J.-E. Ovaldsen, A. O. Jaunsen, J. P. U. Fynbo, J. Hjorth, C. C. Thöne, C. Féron, D. Xu, J. H. Selj, and J. Teuber, 2007, The Astrophysical Journal, vol. 662, pp. 294–303
We report the results from observations of 24 gamma-ray burst (GRB) fields from 2005 and 2006 undertaken at the Danish 1.54 m telescope at ESO/La Silla. Photometry and positions for two previously unpublished host galaxy candidates (GRBs 050915 and 051021) are presented, as well as for eight other detected objects that are either known GRB hosts or candidate hosts. The candidates are suitable for spectroscopic follow-up in order to have their redshifts and other physical characteristics determined. In the cases where no likely host candidate is detected inside the refined Swift XRT error circle, we are still able to put interesting and rather deep limits on the host magnitude. On the basis of our detections and upper limits, we have performed simulations that suggest that the host galaxies are drawn from a fainter sample than those in previous (i.e., pre-Swift) studies.
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J.-E. Ovaldsen, J. Teuber, R. Stabell, and A. K. D. Evans, 2003, Monthly Notices of the Royal Astronomical Society, vol. 345, pp. 795–799
We present R- and V-band photometry of the gravitational lens system QSO 0957+561 from five nights (one in 2000 January and four in 2001 March, corresponding to the approximate time-delay for the system) of uninterrupted monitoring at the Nordic Optical Telescope. In the photometry scheme we have stressed careful magnitude calibration as well as corrections for the lens galaxy contamination and the crosstalk between the twin (A and B) quasar images. The resulting, very densely sampled light curves are quite stable, in conflict with earlier claims derived from the same data material. We estimate high-precision timelag-corrected B/A flux ratios in both colour bands, as well as V-R colour indices for A and B, and discuss the short time-scale variability of the system.
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J.-E. Ovaldsen, J. Teuber, R. E. Schild, and R. Stabell, 2003, Astronomy & Astrophysics, vol. 402, pp. 891–904
We present a re-reduction of archival CCD frames of the doubly imaged quasar 0957+561 using a new photometry code. Aperture photometry with corrections for both cross contamination between the quasar images and galaxy contamination is performed on about 2650 R-band images from a five year period (1992-1997). From the brightness data a time delay of 424.9 ± 1.2 days is derived using two different statistical techniques. The amount of gravitational microlensing in the quasar light curves is briefly investigated, and we find unambiguous evidence of both long term and short term microlensing. We also note the unusual circumstance regarding time delay estimates for this gravitational lens. Estimates by different observers from different data sets or even with the same data sets give lag estimates differing by typically 8 days, and error bars of only a day or two. This probably indicates several complexities where the result of each estimate depends upon the details of the calculation.
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PS: Photometry data (light curves and data table)
J.-E. Ovaldsen, 2002, astronomy thesis (144 pages), see here.
J.-E. Ovaldsen et al., 2007, Il Nuovo Cimento (conf. proc.), vol. 121, N. 12
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J. Sollerman et al. (25 co-authors incl. J.-E. Ovaldsen), 2006, Astronomy & Astrophysics, vol. 454, pp. 503–509, NASA ADS
L. J. Goicoechea, A. Ullan, J.-E. Ovaldsen, E. Koptelova, V. N. Shalyapin, R. Gil-Merino, 2006, Conference proceedings, astro-ph/0609647