Showing papers by "I. M. Hook published in 1998"

Discovery of a supernova explosion at half the age of the Universe

Abstract: The ultimate fate of the Universe, infinite expansion or a big crunch, can be determined by using the redshifts and distances of very distant supernovae to monitor changes in the expansion rate. We can now find1 large numbers of these distant supernovae, and measure their redshifts and apparent brightnesses; moreover, recent studies of nearby type Ia supernovae have shown how to determine their intrinsic luminosities2,3,4—and therefore with their apparent brightnesses obtain their distances. The >50 distant supernovae discovered so far provide a record of changes in the expansion rate over the past several billion years5,6,7. However, it is necessary to extend this expansion history still farther away (hence further back in time) in order to begin to distinguish the causes of the expansion-rate changes—such as the slowing caused by the gravitational attraction of the Universe's mass density, and the possibly counteracting effect of the cosmological constant8. Here we report the most distant spectroscopically confirmed supernova. Spectra and photometry from the largest telescopes on the ground and in space show that this ancient supernova is strikingly similar to nearby, recent type Ia supernovae. When combined with previous measurements of nearer supernovae2,5, these new measurements suggest that we may live in a low-mass-density universe.

Cosmology from Type Ia supernovae

Abstract: This presentation reports on first evidence for a low-mass-density/positive-cosmological-constant universe that will expand forever, based on observations of a set of 40 high-redshift supernovae. The experimental strategy, data sets, and analysis techniques are described. More extensive analyses of these results with some additional methods and data are presented in the more recent LBNL report #41801 (Perlmutter et al., 1998; accepted for publication in Ap.J.), astro-ph/9812133 . This Lawrence Berkeley National Laboratory reprint is a reduction of a poster presentation from the Cosmology Display Session #85 on 9 January 1998 at the American Astronomical Society meeting in Washington D.C. It is also available on the World Wide Web at http://supernova.LBL.gov/ This work has also been referenced in the literature by the pre-meeting abstract citation: Perlmutter et al., B.A.A.S., volume 29, page 1351 (1997).

Discovery of radio‐loud quasars with z=4.72 and z=4.010

Abstract: We report the discovery of two radio-loud quasars with redshifts greater than four; GB1428+4217 with z=4.72 and GB1713+2148 with z=4.01. This doubles the number of published radio-selected quasars with z > 4, bringing the total to 4. GB1428+4217 is the third most distant quasar known and the highest redshift radio and X-ray source currently known. It has a radio flux density at 5GHz of 259 +/- 31 mJy and an optical magnitude of R approximately 20.9. The rest frame absolute UV magnitude, M(nu=1450A), is -26.7 similar to that of the archetypal radio-selected quasar 3C273 (z=0.158; M(nu=1450A)=-26.4). GB1428+4217 has a tentative detection in ROSAT PSPC observations, which has been confirmed by more recent ROSAT observations, described in a companion paper by Fabian et al. Both quasars were discovered during the CCD imaging phase of an investigation into the evolution of the space density of radio-loud quasars at high redshift. Combined with our earlier survey results these objects give a lower limit on the space density of quasars with radio power P(5GHz) > 5.8 x 10^{26} W/Hz/sr between z=4 and z=5 of 1.4 +/- 0.9 x 10^{-10} Mpc^{-3}. This can be compared to 2.9 +/- 0.2 x 10^{-10} Mpc^-3 at z=2 from Dunlop & Peacock (1990) for flat-spectrum sources of the same luminosity.

Discovery of radio-loud quasars with z=4.72 and z=4.01

Abstract: We report the discovery of two radio-loud quasars with redshifts greater than four; GB1428+4217 with z=4.72 and GB1713+2148 with z=4.01. This doubles the number of published radio-selected quasars with z > 4, bringing the total to 4. GB1428+4217 is the third most distant quasar known and the highest redshift radio and X-ray source currently known. It has a radio flux density at 5GHz of 259 +/- 31 mJy and an optical magnitude of R approximately 20.9. The rest frame absolute UV magnitude, M(nu=1450A), is -26.7 similar to that of the archetypal radio-selected quasar 3C273 (z=0.158; M(nu=1450A)=-26.4). GB1428+4217 has a tentative detection in ROSAT PSPC observations, which has been confirmed by more recent ROSAT observations, described in a companion paper by Fabian et al. Both quasars were discovered during the CCD imaging phase of an investigation into the evolution of the space density of radio-loud quasars at high redshift. Combined with our earlier survey results these objects give a lower limit on the space density of quasars with radio power P(5GHz) > 5.8 x 10^{26} W/Hz/sr between z=4 and z=5 of 1.4 +/- 0.9 x 10^{-10} Mpc^{-3}. This can be compared to 2.9 +/- 0.2 x 10^{-10} Mpc^-3 at z=2 from Dunlop & Peacock (1990) for flat-spectrum sources of the same luminosity.

The ASCA spectrum of the z=4.72 blazar GB 1428+4217.

