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Testing the ubiquitous presence of very high energy emission in gamma-ray bursts with the MAGIC telescopes

S. Abe, J. Abhir, A. Abhishek, V. A. Acciari, A. Aguasca-Cabot, I. Agudo, T. Aniello, S. Ansoldi, L. A. Antonelli, A. Arbet Engels, C. Arcaro, T. T. H. Arnesen, K. Asano, A. Babic, C. Bakshi, U. Barres de Almeida, J. A. Barrio, L. Barrios-Jimenez, I. Batkovic, J. Baxter, J. Becerra Gonzalez, W. Bednarek, E. Bernardini, J. Bernete, A. Berti, J. Besenrieder, C. Bigongiari, A. Biland, O. Blanch, G. Bonnoli, Ž. Bošnjak, E. Bronzini, I. Burelli, A. Campoy-Ordaz, A. Carosi, R. Carosi, M. Carretero-Castrillo, A. J. Castro-Tirado, D. Cerasole, G. Ceribella, Y. Chai, A. Cifuentes, J. L. Contreras, J. Cortina, S. Covino, G. D'Amico, P. Da Vela, F. Dazzi, A. De Angelis, B. De Lotto, R. de Menezes, M. Delfino, J. Delgado, C. Delgado Mendez, F. Di Pierro, R. Di Tria, L. Di Venere, A. Dinesh, D. Dominis Prester, A. Donini, D. Dorner, M. Doro, L. Eisenberger, D. Elsaesser, J. Escudero, L. Fariña, A. Fattorini, L. Foffano, L. Font, S. Fröse, S. Fukami, Y. Fukazawa, R. J. García López, S. García Soto, M. Garczarczyk, S. Gasparyan, M. Gaug, J. G. Giesbrecht Paiva, N. Giglietto, F. Giordano, P. Gliwny, N. Godinovic, T. Gradetzke, R. Grau, D. Green, J. G. Green, P. Günther, D. Hadasch, A. Hahn, T. Hassan, L. Heckmann, J. Herrera Llorente, D. Hrupec, R. Imazawa, S. Inoue, D. Israyelyan, J. Jahanvi, I. Jiménez Martínez, J. Jiménez Quiles, J. Jormanainen, S. Kankkunen, T. Kayanoki, J. Konrad, P. M. Kouch, H. Kubo, J. Kushida, M. Láinez, A. Lamastra, E. Lindfors, S. Lombardi, F. Longo, R. López-Coto, M. López-Moya, A. López-Oramas, S. Loporchio, L. Lulic, E. Lyard, P. Majumdar, M. Makariev, M. Mallamaci, G. Maneva, M. Manganaro, S. Mangano, K. Mannheim, S. Marchesi, M. Mariotti, M. Martínez, P. Maruševec, A. Mas-Aguilar, D. Mazin, S. Menchiari, J. Méndez Gallego, S. Menon, D. Miceli, J. M. Miranda, R. Mirzoyan, M. Molero González, E. Molina, H. A. Mondal, A. Moralejo, E. Moretti, T. Nakamori, C. Nanci, L. Nava, V. Neustroev, L. Nickel, M. Nievas Rosillo, C. Nigro, L. Nikolic, K. Nilsson, K. Nishijima, K. Noda, S. Nozaki, A. Okumura, J. Otero-Santos, S. Paiano, D. Paneque, R. Paoletti, J. M. Paredes, M. Peresano, M. Persic, M. Pihet, G. Pirola, F. Podobnik, P. G. Prada Moroni, E. Prandini, M. Ribó, J. Rico, C. Righi, N. Sahakyan, T. Saito, F. G. Saturni, K. Schmitz, F. Schmuckermaier, A. Sciaccaluga, G. Silvestri, A. Simongini, J. Sitarek, V. Sliusar, D. Sobczynska, A. Stamerra, J. Striškovic, D. Strom, M. Strzys, Y. Suda, H. Tajima, M. Takahashi, R. Takeishi, P. Temnikov, K. Terauchi, T. Terzic, M. Teshima, A. Tutone, S. Ubach, J. van Scherpenberg, M. Vazquez Acosta, S. Ventura, G. Verna, I. Viale, A. Vigliano, C. F. Vigorito, E. Visentin, V. Vitale, I. Vovk, R. Walter, F. Wersig, M. Will, T. Yamamoto, P. K. H. Yeung

