# The Signature of the Blandford-Znajek Mechanism in GRB Light Curves

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## Abstract

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## 1. Introduction

## 2. XRT Observations

## 3. Summary

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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1. | http://ww.wift.ac.uk/xrt.curves/ |

**Figure 1.**Schematic structure of the magnetosphere close to the event horizon of a rotating black hole. Magnetic field lines in dark red and orange. A massive torus of material (transparent) holds the magnetic flux on the event horizon (from Nathanail et al. [10]).

**Figure 2.**Typical Gamma-Ray Burst (GRB) light curve obtained with Swift (shown the one for $GRB\phantom{\rule{3.33333pt}{0ex}}120326A$). Log-Log plot. Blue crosses: BAT $\gamma $-ray prompt emission. Black crosses: XRT X-ray afterglow. We are mostly interested in the first part of the afterglow, the so-called rapid decay phase, which is suspected to be of internal origin (central engine activity). In a large number of bursts, this rapid decay phase follows an exponential, compatible with electromagnetic black hole spindown (from Nathanail et al. [10]).

**Figure 3.**Nine characteristic GRB XRT light curves in Log-Linear scale. Notice that in Log-Linear plots an exponential is shown as a straight (blue) line. Energy flux at 0.3–10 keV. We focus on the first part of the afterglow, the rapid decay phase (from Nathanail et al. [10]).

**Table 1.**The 60 GRBs with a clear exponential decay (from Nathanail et al. [10]).

GRB | ${\mathbf{\tau}}_{\mathbf{BZ}}$ (sec) | GRB | ${\mathbf{\tau}}_{\mathbf{BZ}}$ (sec) | GRB | ${\mathbf{\tau}}_{\mathbf{BZ}}$ (sec) |
---|---|---|---|---|---|

050716 | $140\phantom{\rule{3.33333pt}{0ex}}(\pm 4)\phantom{\rule{3.33333pt}{0ex}}$ | 050724 | $60\phantom{\rule{3.33333pt}{0ex}}(\pm 4)\phantom{\rule{3.33333pt}{0ex}}$ | $050915B$ | $31\phantom{\rule{3.33333pt}{0ex}}(\pm 4)\phantom{\rule{3.33333pt}{0ex}}$ |

051210 | $90\phantom{\rule{3.33333pt}{0ex}}(\pm 8)\phantom{\rule{3.33333pt}{0ex}}$ | 060413 | $82\phantom{\rule{3.33333pt}{0ex}}(\pm 13)\phantom{\rule{3.33333pt}{0ex}}$ | 060614 | $55\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ |

060708 | $25\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ | 060729 | $35\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ | $061110A$ | $50\phantom{\rule{3.33333pt}{0ex}}(\pm 4)\phantom{\rule{3.33333pt}{0ex}}$ |

061121 | $14\phantom{\rule{3.33333pt}{0ex}}(\pm 1)\phantom{\rule{3.33333pt}{0ex}}$ | $061222A$ | $34\phantom{\rule{3.33333pt}{0ex}}(\pm 4)\phantom{\rule{3.33333pt}{0ex}}$ | 070306 | $38\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ |

070420 | $36\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ | 070621 | $50\phantom{\rule{3.33333pt}{0ex}}(\pm 6)\phantom{\rule{3.33333pt}{0ex}}$ | 071227 | $72\phantom{\rule{3.33333pt}{0ex}}(\pm 20)\phantom{\rule{3.33333pt}{0ex}}$ |

080205 | $32\phantom{\rule{3.33333pt}{0ex}}(\pm 4)\phantom{\rule{3.33333pt}{0ex}}$ | $080229A$ | $33\phantom{\rule{3.33333pt}{0ex}}(\pm 5)\phantom{\rule{3.33333pt}{0ex}}$ | 080503 | $60\phantom{\rule{3.33333pt}{0ex}}(\pm 4)\phantom{\rule{3.33333pt}{0ex}}$ |

081028 | $145\phantom{\rule{3.33333pt}{0ex}}(\pm 25)\phantom{\rule{3.33333pt}{0ex}}$ | 081128 | $50\phantom{\rule{3.33333pt}{0ex}}(\pm 5)\phantom{\rule{3.33333pt}{0ex}}$ | 081221 | $32\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ |

081230 | $17\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ | 090111 | $28\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ | 090404 | $28\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ |

090618 | $18\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ | 091026 | $40\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ | 091029 | $30\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ |

091104 | $70\phantom{\rule{3.33333pt}{0ex}}(\pm 10)\phantom{\rule{3.33333pt}{0ex}}$ | $100418A$ | $30\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ | $100425A$ | $25\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ |

$100514A$ | $32\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ | $100522A$ | $18\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ | $100526A$ | $57\phantom{\rule{3.33333pt}{0ex}}(\pm 5)\phantom{\rule{3.33333pt}{0ex}}$ |

$100615A$ | $26\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ | $100621A$ | $38\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ | $100725A$ | $95\phantom{\rule{3.33333pt}{0ex}}(\pm 7)\phantom{\rule{3.33333pt}{0ex}}$ |

$101030A$ | $36\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ | $101213A$ | $75\phantom{\rule{3.33333pt}{0ex}}(\pm 9)\phantom{\rule{3.33333pt}{0ex}}$ | $101225A$ | $6200\phantom{\rule{3.33333pt}{0ex}}(\pm 500)\phantom{\rule{3.33333pt}{0ex}}$ |

$110210A$ | $90\phantom{\rule{3.33333pt}{0ex}}(\pm 8)\phantom{\rule{3.33333pt}{0ex}}$ | $110414A$ | $30\phantom{\rule{3.33333pt}{0ex}}(\pm 6)\phantom{\rule{3.33333pt}{0ex}}$ | $110420A$ | $26\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ |

$110808A$ | $50\phantom{\rule{3.33333pt}{0ex}}(\pm 6)\phantom{\rule{3.33333pt}{0ex}}$ | $111123A$ | $130\phantom{\rule{3.33333pt}{0ex}}(\pm 6)\phantom{\rule{3.33333pt}{0ex}}$ | $111209A$ | $6400\phantom{\rule{3.33333pt}{0ex}}(\pm 500)\phantom{\rule{3.33333pt}{0ex}}$ |

$111225A$ | $110\phantom{\rule{3.33333pt}{0ex}}(\pm 18)\phantom{\rule{3.33333pt}{0ex}}$ | $120106A$ | $21\phantom{\rule{3.33333pt}{0ex}}(\pm 1)\phantom{\rule{3.33333pt}{0ex}}$ | $120116A$ | $39\phantom{\rule{3.33333pt}{0ex}}(\pm 6)\phantom{\rule{3.33333pt}{0ex}}$ |

$120213A$ | $60\phantom{\rule{3.33333pt}{0ex}}(\pm 5)\phantom{\rule{3.33333pt}{0ex}}$ | $120215A$ | $65\phantom{\rule{3.33333pt}{0ex}}(\pm 8)\phantom{\rule{3.33333pt}{0ex}}$ | $120324A$ | $44\phantom{\rule{3.33333pt}{0ex}}(\pm 4)\phantom{\rule{3.33333pt}{0ex}}$ |

$120326A$ | $28\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ | $120401A$ | $270\phantom{\rule{3.33333pt}{0ex}}(\pm 30)\phantom{\rule{3.33333pt}{0ex}}$ | $120514A$ | $30\phantom{\rule{3.33333pt}{0ex}}(\pm 4)\phantom{\rule{3.33333pt}{0ex}}$ |

$120922A$ | $75\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ | $121108A$ | $15\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ | $130315A$ | $80\phantom{\rule{3.33333pt}{0ex}}(\pm 5)\phantom{\rule{3.33333pt}{0ex}}$ |

$130528A$ | $25\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ | $131018A$ | $50\phantom{\rule{3.33333pt}{0ex}}(\pm 13)\phantom{\rule{3.33333pt}{0ex}}$ | $131127A$ | $30\phantom{\rule{3.33333pt}{0ex}}(\pm 5)\phantom{\rule{3.33333pt}{0ex}}$ |

**Table 2.**The 22 GRBs with a clear exponential decay after a flare (from Nathanail et al. [10]).

GRB | ${\mathbf{\tau}}_{\mathbf{BZ}}$ (sec) | GRB | ${\mathbf{\tau}}_{\mathbf{BZ}}$ (sec) | GRB | ${\mathbf{\tau}}_{\mathbf{BZ}}$ (sec) |
---|---|---|---|---|---|

