Very Bright Prompt and Reverse Shock Emission of GRB 140512a

Abstract

We report our observations of very bright prompt optical and reverse shock (RS) optical emission of GRB 140512A and analyze its multi-wavelength data observed with the Swift and Fermi missions. It is found that the joint optical-X-ray-gamma-ray spectrum with our first optical detection (R=13.09 mag) at T 0 + 136 seconds during the second episode of the prompt gamma-rays can be fit by a single power-law with index −1.32 ± 0.01. Our empirical fit to the afterglow lightcurves indicates that the observed bright optical afterglow with R=13.00 mag at the peak time is consistent with predictions of the RS and forward shock (FS) emission of external shock models. Joint optical-X-ray afterglow spectrum is well fit with an absorbed single power-law, with an index evolving with time from −1.86 ± 0.01 at the peak time to −1.57 ± 0.01 at late epoch, which could be due to the evolution of the ratio of the RS to FS emission fluxes. We fit the lightcurves with standard external models, and derive the physical properties of the outflow. It is found that the ratio R B ≡ ǫ B,r /ǫ B,f is 8187, indicating a high magnetization degree in the RS region. Measuring the relative radiation efficiency with R e ≡ ǫ e,r /ǫ e,f , we have R e = 0.02, implying the radiation efficiency of the RS is much lower than that in FS. We also show that the R B of GRBs 990123, 090102, and 130427A are similar to that of GRB 140512A and their apparent difference may be mainly attributed to the difference of the jet kinetic energy, initial Lorentz factor, and medium density among them.

Reverse shocks in the relativistic outflows of gravitational wave-detected neutron star binary mergers

“…As the reverse shock probes the shell material towards the central engine that is driving the outflow, a strong magnetic field associated with the engine will further enhance the reverse shock parameters by a factor R 1/2 B for both F max,r and ν m,r , and by the factor R −3/2 B for ν c,r ; where R B ≡ ε B,r /ε B, f and ε B is the magnetic microphysical parameter and the subscript f or r refers to forward or reverse shock respectively (Zhang, Kobayashi & Mészáros 2003;Gomboc, et al 2008). Very high values of R B have been obtained for some long GRBs (Zhang, Kobayashi & Mészáros 2003;Harrison & Kobayashi 2013;Huang, et al 2016) and a value of a ∼few for the short GRB 160821B (Lamb, et al 2019b).…”

“…The phenomenology of the reverse shock emission can be used as a probe for the magnetisation of the central engine (e.g. Fan, Dai, Huang & Lu 2002;Zhang, Kobayashi & Mészáros 2003;Zhang & Kobayashi 2005;Giannios, Mimica & Aloy 2008;Gomboc, et al 2008;Steele, Mundell, Smith, Kobayashi & Guidorzi 2009;Mimica, Giannios & Aloy 2010;Granot 2012;Harrison & Kobayashi 2013;Japelj, et al 2014;Guidorzi, et al 2014;Fraija 2015;Gao, Wang, Mészáros & Zhang 2015;Kopač, et al 2015;Zhang, Jin & Wei 2015;Huang, et al 2016;Liu, Wang & Dai 2016;Alexander, et al 2017;Laskar, et al 2016Laskar, et al , 2018Lamb, et al 2019b) and potentially assist in identifying the likely outflow structure.…”

Exceptionally bright optical emission from a rare and distant gamma-ray burst

“…For GRB 080319B, data before and after 60 s are from the optical V-band and optical R-band, respectively. The grey solid lines represent the GRBs (GRB 021004 70 , GRB 021211 71 ,GRB 050525A 72 , GRB 061126 73 , GRB 081007 74 , GRB 090102 75 , GRB 091024 76,77,78,79 , GRB 130427A 80 , GRB 140102A 81 , GRB 140512A 82 , and GRB 190114C 83 ) observed with (possible) RS component. Due to strong wind at the telescope site the images were distorted.…”

Extremely Bright GRB 160625B with Multiple Emission Episodes: Evidence for Long-term Ejecta Evolution

“…We derive the jet properties from the afterglow data in this section. The details of our model and fitting strategy please refer to Huang et al (2016). With the observed spectral index and temporal decay slope of the normal decay segment (from 10 5 to 10 6 seconds), we suggest that both the optical and X-ray emission should be in the spectral regime between ν m and ν c , and take p = 2β + 1 ∼ 2.4, where we take β ∼ 0.70 derived from the time slice [1.5−2.0]×10 5 seconds.…”