High-energy observations of XRF 030723: Evidence for an off-axis gamma-ray burst?

N. R. Butler, T. Sakamoto, M. Suzuki, N. Kawai, D. Q. Lamb, C. Graziani, T. Q. Donaghy, A. Dullighan, R. Vanderspek, G. B. Crew, P. Ford, G. Ricker, J. L. Atteia, A. Yoshida, Y. Shirasaki, T. Tamagawa, K. Torii, M. Matsuoka, E. E. Fenimore, M. GalassiJ. Doty, J. Villasenor, G. Prigozhin, J. G. Jernigan, C. Barraud, M. Boer, J. P. Dezalay, J. F. Olive, K. Hurley, A. Levine, F. Martel, E. Morgan, S. E. Woosley, T. Cline, J. Braga, R. Manchanda, G. Pizzichini

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


We report High Energy Transient Explorer 2 (HETE-2) Wide Field X-ray Monitor (WXM) and French Gamma Telescope observations of XRF 030723 along with observations of the XRF afterglow made using the 6.5 m Magellan Clay telescope and Chandra. The observed peak energy Epkobs of the vFv burst spectrum is found to lie within (or below) the WXM 2-25 keV passband at 98.5% confidence, and no counts are detected above 30 keV. Our best-fit value is Epkobs = 8.4-3.4 +3.5 keV. The ratio of X-ray to γ-ray flux for the burst follows a correlation found for GRBs observed with HETE-2, and the duration of the burst is similar to that typical of long-duration GRBs. If we require that the burst isotropic equivalent energy Eiso and E pk'satisfy the relation discovered by Amati et al. (2002), a redshift of z = 0.38-0.18+0.36 can be determined, in agreement with constraints determined from optical observations. We are able to fit the X-ray afterglow spectrum and to measure its temporal fade. Although the best-fit fade is shallower than the concurrent fade in the optical, the spectral similarity between the two bands indicates that the X-ray fade may actually trace the optical fade. If this is the case, the late-time rebrightening observed in the optical cannot be due to a supernova bump. We interpret the prompt and afterglow X-ray emission as arising from a jetted GRB observed off-axis and possibly viewed through a complex circumburst medium that is due to a progenitor wind.

Original languageEnglish (US)
Pages (from-to)884-893
Number of pages10
JournalAstrophysical Journal
Issue number2 I
StatePublished - Mar 10 2005
Externally publishedYes


  • Gamma rays: bursts
  • Supernovae: general
  • X-rays: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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