Gamma-ray signature of superluminous supernovae: Fermi-LAT GeV detection of SN 2017egm and evidence of a central engine

Abstract

Superluminous supernovae (SLSNe) are a rare class of transients with peak luminosities 10-100 times greater than those of standard core-collapse 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. To further constrain the underlying mechanism, we carried out a systematic search for GeV gamma-ray emission using the Fermi-LAT telescope from a sample of nearby hydrogen-poor (Type I) and hydrogen-rich (Type II) SLSNe over the past 16 years. Among the sample, only SN 2017egm shows significant gamma-ray emission, with likelihood test statistic (TS) values of 26-33 (i.e., >5$\sigma$) 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 $\Gamma =2.17\pm 0.23$. 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 gamma-ray signal. In addition, the observed ratio, $L_{\gamma }/L_{opt}\sim 1$, 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 $10^{-2}$. 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 gamma-ray light curves properties. Finally, simulations of 50 hours of CTAO observations indicate that a SN 2017egm-like event would be detectable up to 140 Mpc in the magnetar model but not in the CSM model due to strong gamma-gamma absorption.

Published in open access A&A, 17 pages

References in corpus (34)

• Gaia Data Release 3: Summary of the content and survey properties
• HI4PI: A full-sky HI survey based on EBHIS and GASS
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• Pulsational Pair-Instability Supernovae
• Pulsational pair instability as an explanation for the most luminous supernovae
• Incremental Fermi Large Area Telescope Fourth Source Catalog
• The XMM-Newton serendipitous survey IX. The fourth XMM-Newton serendipitous source catalogue
• Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies
• Galaxies with Wolf-Rayet signatures in the low-redshift Universe - A survey using the Sloan Digital Sky Survey
• Gammapy: A Python package for gamma-ray astronomy
• Predictions for the hydrogen-free ejecta of pulsational pair-instability supernovae
• Gamma-ray Thermalization and Leakage from Millisecond Magnetar Nebulae: Towards a Self-Consistent Model for Superluminous Supernovae
• The superluminous supernova SN 2017egm in the nearby galaxy NGC 3191: a metal-rich environment can support a typical SLSN evolution
• High-Energy Neutrinos and Gamma-Rays from Non-Relativistic Shock-Powered Transients
• Bumpy Declining Light Curves Are Common in Hydrogen-poor Superluminous Supernovae
• Superluminous supernovae: an explosive decade
• The Pre-Explosion Mass Distribution of Hydrogen-Poor Superluminous Supernova Progenitors and New Evidence for a Mass-Spin Correlation
• Luminous Supernovae: Unveiling a Population Between Superluminous and Normal Core-collapse Supernovae
• Monte-Carlo simulations of relativistic radiation mediated shocks: I. photon rich regime
• Fermi-LAT Gamma-ray Detection of the Recurrent Nova RS Ophiuchi during its 2021 Outburst
• Circumstellar Interaction Models for the Bolometric Light Curve of SN 2017egm
• Search for Early Gamma-ray Production in Supernovae Located in a Dense Circumstellar Medium with the Fermi LAT
• Collisionless Shocks and TeV Neutrinos before Supernova Shock Breakout from an Optically Thick Wind
• Multi-scale time- and frequency-domain likelihood analysis with photon weights
• SN2017egm: A Helium-rich Superluminous Supernova with Multiple Bumps in the Light Curves
• Sample of hydrogen-rich superluminous supernovae from the Zwicky Transient Facility
• SN 2021adxl: A luminous nearby interacting supernova in an extremely low metallicity environment
• Supernova 2020wnt: An Atypical Superluminous Supernova with a Hidden Central Engine
• Characterization of the GeV emission from the Kepler supernova remnant
• The Millions of Optical-Radio/X-ray Associations (MORX) Catalogue, v2
• Early-time gamma-ray constraints on cosmic-ray acceleration in the core-collapse SN 2023ixf with the Fermi Large Area Telescope
• The first days of type II-P core collapse supernovae in the gamma-ray range
• Search for gamma rays from SNe with a variable-size sliding-time-window analysis of the Fermi-LAT data
• VERITAS and Fermi-LAT constraints on the Gamma-ray Emission from Superluminous Supernovae SN2015bn and SN2017egm