IAFE   05512
INSTITUTO DE ASTRONOMIA Y FISICA DEL ESPACIO
Unidad Ejecutora - UE
artículos
Título:
VERITAS 2008 - 2009 monitoring of the time-varying gamma-ray source M87
Autor/es:
THE VERITAS COLLABORATION. SON 86 AUTORES, A. PICHEL
Revista:
ASTROPHYSICAL JOURNAL
Editorial:
IOP PUBLISHING LTD
Referencias:
Año: 2010 vol. 716 p. 819 - 824
ISSN:
0004-637X
Resumen:
M 87 is a nearby radio galaxy that is detected at energies ranging from
radio to very high energy (VHE) gamma rays. Its proximity and its jet,
misaligned from our line of sight, enable detailed morphological
studies and extensive modeling at radio, optical, and X-ray energies.
Flaring activity was observed at all energies, and multi-wavelength
correlations would help clarify the origin of the VHE emission. In this
paper, we describe a detailed temporal and spectral analysis of the
VERITAS VHE gamma-ray observations of M 87 in 2008 and 2009. In the
2008 observing season, VERITAS detected an excess with a statistical
significance of 7.2 standard deviations (σ) from M 87 during a joint
multi-wavelength monitoring campaign conducted by three major VHE
experiments along with the Chandra X-ray Observatory. In 2008
February, VERITAS observed a VHE flare from M 87 occurring over a 4 day
timespan. The peak nightly flux above 250 GeV was (1.14 ± 0.26) × 1011 cm2 s1,
which corresponded to 7.7% of the Crab Nebula flux. M 87 was marginally
detected before this 4 day flare period, and was not detected
afterward. Spectral analysis of the VERITAS observations showed no
significant change in the photon index between the flare and pre-flare
states. Shortly after the VHE flare seen by VERITAS, the Chandra X-ray Observatory
detected the flux from the core of M 87 at a historical maximum, while
the flux from the nearby knot HST-1 remained quiescent. Acciari et al.
presented the 2008 contemporaneous VHE gamma-ray, Chandra
X-ray, and Very Long Baseline Array radio observations which suggest
the core as the most likely source of VHE emission, in contrast to the
2005 VHE flare that was simultaneous with an X-ray flare in the HST-1
knot. In 2009, VERITAS continued its monitoring of M 87 and marginally
detected a 4.2sigma excess corresponding to a flux of ~1% of the Crab
Nebula. No VHE flaring activity was observed in 2009.