A bright , X-ray-rich gamma-ray burst ( GRB ) was detected by the French Gamma Telescope ( FREGATE ) and localized with the Wide-field X-ray Monitor ( WXM ) and Soft X-ray Camera ( SXC ) instruments on the High Energy Transient Explorer 2 satellite ( HETE-2 ) at 11:18:34.03 UT ( 40714.03 SOD ) on 11 December 2002 . The WXM flight software localized the burst to a 14′ radius ; this was relayed to the astronomical community 22 seconds after the start of the burst . Ground analysis of WXM and SXC data provided refined localizations ; the latter can be described as a circle with a radius of 2′ centered at R.A. 08 ^ { h } 09 ^ { m } 00 ^ { s } , Dec 06° 44′ 20″ ( J2000 ) . GRB 021211 consists of a single , FRED-like pulse with a duration t _ { 90 } \approx 2.3 s at high energies ( 85–400 keV ) which increases to t _ { 90 } \approx 8.5 s at low energies ( 2–10 keV ) . The peak photon number and photon energy fluxes in the 2–400 keV band are ( 34.0 \pm 1.8 ) ph cm ^ { -2 } s ^ { -1 } and ( 1.68 \pm 0.11 ) \times 10 ^ { -6 } erg cm ^ { -2 } s ^ { -1 } , respectively . The energy fluences in the 2–30 keV and 30–400 keV energy bands are S _ { X } = ( 1.36 \pm 0.05 ) \times 10 ^ { -6 } erg cm ^ { -2 } and S _ { \gamma } = ( 2.17 \pm 0.15 ) \times 10 ^ { -6 } erg cm ^ { -2 } , respectively . Thus GRB 021211 is an “ X-ray-rich ” GRB ( S _ { X } / S _ { \gamma } = 0.63 > 0.32 ) . The average spectrum of the the burst is well-fit by a Band function ( low-energy power-law index \alpha = -0.805 ^ { +0.112 } _ { -0.105 } ; high-energy power-law index \beta = -2.37 ^ { +0.18 } _ { -0.31 } ; and energy of the peak of the spectrum in \nu F _ { \nu } , E ^ { obs } _ { peak } = 46.8 ^ { +5.8 } _ { -5.1 } keV ) . The near-real time optical follow-up of GRB 021211 made possible by HETE-2 led to the detection of an optical afterglow for what otherwise would quite likely have been classified as an “ optically dark ” GRB , since the optical transient faded rapidly ( from R < 14 to R \approx 19 ) within the first 20 minutes , and was fainter than R \approx 23 within 24 hours after the burst . GRB 021211 demonstrates that some fraction of burst afterglows are “ optically dark ” because their optical afterglows at times > 1 hour after the burst are very faint , and previously have often escaped detection . Such bursts are “ optically dim ” rather than truly “ optically dark. ” GRB 021211 also shows that even such “ optically dim ” bursts can have very bright optical afterglows at times < 20 minutes after the burst .