20 research outputs found
Hadronic origin of the TeV flare of M87 in April 2010
M87 is a giant radio galaxy with FR-I morphology. It underwent three episodes of TeV flaring in recent years with the strongest one in April 2010 which was jointly monitored by MAGIC, VERITAS and H.E.S.S. We explain its spectral energy distribution in the energy range 0.3–5 TeV by assuming that the flaring occurs in the innermost region of the jet. In this region the low energy SSC photons serve as the target for the Fermi-accelerated high energy protons of energy TeV to form a delta resonance. The TeV photons are produced from the subsequent decay of the delta resonance to neutral pions. In this scenario the observed TeV flux of April 2010 flare is fitted very well
Observational Properties of Jets in Active Galactic Nuclei
Parsec scale jet properties are shortly presented and discussed.
Observational data are used to derive constraints on the jet velocity and
orientation, the presence of velocity structures, and the connection between
the pc and kpc scale. Two peculiar sources with limb-brightened jets: 1144+35
and Mkn 501 are discussed in detail.Comment: 13 pages with 7 figures. To appear in "Virtual Astrophysical Jets"
APSS, Kluwer Academic Publisher - Massaglia, Bodo, Rossi eds - in pres
The optical counterpart to gamma-ray burst GRB970228 observed using the Hubble Space Telescope
Although more than 2,000 astronomical gamma-ray bursts (GRBs) have been
detected, and numerous models proposed to explain their occurrence, they have
remained enigmatic owing to the lack of an obvious counterpart at other
wavelengths. The recent ground-based detection of a transient source in the
vicinity of GRB 970228 may therefore have provided a breakthrough. The optical
counterpart appears to be embedded in an extended source which, if a galaxy as
has been suggested, would lend weight to those models that place GRBs at
cosmological distances. Here we report the observations using the Hubble Space
Telescope of the transient counterpart and extended source 26 and 39 days after
the initial gamma-ray outburst. We find that the counterpart has faded since
the initial detection (and continues to fade), but the extended source exhibits
no significant change in brightness between the two dates of observations
reported here. The size and apparent constancy between the two epochs of HST
observations imply that it is extragalactic, but its faintness makes a
definitive statement about its nature difficult. Nevertheless, the decay
profile of the transient source is consistent with a popular impulsive-fireball
model, which assumes a merger between two neutron stars in a distant galaxy.Comment: 11 pages + 2 figures. To appear in Nature (29 May 1997 issue