TL;DR

The study evaluates the prevalence of very high energy emission from GRBs using MAGIC data collected between 2013 and 2019, focusing on a large non-detection sample and deriving energy-flux ULs that account for EBL attenuation. By comparing EBL-corrected VHE ULs with simultaneous X-ray fluxes, the work tests the hypothesis of a universal VHE component and finds that, while EBL absorption explains many non-detections, a VHE component with luminosity similar to the X-ray band cannot be ruled out for a subset of nearby events. The analysis confirms two TeV detections by MAGIC (GRB 190114C and GRB 201216C) and demonstrates that improved sensitivity (e.g., CTAO) will be crucial to uncovering and constraining TeV emission in the broader GRB population. The results guide future follow-up strategies and emphasize the value of multi-wavelength comparisons in understanding GRB high-energy emission mechanisms.

Abstract

Gamma-ray bursts (GRBs) are the most powerful transient objects in the Universe, and they are a primary target for the MAGIC Collaboration. Recognizing the challenges of observing these elusive objects with Imaging Atmospheric Cherenkov Telescopes (IACTs), we implemented a dedicated observational strategy that included an automated procedure for rapid re-pointing to transient sources. Since 2013, this automated procedure has enabled MAGIC to observe GRBs at a rate of approximately ten per year, which led to the successful detection of two GRBs at very high energies (VHE; E > 100 GeV). We present a comprehensive analysis of 42 non-detected GRBs (4 short GRBs) observed by MAGIC from 2013 to 2019. We derived upper limits (ULs) on the observed energy flux as well as on the intrinsic energy flux corrected for absorption by the extragalactic background light (EBL) from the MAGIC observations in selected energy and time intervals. We conducted a comprehensive study of their properties to investigate the reasons for these non-detections, including the possible peculiar properties of TeV-detected GRBs. We find that strong EBL absorption significantly hinders TeV detection for the majority of GRBs in our sample. For a subset of 6 GRBs with redshift z < 2, we compared the UL on the intrinsic flux in the VHE domain with the simultaneous X-ray flux, which is observed to be at the same level in the current population of TeV-detected GRBs. Based on these inferred MAGIC ULs, we conclude that a VHE component with a luminosity comparable to the simultaneously observed X-ray luminosity cannot be ruled out for this sample.

Testing the ubiquitous presence of very high energy emission in gamma-ray bursts with the MAGIC telescopes

TL;DR

The study evaluates the prevalence of very high energy emission from GRBs using MAGIC data collected between 2013 and 2019, focusing on a large non-detection sample and deriving energy-flux ULs that account for EBL attenuation. By comparing EBL-corrected VHE ULs with simultaneous X-ray fluxes, the work tests the hypothesis of a universal VHE component and finds that, while EBL absorption explains many non-detections, a VHE component with luminosity similar to the X-ray band cannot be ruled out for a subset of nearby events. The analysis confirms two TeV detections by MAGIC (GRB 190114C and GRB 201216C) and demonstrates that improved sensitivity (e.g., CTAO) will be crucial to uncovering and constraining TeV emission in the broader GRB population. The results guide future follow-up strategies and emphasize the value of multi-wavelength comparisons in understanding GRB high-energy emission mechanisms.