Abstract: The X-ray luminous quasar GB 1428+4217 at redshift 472 has been observed with ASCA The observed 05-10 keV flux is 32E-12 erg/s/cm2 We report here on the intrinsic 4-57 keV X-ray spectrum, which is very flat (photon index of 129) We find no evidence for flux variability within the ASCA dataset or between it and ROSAT data We show that the overall spectral energy distribution of GB 1428+4217 is similar to that of lower redshift MeV blazars and present models which fit the available data The Doppler beaming factor is likely to be at least 8 We speculate on the number density of such high redshift blazars, which must contain rapidly-formed massive black holes

Commissioning of a 4Kx4K CCD mosaic and the new ESO FIERA CCD controller at the SUSI-2 imager of the NTT

Abstract: We present the characteristics of the new CCD imager, SUSI2, installed at the ESO 3.5 m NTT. The instrument shares the Nasmyth focus A with the new infrared imager-spectrograph SOFI. The focal plane array of USSI2 is a mosaic of 2 EEV44- 82, 2k X 4k, 15 micrometer pixels, thinned, anti-reflection coated CCDs, which are placed at the direct focus of the telescope (scale 0.08 arcsec/pixel, field of view 5.5 X 5.5 arcmin). The average QE for the two devices is 76, 90, 85, 80, 68, 49, 23% at 350, 400, 500, 600, 700, 800, 900 nm respectively. The overall instrument efficiency, including the three mirrors of the telescope and the detector but without filters, is computed to be 46, 55, 51, and 48% at the central wavelengths of the U, B, V and R bands. The CCDs are driven by the new ESO CCD controller FIERA. The system performance was measured during the commissioning of the instrument at the telescope in February 98. The mosaic is read in 16 seconds in the standard operating mode (2 X 2 binning of the CCDs) with a read-out-noise of 4.7 e-/pixel. The other CCD parameters such as CTE, dark current and linearity, were also found to comply with the requirements. The FWHM of stellar sources in images obtained in good seeing conditions were measured to be 0.49 arcsec, with no significant variation over the field of view.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Cosmology from Type Ia Supernovae

Abstract: This presentation reports on first evidence for a low-mass-density/positive-cosmological-constant universe that will expand forever, based on observations of a set of 40 high-redshift supernovae. The experimental strategy, data sets, and analysis techniques are described. More extensive analyses of these results with some additional methods and data are presented in the more recent LBNL report #41801 (Perlmutter et al., 1998; accepted for publication in Ap.J.), astro-ph/9812133 . This Lawrence Berkeley National Laboratory reprint is a reduction of a poster presentation from the Cosmology Display Session #85 on 9 January 1998 at the American Astronomical Society meeting in Washington D.C. It is also available on the World Wide Web at this http URL This work has also been referenced in the literature by the pre-meeting abstract citation: Perlmutter et al., B.A.A.S., volume 29, page 1351 (1997).

The ESO Imaging Survey: Status Report and Preliminary Results

Abstract: The ESO Imaging Survey (EIS) presented in early issues of the Messenger, and with up-to-date information on the ongoing observations available on the Web (this http URL), is a concerted effort by ESO and the Member State community to provide targets for the first year of operation of the VLT. It consists of two parts: a relatively wide-angle survey (EIS-WIDE) to cover four pre-selected patches of sky, 6 square degrees each, spread in right ascension to search for distant clusters and quasars and a deep, multicolor survey of four optical (SUSI-2) and two infrared (SOFI) covering the HST/Hubble Deep Field South (HDFS) and its flanking fields (EIS-DEEP). From the start, the main challenge has been to carry out a public survey in a limited amount of time requiring observations, software development and data reduction with the goal of distributing the survey data products before the call for proposal for the VLT. To cope with this one-year timetable, a novel type of collaboration between ESO and the community has been established which has allowed EIS to combine the scientific and technical expertise fo the community with in-house know-how and infrastructure. In spite of the adverse weather conditions in some of the earlier runs, EIS has already proved to be successful experiment achieving most of its scientific and technical goals, thereby laying the ground work for future imaging surveys.

The ESO Imaging Survey: status report and preliminary results.

Abstract: The ESO Imaging Survey (EIS) presented in early issues of the Messenger, and with up-to-date information on the ongoing observations available on the Web (this http URL), is a concerted effort by ESO and the Member State community to provide targets for the first year of operation of the VLT. It consists of two parts: a relatively wide-angle survey (EIS-WIDE) to cover four pre-selected patches of sky, 6 square degrees each, spread in right ascension to search for distant clusters and quasars and a deep, multicolor survey of four optical (SUSI-2) and two infrared (SOFI) covering the HST/Hubble Deep Field South (HDFS) and its flanking fields (EIS-DEEP). From the start, the main challenge has been to carry out a public survey in a limited amount of time requiring observations, software development and data reduction with the goal of distributing the survey data products before the call for proposal for the VLT. To cope with this one-year timetable, a novel type of collaboration between ESO and the community has been established which has allowed EIS to combine the scientific and technical expertise fo the community with in-house know-how and infrastructure. In spite of the adverse weather conditions in some of the earlier runs, EIS has already proved to be successful experiment achieving most of its scientific and technical goals, thereby laying the ground work for future imaging surveys.