Browsing Articles by Subject "Quasars"

Now showing items 1-6 of 6

The discovery of the first “changing look” quasar: new insights into the physics and phenomenology of active galactic nuclei

LaMassa, Stephanie M.; Cales, Sabrina; Moran, Edward C.; Myers, Adam D.; Richards, Gordon T.; Eracleous, Michael; Heckman, Timothy M.; Gallo, Luigi C.; Urry, C. Megan (American Astronomical Society, 2015-02-20)

SDSS J015957.64+003310.5 is an X-ray selected, z = 0.31 active galactic nucleus (AGN) from the Stripe 82X survey that transitioned from a Type 1 quasar to a Type 1.9 AGN between 2000 and 2010. This is the most distant AGN, ...
Four quasars above redshift 6 discovered by the Canada-France High-z Quasar Survey

Willott, Chris J.; Delorme, Philippe; Omont, Alain; Bergeron, Jacqueline; Delfosse, Xavier; Forveille, Thierry; Albert, Loic; Reyle, Celine; Hill, Gary J.; Gully-Santiago, Michael; Sawicki, Marcin, 1969- (American Astronomical SocietyIOP Publishing, 2007-12)

The Canada-France High-z Quasar Survey (CFHQS) is an optical survey designed to locate quasars during the epoch of reionization. In this paper we present the discovery of the first four CFHQS quasars at redshifts greater ...
Insights on the X-ray weak quasar phenomenon from XMM–Newton monitoring of PHL1092

Gallo, Luigi C.; Miniutti, G.; Brandt, W. N.; Schneider, D. P.; Fabian, A. C.; Boller, Th. (Royal Astronomical SocietyOxford University Press, 2012)

PHL 1092 is a z ∼ 0.4 high-luminosity counterpart of the class of Narrow-Line Seyfert 1 galaxies. In 2008, PHL 1092 was found to be in a remarkably low X-ray flux state during an XMM–Newton observation. Its 2 keV flux ...
The quasar PG 0844+349 in an X-ray weak state

Gallo, Luigi C.; Grupe, D.; Schartel, N.; Komossa, S.; Miniutti, G.; Fabian, A. C.; Santos-Lleo, M. (Oxford University Press, 2011-03)

In 2009 March the well-studied quasar, PG 0844+349, was discovered with Swift to be in an X-ray weak state. A follow-up XMM–Newton observation several weeks later generated a good-quality spectrum of the source, showing ...
A selection effect boosting the contribution from rapidly spinning black holes to the cosmic X-ray background

Vasudevan, R. V.; Fabian, A. C.; Reynolds, C. S.; Aird, J.; Dauser, T.; Gallo, Luigi C. (Oxford University Press, 2016-05-11)

The cosmic X-ray background (CXB) is the total emission from past accretion activity on to supermassive black holes in active galactic nuclei (AGN) and peaks in the hard X-ray band (30 keV). In this paper, we identify a ...
Studying X-ray reprocessing and continuum variability in quasars: PG 1211+143

Gallo, Luigi C.; Bachev, R.; Grupe, D.; Boeva, S.; Ovcharov, E.; Valcheva, A.; Semkov, E.; Georgiev, Ts. (Oxford University Press, 2009-10)

We present the results from a monitoring campaign of the Narrow-Line Seyfert 1 galaxy PG 1211+143. The object was monitored with ground-based facilities (UBVRI photometry; from 2007 February to July) and with Swift [X-ray ...