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ESO & NOT Photometric Monitoring of the Cloverleaf Quasar University of Groningen ESO & NOT photometric monitoring of the Cloverleaf quasar Ostensen, R; Remy, M; Lindblad, P O; Refsdal, S; Stabell, R; Surdej, J; Barthel, P D; Emanuelsen, P I; Festin, L; Gosset, E Published in: Astronomy & astrophysics supplement series DOI: 10.1051/aas:1997273 IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 1997 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Ostensen, R., Remy, M., Lindblad, P. O., Refsdal, S., Stabell, R., Surdej, J., Barthel, P. D., Emanuelsen, P. I., Festin, L., Gosset, E., Hainaut, O., Hakala, P., Hjelm, M., Hjorth, J., Hutsemekers, D., Jablonski, M., Kaas, A. A., Kristen, H., Larsson, S., ... Van Drom, E. (1997). ESO & NOT photometric monitoring of the Cloverleaf quasar. Astronomy & astrophysics supplement series, 126(3), 393-400. https://doi.org/10.1051/aas:1997273 Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license. More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne- amendment. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 01-10-2021 ASTRONOMY & ASTROPHYSICS DECEMBER II 1997, PAGE 393 SUPPLEMENT SERIES Astron. Astrophys. Suppl. Ser. 126, 393-400 (1997) ESO & NOT photometric monitoring of the Cloverleaf quasar?,?? R. Østensen1, M. Remy2, P.O. Lindblad3, S. Refsdal4, R. Stabell5, J. Surdej2,???, P.D. Barthel6, P.I. Emanuelsen 1 ,L.Festin7, E. Gosset2,†, O. Hainaut8,P.Hakala9,M.Hjelm3,J.Hjorth10, D. Hutsem´ekers2,???,M.Jablonski5,A.A.Kaas3,H.Kristen3,S.Larsson3, P. Magain2‡, B. Pettersson7, A. Pospieszalska-Surdej2,A.Smette6,J.Teuber11,B.Thomsen12, and E. Van Drom2 1 Institute of Mathematical and Physical Sciences, University of Tromsø, N-9037 Tromsø, Norway 2 Institut d’Astrophysique, Universit´edeLi`ege, Belgium 3 Stockholm Observatory, S-13336 Saltsj¨obaden, Sweden 4 Hamburger Sternwarte, Gojenbergsweg 112, D-21029, Germany 5 Institute of Theoretical Astrophysics, University of Oslo, Box 1029 Blindern, N-0315 Oslo, Norway 6 Kapteyn Astronomical Institute, Rijksuniversiteit, Landleven 12, Postbus 800, 9700 AV Groningen, The Netherlands 7 Astron. Obs. Box 515, S-751 20 Uppsala, Sweden 8 Institute for Astronomy, 2680 Woodlawn Drive, Honolulu HI 96822, U.S.A. 9 Helsinki University Observatory, Tahtitorninmaki, SF-00014 Helsinki, Finland 10 NORDITA, Blegdamsvej 17, DK-2100 Copenhagen, Denmark 11 Copenhagen University Observatory, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark 12 Institute of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark Received November 18, 1996; accepted March 18, 1997 Abstract. The Cloverleaf quasar, H1413+117, has been photometric lightcurves of this quadruply imaged variable photometrically monitored at ESO (La Silla, Chile) and QSO, are derived. This is unfortunately too large to con- with the NOT (La Palma, Spain) during the period 1987– strain the lens model but there is little doubt that a better 1994. All good quality CCD frames have been successfully sampling of the lightcurves should allow to accurately de- analysed using two independent methods (i.e. an auto- rive these time delays. Pending a direct detection of the matic image decomposition technique and an interactive lensing galaxy (position and redshift), this system thus CLEAN algorithm). The photometric results from the two constitutes another good candidate for a direct and inde- methods are found to be very similar, and they show that pendent determination of the Hubble parameter. the four lensed QSO images vary significantly in brightness (by up to 0.45 mag), nearly in parallel. The lightcurve of Key words: gravitational lensing — techniques: image the D component presents some slight departures from the processing — quasars: H1413+117 general trend which are very likely caused by micro-lensing effects. Upper limits, at the 99% confidence level, of 150 days on the absolute value for the time delays between the 1. Introduction Send offprint requests to: [email protected] ? Based on observations collected at the European Southern The Cloverleaf quasar, H1413+117, was discovered to be Observatory (La Silla, Chile) and with the Nordic Optical a quadruply imaged QSO by Magain et al. (1988). Since Telescope (La Palma, Spain). then, it has been photometrically monitored essentially as ?? Table 1. Logbook for the ESO and NOT observations to- part of the ESO Key-Program Gravitational Lensing (La gether