References of "Hjorth, J"
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See detailORIGIN: metal creation and evolution from the cosmic dawn
den Herder, Jan-Willem; Piro, Luigi; Ohashi, Takaya et al

in Experimental Astronomy (2012), 34

ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of metal creation from the epoch of cosmic dawn. Using high-spectral resolution in the soft X-ray band, ORIGIN will be able to ... [more ▼]

ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of metal creation from the epoch of cosmic dawn. Using high-spectral resolution in the soft X-ray band, ORIGIN will be able to identify the physical conditions of all abundant elements between C and Ni to red-shifts of z = 10, and beyond. The mission will answer questions such as: When were the first metals created? How does the cosmic metal content evolve? Where do most of the metals reside in the Universe? What is the role of metals in structure formation and evolution? To reach out to the early Universe ORIGIN will use Gamma-Ray Bursts (GRBs) to study their local environments in their host galaxies. This requires the capability to slew the satellite in less than a minute to the GRB location. By studying the chemical composition and properties of clusters of galaxies we can extend the range of exploration to lower redshifts ( z ˜0.2). For this task we need a high-resolution spectral imaging instrument with a large field of view. Using the same instrument, we can also study the so far only partially detected baryons in the Warm-Hot Intergalactic Medium (WHIM). The less dense part of the WHIM will be studied using absorption lines at low redshift in the spectra for GRBs. The ORIGIN mission includes a Transient Event Detector (coded mask with a sensitivity of 0.4 photon/cm[SUP]2[/SUP]/s in 10 s in the 5-150 keV band) to identify and localize 2000 GRBs over a five year mission, of which ˜65 GRBs have a redshift >7. The Cryogenic Imaging Spectrometer, with a spectral resolution of 2.5 eV, a field of view of 30 arcmin and large effective area below 1 keV has the sensitivity to study clusters up to a significant fraction of the virial radius and to map the denser parts of the WHIM (factor 30 higher than achievable with current instruments). The payload is complemented by a Burst InfraRed Telescope to enable onboard red-shift determination of GRBs (hence securing proper follow up of high-z bursts) and also probes the mildly ionized state of the gas. Fast repointing is achieved by a dedicated Controlled Momentum Gyro and a low background is achieved by the selected low Earth orbit. [less ▲]

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See detailGRB 080913 at Redshift 6.7
Greiner, J.; Krühler, T.; Fynbo, J. P. U. et al

in Astrophysical Journal (2009), 693

We report on the detection by Swift of GRB 080913, and subsequent optical/near-infrared follow-up observations by GROND, which led to the discovery of its optical/NIR afterglow and the recognition of its ... [more ▼]

We report on the detection by Swift of GRB 080913, and subsequent optical/near-infrared follow-up observations by GROND, which led to the discovery of its optical/NIR afterglow and the recognition of its high-z nature via the detection of a spectral break between the i' and z' bands. Spectroscopy obtained at the ESO-VLT revealed a continuum extending down to λ = 9400 Å, and zero flux for 7500 Å<λ < 9400 Å, which we interpret as the onset of a Gunn-Peterson trough at z = 6.695± 0.025 (95.5% confidence level), making GRB 080913 the highest-redshift gamma-ray burst (GRB) to date, and more distant than the highest-redshift QSO. We note that many redshift indicators that are based on promptly available burst or afterglow properties have failed for GRB 080913. We report on our follow-up campaign and compare the properties of GRB 080913 with bursts at lower redshift. In particular, since the afterglow of this burst is fainter than typical for GRBs, we show that 2 m class telescopes can identify most high-redshift GRBs. [less ▲]

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See detailPhotometric monitoring of the doubly imaged quasar UM 673: possible evidence for chromatic microlensing
Nakos, Theodoros; Courbin, F.; Poels, Joël ULg et al

in Astronomy and Astrophysics (2005), 441

We present the results of two-band CCD photometric monitoring of the gravitationally lensed quasar Q 0142-100 (UM 673). The data, obtained at ESO-La Silla with the 1.54 m Danish telescope in the Gunn i ... [more ▼]

