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Search of the pair echo signatures in the high-energy light curve of GRB190114C

Ievgen Vovk
Phys. Rev. D 107, 043020 – Published 16 February 2023
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  • INTRODUCTION
  • CALCULATION OF THE PAIR ECHO EMISSION
  • GRB190114C DELAYED-EMISSION MODELING
  • DISCUSSION
  • ACKNOWLEDGMENTS
    • References

    Abstract

    A model of the time-delayed electromagnetic cascade “echo” is applied to the bright gamma-ray burst GRB190114C—the first gamma-ray burst to be contemporaneously detected in high and very high-energy gamma-ray bands. It is shown that the internal spread of the cascade in the absence of the intervening magnetic fields dilutes the “echo” emission over 103–105 seconds depending on the energy. Accounting for the measured source flux in the 0.3–1 TeV gamma-ray band, the prediction of the “echo” model is shown to match the detected lower-energy gamma-ray emission 104 seconds after the burst. However, the “echo” emission remains indistinguishable from the intrinsic GRB190114C flux within the measurement uncertainties. Implications of this in the context of the intergalactic magnetic field measurement are discussed.

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    • Received 15 July 2022
    • Accepted 9 January 2023

    DOI:https://doi.org/10.1103/PhysRevD.107.043020

    © 2023 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Gamma ray astronomyGamma ray burstsPrimordial magnetic fields
    Gravitation, Cosmology & Astrophysics

    Authors & Affiliations

    Ievgen Vovk*

    • Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwa-no-Ha, Kashiwa City, Chiba 277-8582, Japan

    • *vovk@icrr.u-tokyo.ac.jp

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    Vol. 107, Iss. 4 — 15 February 2023

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    • Figure 1
      Figure 1

      Differential pair production rate for Eγ=1  TeV gamma ray as function of the generated electron (positron) energy and motion direction offset angle with respect to that of the gamma ray. Calculations performed for the EBL photon field at redshift z=0. Apparent layering at Ee≳0.6  TeV is a numerical artifact coming from the energy binning of the used EBL model [35].

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    • Figure 2
      Figure 2

      Inverse Compton emission profiles of a single electron with the Lorentz factor γ=106, scattering the isotropic black body photon field with the temperature T=2.725  K, evaluated at multiples of the mean scattered photon energy ⟨ε1⟩=3.6γ2kT≈0.85  GeV.

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    • Figure 3
      Figure 3

      Inverse Compton emission spectra of a single electron with the Lorentz factor γ=106, scattering the isotropic black body photon field with the temperature T=2.725  K, evaluated at several offset angles with respect to the electron motion direction.

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    • Figure 4
      Figure 4

      Sketch of the secondary emission problem. Observer (on the left) is separated from the source (on the right) by the distance rs. An photon emitted by the source at an angle α is absorbed having traveled over the distance r0 and generates an electron (positron) at the relative angle θe. The latter travels over the distance de before emitting the secondary photon reaching the observer after crossing the distance of rt.

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    • Figure 5
      Figure 5

      Time dependency of the cascade kernel K(ε1,Eγ,Δt), integrated over the initial photon energy Eγ, evaluated at several emission energies ε1. Calculation was performed for a putative source at the redshift of GRB190114C (z=0.42) with an exponentially cutoff power law spectrum with the index Γ=−2, normalization at E0=100  GeV of N=10−221/(cm2  s eV) and the cut off energy Ec=5  TeV.

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    • Figure 6
      Figure 6

      Energy dependency of the cascade kernel K(ε1,Eγ,Δt), integrated over the initial photon energy Eγ and evaluated at several values of time delay Δt. The assumed emission source is the same as in Fig. 5.

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    • Figure 7
      Figure 7

      Expected secondary (cascade) flux from GRB190114C compared to the actual measurements in TeV and GeV bands [34]. Cascade flux is estimated from the power law primary source emission in the T−T0=[68;2400]  s time window, where the VHE emission was measured. An estimate assuming an exponential energy cutoff at Ec=1  TeV is shown with the dashed orange line. Extrapolation of the initial source flux assuming the F(t)∝t−1.5 scaling found in [34] is shown with the gray dash-dotted line. Cascade resulting from this extrapolation down to T−T0=5  s is depicted with the dotted orange line.

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