with photometric results for the Cloverleaf quasar. This Silla) and as part of the Gravitational Lens Monitoring long table can be accessed on the WWW at the URL address: Program at the Nordic Optical Telescope (NOT) on the http://vela.astro.ulg.ac.be/grav lens/glp homepage.html ??? Research Director, Belgian Fund for Scientific Research island of La Palma. This quasar, at a redshift of 2.55, (FNRS). and with an apparent visual magnitude of 17, is one of † Research Associate, Belgian Fund for Scientific Research the brightest members of the class of broad absorption (FNRS). line (BAL) QSOs. In addition, its spectrum shows at least ‡ Senior Research Associate, Belgian Fund for Scientific three narrow absorption line systems at redshifts z =1.44, Research (FNRS). 1.66 and 2.07. These are attributed to intervening gas 394 R. Østensen et al.: ESO & NOT photometric monitoring of the Cloverleaf quasar clouds (Hazard et al. 1984; Drew & Boksenberg 1984; “classical” Double Quasar), H1413+117 and Q2237+0305. Turnshek et al. 1988), possibly associated with the lens(es) Although observations were similarly aimed at weekly in- (Magain et al. 1988). Imaging of H1413+117 shows that tervals, several large gaps in the NOT data have occurred the four lensed components are separated by approxi- for the same reasons as those mentioned above. Results mately one arcsecond (00). However, no lensing object has for the Einstein Cross have been published by Østensen yet been detected. The spectra of two of the four images et al. (1996), for UM425 by Courbin et al. (1995) and have been found by Magain et al. (1988) to be identical, for Q0142 − 100 by Hjorth et al. (1996) and Daulie et al. except for narrow absorption line systems at z =1.44 (1993). and 1.66, which are much stronger in component B than In this paper we present results for the Cloverleaf, ob- in C. Two-dimensional spectroscopy by Angonin et al. tained using two independent methods of analysis, com- (1990) also shows that the spectrum of component D has bining all ESO and NOT observations. smaller values for the emission lines/continuum ratios and a larger equivalent width for the absorption features in the 2. Observations and instrumentation P Cygni profiles, compared to the other three lensed QSO components. This is most likely caused by micro-lensing The ESO Key-Program observations of the Cloverleaf effects. Observations from the VLA at NRAO show radio were made using several different telescopes, and with counterparts for the four QSO components, as well as an a number of different CCD detectors. All telescopes and additional strong radio source between images B and D cameras used are listed in Table 1, together with the fil- (Kayser et al. 1990), but no radio source has been found ters, observing dates, average seeing and the name of the that can be associated with a lensing object. principal investigator(s). The ESO telescopes that were As part of the Gravitational Lensing ESO Key- used are the 3.5 m New Technology Telescope (NTT), the Program, CCD photometry of H1413+117 has been car- 2.2 m ESO-Max Planck Institut (MPI) telescope and the ried out with the aim of detecting photometric vari- Danish 1.54 m telescope (DAN) at La Silla, Chile (the ability of the QSO itself, and thereby determining the ESO 3.6 m telescope has also been used occasionally). time delay(s), or the signature of micro-lensing effects. Observations from the NOT Monitoring program were Preliminary results for the four images have been pre- made with the 2.56 m Nordic Optical Telescope, at Roque sented by Arnould et al. (1993) and by Remy et al. (1996). de los Muchachos, La Palma, Canary Islands (Spain) from These authors report that from 1987 to 1993 the four April 1990 to August 1994. During the first four years, 00 lensed components apparently display brightness varia- a Tektronix 512 × 512 CCD camera with 0.197 pixels tions quasi-simultaneously and in parallel. They set an was the only detector available. In 1994, a more sensitive 00 upper limit for the time delays of roughly a few months. 1024×1024 CCD camera with 0.177 pixels was installed. In addition to these variations, which are ascribed to the Reasonable signal-to-noise ratios were obtained for expo- source, the D component has been found to show extra sure times of 4 minutes or more when the seeing was better 00 light variations with respect to the other components.
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