@article{650e58bc2ed0461a838279410ad271c0,
title = "Swift X-ray telescope and very large telescope observations of the afterglow of GRB 041223",
abstract = "GRB 041223 was the first gamma-ray burst detected by the Swift X-Ray Telescope (XRT), beginning 4.6 hr after the burst. The X-ray detection triggered a VLT observation of the optical/near-infrared (NIR) counterpart, located about 1″.1 from the XRT position. The X-ray counterpart faded rapidly, with a power-law index of - 1.72 ± 0.20, with an average unabsorbed X-ray flux of 6.5 × 10-12 ergs cm-2 s-1 in the 0.5-10 keV band for a power-law spectrum of photon index 2.02 ± 0.13 with Galactic absorption. The NIR counterpart was observed at three epochs between 16 and 87 hr after the burst and faded with a power-law index of -1.14 ± 0.08 with a reddening-corrected spectral energy distribution power-law slope of -0.40 ± 0.03. We find that the X-ray and NIR data are consistent with a two-component jet in a wind medium.",
author = "Burrows, {D. N.} and Hill, {J. E.} and G. Chincarini and G. Tagliaferri and S. Campana and A. Moretti and P. Romano and D. Malesani and Racusin, {J. L.} and S. Kobayashi and B. Zhang and P. M{\'e}sz{\'a}ros and O'Brien, {P. T.} and R. Willingale and Osborne, {J. P.} and G. Cusumano and P. Giommi and L. Angelini and Abbey, {A. F.} and Antonelli, {L. A.} and Beardmore, {A. P.} and M. Capalbi and S. Covino and P. D'Avanzo and Goad, {M. R.} and Kennea, {J. A.} and Morris, {D. C.} and C. Pagani and Page, {K. L.} and L. Stella and Nousek, {J. A.} and Wells, {A. A.} and N. Gehrels",
note = "Funding Information: This work is supported at Pennsylvania State University (PSU) by NASA contract NAS5-00136, at the University of Leicester (UL) by the Particle Physics and Astronomy Research Council on grant numbers PPA/G/S/00524 and PPA/Z/S/2003/00507, and at the Osservatorio Astronomico di Brera (OAB) by funding from ASI on grant number I/R/039/04. We gratefully acknowledge the contributions of dozens of members of the XRT team at PSU, UL, OAB, GSFC, ASI Science Data Center, and our subcontractors, who helped make this instrument possible. This work is partly based on observations performed with ESO telescopes under program 074.D-0418. We thank the MISTICI collaboration for use of their VLT photometric data in this Letter, and we are grateful to the ESO staff at Paranal, in particular Olivier Marco and Jonathan Smoker, for carefully performing the VLT observations in service mode. Finally, we thank the referee for a prompt and helpful review of this Letter.",
year = "2005",
month = apr,
day = "1",
doi = "10.1086/429666",
language = "English (US)",
volume = "622",
pages = "L85--L88",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2 II",
}