3 research outputs found
The Sudden Death of the Nearest Quasar
Galaxy formation is significantly modulated by energy output from
supermassive black holes at the centers of galaxies which grow in highly
efficient luminous quasar phases. The timescale on which black holes transition
into and out of such phases is, however, unknown. We present the first
measurement of the shutdown timescale for an individual quasar using X-ray
observations of the nearby galaxy IC 2497, which hosted a luminous quasar no
more than 70,000 years ago that is still seen as a light echo in `Hanny's
Voorwerp', but whose present-day radiative output is lower by at least 2 and
more likely by over 4 orders of magnitude. This extremely rapid shutdown
provides new insights into the physics of accretion in supermassive black
holes, and may signal a transition of the accretion disk to a radiatively
inefficient state.Comment: 4 pages, 2 figures. Astrophysical Journal Letters, in pres
Galaxy Zoo: ‘Hanny\u27s Voorwerp’, a quasar light echo?
We report the discovery of an unusual object near the spiral galaxy IC 2497, discovered by visual inspection of the Sloan Digital Sky Survey (SDSS) as part of the Galaxy Zoo project. The object, known as Hanny\u27s Voorwerp, is bright in the SDSS g band due to unusually strong [O iii]4959, 5007 emission lines. We present the results of the first targeted observations of the object in the optical, ultraviolet and X-ray, which show that the object contains highly ionized gas. Although the line ratios are similar to extended emission-line regions near luminous active galactic nucleus (AGN), the source of this ionization is not apparent. The emission-line properties, and lack of X-ray emission from IC 2497, suggest either a highly obscured AGN with a novel geometry arranged to allow photoionization of the object but not the galaxy\u27s own circumnuclear gas, or, as we argue, the first detection of a quasar light echo. In this case, either the luminosity of the central source has decreased dramatically or else the obscuration in the system has increased within 105 yr. This object may thus represent the first direct probe of quasar history on these time-scales
Galaxy Zoo: Hanny's Voorwerp, a quasar light echo?
‘The definitive version is available at www3.interscience.wiley.com '. Copyright Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.15299.xWe report the discovery of an unusual object near the spiral galaxy IC 2497, discovered by visual inspection of the Sloan Digital Sky Survey (SDSS) as part of the Galaxy Zoo project. The object, known as Hanny's Voorwerp, is bright in the SDSS g band due to unusually strong [O iii]4959, 5007 emission lines. We present the results of the first targeted observations of the object in the optical, ultraviolet and X-ray, which show that the object contains highly ionized gas. Although the line ratios are similar to extended emission-line regions near luminous active galactic nucleus (AGN), the source of this ionization is not apparent. The emission-line properties, and lack of X-ray emission from IC 2497, suggest either a highly obscured AGN with a novel geometry arranged to allow photoionization of the object but not the galaxy's own circumnuclear gas, or, as we argue, the first detection of a quasar light echo. In this case, either the luminosity of the central source has decreased dramatically or else the obscuration in the system has increased within 105 yr. This object may thus represent the first direct probe of quasar history on these time-scales.Peer reviewe