Context. Superluminous supernovae (SLSNe) are a rare class of transients with peak luminosities 10–100 times greater than those of standard corecollapse supernovae (SNe). The mechanisms powering their extreme brightness remain debated, with circumstellar medium (CSM) interaction, or energy injection from a central engine like a magnetar wind nebula being the most plausible scenarios. While the optical properties of SLSNe are extensively studied, their -ray signatures remain poorly constrained. Aims. To further constrain the underlying mechanism, we carried out a systematic search for giga-electronvolt -ray emission using the Fermi Large Area Telescope (LAT) from a sample of nearby hydrogen-poor (Type I) and hydrogen-rich (Type II) SLSNe over the past 16 years. Our objective is to test predictions from CSM and magnetar models, and to assess the prospects for future detections with the Cherenkov Telescope Array Observatory (CTAO). Methods. For the six targets of this sample, we studied the time variability of a putative -ray signal at the optical position of the SLSN on a sixmonth timescale, and in the case of SN 2017egm, we further investigated variability on 15-day intervals and applied a Bayesian block algorithm to characterize the time variability of the signal. We then compared the temporal evolution and spectral properties to the predictions from a magnetar and CSM interaction model. Results. Among the sample, only SN 2017egm shows significant -ray emission, with likelihood test statistic (TS) values of 26–33 (i.e., >5) depending on the adopted time window. The signal arises between 50 and 160 days after explosion and is well described by a power-law spectrum with index = 2:17  0:23. The emission is consistent both in terms of its light curve and its spectrum, with predictions from magnetar models requiring either low nebular magnetization or faster spin-down than dipole losses. The CSM shell interaction scenario can reproduce the observed flux level but not the observed timing of the -ray signal. In addition, the observed ratio, L =Lopt  1, is inconsistent with theoretical expectations and not in line with ratio measurements in other interacting CSM-dominated objects (e.g., novae or SNe) where this ratio is less than 102. Conclusions. Our study strongly suggests that a central engine like a magnetar plays a key role in this SLSN and could explain the bulk of the optical and -ray light curves properties. In order to explain the observed late-time bumps in the optical light curve of SN 2017egm, we require
Gamma-ray signature of superluminous supernovae: Fermi-LAT GeV detection of SN 2017egm and evidence of a central engine / Acero, F.; Acharyya, A.; Adelfio, A.; Ajello, M.; Aviano, E.; Baldini, L.; Ballet, J.; Bartolini, C.; Bastieri, D.; Becerra Gonzalez, J.; Bellazzini, R.; Bissaldi, E.; Bonino, R.; Bruel, P.; Buson, S.; Cameron, R. A.; Caraveo, P. A.; Casaburo, F.; Casini, F.; Cavazzuti, E.; Cheung, C. C.; Cibrario, N.; Cozzolongo, G.; Cristarella Orestano, P.; Cuna, F.; Cutini, S.; D'Ammando, F.; Depalo, D.; Digel, S. W.; Di Lalla, N.; Dinesh, A.; Di Venere, L.; Fauverge, P.; Fiori, A.; Franckowiak, A.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasbarra, C.; Gasparrini, D.; Germani, S.; Giacchino, F.; Giglietto, N.; Giliberti, M.; Giordano, F.; Giroletti, M.; Grenier, I. A.; Grondin, M. -H.; Guiriec, S.; Gupta, R.; Hays, E.; Hewitt, J. W.; Holzmann Airasca, A.; Horan, D.; Hou, X.; Kayanoki, T.; Kerr, M.; Kuss, M.; Laviron, A.; Lemoine-Goumard, M.; Liguori, A.; Li, J.; Liodakis, I.; Loizzo, P.; Longo, F.; Loparco, F.; López Pérez, S.; Lorusso, L.; Lovellette, M. N.; Lubrano, P.; Maldera, S.; Manfreda, A.; Martí-Devesa, G.; Martinelli, R.; Mazziotta, M. N.; Michailidis, M.; Michelson, P. F.; Mirabal, N.; Mizuno, T.; Monti-Guarnieri, P.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Negro, M.; Omodei, N.; Orienti, M.; Orlando, E.; Panzarini, G.; Persic, M.; Pesce-Rollins, M.; Pillera, R.; Porter, T. A.; Principe, G.; Rainò, S.; Rando, R.; Rani, B.; Razzano, M.; Reimer, A.; Reimer, O.; Sánchez-Conde, M.; Saz Parkinson, P. M.; Serini, D.; Sgrò, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Suson, D. J.; Tajima, H.; Thompson, D. J.; Torres, D. F.; Wadiasingh, Z.; Wood, K.; Zaharijas, G.; Zhang, W.; Chatzopoulos, E.; Metzger, B. D.; Pessi, P. J.; Vurm, I.. - In: ASTRONOMY & ASTROPHYSICS. - ISSN 0004-6361. - 709:(2026). [10.1051/0004-6361/202558547]
Gamma-ray signature of superluminous supernovae: Fermi-LAT GeV detection of SN 2017egm and evidence of a central engine
Casaburo, F.;
2026
Abstract
Context. Superluminous supernovae (SLSNe) are a rare class of transients with peak luminosities 10–100 times greater than those of standard corecollapse supernovae (SNe). The mechanisms powering their extreme brightness remain debated, with circumstellar medium (CSM) interaction, or energy injection from a central engine like a magnetar wind nebula being the most plausible scenarios. While the optical properties of SLSNe are extensively studied, their -ray signatures remain poorly constrained. Aims. To further constrain the underlying mechanism, we carried out a systematic search for giga-electronvolt -ray emission using the Fermi Large Area Telescope (LAT) from a sample of nearby hydrogen-poor (Type I) and hydrogen-rich (Type II) SLSNe over the past 16 years. Our objective is to test predictions from CSM and magnetar models, and to assess the prospects for future detections with the Cherenkov Telescope Array Observatory (CTAO). Methods. For the six targets of this sample, we studied the time variability of a putative -ray signal at the optical position of the SLSN on a sixmonth timescale, and in the case of SN 2017egm, we further investigated variability on 15-day intervals and applied a Bayesian block algorithm to characterize the time variability of the signal. We then compared the temporal evolution and spectral properties to the predictions from a magnetar and CSM interaction model. Results. Among the sample, only SN 2017egm shows significant -ray emission, with likelihood test statistic (TS) values of 26–33 (i.e., >5) depending on the adopted time window. The signal arises between 50 and 160 days after explosion and is well described by a power-law spectrum with index = 2:17 0:23. The emission is consistent both in terms of its light curve and its spectrum, with predictions from magnetar models requiring either low nebular magnetization or faster spin-down than dipole losses. The CSM shell interaction scenario can reproduce the observed flux level but not the observed timing of the -ray signal. In addition, the observed ratio, L =Lopt 1, is inconsistent with theoretical expectations and not in line with ratio measurements in other interacting CSM-dominated objects (e.g., novae or SNe) where this ratio is less than 102. Conclusions. Our study strongly suggests that a central engine like a magnetar plays a key role in this SLSN and could explain the bulk of the optical and -ray light curves properties. In order to explain the observed late-time bumps in the optical light curve of SN 2017egm, we requireI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