$050502B$ | $95\phantom{\rule{3.33333pt}{0ex}}(\pm 8)\phantom{\rule{3.33333pt}{0ex}}$ | 060929 | $90\phantom{\rule{3.33333pt}{0ex}}(\pm 14)\phantom{\rule{3.33333pt}{0ex}}$ | 061202 | $55\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ |

$070720B$ | $55\phantom{\rule{3.33333pt}{0ex}}(\pm 7)\phantom{\rule{3.33333pt}{0ex}}$ | 080212 | $47\phantom{\rule{3.33333pt}{0ex}}(\pm 4)\phantom{\rule{3.33333pt}{0ex}}$ | 080325 | $95\phantom{\rule{3.33333pt}{0ex}}(\pm 8)\phantom{\rule{3.33333pt}{0ex}}$ |

$090621A$ | $27\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ | 090904 | $40\phantom{\rule{3.33333pt}{0ex}}(\pm 6)\phantom{\rule{3.33333pt}{0ex}}$ | $100619A$ | $11\phantom{\rule{3.33333pt}{0ex}}(\pm 1)\phantom{\rule{3.33333pt}{0ex}}$ |

$100704A$ | $36\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ | $100727A$ | $45\phantom{\rule{3.33333pt}{0ex}}(\pm 6)\phantom{\rule{3.33333pt}{0ex}}$ | $100802A$ | $110\phantom{\rule{3.33333pt}{0ex}}(\pm 17)\phantom{\rule{3.33333pt}{0ex}}$ |

$100814A$ | $65\phantom{\rule{3.33333pt}{0ex}}(\pm 5)\phantom{\rule{3.33333pt}{0ex}}$ | $100902A$ | $37\phantom{\rule{3.33333pt}{0ex}}(\pm 3)\phantom{\rule{3.33333pt}{0ex}}$ | $100906A$ | $12\phantom{\rule{3.33333pt}{0ex}}(\pm 1)\phantom{\rule{3.33333pt}{0ex}}$ |

$120308A$ | $52\phantom{\rule{3.33333pt}{0ex}}(\pm 4)\phantom{\rule{3.33333pt}{0ex}}$ | $121027A\left(1\right)$ | $110\phantom{\rule{3.33333pt}{0ex}}(\pm 6)\phantom{\rule{3.33333pt}{0ex}}$ | $121027A\left(2\right)$ | $3800\phantom{\rule{3.33333pt}{0ex}}(\pm 300)\phantom{\rule{3.33333pt}{0ex}}$ |

$121123A$ | $110\phantom{\rule{3.33333pt}{0ex}}(\pm 12)\phantom{\rule{3.33333pt}{0ex}}$ | $121217A$ | $80\phantom{\rule{3.33333pt}{0ex}}(\pm 8)\phantom{\rule{3.33333pt}{0ex}}$ | $131030A$ | $25\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ |

$140108A$ | $12\phantom{\rule{3.33333pt}{0ex}}(\pm 2)\phantom{\rule{3.33333pt}{0ex}}$ | $140114A$ | $65\phantom{\rule{3.33333pt}{0ex}}(\pm 4)\phantom{\rule{3.33333pt}{0ex}}$ |

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**MDPI and ACS Style**

Contopoulos, I.; Nathanail, A.; Strantzalis, A.
The Signature of the Blandford-Znajek Mechanism in GRB Light Curves. *Galaxies* **2017**, *5*, 21.
https://doi.org/10.3390/galaxies5020021

**AMA Style**

Contopoulos I, Nathanail A, Strantzalis A.
The Signature of the Blandford-Znajek Mechanism in GRB Light Curves. *Galaxies*. 2017; 5(2):21.
https://doi.org/10.3390/galaxies5020021

**Chicago/Turabian Style**

Contopoulos, Ioannis, Antonios Nathanail, and Achillies Strantzalis.
2017. "The Signature of the Blandford-Znajek Mechanism in GRB Light Curves" *Galaxies* 5, no. 2: 21.
https://doi.org/10.3390/galaxies5020021