Towards Understanding the Origin of Swift Gamma-Ray Bursts Driven by Magnetars

TL;DR

This study tests the magnetar central-engine hypothesis for Swift GRBs displaying extended emission and X-ray plateaus by combining multi-wavelength data with magnetar spin-down physics. It derives a three-parameter L_X–T_a–E_gamma_iso relation and uses the B–P diagram to identify magnetar-like engines, finding that about 90 of 109 plateaus are magnetar-powered; many imply magnetic fields surpass 10^{16} G and millisecond spin periods. Spin-down modeling together with jet beaming constraints places most events within a magnetar-like region, with GRB 211024B as a notable exception. The results support a multi-channel magnetar formation picture that can power both short and long GRBs with either internal or external X-ray plateaus and extended emission, and reveal redshift and energy distributions consistent with magnetar-driven scenarios across diverse GRB classes.

Abstract

We analyze a sample of\textit{ Swift} gamma-ray bursts (GRBs) with extended emissions in $γ$-rays and/or X-ray plateaus that may be driven by magnetars. Multi-wavelength data and multi-standards have been adopted to investigate the issue jointly. First, we find that GRBs with both extended emission and X-ray plateau satisfy a three-parameter relation between the luminosity and the end time of X-ray plateaus and the $γ$-ray isotropic energy as $L_X\varpropto T_a^{-1.13}E_{γ,iso}^{0.74}$, which is consistent with that of normal GRBs. Second, we distinguish these GRBs in the plane of magnetic field versus period of neutron star and find that almost all GRBs but GRB 211024B have reasonable periods and majority of them could be powered by magnetars. Third, we standardize the X-ray afterglows with distinct characteristics and find that the standard X-ray light curves with/without plateaus are significantly different. The standardized X-ray plateaus are similar to the mean temporal profile of magnetars. Fourth, it is verified with a K-S test that all types of GRBs except short ones have the similar distributions of redshift and isotropic energy in the observer/rest frame. GRBs with internal plateaus are significantly different from those of normal long GRBs and GRBs with external plateaus and/or extended emissions. Interestingly, the isotropic energy distributions of GRBs with internal and external plateaus are identical with those of short and long GRBs, respectively. Overall, our study can bring solid evidence that the fascinating magnetars could have multi-formation channels to account for not only short but also long GRBs with either internal or external X-ray plateaus as well.

Figures (7)

• Figure 1: The $L-T-E$ relation of 109 GRBs with well-measured X-ray afterglows. The solid, dashed and dash-dotted lines correspond to the best fit, 2$\sigma$ and 3$\sigma$ confidence levels. All symbols are illustrated in the insert.
• Figure 2: The $B-P$ of 109 GRBs with EEs and/or X-ray plateaus. The dashed and dash-dotted lines indicates the $B-P$ correlations within the upper and lower mass accretion limits, respectively, The dotted line on the left is the minimum rotation period of 0.81ms.
• Figure 3: The observed (left panel) and standardized (right panel) X-ray light curves with IXPs (top), EXPs (middle) and IFs (bottom), respectively.
• Figure 4: Cumulative redshift (left panel) and energy (right panel) distributions of different types of GRBs in our sample. The black solid line stands for the $z$ distribution of 163 GRBs in total. All symbols have been interpreted in the illustraion of each panel.
• Figure 5: Distributional histograms of Swift GRBs are displayed in the observer (left panel) and rest (right panel) frames. The red solid curves stand for the best fit with a two-Gauss function. The vertical line denotes a duration of 2 seconds.