We present the results of two-band CCD photometric monitoring of the gravitationally lensed quasar Q 0142-100 (UM 673). The data, obtained at ESO-La Silla with the 1.54 m Danish telescope in the Gunn i-band (October 1998-September 1999) and in the Johnson V-band (October 1998 to December 2001), were analyzed using three different photometric methods. The light-curves obtained with all methods show variations, with a peak-to-peak amplitude of 0.14 mag in V. Although it was not possible to measure the time delay between the two lensed QSO images, the brighter component displays possible evidence for microlensing: it becomes bluer as it gets brighter, as expected under the assumption of differential magnification of a quasar accretion disk. [less ▲]

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See detailAn optical time delay for the double gravitational lens system FBQ 0951+2635
Jakobsson, P.; Hjorth, J.; Burud, I. et al

in Astronomy and Astrophysics (2005), 431(1), 103-109

We present optical R-band light curves of the double gravitationally lensed quasar FBQ 0951+2635 from observations obtained at the Nordic Optical Telescope between March 1999 and June 2001. A time delay ... [more ▼]

We present optical R-band light curves of the double gravitationally lensed quasar FBQ 0951+2635 from observations obtained at the Nordic Optical Telescope between March 1999 and June 2001. A time delay of Deltatau = 16 +/- 2 days (1sigma) is determined from the light curves. New constraints on the lensing geometry are provided by the position and ellipticity of the lensing galaxy. For a (Omega(m), Omega(Lambda)) = (0.3, 0.7) cosmology, the time delay yields a Hubble parameter of H-0 = 60(-7)(+9) (random, 1sigma) +/-2 (systematic) km s(-1) Mpc(-1) for a singular isothermal ellipsoid model and H-0 = 63(-7)(+9) (random, 1sigma) +/-1 (systematic) km s(-1) Mpc(-1) for a constant mass-to-light ratio model. In both models, the errors are mainly due to the time-delay uncertainties. Non-parametric models yield H-0 = 64(-7)(+9) (random, 1sigma) +/- 14 (systematic) km s(-1) Mpc(-1). [less ▲]

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See detailThe Polarization Evolution of the Optical Afterglow of GRB 030329
Greiner, J.; Klose, S.; Reinsch, K. et al

in GAMMA-RAY BURSTS: 30 YEARS OF DISCOVERY (2004, September 01)

We report 31 polarimetric observations of the afterglow of GRB 030329 with high signal-to-noise and high sampling frequency. The data imply that the afterglow magnetic field has small coherence length and ... [more ▼]

We report 31 polarimetric observations of the afterglow of GRB 030329 with high signal-to-noise and high sampling frequency. The data imply that the afterglow magnetic field has small coherence length and is mostly random, probably generated by turbulence. [less ▲]

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See detailTime delay and lens redshift for the doubly imaged BAL quasar SBS 1520+530
Burud, I.; Hjorth, J.; Courbin, F. et al

in Astronomy and Astrophysics (2002), 391

We present optical R-band light curves of the gravitationally lensed quasar <ASTROBJ>SBS 1520+530</ASTROBJ> derived from data obtained at the Nordic Optical Telescope. A time delay of 130+/-3 days (1sigma ... [more ▼]

We present optical R-band light curves of the gravitationally lensed quasar <ASTROBJ>SBS 1520+530</ASTROBJ> derived from data obtained at the Nordic Optical Telescope. A time delay of 130+/-3 days (1sigma ) is determined from the light curves. In addition, spectra of <ASTROBJ>SBS 1520+530</ASTROBJ> obtained at the Keck Observatory are spatially deconvolved in order to extract the spectrum of the faint lensing galaxy, free of any contamination by the light from the bright quasar images. This spectrum indicates a lens redshift z=0.717, in agreement with one of the absorption systems found in the quasar spectra. The best mass model of the system includes a second nearby galaxy and a cluster of galaxies in addition to the main lensing galaxy. Adopting this model and an Omega =0.3, Lambda =0.7 cosmology, our time-delay measurement yields a Hubble constant of H[SUB]0[/SUB]=51 +/- 9 km s[SUP]-1[/SUP] Mpc[SUP]-1[/SUP] (1sigma error). Based on observations made with the Nordic Optical, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias and the W. M. Keck Observatory which is operated jointly by the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/481 [less ▲]

