arXiv subjects

J. Wambsganss

Publications and source records attributed to J. Wambsganss.

111 records · Page 7Linked to original sources

arXiv1996

VLA Observations of the Gravitational Lens System Q2237+0305

We report observations of the four-image gravitational lens system Q2237+0305 with the VLA at 20 cm and 3.6 cm. The quasar was detected at both frequencies (\approx 0.7 mJy) with a flat spectrum. All four lensed images are clearly resolved at 3.6 cm, and the agreement of the radio and optical image positions is excellent. No radio emission is detected from the lensing galaxy, and any fifth lensed quasar image must be fainter than \sim 20% of the A image flux density. Since the optical quasar images are variable and susceptible to extinction, radio flux ratios provide the best measurement of the macrolensing magnification ratios. The radio B/A and C/A image flux ratios are consistent with the observed range of optical variations, but the D/A ratio is consistently higher in the radio than in the optical. The radio ratios are consistent with magnification ratios predicted by lens models, and weaken alternative interpretations for Q2237+0305. More accurate radio ratios can distinguish between the models, as well as improve our understanding of both microlensing and extinction in this system.

astro-ph↗

arXiv1995

ROSAT/PSPC observation of the distant cluster CL0939+472

We present results and an analysis of a ROSAT PSPC pointed observation of the galaxy cluster CL0939+472. This very rich and very distant cluster is known to contain an unusually high fraction of blue and E+A galaxies, and a lot of merging of galaxies is going on. The X-ray properties we find are also quite unusual. The luminosity in the ROSAT band (0.1-2.4 keV) is $L_X = (6.7\pm 0.3) \times 10^{44}$erg/s, rather on the low side for such a rich cluster. We find a temperature of 2.9$_{-0.8}^{+1.3}$ keV, which is also relatively low, but has also a large uncertainty. The cluster shows indications of substructure, which results in a high value for the core radius and a steep drop off outside the core, if one fits a spherically symmetric $β$-model. The lower limit on the mass inside a radius of $1.0 h_{50}^{-1}$Mpc is $2.6 \times 10^{14} \msol$, and the upper limit on the gas mass fraction is 50\%. All the unusual properties of this cluster can be explained if in fact we see the merging of two clusters of roughly equal mass, which is also supported by recent optical observations.

astro-ph↗

arXiv1995

A Sharp Event in the Image a Light Curve of the Double Quasar 0957+561 and Prediction of the 1996 Image B Light Curve

CCD photometry of the gravitational lens system 0957+561A,B in the g and r bands was obtained on alternate nights, weather permitting, from December 1994 through May 1995 using the Double Imaging Spectrograph (DIS) on the Apache Point Observatory (APO) 3.5-meter telescope. The remote observing and fast instrument change capabilities of this facility allowed accumulation of light curves sampled frequently and consistently. The Honeycutt ensemble photometry algorithm was applied to the data set and yielded typical relative photometric errors of approximately 0.01 magnitudes. Image A exhibited a sharp drop of about 0.1 magnitudes in late December 1994; no other strong features were recorded in either image. This event displays none of the expected generic features of a microlensing-induced flux variation and is likely to be intrinsic to the quasar; if so, it should also be seen in the B image with the lensing differential time delay. We give the expected 1996 image B light curves based on two values of the time delay and brightness ratio which have been proposed and debated in the literature. Continued monitoring of the system in the first half of 1996 should easily detect the image B event and thus resolve the time-delay controversy.

astro-ph↗