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Title: Identification and properties of the photospheric emission in GRB090902B

Abstract

We observed the Fermi Gamma-ray Space Telescope using the bright and long GRB090902B, lying at a redshift of z = 1.822. Together the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM) cover the spectral range from 8 keV to >300 GeV. Here we show that the prompt burst spectrum is consistent with emission from the jet photosphere combined with nonthermal emission described by a single power law with photon index –1.9. The photosphere gives rise to a strong quasi-blackbody spectrum which is somewhat broader than a single Planck function and has a characteristic temperature of ~290 keV. We model the photospheric emission with a multicolor blackbody, and its shape indicates that the photospheric radius increases at higher latitudes. We derive the averaged photospheric radius R ph = (1.1 ± 0.3) × 10 12 Y 1/4 cm and the bulk Lorentz factor of the flow, which is found to vary by a factor of 2 and has a maximal value of Γ = 750 Y 1/4. Here, Y is the ratio between the total fireball energy and the energy emitted in the gamma rays. Here, we find that during the first quarter of the prompt phase the photosphericmore » emission dominates, which explains the delayed onset of the observed flux in the LAT compared to the GBM. We also interpret the broadband emission as synchrotron emission at R ~ 4 × 10 15 cm. Our analysis emphasizes the importance of having high temporal resolution when performing spectral analysis on gamma-ray bursts, since there is strong spectral evolution.« less

Authors:
 [1];  [2];  [3];  [1];  [4];  [1];  [5];  [1];  [3];  [6];  [7];  [8];  [9];  [10];  [8];  [2];  [11];  [12];  [13];  [14] more »;  [8];  [15] « less
  1. KTH Royal Inst. of Technology, Stockholm (Sweden). Dept. of Physics; Oskar Klein Centre for Cosmoparticle Physics, Stockholm (Sweden)
  2. Oskar Klein Centre for Cosmoparticle Physics, Stockholm (Sweden).; Stockholm Univ. (Sweden). Dept. of Astronomy
  3. Univ. of Nevada, Las Vegas, NV (United States). Dept. of Physics and Astronomy
  4. Space Telescope Science Inst., Baltimore, MD (United States)
  5. Oskar Klein Centre for Cosmoparticle Physics, Stockholm (Sweden); Stockholm Univ. (Sweden). Dept. of Physics
  6. Max Planck Inst. for Extraterrestrial Physics, Garching (Germany)
  7. National Inst. of Nuclear Physics, Pisa (Italy)
  8. Univ. of Alabama, Huntsville, AL (United States). Center for Space Plasma and Aeronomic Research (CSPAR)
  9. Stanford Univ. and SLAC National Accelerator Lab., CA (United States). Kavli Inst. for Particle Astrophysics and Cosmology
  10. Polytechnic Univ. of Bari (Italy). Dept. of Physics; National Inst. of Nuclear Physics, Bari (Italy)
  11. National Inst. of Nuclear Physics, Trieste (Italy); Univ. of Trieste (Italy). Dept. of Physics
  12. Max Planck Inst. for Extraterrestrial Physics, Garching (Germany); Univ. of College, Dublin (Ireland)
  13. National Inst. of Nuclear Physics, Bari (Italy)
  14. Stanford Univ., CA (United States). Center for Space Science and Astrophysics
  15. NASA Marshall Space Flight Center (MSFC), Huntsville, AL (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
Contributing Org.:
Fermi LAT Collaboration
OSTI Identifier:
1357583
Grant/Contract Number:  
AC02-76SF00515
Resource Type:
Accepted Manuscript
Journal Name:
Astrophysical Journal Letters
Additional Journal Information:
Journal Volume: 709; Journal Issue: 2; Journal ID: ISSN 2041-8205
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; gamma-ray burst: individual (GRB090902B); gamma rays: general; radiation mechanisms: thermal

Citation Formats

Ryde, F., Axelsson, M., Zhang, B. B., McGlynn, S., Pe'er, A., Lundman, C., Larsson, S., Battelino, M., Zhang, B., Bissaldi, E., Bregeon, J., Briggs, M. S., Chiang, J., de Palma, F., Guiriec, S., Larsson, J., Longo, F., McBreen, S., Omodei, N., Petrosian, V., Preece, R., and van der Horst, A. J. Identification and properties of the photospheric emission in GRB090902B. United States: N. p., 2010. Web. doi:10.1088/2041-8205/709/2/L172.
Ryde, F., Axelsson, M., Zhang, B. B., McGlynn, S., Pe'er, A., Lundman, C., Larsson, S., Battelino, M., Zhang, B., Bissaldi, E., Bregeon, J., Briggs, M. S., Chiang, J., de Palma, F., Guiriec, S., Larsson, J., Longo, F., McBreen, S., Omodei, N., Petrosian, V., Preece, R., & van der Horst, A. J. Identification and properties of the photospheric emission in GRB090902B. United States. doi:10.1088/2041-8205/709/2/L172.
Ryde, F., Axelsson, M., Zhang, B. B., McGlynn, S., Pe'er, A., Lundman, C., Larsson, S., Battelino, M., Zhang, B., Bissaldi, E., Bregeon, J., Briggs, M. S., Chiang, J., de Palma, F., Guiriec, S., Larsson, J., Longo, F., McBreen, S., Omodei, N., Petrosian, V., Preece, R., and van der Horst, A. J. Thu . "Identification and properties of the photospheric emission in GRB090902B". United States. doi:10.1088/2041-8205/709/2/L172. https://www.osti.gov/servlets/purl/1357583.
@article{osti_1357583,
title = {Identification and properties of the photospheric emission in GRB090902B},
author = {Ryde, F. and Axelsson, M. and Zhang, B. B. and McGlynn, S. and Pe'er, A. and Lundman, C. and Larsson, S. and Battelino, M. and Zhang, B. and Bissaldi, E. and Bregeon, J. and Briggs, M. S. and Chiang, J. and de Palma, F. and Guiriec, S. and Larsson, J. and Longo, F. and McBreen, S. and Omodei, N. and Petrosian, V. and Preece, R. and van der Horst, A. J.},
abstractNote = {We observed the Fermi Gamma-ray Space Telescope using the bright and long GRB090902B, lying at a redshift of z = 1.822. Together the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM) cover the spectral range from 8 keV to >300 GeV. Here we show that the prompt burst spectrum is consistent with emission from the jet photosphere combined with nonthermal emission described by a single power law with photon index –1.9. The photosphere gives rise to a strong quasi-blackbody spectrum which is somewhat broader than a single Planck function and has a characteristic temperature of ~290 keV. We model the photospheric emission with a multicolor blackbody, and its shape indicates that the photospheric radius increases at higher latitudes. We derive the averaged photospheric radius R ph = (1.1 ± 0.3) × 1012 Y 1/4 cm and the bulk Lorentz factor of the flow, which is found to vary by a factor of 2 and has a maximal value of Γ = 750 Y 1/4. Here, Y is the ratio between the total fireball energy and the energy emitted in the gamma rays. Here, we find that during the first quarter of the prompt phase the photospheric emission dominates, which explains the delayed onset of the observed flux in the LAT compared to the GBM. We also interpret the broadband emission as synchrotron emission at R ~ 4 × 1015 cm. Our analysis emphasizes the importance of having high temporal resolution when performing spectral analysis on gamma-ray bursts, since there is strong spectral evolution.},
doi = {10.1088/2041-8205/709/2/L172},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 709,
place = {United States},
year = {2010},
month = {1}
}

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