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See detailAn optical time-delay for the lensed BAL quasar HE 2149-2745
Burud, I.; Courbin, F.; Magain, Pierre ULg et al

in Astronomy and Astrophysics (2002), 383(1), 71-81

We present optical V and i-band light curves of the gravitationally lensed BAL quasar HE 2149-2745. The data, obtained with the 1.5 m Danish Telescope (ESO-La Silla) between October 1998 and December 2000 ... [more ▼]

We present optical V and i-band light curves of the gravitationally lensed BAL quasar HE 2149-2745. The data, obtained with the 1.5 m Danish Telescope (ESO-La Silla) between October 1998 and December 2000, are the first from a long-term project aimed at monitoring selected lensed quasars in the Southern Hemisphere. A time delay of 103+/-12 days is determined from the light curves. In addition, VLT/FORS1 spectra of HE 2149 2745 are deconvolved in order to obtain the spectrum of the faint lensing galaxy, free of any contamination by the bright nearby two quasar images. By cross-correlating the spectrum with galaxy-templates we obtain a tentative redshift estimate of z = 0.495+/-0:01. Adopting this redshift, a Omega = 0.3, Lambda = 0.7 cosmology, and a chosen analytical lens model, our time-delay measurement yields a Hubble constant of H-0 = 66+/-8 km s(-1) Mpc(-1) (1sigma error) with an estimated systematic error of +/-3 km s(-1) Mpc(-1). Using non-parametric models yields H-0 = 65+/-8 km s(-1) Mpc(-1) (1sigma error) and confirms that the lens exhibits a very dense/concentrated mass profile. Finally, we note, as in other cases, that the flux ratio between the two quasar components is wavelength dependent. While the flux ratio in the broad emission lines-equal to 3.7-remains constant with wavelength, the continuum of the brighter component is bluer. Although the data do not rule out extinction of one quasar image relative to the other as a possible explanation, the effect could also be produced by differential microlensing by stars in the lensing galaxy. [less ▲]

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See detailA novel approach for extracting time-delays from lightcurves of lensed quasar images
Burud, I.; Magain, Pierre ULg; Sohy, Sandrine ULg et al

in Astronomy and Astrophysics (2001), 380

We present a new method to estimate time delays from light curves of lensed quasars. The method is based on chi [SUP]2[/SUP] minimization between the data and a numerical model light curve. A linear ... [more ▼]

We present a new method to estimate time delays from light curves of lensed quasars. The method is based on chi [SUP]2[/SUP] minimization between the data and a numerical model light curve. A linear variation can be included in order to correct for slow long-term microlensing effects in one of the lensed images. An iterative version of the method can be applied in order to correct for higher-order microlensing effects. The method is tested on simulated light curves. When higher-order microlensing effects are present, the time delay is best constrained with the iterative method. Analysis of a published data set for the lensed double Q 0957+561 yields results in agreement with other published estimates. [less ▲]

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See detailThe XMM Large Scale Structure Survey and its multi-lambda follow-up
Pierre, M.; Alloin, D.; Altieri, B. et al

Article for general public (2001)

We present a unique European project which aims at mapping the matter distribution in the distant universe from hundreds of megaparsecs to galaxy scales. This comprehensive scientific approach constitutes ... [more ▼]

We present a unique European project which aims at mapping the matter distribution in the distant universe from hundreds of megaparsecs to galaxy scales. This comprehensive scientific approach constitutes a new step in the synergy between space- and ground-based observatory resources and therefore a building block of the forthcoming Virtual Observatory. [less ▲]

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See detailAn Optical Time Delay Estimate for the Double Gravitational Lens System B1600+434
Burud, I.; Hjorth, J.; Jaunsen, A. O. et al

in Astrophysical Journal (2000), 544

We present optical I-band light curves of the gravitationally lensed double QSO B1600+434 from observations obtained at the Nordic Optical Telescope (NOT) between 1998 April and 1999 November. The ... [more ▼]

