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MAGIC observations of NGC 4278. The first low-luminosity radio galaxy with compact jets detected at TeV energies

S. Abe, J. Abhir, V. A. Acciari, A. Aguasca-Cabot, I. Agudo, T. Aniello, S. Ansoldi, L. A. Antonelli, A. Arbet Engels, C. Arcaro, T. T. H. Arnesen, A. Babić, C. Bakshi, U. Barres de Almeida, J. A. Barrio, L. Barrios-Jiménez, I. Batković, J. Baxter, J. Becerra González, 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, A. Cerviño, A. Chilingarian, A. Cifuentes Santos, J. L. Contreras, J. Cortina, S. Covino, F. D'Ammando, G. D'Amico, P. Da Vela, F. Dazzi, A. De Angelis, B. De Lotto, R. de Menezes, J. Delgado, C. Delgado Mendez, F. Di Pierro, R. Di Tria, L. Di Venere, A. Dinesh, D. Dominis Prester, D. Dorner, M. Doro, L. Eisenberger, D. Elsaesser, L. Fariña, L. Foffano, L. Font, S. Fröse, Y. Fukazawa, R. J. García López, S. García Soto, S. Gasparyan, M. Gaug, J. G. Giesbrecht Paiva, N. Giglietto, F. Giordano, P. Gliwny, T. Gradetzke, R. Grau, J. G. Green, P. Günther, D. Hadasch, A. Hahn, G. Harutyunyan, T. Hassan, L. Heckmann, J. Herrera Llorente, D. Hrupec, D. Israyelyan, J. Jahanvi, I. Jiménez Martínez, J. Jiménez Quiles, J. Jormanainen, S. Kankkunen, T. Kayanoki, P. M. Kouch, G. Koziol, 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 Lulić, P. Majumdar, M. Makariev, G. Maneva, M. Manganaro, S. Mangano, S. Marchesi, M. Mariotti, M. Martínez, P. Maruševec, D. Mazin, S. Menchiari, J. Méndez Gallego, S. Menon, D. Miceli, R. Mirzoyan, M. Molero González, E. Molina, H. A. Mondal, A. Moralejo, C. Nanci, A. Negro, V. Neustroev, M. Nievas Rosillo, C. Nigro, L. Nikolić, K. Nilsson, 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, W. Rhode, M. Ribó, J. Rico, A. Roy, N. Sahakyan, F. G. Saturni, K. Schmitz, F. Schmuckermaier, T. Schweizer, A. Sciaccaluga, G. Silvestri, A. Simongini, J. Sitarek, D. Sobczynska, A. Stamerra, J. Strišković, D. Strom, M. Strzys, Y. Suda, H. Tajima, M. Takahashi, R. Takeishi, J. Tartera Barberà, P. Temnikov, T. Terzić, 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, C. Walther, F. Wersig, M. Will, P. K. H. Yeung, E. Torresi, G. Migliori, P. Grandi

Abstract

The Large High Altitude Air Shower Observatory (LHAASO) Collaboration has recently reported the first detection at TeV energies of a low-luminosity radio galaxy, NGC 4278. The aim of this work is to investigate the high-energy properties of NGC 4278 during the flaring and subsequent quasi-quiescent states with the Florian Goebel Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes. NGC 4278 is located in the field of view of two blazars, 1ES 1215+303 and 1ES 1218+304, previously observed by the MAGIC telescopes. Therefore, we re-analyzed MAGIC observations made between 2010 and 2024 on these sources. We also modeled the broadband spectral energy distribution of the source during and after the flaring state at TeV energies. We did not detect any statistically significant $γ$-ray emission from NGC 4278 with MAGIC. The corresponding upper limits obtained using the entire MAGIC dataset ($F_{{\rm UL, }\, >150\, \mathrm{GeV}}=1.5 \times 10^{-12}\, \mathrm{ph \, s^{-1}\, cm^{-2}}$) are consistent with the LHAASO results. The best-fit models obtained for both emission states suggest that the emitting region is strongly particle-dominated, and an efficient acceleration mechanism has to be in action in order to reach TeV energies. The transition between the flaring and quasi-quiescent state cannot be explained by a simple radiative cooling of the emitting particles. The inferred jet power, of the order of $L_{\rm jet}\sim 10^{42}\, \mathrm{erg\,s^{-1}}$, is dominated by the kinetic component in both states and it is in a good agreement with previous, time-averaged observational estimates, supporting the idea that such high-energy flares might be recurrent. The jet, however, remains too weak to break the host-galaxy confinement.

