2018/04/06 by Li-Ye Huang, Xiang-Gao Wang, WeiKang Zheng +8
Engineering · Physics and Astronomy · #Achromatic lens #Afterglow #Astronomy and Astrophysical Research #CCD and CMOS Imaging Sensors #Gamma-ray burst #Gamma-ray bursts and supernovae #Light curve #Photon #Shock (circulatory) #Spectral energy distribution #astro-ph.HE
paper · pdf · doi:10.3847/1538-4357/aaba6e
23 pages, 9 figures,Accepted for publication in ApJ
arxiv created 2018/04/06 · openalex created_date 2018/04/13 · openalex publication_date 2018/06/01 · arxiv updated 2018/06/27 · openalex updated_date 2026/08/05
Abstract Gamma-ray burst (GRB) 120729A was detected by Swift /BAT and Fermi /GBM, and then rapidly observed by Swift /XRT, Swift /UVOT, and ground-based telescopes. It had a single long and smooth γ -ray emission pulse, which extends continuously to the X-rays. We report Lick/KAIT observations of the source, and make temporal and spectral joint fits of the multiwavelength light curves of GRB 120729A. It exhibits achromatic light-curve behavior, consistent with the predictions of the external shock model. The light curves are decomposed into four typical phases: onset bump (Phase I), normal decay (Phase II), shallow decay (Phase III), and post-jet break (Phase IV). The spectral energy distribution (SED) evolves from prompt γ -ray emission to the afterglow with a photon index from Γ γ = 1.36 to Γ ≈ 1.75. There is no obvious evolution of the SED during the afterglow. The multiwavelength light curves from γ -ray to optical can be well modeled with an external shock by considering energy injection, and a time-dependent microphysics model with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ϵ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∝</mml:mo> <mml:msup> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msup> </mml:math> for the emission at early times, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>T</mml:mi> <mml:mo><</mml:mo> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mo>+</mml:mo> <mml:mn>157</mml:mn> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">s</mml:mi> </mml:math> . Therefore, we conclude that both the prompt γ -ray emission and afterglow of GRB 120729A have the same external shock physical origin. Our model indicates that the ϵ B evolution can be described as a broken power-law function with α B ,1 = 0.18 ± 0.04 and α B ,2 = 0.84 ± 0.04. We also systematically investigate single-pulse GRBs in the Swift era, finding that only a small fraction of GRBs (GRBs 120729A, 051111, and 070318) are likely to originate from an external shock for both the prompt γ -ray emission and afterglow.