We present optical I-band light curves of the gravitationally lensed double QSO B1600+434 from observations obtained at the Nordic Optical Telescope (NOT) between 1998 April and 1999 November. The photometry has been performed by simultaneous deconvolution of all the data frames, involving a numerical lens galaxy model. Four methods have been applied to determine the time delay between the two QSO components, giving a mean estimate of Deltat=51+/-4 days (95% confidence level). This is the fourth optical time delay ever measured. Adopting a Omega=0.3, Lambda=0 universe and using the mass model of Maller et al., this time delay estimate yields a Hubble parameter of H[SUB]0[/SUB]=52[SUP]+14[/SUP][SUB]-8[/SUB] km s[SUP]-1[/SUP] Mpc[SUP]-1[/SUP] (95% confidence level), where the errors include time delay as well as model uncertainties. There are time-dependent offsets between the two (appropriately shifted) light curves that indicate the presence of external variations due to microlensing. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. [less ▲]

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See detailLensed quasars: a matter of resolution
Courbin, F.; Lidman, C.; Burud, I. et al

in The Messenger (2000), 101

Not Available

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See detailHigh-Resolution Optical and Near-Infrared Imaging of the Quadruple Quasar RX J0911.4+0551
Burud, I.; Courbin, F.; Lidman, C. et al

in Astrophysical Journal (1998), 501

We report the detection of four images in the recently discovered lensed QSO RX J0911.4+0551. With a maximum angular separation of 3."1, it is the quadruply imaged QSO with the widest known angular ... [more ▼]

We report the detection of four images in the recently discovered lensed QSO RX J0911.4+0551. With a maximum angular separation of 3."1, it is the quadruply imaged QSO with the widest known angular separation. Raw and deconvolved data reveal an elongated lens galaxy. The observed reddening in at least two of the four QSO images suggests differential extinction by this lensing galaxy. We show that both an ellipticity of the galaxy ( epsilon _{{min}}=0.075 ) and an external shear ( gamma _{{min}}=0.15 ) from a nearby mass have to be included in the lensing potential in order to reproduce the complex geometry observed in RX J0911.4+0551. A possible galaxy cluster is detected about 38" from RX J0911.4+0551 and could contribute to the X-ray emission observed by ROSAT in this field. The color of these galaxies indicates a plausible redshift in the range of 0.6-0.8. [less ▲]

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See detailRX J0911.4+0551: a complex quadruply imaged gravitationally lensed QSO.
Burud, I.; Courbin, F.; Lidman, C. et al

in The Messenger (1998), 92

The authors present their first observations of RX J0911.4+0551 at the 2.2-m ESO/MPI IRAC 2b in K-band which made them suspect that the QSO might be quadruple. This was confirmed on the optical data from ... [more ▼]

The authors present their first observations of RX J0911.4+0551 at the 2.2-m ESO/MPI IRAC 2b in K-band which made them suspect that the QSO might be quadruple. This was confirmed on the optical data from the 2.56-m Nordic Optical Telescope, and on the NTT/SOFI data of the object. Careful deconvolution of the data allows to clearly resolve the object into four QSO components and a lensing galaxy. [less ▲]

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See detailDetection of the lensing galaxy for the double QSO HE 1104-1805
Remy, M.; Claeskens, Jean-François ULg; Surdej, Jean ULg et al

in New Astronomy (1998), 3

High angular resolution ground-based direct imaging (V, R, I_c) of the double QSO HE 1104-1805 has been obtained with the NOT and NTT telescopes. Analysis of these data led to the first detection of the ... [more ▼]

