Interpretations of multiple absorption features in a gamma-ray burst spectrum

Fenimore, E. E.; Conner, J. P.; Epstein, Richard I.; Klebesadel, R. W.; Laros, J. G.; Yoshida, A.; Fujii, Masami; Hayashida, Kentaro; Itoh, Minoru; Murakami, T.; Nishimura, Jun; Yamagami, Y.; Kondò, I.; Kawai, N.

doi:10.1086/185342

Cited by 91 publications

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“…We take the detector response function to be that for an angle of 37° between the direction of the burst source and the normal to the detectors, the same as assumed in Fenimore et al 8 We find best-fit parameter values A -0.08 cm^s^keV" 1 , £*-101.3 keV, and a-0.846 (1<^< 101.3 keV) and 1.174 (101.3 <^< 1000 keV), with x 1 ~ 14-2 for 23 degrees of freedom. We then inject photons with this spectrum isotropically into a slab with constant B, T c , and N e (-^7Vj os ), with the slab normal parallel to B.…”

Section: N(e)-a(e/eb)~amentioning

confidence: 99%

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Cyclotron resonant scattering in the spectra ofγ-ray bursts

et al. 1989

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Fits of theoretical spectra from Monte Carlo radiation-transfer calculations to dips at « 20 and 40 keV in a spectrum of the "classical" /-ray burst GB 880205 give best-fit values and 68%-confidence intervals £-(1.71±0.07)xl0 12 G, A^e-(L2±0.6)xl0 21 electrons/cm 2 , and ^ ~cos0-0.31 ±0.05, where 6 is the viewing angle relative to the field. Physical self-consistency fixes the temperature and Tc^5.3-M keV. These results suggest that this /-ray burst and many others which exhibit a lowenergy dip originate from strongly magnetic neutron stars and are galactic in origin.PACS numbers: 98.70.Rz, 95.30.Jx, 95.85.Qx, 97.60.Jd y-ray bursts were discovered over twenty years ago, 1 yet their nature and origin have remained a profound mystery. 2 Mazets et al. 3 reported single low-energy (E « 50 keV) dips in the spectra of more than 20% of the bursts observed with the Konus experiment on Venera 11-14. Hueter 4 reported single low-energy dips in several bursts observed with the A4 experiment on HEAO-1. These features have been interpreted as due to absorption at the cyclotron first harmonic (fundamental), h (OB « 11.6Z?i2 keV, where Bn is the magnetic field strength in units of 10 12 G. They constitute the strongest evidence in favor of a magnetic-neutron-star origin for y-ray bursts. 2 The statistical significance of these low-energy dips is low. Moreover, low-energy dips can be an artifact of the spectral deconvolution and their properties depend sensitively on the assumed form of the continuum spectrum. 5 Consequently, the existence and interpretation of these dips, and therefore the magnetic-neutron-star model of y-ray bursts, have remained controversial.Low-energy dips have recently been seen during certain time intervals in the spectra of two of the y-ray bursts detected with the burst detector on the Ginga satellite. 6 These dips are better resolved than previously: They span six or eight detector energy channels, not just one, as in the Konus data. 3 Furthermore, the spectra of both bursts show two dips-not just one, as in the Konus (Ref. 3) and A4 (Ref. 4) data-and the dips are nearly harmonically spaced at « 20 and 40 keV, as is expected for cyclotron features. Ginga could confidently identify line features with energies as low as 15 keV, 6 lower than in previous y-ray observations, making it ideal for detecting first-harmonic cyclotron lines for /?« 10 12 G. The single features at 40-60 keV reported by Konus (sensitive to E^30 keV) could be second-harmonic lines, analogous to the lines at «40 keV seen in GB 870303 and GB 880205. Finally, the continuum spectra of both bursts are characteristic of "classical" y-ray bursts. In the case of GB 880205, PVO data show that there is substantial emission above 1 MeV, 7 as is typical of classical bursts.Two aspects of the dips might seem puzzling. First, the dips are narrow, indicating that the scattering medium is much cooler than the typical photon energy E r^\ MeV in the continuum spectrum. Second, the strengths of the dips at the first and second harmonics are similar, d...

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Section: N(e)-a(e/eb)~amentioning

confidence: 99%

“…Because most of the photons which undergo scattering at the second harmonic are destroyed, the resulting line feature is approximately that for absorption. 8 This is a general property of higher-harmonic cyclotron lines when the magnetic field strength B<£B C . There is no observable dip at «60 keV in GB 880205 because the third harmonic is optically thin.…”

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confidence: 95%

Cyclotron resonant scattering in the spectra ofγ-ray bursts

et al. 1989

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“…In spite of this uncertainty, by the mid-1980s there was a general belief that GRBs originate from galactic neutron stars-a belief that was supported by the cyclotron lines in the spectra of some GRBs reported by the Ginga team (Murakami et al 1988, Fenimore et al 1988, and by line features near 500 keV reported by the Konus team (Mazets et al 1981).…”

Section: Introductionmentioning

confidence: 99%

Gamma-Ray Burst Afterglows

Paradijs

Kouveliotou

Wijers

2000

Annu. Rev. Astron. Astrophys.

322

248

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The discovery of counterparts in X-ray and optical to radio wavelengths has revolutionized the study of γ -ray bursts, until recently the most enigmatic of astrophysical phenomena. We now know that γ -ray bursts are the biggest explosions in nature, caused by the ejection of ultrarelativistic matter from a powerful energy source and its subsequent collision with its environment. We have just begun to uncover a connection between supernovae and γ -ray bursts, and are finally constraining the properties of the ultimate source of γ -ray burst energy. We review here the observations that have led to this breakthrough in the field; we describe the basic theory of the fireball model and discuss the theoretical understanding that has been gained from interpreting the new wealth of data on γ -ray bursts.

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“…More recently, equally-spaced lines were seen by Ginga in the spectra of three bursts (54-57) with high significance (55,56,58). The line features in these three bursts have been studied extensively, and there is no doubt that they exist.…”

Section: Cyclotron Linesmentioning

confidence: 99%