
  18. ^ Schilling 2002, p. 173
  19. ^ a b Reichart 1999
  20. ^ Galama 2000
  21. ^ Bloom 1999
  22. ^ Reichart 2001
  23. ^ Butler 2003
  24. ^ Stanek 2003
  25. ^ Moran 2005
  26. ^ Schilling 2002, p. 102
  27. ^ Reichart 1998
  28. ^ Djorgovski 1999

References

  • Bloom, J. S.; ve diğerleri. (30 September 1999). "The unusual afterglow of the γ-ray burst of 26 March 1998 as evidence for a supernova connection". Nature. 401: 453–456. doi:10.1038/46744. arXiv:astro-ph/9905301. 
  • Groot, P. J. et al. (12 March 1997) "IAU Circular 6584: GRB 970228". International Astronomical Union. Retrieved on 16 April 2009.
  • Huang, Yong-feng; ve diğerleri. (2002). "Are Gamma-ray Bursts Due to Isotropic Fireballs or Cylindrical Jets?". Chinese Astronomy and Astrophysics. 26: 414–423. doi:10.1016/S0275-1062(02)00092-9. 
  • Hurley, K. et al. (8 March 1997) "IAU Circular 6578: GRB 970228". International Astronomical Union. Retrieved on 23 February 2010.
  • Katz, J. I. (1994). "Low-Frequency Spectra of Gamma-Ray Bursts". Astrophysical Journal. 432 (2): L107–L109. doi:10.1086/187523. 
  • Moran, Jane A. and Reichart, Daniel E. (10 October 2005). "Gamma-Ray Burst Dust Echoes Revisited: Expectations at Early Times". Astrophysical Journal. 632 (1): 438–442. doi:10.1086/432634. 
  • Paczyński, Bohdan and Rhoads, James E. (1993). "Radio Transients from Gamma-Ray Bursters". Astrophysical Journal. 418: L5–L8. doi:10.1086/187102. 
  • Panaitescu, A. (15 May 2007). "Decay phases of Swift X-ray afterglows and the forward-shock model". Philosophical Transactions of the Royal Society A. 365 (1854): 1197–1205. doi:10.1098/rsta.2006.1985. PMID 17293326. 
  • Reichart, Daniel E. (2001). "Light Curves and Spectra of Dust Echoes from Gamma-Ray Bursts and Their Afterglows: Continued Evidence That GRB 970228 Is Associated with a Supernova". Astrophysical Journal. 554 (2): 649–659. doi:10.1086/321428. 
  • Schilling, Govert (2002). Flash! The Hunt for the Biggest Explosions in the Universe. Cambridge: Cambridge University Press. ISBN 0-521-80053-6. 
  • Stanek, Krzysztof Z.; Matheson, T.; Garnavich, P. M.; Martini, P.; Berlind, P.; Caldwell, N.; Challis, P.; Brown, W. R.; Schild, R. (12 June 2003). "Spectroscopic Discovery of the Supernova 2003dh Associated with GRB0303291". Astrophysical Journal. 591: L17–L20. doi:10.1086/376976. 
  • van Paradijs, J.; ve diğerleri. (1997). "Transient optical emission from the error box of the γ-ray burst of 28 February 1997". Nature. 386: 686–689. doi:10.1038/386686a0. 
  • Varendoff, Martin (2001). "Gamma-Ray Bursts". Volken Schönfelder (Ed.). The Universe in Gamma Rays. Berlin: Springer. ISBN 3-540-67874-3. 
"https://tr.wikipedia.org/w/index.php?title=Kullanıcı:Santos/Deneme4&oldid=8226712" sayfasından alınmıştır