Happy Birthday Swift: Ultra-long GRB141121A and its broad-band Afterglow

TL;DR

This paper presents a detailed multi-wavelength observational study of the ultra-long GRB141121A, analyzing its unique features and emission mechanisms over a 30-day period, and discusses implications for the class of UL-GRBs.

Contribution

The study provides one of the first comprehensive broadband analyses of an UL-GRB, highlighting its peculiar features and proposing a two-component jet model for its early behavior.

Findings

GRB141121A is an ultra-long GRB with a duration of 1410 s.

The burst shows a flat early optical light curve and a radio-to-X-ray rebrightening around 3 days.

Analysis supports a two-component jet model to explain early-time behavior.

Abstract

We present our extensive observational campaign on the Swift-discovered GRB141121A, al- most ten years after its launch. Our observations covers radio through X-rays, and extends for more than 30 days after discovery. The prompt phase of GRB 141121A lasted 1410 s and, at the derived redshift of z = 1.469, the isotropic energy is E{\gamma},iso = 8.0x10^52 erg. Due to the long prompt duration, GRB141121A falls into the recently discovered class of UL-GRBs. Peculiar features of this burst are a flat early-time optical light curve and a radio-to-X-ray rebrightening around 3 days after the burst. The latter is followed by a steep optical-to-X-ray decay and a much shallower radio fading. We analyze GRB 141121A in the context of the standard forward-reverse shock (FS,RS) scenario and we disentangle the FS and RS contributions. Finally, we comment on the puzzling early-time (t ~3 d) behavior of GRB 141121A, and suggest that its interpretation may require a two-component jet model. Overall, our analysis confirms that the class of UL-GRBs represents our best opportunity to firmly establish the prominent emission mechanisms in action during powerful GRB explosions, and future missions (like SVOM, XTiDE, or ISS-Lobster) will provide many more of such objects.