VERITAS 2008 - 2009 monitoring of the variable gamma-ray source M87
Abstract
M87 is a nearby radio galaxy that is detected at energies ranging from radio to 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 M87 in 2008 and 2009. In the 2008 observing season, VERITAS detected an excess with a statistical significance of 7.2 sigma from M87 during a joint multi-wavelength monitoring campaign conducted by three major VHE experiments along with the Chandra X-ray Observatory. In February 2008, VERITAS observed a VHE flare from M87 occurring over a 4-day timespan. The peak nightly flux above 250GeV was 7.7% of the Crab Nebula flux. M87 was marginally detected before this 4-day flare period, and was not detected afterwards. 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 M87 at a historical maximum, while the flux from the nearby knot HST-1 remained quiescent. Acciari et al. (2009) presented the 2008 contemporaneous VHE gamma-ray, Chandra X-ray, and VLBA 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 M87 and marginally detected a 4.2 sigma excess corresponding to a flux of ~1% of the Crab Nebula. No VHE flaring activity was observed in 2009.
Keywords
Cite
@article{arxiv.1005.0367,
title = {VERITAS 2008 - 2009 monitoring of the variable gamma-ray source M87},
author = {The VERITAS Collaboration and V. A. Acciari and E. Aliu and T. Arlen and T. Aune and M. Beilicke and W. Benbow and D. Boltuch and S. M. Bradbury and J. H. Buckley and V. Bugaev and K. Byrum and A. Cannon and A. Cesarini and Y. C. Chow and L. Ciupik and P. Cogan and W. Cui and R. Dickherber and C. Duke and J. P. Finley and G. Finnegan and P. Fortin and L. Fortson and A. Furniss and N. Galante and D. Gall and G. H. Gillanders and S. Godambe and J. Grube and R. Guenette and G. Gyuk and D. Hanna and J. Holder and C. M. Hui and T. B. Humensky and A. Imran and P. Kaaret and N. Karlsson and M. Kertzman and D. Kieda and A. Konopelko and H. Krawczynski and F. Krennrich and M. J. Lang and S. LeBohec and G. Maier and S. McArthur and A. McCann and M. McCutcheon and J. Millis and P. Moriarty and R. A. Ong and A. N. Otte and D. Pandel and J. S. Perkins and A. M. J. Quinn and K. Ragan and L. C. Reyes and P. T. Reynolds and E. Roache and H. J. Rose and A. C. Rovero and M. Schroedter and G. H. Sembroski and G. Demet Senturk and A. W. Smith and D. Steele and S. P. Swordy and M. Theiling and S. Thibadeau and A. Varlotta and S. Vincent and R. G. Wagner and S. P. Wakely and J. E. Ward and T. C. Weekes and A. Weinstein and T. Weisgarber and D. A. Williams and S. Wissel and M. Wood and B. Zitzer and Chandra M87 Monitoring and : and D. E. Harris and F. Massaro},
journal= {arXiv preprint arXiv:1005.0367},
year = {2019}
}
Comments
17 pages, 5 figures, accepted for publication in ApJ