# Statistical Study of Gamma-Ray Bursts with a Plateau Phase in the X-ray Afterglow

## TL;DR

This study analyzes a large sample of Swift GRBs with plateau phases, confirming a key correlation among their X-ray luminosity, plateau end time, and prompt energy, supporting the magnetar central engine model and potential cosmological applications.

## Contribution

It provides an updated, comprehensive correlation among GRB parameters using 174 bursts, including short GRBs and those with internal plateaus, enhancing understanding of their central engines.

## Key findings

- Confirmed the $L_{X}$-$T_{a}$-$E_{γ,iso}$ correlation with a new fit.
- Short GRBs follow the same correlation as long GRBs.
- GRBs with internal plateaus also obey the correlation.

## Abstract

A plateau phase in the X-ray afterglow is observed in a significant fraction of gamma-ray bursts (GRBs). Previously, it has been found that there exists a correlation among three key parameters concerning the plateau phase, i.e., the end time of the plateau phase in the GRB rest frame ($T_{a}$), the corresponding X-ray luminosity at the end time ($L_{X}$) and the isotropic energy of the prompt GRB ($E_{\gamma,\rm{iso}}$). In this study, we systematically search through all the \emph{Swift} GRBs with a plateau phase that occurred between 2005 May and 2018 August. We collect 174 GRBs, with redshifts available for all of them. For the whole sample, the correlation between $L_{X}$, $T_{a}$ and $E_{\gamma,\rm{iso}}$ is confirmed, with the best fit relation being $L_{X}\propto T_{a}^{-1.01}E_{\gamma,\rm{iso}}^{0.84}$. Such an updated three-parameter correlation still supports that the central leftover after GRBs is probably a millisecond magnetar. It is interesting to note that short GRBs with duration less than 2 s in our sample also follow the same correlation, which hints that the merger production of two neutron stars could be a high mass magnetar, but not necessarily a black hole. Moreover, GRBs having an "internal" plateau (i.e., with a following decay index being generally smaller than -3) also obey this correlation. It further strengthens the idea that the internal plateau is due to the delayed collapse of a high mass neutron star into a black hole. The updated three-parameter correlation indicates that GRBs with a plateau phase may act as a standard candle for cosmology study.