The X-ray Properties of z>4 Quasars

We report on a search for X-ray emission from quasars with redshifts greater than four using the ROSAT public database. Our search has doubled the number of z>4 quasars detected in X-rays from 6 to 12. Most of those known prior to this work were radio-loud and X-ray selected sources; our study increases the number of X-ray detected, optically selected z>4 quasars from one to seven. We present their basic X-ray properties and compare these to those of lower redshift quasars. We do not find any evidence for strong broad-band spectral differences between optically selected z>4 quasars and those at lower redshifts.Comment: 7 pages, 4 figures included, LaTeX emulateapj.sty, accepted for publication in the Astronomical Journa

Multiwavelength observations of the field HS 47.5/22 in Ursa Major

We present the X–ray source catalogue obtained from a ROSAT survey in the HQS field HS 47.5/22. The survey consists of 48 overlapping PSPC pointings which were first analysed individually, and then merged to increase the sensitivity. Both modes bring forth sources missed in the other, showing that both are necessary to detect all X–ray sources in the field. The final catalogue contains 574 X–ray sources. The identifications are mainly based on the HQS objective prism plate which allows object classification down to a magnitude \rm {\it m}_b\, \raisebox{0.4ex}{<}\raisebox{-0.4ex}{\!\!\!\!\!\!\;\sim}\,18\hbox{.\!\!^{\rm m}}5, and a rough distinction between red and blue objects more than a magnitude deeper. Follow–up observations were performed for a number of objects, mainly faint quasar candidates

Calibration of the forward and rear ZEUS calorimeter using cosmic ray muons

The forward and rear calorimeter of the ZEUS experiment consists of 48 modules. Before their installation into the ZEUS detector they were calibrated at DESY using cosmic ray muons in order to check their performance and to compare the response to cosmic muons to the response, obtained for some modules, to 100 GeV beam muons. The setup, the test procedure and the analysis of the data are described in this paper. The relative calibration of the different modules, as well as of the different cells within a module can be obtained with cosmic ray muons with an accuracy of about one percent for a measurement time of 3–5 days/module

Calibration of the forward and rear ZEUS calorimeter using cosmic ray muons

The forward and rear calorimeter of the ZEUS experiment consists of 48 modules. Before their installation into the ZEUS detector they were calibrated at DESY using cosmic ray muons in order to check their performance and to compare the response to cosmic muons to the response, obtained for some modules, to 100 GeV beam muons. The setup, the test procedure and the analysis of the data are described in this paper. The relative calibration of the different modules, as well as of the different cells within a module can be obtained with cosmic ray muons with an accuracy of about one percent for a measurement time of 3–5 days/module

The Hamburg/RASS Catalogue of optical identifications

We present the Hamburg/RASS Catalogue of optical identifications (HRC). The catalogue contains optical information about objects inside the error circles of ROSAT All-Sky Survey (RASS) sources. The information was gathered from objective prism and direct plates taken by the Hamburg Quasar Survey (HQS). The plates enable an effective selection of several X-ray emitting classes of objects, as there are galaxies, AGN, QSOs, galaxy clusters and several types of galactic stars, in particular M dwarfs, hot white dwarfs and cataclysmic variables. In the current state (November 1996) the HRC contains information about 3847 X-ray positions and covers about 8480 deg2 of the high galactic latitude |b| > 20°) northern sky. For 81.2% of the X-ray sources a plausible optical counterpart is given. The counterparts of the remaining sources are probably faint (B > 18.5) AGN and galaxy clusters. The HRC is available electronically together with finding charts taken from the digitized direct HQS plates

Calibration of the forward and rear ZEUS calorimeter using cosmic ray muons

The forward and rear calorimeter of the ZEUS experiment consists of 48 modules. Before their installation into the ZEUS detector they were calibrated at DESY using cosmic ray muons in order to check their performance and to compare the response to cosmic muons to the response, obtained for some modules, to 100 GeV beam muons. The set-up, the test procedure and the analysis of the data are described in this paper. The relative calibration of the different modules, as well as of the different cells within a module can be obtained with cosmic ray muons with an accuracy of about one percent for a measurement time of 3-5 days/module. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(93-121) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman