Detection of a Spectral Break in the Extra Hard Component of GRB 090926A

M. Ackermann; M. Ajello; K. Asano; Magnus Axelsson; L. Baldini; J. Ballet; G. Barbiellini; M. G. Baring; D. Bastieri; K. Bechtol; R. Bellazzini; B. Berenji; P. N. Bhat; E. Bissaldi; R. D. Blandford; E. Bonamente; A. W. Borgland; A. Bouvier; J. Bregeon; A. Brez; M. S. Briggs; M. Brigida; P. Bruel; R. Buehler; S. Buson; G. A. Caliandro; R. A. Cameron; P. A. Caraveo; S. Carrigan; J. M. Casandjian; C. Cecchi; O. Celik; V. Chaplin; E. Charles; A. Chekhtman; J. Chiang; S. Ciprini; R. Claus; J. Cohen-Tanugi; V. Connaughton; J. Conrad; S. Cutini; C. D. Dermer; A. De Angelis; F. De Palma; B. L. Dingus; E. Do Couto E. Silva; P. S. Drell; R. Dubois; C. Favuzzi; S. J. Fegan; E. C. Ferrara; W. B. Focke; M. Frailis; Y. Fukazawa; S. Funk; P. Fusco; F. Gargano; D. Gasparrini; N. Gehrels; S. Germani; N. Giglietto; F. Giordano; M. Giroletti; T. Glanzman; G. Godfrey; A. Goldstein; J. Granot; J. Greiner; I. A. Grenier; J. E. Grove; S. Guiriec; D. Hadasch; Y. Hanabata; A. K. Harding; K. Hayashi; M. Hayashida; E. Hays; D. Horan; R. E. Hughes; R. Itoh; G. Johannesson; A. S. Johnson; W. N. Johnson; T. Kamae; H. Katagiri; J. Kataoka; R. M. Kippen; J. Knoedlseder; D. Kocevski; C. Kouveliotou; M. Kuss; J. Lande; L. Latronico; S. -H. Lee; M. Llena Garde; F. Longo; F. Loparco; M. N. Lovellette; P. Lubrano; A. Makeev; M. N. Mazziotta; S. McBreen; J. E. McEnery; S. McGlynn; C. Meegan; J. Mehault; P. Meszaros; P. F. Michelson; T. Mizuno; C. Monte; M. E. Monzani; E. Moretti; A. Morselli; I. V. Moskalenko; S. Murgia; H. Nakajima; T. Nakamori; M. Naumann-Godo; S. Nishino; P. L. Nolan; J. P. Norris; E. Nuss; M. Ohno; T. Ohsugi; A. Okumura; N. Omodei; E. Orlando; J. F. Ormes; M. Ozaki; W. S. Paciesas; D. Paneque; J. H. Panetta; D. Parent; V. Pelassa; M. Pepe; M. Pesce-Rollins; V. Petrosian; F. Piron; T. A. Porter; R. Preece; J. L. Racusin; S. Raino; R. Rando; A. Rau; M. Razzano; S. Razzaque; A. Reimer; O. Reimer; T. Reposeur; L. C. Reyes; J. Ripken; S. Ritz; M. Roth; F. Ryde; H. F. -W. Sadrozinski; A. Sander; J. D. Scargle; M. S. Strickman; D. J. Suson; H. Tajima; H. Takahashi; T. Tanaka; Y. Tanaka; J. B. Thayer; J. G. Thayer; L. Tibaldo; D. Tierney; K. Toma; D. F. Torres; G. Tosti; A. Tramacere; Y. Uchiyama; T. Uehara; T. L. Usher; J. Vandenbroucke; A. J. van der Horst; V. Vasileiou; N. Vilchez; V. Vitale; A. von Kienlin; A. P. Waite; P. Wang; C. Wilson-Hodge; B. L. Winer; K. S. Wood; X. F. Wu; R. Yamazaki; Z. Yang; T. Ylinen; M. Ziegler

doi:10.1088/0004-637X/729/2/114

Detection of a Spectral Break in the Extra Hard Component of GRB 090926A

M. Ackermann, M. Ajello, K. Asano, Magnus Axelsson, L. Baldini, J. Ballet, G. Barbiellini, M. G. Baring, D. Bastieri, K. Bechtol, R. Bellazzini, B. Berenji, P. N. Bhat, E. Bissaldi, R. D. Blandford, E. Bonamente, A. W. Borgland, A. Bouvier, J. Bregeon, A. BrezM. S. Briggs, M. Brigida, P. Bruel, R. Buehler, S. Buson, G. A. Caliandro, R. A. Cameron, P. A. Caraveo, S. Carrigan, J. M. Casandjian, C. Cecchi, O. Celik, V. Chaplin, E. Charles, A. Chekhtman, J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, V. Connaughton, J. Conrad, S. Cutini, C. D. Dermer, A. De Angelis, F. De Palma, B. L. Dingus, E. Do Couto E. Silva, P. S. Drell, R. Dubois, C. Favuzzi, S. J. Fegan, E. C. Ferrara, W. B. Focke, M. Frailis, Y. Fukazawa, S. Funk, P. Fusco, F. Gargano, D. Gasparrini, N. Gehrels, S. Germani, N. Giglietto, F. Giordano, M. Giroletti, T. Glanzman, G. Godfrey, A. Goldstein, J. Granot, J. Greiner, I. A. Grenier, J. E. Grove, S. Guiriec, D. Hadasch, Y. Hanabata, A. K. Harding, K. Hayashi, M. Hayashida, E. Hays, D. Horan, R. E. Hughes, R. Itoh, G. Johannesson, A. S. Johnson, W. N. Johnson, T. Kamae, H. Katagiri, J. Kataoka, R. M. Kippen, J. Knoedlseder, D. Kocevski, C. Kouveliotou, M. Kuss, J. Lande, L. Latronico, S. -H. Lee, M. Llena Garde, F. Longo, F. Loparco, M. N. Lovellette, P. Lubrano, A. Makeev, M. N. Mazziotta, S. McBreen, J. E. McEnery, S. McGlynn, C. Meegan, J. Mehault, P. Meszaros, P. F. Michelson, T. Mizuno, C. Monte, M. E. Monzani, E. Moretti, A. Morselli, I. V. Moskalenko, S. Murgia, H. Nakajima, T. Nakamori, M. Naumann-Godo, S. Nishino, P. L. Nolan, J. P. Norris, E. Nuss, M. Ohno, T. Ohsugi, A. Okumura, N. Omodei, E. Orlando, J. F. Ormes, M. Ozaki, W. S. Paciesas, D. Paneque, J. H. Panetta, D. Parent, V. Pelassa, M. Pepe, M. Pesce-Rollins, V. Petrosian, F. Piron, T. A. Porter, R. Preece, J. L. Racusin, S. Raino, R. Rando, A. Rau, M. Razzano, S. Razzaque, A. Reimer, O. Reimer, T. Reposeur, L. C. Reyes, J. Ripken, S. Ritz, M. Roth, F. Ryde, H. F. -W. Sadrozinski, A. Sander, J. D. Scargle, M. S. Strickman, D. J. Suson, H. Tajima, H. Takahashi, T. Tanaka, Y. Tanaka, J. B. Thayer, J. G. Thayer, L. Tibaldo, D. Tierney, K. Toma, D. F. Torres, G. Tosti, A. Tramacere, Y. Uchiyama, T. Uehara, T. L. Usher, J. Vandenbroucke, A. J. van der Horst, V. Vasileiou, N. Vilchez, V. Vitale, A. von Kienlin, A. P. Waite, P. Wang, C. Wilson-Hodge, B. L. Winer, K. S. Wood, X. F. Wu, R. Yamazaki, Z. Yang, T. Ylinen, M. Ziegler

Research output: Contribution to journal › Article › peer-review

Abstract

We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray Burst Monitor and Large Area Telescope (LAT) instruments on board the Fermi Gamma-ray Space Telescope. GRB 090926A shares several features with other bright LAT bursts. In particular, it clearly shows a short spike in the light curve that is present in all detectors that see the burst, and this in turn suggests that there is a common region of emission across the entire Fermi energy range. In addition, while a separate high-energy power-law component has already been observed in other gamma-ray bursts, here we report for the first time the detection with good significance of a high-energy spectral break (or cutoff) in this power-law component around 1.4 GeV in the time-integrated spectrum. If the spectral break is caused by opacity to electron-positron pair production within the source, then this observation allows us to compute the bulk Lorentz factor for the outflow, rather than a lower limit.

Original language	English
Journal	Astrophysical Journal
Volume	729
Issue number	2
DOIs	https://doi.org/10.1088/0004-637X/729/2/114
Publication status	Published - 2011

Subject classification (UKÄ)

Astronomy, Astrophysics and Cosmology

Free keywords

gamma-ray burst: individual (GRB 090926A)

Access to Document

10.1088/0004-637X/729/2/114

Cite this

Ackermann, M., Ajello, M., Asano, K., Axelsson, M., Baldini, L., Ballet, J., Barbiellini, G., Baring, M. G., Bastieri, D., Bechtol, K., Bellazzini, R., Berenji, B., Bhat, P. N., Bissaldi, E., Blandford, R. D., Bonamente, E., Borgland, A. W., Bouvier, A., Bregeon, J., ... Ziegler, M. (2011). Detection of a Spectral Break in the Extra Hard Component of GRB 090926A. Astrophysical Journal, 729(2). https://doi.org/10.1088/0004-637X/729/2/114

@article{70bc9c147e88444db0244e4816e48e36,

title = "Detection of a Spectral Break in the Extra Hard Component of GRB 090926A",

abstract = "We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray Burst Monitor and Large Area Telescope (LAT) instruments on board the Fermi Gamma-ray Space Telescope. GRB 090926A shares several features with other bright LAT bursts. In particular, it clearly shows a short spike in the light curve that is present in all detectors that see the burst, and this in turn suggests that there is a common region of emission across the entire Fermi energy range. In addition, while a separate high-energy power-law component has already been observed in other gamma-ray bursts, here we report for the first time the detection with good significance of a high-energy spectral break (or cutoff) in this power-law component around 1.4 GeV in the time-integrated spectrum. If the spectral break is caused by opacity to electron-positron pair production within the source, then this observation allows us to compute the bulk Lorentz factor for the outflow, rather than a lower limit.",

keywords = "gamma-ray burst: individual (GRB 090926A)",

author = "M. Ackermann and M. Ajello and K. Asano and Magnus Axelsson and L. Baldini and J. Ballet and G. Barbiellini and Baring, {M. G.} and D. Bastieri and K. Bechtol and R. Bellazzini and B. Berenji and Bhat, {P. N.} and E. Bissaldi and Blandford, {R. D.} and E. Bonamente and Borgland, {A. W.} and A. Bouvier and J. Bregeon and A. Brez and Briggs, {M. S.} and M. Brigida and P. Bruel and R. Buehler and S. Buson and Caliandro, {G. A.} and Cameron, {R. A.} and Caraveo, {P. A.} and S. Carrigan and Casandjian, {J. M.} and C. Cecchi and O. Celik and V. Chaplin and E. Charles and A. Chekhtman and J. Chiang and S. Ciprini and R. Claus and J. Cohen-Tanugi and V. Connaughton and J. Conrad and S. Cutini and Dermer, {C. D.} and {De Angelis}, A. and {De Palma}, F. and Dingus, {B. L.} and Silva, {E. Do Couto E.} and Drell, {P. S.} and R. Dubois and C. Favuzzi and Fegan, {S. J.} and Ferrara, {E. C.} and Focke, {W. B.} and M. Frailis and Y. Fukazawa and S. Funk and P. Fusco and F. Gargano and D. Gasparrini and N. Gehrels and S. Germani and N. Giglietto and F. Giordano and M. Giroletti and T. Glanzman and G. Godfrey and A. Goldstein and J. Granot and J. Greiner and Grenier, {I. A.} and Grove, {J. E.} and S. Guiriec and D. Hadasch and Y. Hanabata and Harding, {A. K.} and K. Hayashi and M. Hayashida and E. Hays and D. Horan and Hughes, {R. E.} and R. Itoh and G. Johannesson and Johnson, {A. S.} and Johnson, {W. N.} and T. Kamae and H. Katagiri and J. Kataoka and Kippen, {R. M.} and J. Knoedlseder and D. Kocevski and C. Kouveliotou and M. Kuss and J. Lande and L. Latronico and Lee, {S. -H.} and Garde, {M. Llena} and F. Longo and F. Loparco and Lovellette, {M. N.} and P. Lubrano and A. Makeev and Mazziotta, {M. N.} and S. McBreen and McEnery, {J. E.} and S. McGlynn and C. Meegan and J. Mehault and P. Meszaros and Michelson, {P. F.} and T. Mizuno and C. Monte and Monzani, {M. E.} and E. Moretti and A. Morselli and Moskalenko, {I. V.} and S. Murgia and H. Nakajima and T. Nakamori and M. Naumann-Godo and S. Nishino and Nolan, {P. L.} and Norris, {J. P.} and E. Nuss and M. Ohno and T. Ohsugi and A. Okumura and N. Omodei and E. Orlando and Ormes, {J. F.} and M. Ozaki and Paciesas, {W. S.} and D. Paneque and Panetta, {J. H.} and D. Parent and V. Pelassa and M. Pepe and M. Pesce-Rollins and V. Petrosian and F. Piron and Porter, {T. A.} and R. Preece and Racusin, {J. L.} and S. Raino and R. Rando and A. Rau and M. Razzano and S. Razzaque and A. Reimer and O. Reimer and T. Reposeur and Reyes, {L. C.} and J. Ripken and S. Ritz and M. Roth and F. Ryde and Sadrozinski, {H. F. -W.} and A. Sander and Scargle, {J. D.} and Strickman, {M. S.} and Suson, {D. J.} and H. Tajima and H. Takahashi and T. Tanaka and Y. Tanaka and Thayer, {J. B.} and Thayer, {J. G.} and L. Tibaldo and D. Tierney and K. Toma and Torres, {D. F.} and G. Tosti and A. Tramacere and Y. Uchiyama and T. Uehara and Usher, {T. L.} and J. Vandenbroucke and {van der Horst}, {A. J.} and V. Vasileiou and N. Vilchez and V. Vitale and {von Kienlin}, A. and Waite, {A. P.} and P. Wang and C. Wilson-Hodge and Winer, {B. L.} and Wood, {K. S.} and Wu, {X. F.} and R. Yamazaki and Z. Yang and T. Ylinen and M. Ziegler",

year = "2011",

doi = "10.1088/0004-637X/729/2/114",

language = "English",

volume = "729",

journal = "Astrophysical Journal",

issn = "0004-637X",

publisher = "American Astronomical Society",

number = "2",

}

Ackermann, M, Ajello, M, Asano, K, Axelsson, M, Baldini, L, Ballet, J, Barbiellini, G, Baring, MG, Bastieri, D, Bechtol, K, Bellazzini, R, Berenji, B, Bhat, PN, Bissaldi, E, Blandford, RD, Bonamente, E, Borgland, AW, Bouvier, A, Bregeon, J, Brez, A, Briggs, MS, Brigida, M, Bruel, P, Buehler, R, Buson, S, Caliandro, GA, Cameron, RA, Caraveo, PA, Carrigan, S, Casandjian, JM, Cecchi, C, Celik, O, Chaplin, V, Charles, E, Chekhtman, A, Chiang, J, Ciprini, S, Claus, R, Cohen-Tanugi, J, Connaughton, V, Conrad, J, Cutini, S, Dermer, CD, De Angelis, A, De Palma, F, Dingus, BL, Silva, EDCE, Drell, PS, Dubois, R, Favuzzi, C, Fegan, SJ, Ferrara, EC, Focke, WB, Frailis, M, Fukazawa, Y, Funk, S, Fusco, P, Gargano, F, Gasparrini, D, Gehrels, N, Germani, S, Giglietto, N, Giordano, F, Giroletti, M, Glanzman, T, Godfrey, G, Goldstein, A, Granot, J, Greiner, J, Grenier, IA, Grove, JE, Guiriec, S, Hadasch, D, Hanabata, Y, Harding, AK, Hayashi, K, Hayashida, M, Hays, E, Horan, D, Hughes, RE, Itoh, R, Johannesson, G, Johnson, AS, Johnson, WN, Kamae, T, Katagiri, H, Kataoka, J, Kippen, RM, Knoedlseder, J, Kocevski, D, Kouveliotou, C, Kuss, M, Lande, J, Latronico, L, Lee, S-H, Garde, ML, Longo, F, Loparco, F, Lovellette, MN, Lubrano, P, Makeev, A, Mazziotta, MN, McBreen, S, McEnery, JE, McGlynn, S, Meegan, C, Mehault, J, Meszaros, P, Michelson, PF, Mizuno, T, Monte, C, Monzani, ME, Moretti, E, Morselli, A, Moskalenko, IV, Murgia, S, Nakajima, H, Nakamori, T, Naumann-Godo, M, Nishino, S, Nolan, PL, Norris, JP, Nuss, E, Ohno, M, Ohsugi, T, Okumura, A, Omodei, N, Orlando, E, Ormes, JF, Ozaki, M, Paciesas, WS, Paneque, D, Panetta, JH, Parent, D, Pelassa, V, Pepe, M, Pesce-Rollins, M, Petrosian, V, Piron, F, Porter, TA, Preece, R, Racusin, JL, Raino, S, Rando, R, Rau, A, Razzano, M, Razzaque, S, Reimer, A, Reimer, O, Reposeur, T, Reyes, LC, Ripken, J, Ritz, S, Roth, M, Ryde, F, Sadrozinski, HF-W, Sander, A, Scargle, JD, Strickman, MS, Suson, DJ, Tajima, H, Takahashi, H, Tanaka, T, Tanaka, Y, Thayer, JB, Thayer, JG, Tibaldo, L, Tierney, D, Toma, K, Torres, DF, Tosti, G, Tramacere, A, Uchiyama, Y, Uehara, T, Usher, TL, Vandenbroucke, J, van der Horst, AJ, Vasileiou, V, Vilchez, N, Vitale, V, von Kienlin, A, Waite, AP, Wang, P, Wilson-Hodge, C, Winer, BL, Wood, KS, Wu, XF, Yamazaki, R, Yang, Z, Ylinen, T & Ziegler, M 2011, 'Detection of a Spectral Break in the Extra Hard Component of GRB 090926A', Astrophysical Journal, vol. 729, no. 2. https://doi.org/10.1088/0004-637X/729/2/114

TY - JOUR

T1 - Detection of a Spectral Break in the Extra Hard Component of GRB 090926A

AU - Ackermann, M.

AU - Ajello, M.

AU - Asano, K.

AU - Axelsson, Magnus

AU - Baldini, L.

AU - Ballet, J.

AU - Barbiellini, G.

AU - Baring, M. G.

AU - Bastieri, D.

AU - Bechtol, K.

AU - Bellazzini, R.

AU - Berenji, B.

AU - Bhat, P. N.

AU - Bissaldi, E.

AU - Blandford, R. D.

AU - Bonamente, E.

AU - Borgland, A. W.

AU - Bouvier, A.

AU - Bregeon, J.

AU - Brez, A.

AU - Briggs, M. S.

AU - Brigida, M.

AU - Bruel, P.

AU - Buehler, R.

AU - Buson, S.

AU - Caliandro, G. A.

AU - Cameron, R. A.

AU - Caraveo, P. A.

AU - Carrigan, S.

AU - Casandjian, J. M.

AU - Cecchi, C.

AU - Celik, O.

AU - Chaplin, V.

AU - Charles, E.

AU - Chekhtman, A.

AU - Chiang, J.

AU - Ciprini, S.

AU - Claus, R.

AU - Cohen-Tanugi, J.

AU - Connaughton, V.

AU - Conrad, J.

AU - Cutini, S.

AU - Dermer, C. D.

AU - De Angelis, A.

AU - De Palma, F.

AU - Dingus, B. L.

AU - Silva, E. Do Couto E.

AU - Drell, P. S.

AU - Dubois, R.

AU - Favuzzi, C.

AU - Fegan, S. J.

AU - Ferrara, E. C.

AU - Focke, W. B.

AU - Frailis, M.

AU - Fukazawa, Y.

AU - Funk, S.

AU - Fusco, P.

AU - Gargano, F.

AU - Gasparrini, D.

AU - Gehrels, N.

AU - Germani, S.

AU - Giglietto, N.

AU - Giordano, F.

AU - Giroletti, M.

AU - Glanzman, T.

AU - Godfrey, G.

AU - Goldstein, A.

AU - Granot, J.

AU - Greiner, J.

AU - Grenier, I. A.

AU - Grove, J. E.

AU - Guiriec, S.

AU - Hadasch, D.

AU - Hanabata, Y.

AU - Harding, A. K.

AU - Hayashi, K.

AU - Hayashida, M.

AU - Hays, E.

AU - Horan, D.

AU - Hughes, R. E.

AU - Itoh, R.

AU - Johannesson, G.

AU - Johnson, A. S.

AU - Johnson, W. N.

AU - Kamae, T.

AU - Katagiri, H.

AU - Kataoka, J.

AU - Kippen, R. M.

AU - Knoedlseder, J.

AU - Kocevski, D.

AU - Kouveliotou, C.

AU - Kuss, M.

AU - Lande, J.

AU - Latronico, L.

AU - Lee, S. -H.

AU - Garde, M. Llena

AU - Longo, F.

AU - Loparco, F.

AU - Lovellette, M. N.

AU - Lubrano, P.

AU - Makeev, A.

AU - Mazziotta, M. N.

AU - McBreen, S.

AU - McEnery, J. E.

