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

Abstract In this paper, we analyze a sample of Swift gamma-ray bursts (GRBs) with extended emissions in γ -rays and/or X-ray plateaus that may be driven by magnetars. Multiwavelength data and multistandards 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>L</mml:mi> <mml:mi mathvariant="normal">X</mml:mi> </mml:msub> <mml:mo>∝</mml:mo> <mml:msubsup> <mml:mi>T</mml:mi> <mml:mi>a</mml:mi> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.13</mml:mn> </mml:mrow> </mml:msubsup> <mml:msubsup> <mml:mi>E</mml:mi> <mml:mrow> <mml:mi>γ</mml:mi> <mml:mo>,</mml:mo> <mml:mi>iso</mml:mi> </mml:mrow> <mml:mn>0.74</mml:mn> </mml:msubsup> </mml:math> , 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, except GRB 211024B, have reasonable periods, and the 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 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 multiformation channels to account for not only short but also long GRBs with either internal or external X-ray plateaus as well.