Abstract

Gamma-ray bursts (GRBs) are the most powerful transient objects in the Universe, and they are a primary target for the MAGIC Collaboration. Recognizing the challenges of observing these elusive objects with Imaging Atmospheric Cherenkov Telescopes (IACTs), we implemented a dedicated observational strategy that included an automated procedure for rapid re-pointing to transient sources. Since 2013, this automated procedure has enabled MAGIC to observe GRBs at a rate of approximately ten per year, which led to the successful detection of two GRBs at very high energies (VHE; E > 100 GeV). We present a comprehensive analysis of 42 non-detected GRBs (4 short GRBs) observed by MAGIC from 2013 to 2019. We derived upper limits (ULs) on the observed energy flux as well as on the intrinsic energy flux corrected for absorption by the extragalactic background light (EBL) from the MAGIC observations in selected energy and time intervals. We conducted a comprehensive study of their properties to investigate the reasons for these non-detections, including the possible peculiar properties of TeV-detected GRBs. We find that strong EBL absorption significantly hinders TeV detection for the majority of GRBs in our sample. For a subset of 6 GRBs with redshift z < 2, we compared the UL on the intrinsic flux in the VHE domain with the simultaneous X-ray flux, which is observed to be at the same level in the current population of TeV-detected GRBs. Based on these inferred MAGIC ULs, we conclude that a VHE component with a luminosity comparable to the simultaneously observed X-ray luminosity cannot be ruled out for this sample.

Paper Structure

This paper contains 12 sections, 5 figures, 2 tables.

Table of Contents

  1. Introduction
  2. The MAGIC telescopes and the GRB follow-up
  3. The sample
  4. Data analysis and flux calculation
  5. MAGIC data analysis
  6. Energy flux upper limits calculation
  7. GRBs with unknown $z$, $z>2$, or Zd $> 40$ deg
  8. GRBs with $z < 2$ and Zd $< 40$ deg
  9. Comparison with X-ray fluxes
  10. Conclusion
  11. GRBs observed by MAGIC between 2013 and 2019
  12. Observed flux UL for GRBs with unknown $z$ or $z \geq 2$ or Zd $> 40$ deg

Figures (5)

  • Figure 1: Ratio of the observation delay $T_{delay}$ and $T_{90}$ vs. $T_{delay}$ for the GRBs listed in Table \ref{['tab:grb']}. GRBs with and without redshift are denoted by red and blue markers, respectively. The dashed horizontal line denotes when the ratio is equal to one, meaning that for GRBs with a ratio lower than one ,observations started on a timescale comparable to the duration of the prompt emission. For the sample under consideration, the GRBs fulfilling these conditions are GRB131030A, GRB141026A, GRB150428B, GRB170728B, and GRB180720C. The only GRB from this sample that was significantly detected at TeV energies, namely GRB 190114C, is marked with an empty circle.
  • Figure 2: Top panel: EBL attenuation factor in the 0.1 - 10 TeV energy range for three different redshift values (z = 0.5, 1, and 2) and for the three different EBL models we used in this study: Dominguez (D11), ebl_franceschini_2018 (F18), and ebl_gilmore_2012 (G12). Bottom panel: Ratio of the EBL attenuation factors for the three EBL models adopted in this study (D11, G12, and F18) at redshift z = 2.
  • Figure 3: Observed flux points or ULs for TeV-detected GRBs (empty markers) and most stringent ULs for catalog of GRBs non-detected by MAGIC (filled markers) vs. exposure time. The $2\sigma$ sensitivity level curves of the MAGIC and CTAO-North array are also displayed. Two reference energy values are shown: 150 GeV (left plot) and 250 GeV (right plot).
  • Figure 4: Multi-wavelength light curves of the subsample of six GRBs described in Sect. \ref{['subsubsec:interesting_grbs']} and Table \ref{['tab:interesting_uls_grb']}. We show the flux light curves with X-ray data (black for BAT and blue for XRT), average X-ray flux in the MAGIC observational time windows (grey points), LAT data (red, if present), and MAGIC ULs assuming two different photon indices and EBL models for the subsample selected for the comparison with lower-energy bands. The time windows in which MAGIC ULs were computed are marked with vertical red and green stripes.
  • Figure 5: Simultaneous X-ray and MAGIC SEDs for GRB 130701A and GRB 141220A. The X-ray fluxes are corrected for dust extinction. The VHE flux ULs are corrected for EBL absorption. For each GRB, two different time intervals are considered.