MAGIC observations of NGC 4278. The first low-luminosity radio galaxy with compact jets detected at TeV energies

Abstract

The Large High Altitude Air Shower Observatory (LHAASO) Collaboration has recently reported the first detection at TeV energies of a low-luminosity radio galaxy, NGC 4278. The aim of this work is to investigate the high-energy properties of NGC 4278 during the flaring and subsequent quasi-quiescent states with the Florian Goebel Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes. NGC 4278 is located in the field of view of two blazars, 1ES 1215+303 and 1ES 1218+304, previously observed by the MAGIC telescopes. Therefore, we re-analyzed MAGIC observations made between 2010 and 2024 on these sources. We also modeled the broadband spectral energy distribution of the source during and after the flaring state at TeV energies. We did not detect any statistically significant -ray emission from NGC 4278 with MAGIC. The corresponding upper limits obtained using the entire MAGIC dataset () are consistent with the LHAASO results. The best-fit models obtained for both emission states suggest that the emitting region is strongly particle-dominated, and an efficient acceleration mechanism has to be in action in order to reach TeV energies. The transition between the flaring and quasi-quiescent state cannot be explained by a simple radiative cooling of the emitting particles. The inferred jet power, of the order of , is dominated by the kinetic component in both states and it is in a good agreement with previous, time-averaged observational estimates, supporting the idea that such high-energy flares might be recurrent. The jet, however, remains too weak to break the host-galaxy confinement.
Paper Structure (11 sections, 5 equations, 5 figures, 3 tables)

This paper contains 11 sections, 5 equations, 5 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Observations and data analysis
  3. MAGIC
  4. Fermi-LAT
  5. Swift-XRT
  6. SED modeling and discussion
  7. Flaring state
  8. Temporal evolution
  9. Quasi-quiescent state
  10. Jet powers
  11. Conclusions

Figures (5)

  • Figure 1: The squared angular distance ($\theta^2$) shows the number of $\gamma$-ray events as a function of the squared angular separation between the reconstructed $\gamma$-ray direction and the position of NGC 4278. The on-source and background signals are shown in black and gray, respectively. The cut in $\theta^2$ used for the calculation of the number of ON and OFF events is shown with the dashed, vertical line.
  • Figure 2: Significance map of the region surrounding NGC 4278. The positions of NGC 4278, 1ES 1218+304, and 1ES 1215+303 are marked with a white star, a pink cross, and a green square, respectively. The colorbar represents the statistical significance in gaussian units. The gray crosses represent the telescopes' pointing positions.
  • Figure 3: MAGIC light curve above $150\, \mathrm{GeV}$. The 95% confidence upper limits are shown as black downward arrows. The active phase observed by LHAASO Cao2024b is shown as a yellow strip. The period covered in the first LHAASO catalog Cao2024a and in the dedicated paper by the LHAASO Collaboration Cao2024b are shown as pink and burgundy vertical strips with back diagonal and diagonal hatching lines, respectively.
  • Figure 4: SED modeling of the flaring ( left panel) and the quasi-quiescent ( right panel) state. Data used for the fit are shown in pink and green, respectively, while archival data are shown in gray for completeness, but not used in the fitting procedure . Upper limits are here reported at 95% level of confidence. For MAGIC data, we report the upper limits obtained using both the post-flare (2023-2024), in green, and the entire (2010-2024), in burgundy, datasets. The best-fit models are shown in black and the 16%-84% confidence interval of the model is shown as yellow-shaded band.
  • Figure 5: Simulation of the temporal evolution of the blob assuming only radiative cooling in action. The initial parameters for the blob conditions are those of the flaring state, reported in Table \ref{['tab: sed modeling']}. The duration of the simulation is $t_{\rm sim} = 2\, \mathrm{yr}$ and the time step for clarity reasons is $t_{\rm step}\sim 5\, \mathrm{days}$, both in observer rest-frame. The SED at the end of the simulation is marked as a red dashed line. Here, we show only Swift-XRT Bronzini2024b and LHAASO Cao2024b best-fit models for clarity, with the same color code used in Figure \ref{['fig: SED model']}.