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@ARTICLE{Ashkar:622024,
      author       = {Ashkar, Halim and Sangaré, Aurélie and Fegan, Stephen and
                      Mbarubucyeye, Jean Damascene and Ruiz-Velasco, Edna and Zhu,
                      Sylvia Jiechen},
      title        = {{T}he {C}ase of the {M}issing {V}ery {H}igh-energy
                      {G}amma-{R}ay {B}ursts: {A} {R}etrospective {S}tudy of
                      {S}wift {G}amma-{R}ay {B}ursts with {I}maging {A}tmospheric
                      {C}herenkov {T}elescopes},
      reportid     = {PUBDB-2025-00136, arXiv:2402.01421},
      year         = {2024},
      note         = {Submitted to ApJS},
      abstract     = {Gamma-ray bursts (GRBs) are particle acceleration sites
                      that can emit photons in the very high-energy (VHE) domain
                      through nonthermal processes. From 2004 until 2018, the
                      current generation of Imaging Atmospheric Cherenkov
                      Telescopes (IACTs) did not detect any GRB in the VHE domain.
                      However, from 2018 to 2020, five detections were reported.
                      In this work, we try to solve the case of the missing VHE
                      GBRs prior to 2018. We aim to identify GRBs that might have
                      eluded VHE detection in past years by the H.E.S.S., MAGIC,
                      and VERITAS IACTs. To do so, we study GRBs with known
                      redshift detected by Swift from 2004 until June 2022. We
                      first identify all GRBs that could have been observed by
                      these IACTs since 2004, considering observation conditions
                      and visibility constraints. We assume a relation between the
                      X-rays and the VHE gamma rays based on the VHE GRBs detected
                      to date and combine this with the redshift measurements,
                      instrument response information, and observation conditions
                      to predict the observed VHE gamma-ray flux from the Swift
                      X-Ray Telescope measurements. We report findings on 12
                      bright low-redshift GRBs that we identify as most likely to
                      have been detected in the VHE domain by current IACTs. The
                      rate of IACT-detectable GRBs with ideal observation
                      conditions is <1 VHE GRB per year with the current
                      configuration. With its lower energy threshold and higher
                      sensitivity, this rate increases to ∼4 VHE GRBs per year
                      with the Cherenkov Telescope Array.},
      keywords     = {gamma ray: burst (INSPIRE) / gamma ray: VHE (INSPIRE) /
                      energy: threshold (INSPIRE) / particle: acceleration
                      (INSPIRE) / gamma ray: flux (INSPIRE) / redshift (INSPIRE) /
                      Cherenkov counter (INSPIRE) / imaging (INSPIRE) / MAGIC
                      (INSPIRE) / sensitivity (INSPIRE) / photon (INSPIRE) / site
                      (INSPIRE) / Cherenkov Telescope Array (INSPIRE) / VERITAS
                      (INSPIRE) / HESS (INSPIRE) / X-ray (INSPIRE)},
      cin          = {$Z_HESS$},
      ddc          = {520},
      cid          = {$I:(DE-H253)Z_HESS-20210408$},
      pnm          = {613 - Matter and Radiation from the Universe (POF4-613)},
      pid          = {G:(DE-HGF)POF4-613},
      experiment   = {EXP:(DE-H253)HESS-20170101},
      typ          = {PUB:(DE-HGF)25},
      eprint       = {2402.01421},
      howpublished = {arXiv:2402.01421},
      archivePrefix = {arXiv},
      SLACcitation = {$\%\%CITATION$ = $arXiv:2402.01421;\%\%$},
      doi          = {10.3204/PUBDB-2025-00136},
      url          = {https://bib-pubdb1.desy.de/record/622024},
}