22 research outputs found
A powerful bursting radio source towards the Galactic Centre
Transient astronomical sources are typically powered by compact objects and
usually signify highly explosive or dynamic events. While radio astronomy has
an impressive record of obtaining high time resolution observations, usually it
is achieved in quite narrow fields-of-view. Consequently, the dynamic radio sky
is poorly sampled, in contrast to the situation in the X- and gamma-ray bands
in which wide-field instruments routinely detect transient sources. Here we
report a new transient source, GCRT J1745-3009, detected in 2002 during a
moderately wide-field radio transient monitoring program of the Galactic center
(GC) region at 0.33 GHz. The characteristics of its bursts are unlike those
known for any other class of radio transient. If located in or near the GC, its
brightness temperature (~10^16 K) and the implied energy density within GCRT
J1745-3009 vastly exceeds that observed in most other classes of radio
astronomical sources, and is consistent with coherent emission processes rarely
observed. We conclude that GCRT J1745-3009 is the first member of a new class
of radio transient sources, the first of possibly many new classes to be
identified through current and upcoming radio surveys.Comment: 16 pages including 3 figures. Appears in Nature, 3 March 200
High-Energy Gamma Rays and the Large-Scale Distribution of Gas and Cosmic Rays
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
The Supermassive Black Hole at the Galactic Center
The inner few parsecs at the Galactic Center have come under intense scrutiny
in recent years, in part due to the exciting broad-band observations of this
region, but also because of the growing interest from theorists motivated to
study the physics of black hole accretion, magnetized gas dynamics and unusual
star formation. The Galactic Center is now known to contain arguably the most
compelling supermassive black hole candidate, weighing in at a little over 2.6
million suns. Its interaction with the nearby environment, comprised of
clusters of evolved and young stars, a molecular dusty ring, ionized gas
streamers, diffuse hot gas, and a hypernova remnant, is providing a wealth of
accretion phenomenology and high-energy processes for detailed modeling. In
this review, we summarize the latest observational results, and focus on the
physical interpretation of the most intriguing object in this region---the
compact radio source Sgr A*, thought to be the radiative manifestation of the
supermassive black hole.Comment: Annual Review of Astronomy & Astrophysics, Vol. 39 (2001), in press,
48 pages, 20 figures (partially in reduced quality), also available at
http://www.mpifr-bonn.mpg.de/staff/hfalcke/publications.html#gcrevie
Gamma-Ray Sources Observed by Cos-B
Wetensch. publicati