Multiwavelength observations of GRB 140629A

A long burst with an achromatic jet break in the optical and X-ray afterglow^⋆

¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
e-mail: huyoudong072@hotmail.com
² Universidad de Granada, Facultad de Ciencias Campus Fuentenueva, s/n, CP, 18071 Granada, Spain
³ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
⁴ M. V. Lomonosov Moscow State University, Physics Department, Leninskie Gory, GSP-1, 119991 Moscow, Russia
⁵ M. V. Lomonosov Moscow State University, Sternberg Astronomical Institute, Universitetsky pr., 13, 119234 Moscow, Russia
⁶ School of Astronomy and Space Science, Nanjing University, 210093 Nanjing, PR China
e-mail: bbzhang@nju.edu.cn
⁷ Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Ministry of Education, 210093 Nanjing, PR China
⁸ Unidad Asociada CSIC Departamento de Ingeniería de Sistemas y Automática, Escuela de Ingenieros Industriales, Universidad de Málaga, C. Dr. Ortiz Ramos sn, 29071 Málaga, Spain
⁹ Department of Physics, SungKyunKwan University, 16419 Suwon, Korea
¹⁰ INAF, Istituto Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, 00133 Roma, Italy
¹¹ Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401, 141 00 Prague, Czech Republic
¹² Aryabhatta Research Institute of Observational Sciences, Manora Peak, 263002 Nainital, India
¹³ Applied Physics Institute, Irkutsk State University, 20, Gagarin blvd, 664003 Irkutsk, Russia
¹⁴ Kourovka Astronomical Observatory, Ural Federal University, Lenin ave. 51, 620000 Ekaterinburg, Russia
¹⁵ Blagoveshchensk State Pedagogical University, Lenin str., 104, 675000 Blagoveschensk, Amur Region, Russia
¹⁶ Special Astrophysical Observatory, Russian Academy of Sciences, 369167 Nizhnii Arkhyz, Russia
¹⁷ Space Research Institute RAS (IKI), 84/32 Profsoyuznaya, 117997 Moscow, Russia
¹⁸ Moscow Institute of Physics and Technology, Dolgoprudny, Institutsky per., 9, 141700 Moscow, Russia
¹⁹ Universidad Internacional de Valencia (VIU), Calle Pintor Sorolla 21, 46002 Valencia, Spain
²⁰ Mykolaiv National Unuversity, Nikolska 24, 54030 Mykolaiv, Ukraine

Received: 21 December 2018
Accepted: 3 October 2019

Abstract

Aims. We investigate the long gamma-ray burst (GRB) 140629A through multiwavelength observations to derive the properties of the dominant jet and its host galaxy.

Methods. The afterglow and host galaxy observations were taken in the optical (Swift/UVOT and various facilities worldwide), infrared (Spitzer), and X-rays (Swift/XRT) between 40 s and 3 yr after the burst trigger.

Results. Polarisation observations by the MASTER telescope indicate that this burst is weakly polarised. The optical spectrum contains absorption features, from which we confirm the redshift of the GRB as originating at z = 2.276 ± 0.001. We performed spectral fitting of the X-rays to optical afterglow data and find there is no strong spectral evolution. We determine the hydrogen column density N_H to be 7.2 × 10²¹ cm⁻² along the line of sight. The afterglow in this burst can be explained by a blast wave jet with a long-lasting central engine expanding into a uniform medium in the slow cooling regime. At the end of energy injection, a normal decay phase is observed in both the optical and X-ray bands. An achromatic jet break is also found in the afterglow light curves ∼0.4 d after trigger. We fit the multiwavelength data simultaneously with a model based on a numerical simulation and find that the observations can be explained by a narrow uniform jet in a dense environment with an opening angle of 6.7° viewed 3.8° off-axis, which released a total energy of 1.4 × 10⁵⁴ erg. Using the redshift and opening angle, we find GRB 140629A follows both the Ghirlanda and Amati relations. From the peak time of the light curve, identified as the onset of the forward shock (181s after trigger), the initial Lorentz factor (Γ₀) is constrained in the range 82–118. Fitting the host galaxy photometry, we find the host to be a low mass, star-forming galaxy with a star formation rate of log (SFR) 1.1^+0.9_−0.4 M_⊙ yr⁻¹. We obtain a value of the neutral hydrogen density by fitting the optical spectrum, log N_HI = 21.0 ± 0.3, classifying this host as a damped Lyman-alpha. High ionisation lines (N V, Si IV) are also detected in the spectrum.