M87 is the only known nonblazar radio galaxy to emit very high energy (VHE) gamma rays. During a monitoring program of M87, a rapid flare in VHE gamma-rays was detected by the MAGIC telescope in early 2008. The flux was found to be variable above 350 GeV on a timescale as short as 1 day at a significance level of 5.6 sigma. The highest measured flux reached 15% of the Crab Nebula flux. We observed several substantial changes of the flux level during the 13 day observing period. The flux at lower energies (150-350 GeV), instead, is compatible with being constant. The energy spectrum can be described by a power law with a photon index of 2.30 +/- 0.11(stat) +/- 0.20(syst). The observed day-scale flux variability at VHE prefers the M87 core as source of the emission and implies that either the emission region is very compact (just a few Schwarzschild radii) or the Doppler factor of the emitting blob is rather large in the case of a nonexpanding emission region.

VERY HIGH ENERGY GAMMA-RAY OBSERVATIONS OF STRONG FLARING ACTIVITY IN M87 IN 2008 FEBRUARY

DE ANGELIS, Alessandro;DE LOTTO, Barbara;
2008-01-01

Abstract

M87 is the only known nonblazar radio galaxy to emit very high energy (VHE) gamma rays. During a monitoring program of M87, a rapid flare in VHE gamma-rays was detected by the MAGIC telescope in early 2008. The flux was found to be variable above 350 GeV on a timescale as short as 1 day at a significance level of 5.6 sigma. The highest measured flux reached 15% of the Crab Nebula flux. We observed several substantial changes of the flux level during the 13 day observing period. The flux at lower energies (150-350 GeV), instead, is compatible with being constant. The energy spectrum can be described by a power law with a photon index of 2.30 +/- 0.11(stat) +/- 0.20(syst). The observed day-scale flux variability at VHE prefers the M87 core as source of the emission and implies that either the emission region is very compact (just a few Schwarzschild radii) or the Doppler factor of the emitting blob is rather large in the case of a nonexpanding emission region.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11390/879509
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 105
  • ???jsp.display-item.citation.isi??? 86
social impact