AU - McGlynn, S.

AU - Meegan, C.

AU - Mehault, J.

AU - Meszaros, P.

AU - Michelson, P. F.

AU - Mizuno, T.

AU - Monte, C.

AU - Monzani, M. E.

AU - Moretti, E.

AU - Morselli, A.

AU - Moskalenko, I. V.

AU - Murgia, S.

AU - Nakajima, H.

AU - Nakamori, T.

AU - Naumann-Godo, M.

AU - Nishino, S.

AU - Nolan, P. L.

AU - Norris, J. P.

AU - Nuss, E.

AU - Ohno, M.

AU - Ohsugi, T.

AU - Okumura, A.

AU - Omodei, N.

AU - Orlando, E.

AU - Ormes, J. F.

AU - Ozaki, M.

AU - Paciesas, W. S.

AU - Paneque, D.

AU - Panetta, J. H.

AU - Parent, D.

AU - Pelassa, V.

AU - Pepe, M.

AU - Pesce-Rollins, M.

AU - Petrosian, V.

AU - Piron, F.

AU - Porter, T. A.

AU - Preece, R.

AU - Racusin, J. L.

AU - Raino, S.

AU - Rando, R.

AU - Rau, A.

AU - Razzano, M.

AU - Razzaque, S.

AU - Reimer, A.

AU - Reimer, O.

AU - Reposeur, T.

AU - Reyes, L. C.

AU - Ripken, J.

AU - Ritz, S.

AU - Roth, M.

AU - Ryde, F.

AU - Sadrozinski, H. F. -W.

AU - Sander, A.

AU - Scargle, J. D.

AU - Strickman, M. S.

AU - Suson, D. J.

AU - Tajima, H.

AU - Takahashi, H.

AU - Tanaka, T.

AU - Tanaka, Y.

AU - Thayer, J. B.

AU - Thayer, J. G.

AU - Tibaldo, L.

AU - Tierney, D.

AU - Toma, K.

AU - Torres, D. F.

AU - Tosti, G.

AU - Tramacere, A.

AU - Uchiyama, Y.

AU - Uehara, T.

AU - Usher, T. L.

AU - Vandenbroucke, J.

AU - van der Horst, A. J.

AU - Vasileiou, V.

AU - Vilchez, N.

AU - Vitale, V.

AU - von Kienlin, A.

AU - Waite, A. P.

AU - Wang, P.

AU - Wilson-Hodge, C.

AU - Winer, B. L.

AU - Wood, K. S.

AU - Wu, X. F.

AU - Yamazaki, R.

AU - Yang, Z.

AU - Ylinen, T.

AU - Ziegler, M.

PY - 2011

Y1 - 2011

N2 - We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray Burst Monitor and Large Area Telescope (LAT) instruments on board the Fermi Gamma-ray Space Telescope. GRB 090926A shares several features with other bright LAT bursts. In particular, it clearly shows a short spike in the light curve that is present in all detectors that see the burst, and this in turn suggests that there is a common region of emission across the entire Fermi energy range. In addition, while a separate high-energy power-law component has already been observed in other gamma-ray bursts, here we report for the first time the detection with good significance of a high-energy spectral break (or cutoff) in this power-law component around 1.4 GeV in the time-integrated spectrum. If the spectral break is caused by opacity to electron-positron pair production within the source, then this observation allows us to compute the bulk Lorentz factor for the outflow, rather than a lower limit.

AB - We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray Burst Monitor and Large Area Telescope (LAT) instruments on board the Fermi Gamma-ray Space Telescope. GRB 090926A shares several features with other bright LAT bursts. In particular, it clearly shows a short spike in the light curve that is present in all detectors that see the burst, and this in turn suggests that there is a common region of emission across the entire Fermi energy range. In addition, while a separate high-energy power-law component has already been observed in other gamma-ray bursts, here we report for the first time the detection with good significance of a high-energy spectral break (or cutoff) in this power-law component around 1.4 GeV in the time-integrated spectrum. If the spectral break is caused by opacity to electron-positron pair production within the source, then this observation allows us to compute the bulk Lorentz factor for the outflow, rather than a lower limit.

KW - gamma-ray burst: individual (GRB 090926A)

U2 - 10.1088/0004-637X/729/2/114

DO - 10.1088/0004-637X/729/2/114

M3 - Article

SN - 0004-637X

VL - 729

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 2

ER -

Detection of a Spectral Break in the Extra Hard Component of GRB 090926A

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