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The second H.E.S.S. gamma-ray burst catalogue: 15 years of observations with the H.E.S.S. telescopes

A. Acharyya, F. Aharonian, C. Arcaro, H. Ashkar, M. Backes, V. Barbosa Martins, R. Batzofin, Y. Becherini, D. Berge, K. Bernlöhr, M. Böttcher, C. Boisson, J. Bolmont, J. Borowska, F. Brun, B. Bruno, C. Burger-Scheidlin, S. Casanova, J. Celic, M. Cerruti, S. Chandra, A. Chen, M. Chernyakova, J. O. Chibueze, O. Chibueze, T. Collins, B. Cornejo, G. Cotter, J. Damascene Mbarubucyeye, I. D. Davids, J. de Assis Scarpin, M. de Bony de Lavergne, M. de Naurois, E. de Oña Wilhelmi, A. G. Delgado Giler, J. Devin, A. Djannati-Ataï, J. Djuvsland, A. Dmytriiev, K. Egberts, K. Egg, J. -P. Ernenwein, C. Escañuela Nieves, M. D. Filipovic, G. Fontaine, S. Funk, S. Gabici, Y. A. Gallant, M. Genaro, J. F. Glicenstein, J. Glombitza, M. -H. Grondin, L. Heckmann, B. Heß, J. A. Hinton, W. Hofmann, T. L. Holch, M. Holler, D. Horns, Z. Huang, M. Jamrozy, F. Jankowsky, I. Jaroschewski, D. Jimeno Sanchez, I. Jung-Richardt, E. Kasai, K. Kasprzak, K. Katarzyński, D. Kerszberg, B. Khélifi, W. Kluzniak, N. Komin, K. Kosack, D. Kostunin, R. G. Lang, S. Lazarević, M. Lemoine-Goumard, J. -P. Lenain, P. Liniewicz, A. Luashvili, J. Mackey, D. Malyshev, D. Malyshev, V. Marandon, M. Mayer, A. Mehta, A. Mikhno, A. M. W. Mitchell, R. Moderski, M. O. Moghadam, L. Mohrmann, A. Montanari, E. Moulin, J. Niemiec, P. O'Brien, L. Olivera-Nieto, S. Panny, M. Panter, R. D. Parsons, U. Pensec, P. Pichard, S. Pita, G. Pühlhofer, M. Punch, A. Quirrenbach, M. Regeard, A. Reimer, O. Reimer, I. Reis, H. Ren, B. Reville, F. Rieger, G. Rowell, B. Rudak, E. Ruiz-Velasco, K. Sabri, V. Sahakian, H. Salzmann, D. A. Sanchez, A. Santangelo, M. Sasaki, F. Schüssler, M. Senniappan, J. N. S. Shapopi, W. Si Said, H. Sol, S. Spencer, Ł. Stawarz, S. Steinmassl, T. Tanaka, A. M. Taylor, G. L. Taylor, R. Terrier, M. Tsirou, T. Unbehaun, C. van Eldik, M. Vecchi, C. Venter, J. Vink, T. Wach, S. J. Wagner, A. Wierzcholska, M. Zacharias, A. A. Zdziarski, W. Zhong, S. J. Zhu, A. Zech

Abstract

Recent observational efforts using imaging atmospheric Cherenkov telescopes (IACTs) have led to firm detections of very-high-energy (VHE) signals from bright gamma-ray bursts (GRBs), often at moderate redshifts. This work presents 15 years of H.E.S.S. GRB observations and examines their implications through population comparisons and selected modelling cases. GRBs are a key science target of the High Energy Stereoscopic System (H.E.S.S.). With a low-energy threshold ($\lesssim$100 GeV) and rapid repointing capabilities, H.E.S.S. can begin follow-up observations within tens of seconds after a GRB trigger, covering the late prompt or early afterglow phases. We report GRB follow-up observations with H.E.S.S. from 2004 to 2019, which resulted in no significant VHE signals (aside from the detections of GRB~180720B and GRB~190829A). The resulting upper limits comprise the largest set available for GRBs at VHE. A subset of bursts with favourable conditions were selected for X-ray analysis and emission modelling. Population studies were performed to compare detected and non-detected GRBs. The results indicate that VHE-detected GRBs are not a distinct population, but tend to feature luminous X-ray emission and favourable redshift and observing conditions. This highlights the potential of next-generation IACTs such as the Cherenkov Telescope Array Observatory (CTAO), whose lower energy threshold will enhance the detection of fainter and more distant GRBs.