High angular resolution ground-based direct imaging (V, R, I_c) of the double QSO HE 1104-1805 has been obtained with the NOT and NTT telescopes. Analysis of these data led to the first detection of the lensing galaxy. Direct imaging of HE 1104-1805 has subsequently been carried out with the Planetary Camera (WFPC2) through the F555W (nearly Johnson V) and F814W (nearly Kron-Cousins I_c) filters onboard HST. These images confirm the presence of the deflector between the two lensed quasar components (A & B). Direct imaging of this system in the near infrared (IR) at 2.2 mu-m (K'), with IRAC-2b at the Cassegrain focus of the ESO/MPI 2.2 m telescope, indicates that the additional component is indeed a very red extended object with magnitude K ~= 16.5. We present deconvolutions of the HST and IR images using the 2-channel PLUCY method. From the HST observations, we also report very accurate relative positions and brightnesses of the QSO components. By comparison between the ground-based and the HST observations, from February-March 1994 to November 1995, we possibly detect the fading of component A by ~ 0.3 magnitudes in the optical and a corresponding fading of B by about half this value. The observed monotonic decrease of the magnitude difference between B and A as a function of wavelength is consistent with a partial amplification of the A component by microlensing. Evolutionary models for galaxies show that, in order to produce the observed colour indices V - I_c > 2 and 4 < I_c - K < 4.5, the galaxy is likely to be of elliptical type with a redshift 0.95 < z < 1.4. This range is consistent with the redshift z=1.32 measured from the absorption lines of metallic species in the spectra of the quasar components. However, other values for the redshift of the lens inside this range cannot be excluded. This galaxy would presently be among the most distant known gravitational lenses. Several theoretical models are found to fit the observations. The simplest one is a singular isothermal sphere (SIS) lens immersed in an external shear with gamma=0.123. The derived mass-to-light ratio (11 h_50 M_Sun/L_Sun) for the galaxy is large but does not imply an excess of dark matter with respect to other well known lensing galaxies. [less ▲]

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See detailESO & NOT photometric monitoring of the Cloverleaf quasar
Ostensen, R.; Remy, M.; Lindblad, P. O. et al

in Astronomy and Astrophysics. Supplement Series (1997), 126

The Cloverleaf quasar, H1413+117, has been photometrically monitored at ESO (La Silla, Chile) and with the NOT (La Palma, Spain) during the period 1987--1994. All good quality CCD frames have been ... [more ▼]

The Cloverleaf quasar, H1413+117, has been photometrically monitored at ESO (La Silla, Chile) and with the NOT (La Palma, Spain) during the period 1987--1994. All good quality CCD frames have been successfully analysed using two independent methods (i.e. an automatic image decomposition technique and an interactive CLEAN algorithm). The photometric results from the two methods are found to be very similar, and they show that the four lensed QSO images vary significantly in brightness (by up to 0.45 mag), nearly in parallel. The lightcurve of the $D$ component presents some slight departures from the 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 photometric lightcurves of this quadruply imaged variable QSO, are derived. This is unfortunately too large to constrain the lens model but there is little doubt that a better sampling of the lightcurves should allow to accurately derive these time delays. Pending a direct detection of the lensing galaxy (position and redshift), this system thus constitutes another good candidate for a direct and independent determination of the Hubble parameter. Based on observations collected at the European Southern Observatory (La Silla, Chile) and with the Nordic Optical Telescope (La Palma, Spain). Table 1. Logbook for the ESO and NOT observations together with photometric results for the Cloverleaf quasar. This long table can be accessed on the WWW at the URL address: http://vela.astro.ulg.ac.be/grav_lens/glp_homepage.html} [less ▲]

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See detailThe geometry of the quadruply imaged quasar PG 1115+080: implications for H_0_.
Courbin, F.; Magain, Pierre ULg; Keeton, C. R. et al

in Astronomy and Astrophysics (1997), 324

Time delay measurements have recently been reported for the lensed quasar PG 1115+080. These measurements can be used to derive H_0_, but only if we can constrain the lensing potential. We have applied a ... [more ▼]

Time delay measurements have recently been reported for the lensed quasar PG 1115+080. These measurements can be used to derive H_0_, but only if we can constrain the lensing potential. We have applied a recently developed deconvolution technique to analyze sub-arcsecond I band images of PG 1115+080, obtained at the Nordic Optical Telescope (NOT) and the Canada France Hawaii Telescope (CFHT). The high performance of the deconvolution code allows us to derive precise positions and magnitudes for the four lensed images of the quasar, as well as for the lensing galaxy. The new measurement of the galaxy position improves its precision by a factor of 3 and thus strengthens the constraints on the lensing potential. With the new data, a range of models incorporating some of the plausible systematic uncertainties yields H_0_=53^+10^_-7_km/s/Mpc. [less ▲]

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