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QSO 0957+561
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Hubble, Hubble, Seeing Double

In this new Hubble image two objects are clearly visible, shining brightly. When they were first discovered in 1979, they were thought to be separate objects - however, astronomers soon realized that these twins are a little too identical! They are close together, lie at the same distance from us, and have surprisingly similar properties. The reason they are so similar is not some bizarre coincidence; they are in fact the same object.
These cosmic doppelgangers make up a double quasar known as QSO 0957+561, also known as the "Twin Quasar," which lies just under 14 billion light-years from Earth. Quasars are the intensely powerful centers of distant galaxies. So, why are we seeing this quasar twice?

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RE: Quasar Q0957+561
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Title: A 5.5-year robotic optical monitoring of Q0957+561: substructure in a non-local cD galaxy
Authors: V. N. Shalyapin, L. J. Goicoechea, R. Gil-Merino (GLENDAMA team)

New light curves of the gravitationally lensed double quasar Q0957+561 in the gr bands during 2008-2010 include densely sampled, sharp intrinsic fluctuations with unprecedentedly high signal-to-noise ratio. These relatively violent flux variations allow us to very accurately measure the g-band and r-band time delays between the two quasar images A and B. Using correlation functions, we obtain that the two time delays are inconsistent with each other at the 2sigma level, with the r-band delay exceeding the 417-day delay in the g band by about 3 days. We also studied the long-term evolution of the delay-corrected flux ratio B/A from our homogeneous two-band monitoring with the Liverpool Robotic Telescope between 2005 and 2010. This ratio B/A slightly increases in periods of violent activity, which seems to be correlated with the flux level in these periods. The presence of the previously reported dense cloud within the cD lensing galaxy, along the line of sight to the A image, could account for the observed time delay and flux ratio anomalies.

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Title: A New Microlensing Event in the Doubly-Imaged Quasar Q0957+561
Authors: Laura J. Hainline (1), Christopher W. Morgan (1), J. N. Beach (1), C. S. Kochanek (2), Hugh C. Harris (3), T. Tilleman (3), Ross Fadely (4), Emilio E. Falco (5), T. X. Le (1) ((1) U. S. Naval Academy, (2) Ohio State University, (3) U. S. Naval Observatory, Flagstaff, (4) Haverford College, (5) CfA)

We present evidence for ultraviolet/optical microlensing in the gravitationally lensed quasar Q0957+561. We combine new measurements from our optical monitoring campaign at the United States Naval Observatory, Flagstaff (USNO) with measurements from the literature and find that the time-delay-corrected r-band flux ratio m_A - m_B has increased by ~0.1 magnitudes over a period of five years beginning in the fall of 2005. We apply our Monte Carlo microlensing analysis procedure to the composite light curves, obtaining a measurement of the optical accretion disk size, log {(r_s/cm)[cos(i)/0.5]^{½}} = 16.1^{+0.5}_{-0.6}, that is consistent with the quasar accretion disk size - black hole mass relation.

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Posts: 131433
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QSO 0957+561 A/B
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Jodrell's first e-MERLIN image shows curvature of space

A group of UK radio telescopes has taken its first picture of space showing how light is bent by gravity.
Led by Jodrell Bank, the e-MERLIN array focussed on an astronomical phenomenon known as the "double quasar" to demonstrate the curvature of space.
Scientists believe the image proves Einstein's gravitational theory.
It's hoped that by working together, the array of seven telescopes will produce detailed radio images of stars and galaxies.

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RE: Quasar Q0957+561
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Title: New two-colour light curves of Q0957+561: time delays and the origin of intrinsic variations
Authors:  V. N. Shalyapin, L. J. Goicoechea, E. Koptelova, A. Ullán, and R. Gil-Merino

Aims. We extend the gr-band time coverage of the gravitationally lensed double quasar Q0957+561. New gr light curves permit us to detect significant intrinsic fluctuations, to determine new time delays, and thus to gain perspective on the mechanism of intrinsic variability in Q0957+561.
Methods. We use new optical frames of Q0957+561 in the g and r passbands from January 2005 to July 2007. These frames are part of an ongoing long-term monitoring with the Liverpool robotic telescope. We also introduce two photometric pipelines that are applied to the new gr frames of Q0957+561. The transformation pipeline incorporates zero-point, colour, and inhomogeneity corrections to the instrumental magnitudes, so final photometry to the 1- 2% level is achieved for both quasar components. The two-colour final records are then used to measure time delays.
Results. The gr light curves of Q0957+561 show several prominent events and gradients, and some of them (in the g band) lead to a time delay between components \Delta t_ = 417 ± 2 d (1\sigma). We do not find evidence of extrinsic variability in the light curves of Q0957+561. We also explore the possibility of a delay between a large event in the g band and the corresponding event in the r band. The gr cross-correlation reveals a time lag \Delta t_{rg} = 4.0 ±2.0 d (1\sigma; the g-band event is leading) that confirms a previous claim of the existence of a delay between the g and r band in this lensed quasar.
Conclusions. The time delays (between quasar components and between optical bands) from the new records and previous ones in similar bands indicate that most observed variations in Q0957+561 (amplitudes of ~100 mmag and timescales of ~100 d) are very probably due to reverberation within the gas disc around the supermassive black hole.

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Resuelven el misterio del brillo del cuásar gemelo
Las variaciones en el brillo del cuásar Q0957+561, conocido como el "cuásar gemelo" debido a que su imagen llega duplicada a la Tierra, son intrínsecas al propio astro y no son causadas por efectos de la gravedad de posibles planetas o estrellas de una galaxia lejana. Esta es la conclusión de un estudio en el que han participado investigadores españoles, y con el que se resuelve un misterio que intrigaba a los astrónomos desde hace 30 años.

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