The second H.E.S.S. gamma-ray burst catalogue: 15 years of observations with the H.E.S.S. telescopes

Abstract

Recent observational efforts using imaging atmospheric Cherenkov telescopes (IACTs) have led to firm detections of very-high-energy (VHE) signals from bright gamma-ray bursts (GRBs), often at moderate redshifts. This work presents 15 years of H.E.S.S. GRB observations and examines their implications through population comparisons and selected modelling cases. GRBs are a key science target of the High Energy Stereoscopic System (H.E.S.S.). With a low-energy threshold (100 GeV) and rapid repointing capabilities, H.E.S.S. can begin follow-up observations within tens of seconds after a GRB trigger, covering the late prompt or early afterglow phases. We report GRB follow-up observations with H.E.S.S. from 2004 to 2019, which resulted in no significant VHE signals (aside from the detections of GRB~180720B and GRB~190829A). The resulting upper limits comprise the largest set available for GRBs at VHE. A subset of bursts with favourable conditions were selected for X-ray analysis and emission modelling. Population studies were performed to compare detected and non-detected GRBs. The results indicate that VHE-detected GRBs are not a distinct population, but tend to feature luminous X-ray emission and favourable redshift and observing conditions. This highlights the potential of next-generation IACTs such as the Cherenkov Telescope Array Observatory (CTAO), whose lower energy threshold will enhance the detection of fainter and more distant GRBs.
Paper Structure (21 sections, 12 figures, 8 tables)

This paper contains 21 sections, 12 figures, 8 tables.

Table of Contents

  1. Introduction
  2. The H.E.S.S. telescopes and the GRB follow-up programme
  3. The H.E.S.S. experiment
  4. Alert system and GRB follow-up
  5. The observed GRBs
  6. The sample of H.E.S.S. GRB follow-ups
  7. Data quality checks
  8. Data analysis
  9. Results
  10. Specific GRBs
  11. GRB 100621A
  12. GRB 131030A
  13. GRB 161001A
  14. Comparing the properties of GRBs observed at VHEs
  15. Prompt phase: Swift/BAT
  16. ...and 6 more sections

Figures (12)

  • Figure 1: Distribution of GRB follow-ups performed with H.E.S.S. between 2004 and 2019. A total of 89 GRBs are considered in the analysis, classified as either well-localised (loc, typically Swift/BAT alerts with position uncertainty $\lesssim$3$'$) or poorly localised (un-loc, mostly Fermi/GBM alerts with uncertainty $\gtrsim$0.2$^\circ$) as detailed in Sect. \ref{['sec:grbsample']}.
  • Figure 2: Significance distribution of the gamma-ray emission for the loc follow-ups. The distribution is shown in orange, and the fitted Gaussian is shown in blue. Each entry of the histogram corresponds to one GRB or cluster (see text for details).
  • Figure 3: Stacked analysis of the GRB sample. The $\theta^2$ plots of stacked H.E.S.S. ON and OFF events are shown in green and shaded blue, respectively, for the stereo (left panel) and mono (right panel) observations. The orange vertical line corresponds to the $\theta^2$ cut as explained in Sect. \ref{['sec:results']}.
  • Figure 4: SED of GRB 100621A. The Swift/XRT spectrum is shown with the blue butterfly. The H.E.S.S. ULs obtained in this work are shown in black. The H.E.S.S. UL published in 2014AA...565A..16H is shown in orange for comparison. For the modelled emission components, the synchrotron is shown with a pink solid line (ISM case) and yellow dashed-dotted line (wind case), and the SSC with a pink dashed line (ISM case) and yellow dotted line (wind case).
  • Figure 5: SED of GRB 131030A. The Swift/XRT spectrum is shown with the blue butterfly. The H.E.S.S. ULs are shown in black. In the plotted emission components, the synchrotron contribution appears as a pink solid curve for the ISM scenario and a yellow dashed-dotted curve for the wind scenario, while the SSC component is represented by a pink dashed curve (ISM) and a yellow dotted curve (wind).
  • ...and 7 more figures