摘要:

Gamma-ray bursts are among the most energetic explosions in the Universe, and yet their origin has been a mystery since they were discovered in 1973. Early instrumentation showed that the bursts have a huge variety of time profiles and are not associated with any bright or unusual steady sources at other wavelengths. The BATSE instrument on CGRO is more sensitive than any previous GRB detector and is providing a huge (> 2000) and uniform sample. From it we have learned that GRBs are isotropic on the sky and have an intensity distribution that flattens toward fainter bursts. Recently, tremendous progress has been made by measurements performed and enabled by the BeppoSAX mission. X-ray, optical and radio afterglow has been discovered for several bursts. From the accurate positions in these wavelength bands it has been possible to obtain redshifts for 3 bursts and to identify host galaxies for ∼ 10 bursts. From this we now know that most, if not all, GRBs are cosmological in origin with typical distances of∼2&hthinsp;GPc(z≈1).©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58623

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Gamma-ray bursts are much brighter than supernovae, and could therefore possibly probe the Universe to high redshift. The presently established GRB redshifts range from 0.83 to 5, and quite possibly even beyond that. Since most proposed mechanisms for GRB link them closely to deaths of massive stars, it is a reasonable ansatz to assume that their rate density in the past was proportional to the star formation rate. Work with Bloom, Bagla, and Natarajan (1997), as well as by other groups, does indeed show that the GRB flux distribution calculated from this assumption agrees well with the data. This means that GRB are bright lamps which illuminate an era of the Universe that may predate the quasar age somewhat, so they can become useful beacons illuminating the early Universe. It also seems that GRB can become well calibrated lamps, like supernovae. The theory that attributes the afterglows to relativistic blast waves emitting synchrotron radiation has been quite successfully tested, and in the case of GRB 970508 so well measured that the physical parameters of the burst are known. If this could be repeated regularly, GRB can become as precise probes of cosmic geometry at redshifts 2–5 as ordinary supernovae are at redshifts ≲1. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58624

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The estimated GRB energy of around1055ergs for GRB980329 implies that all stellar mass models are inadequate. An original “beam on target” model, based on gravitational collapse forming a galaxy in the presence of a uniform primordial magnetic field, and producing a powerful, highly relativistic, intense, storage ring, is proposed. The afterglow or “fireball” is produced by blowoff of target material as the target crosses the beam. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58625

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Recently we have elaborated a new cosmological model of gamma-ray burst (GRB) origin [1], which employs the dynamical evolution of central dense stellar clusters in the galactic nuclei. Those clusters inevitably contain a large fraction of compact stellar remnants (CSRs), such as neutron stars (NSs) and stellar mass black holes (BHs), and close encounters between them result in radiative captures into short-living binaries, with subsequent merging of the components thereby producing GRBs, typically at large distances from the nucleus. In the present paper, we calculate the redshift distribution of the rate of GRBs produced by close encounters of NSs in distant galactic nuclei. To this end, the following steps are undertaken: (i) we establish a connection between the parameters of the fast evolving central stellar clusters (i.e. those for which the time of dynamical evolution exceeds the age of the Universe) with masses of the forming central supermassive black holes (SMBHs) using a dynamical evolution model; (ii) we connect these masses with the inferred mass distributions of SMBHs in the galactic nuclei and the redshift distribution of quasars by assuming a certain ‘Eddington luminosity phase’ in their activity; (iii) we incorporate available observational data on the redshift distribution of quasars as well as a recently found correlation between the masses of galaxies and their central SMBHs. The resulting redshift distribution of the GRB rate, which accounts for both fast and slowly evolving galactic nuclei is consistent with that inferred from the BATSE data if the fraction of fast evolving galactic nuclei is in the range&egr;≃0.016−0.16.©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58626

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The previous National Academy of Sciences decadal survey for astronomy, the “Bahcall report”, heralded the 90’s as the “decade of the infrared”. The report outlined the many near-infrared (here defined as 1–30 &mgr;m) facilities that would become available. Their vision is now coming to fruition with the advent of large ground-based telescopes equipped with infrared instruments and upcoming space-based infrared (IR) missions. For astronomers, the first decade of the 21st century promises to be the one in which the floodgates open for the IR data from these facilities. In addition, there are many new capabilities for near-IR astronomy in various stages of planning for the future. We outline the current capabilities for near IR astronomy and project how these new observatories and instruments will impact the field. We also list the online sources of information for each of the facilities. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58628

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Observations at far-infrared and submillimeter wavelengths promise to revolutionize the study of high redshift galaxies and AGN by providing a unique probe of the conditions within heavily extinguished regions of star formation and nuclear activity. Observational capabilities in this spectral region will expand greatly in the next decade as new observatories are developed both in space and on the ground. These facilities include the Space Infrared Telescope Facility (SIRTF), the far-infrared and submillimeter telescope (FIRST) and the millimeter array (MMA). In the longer term, the requirements of high angular resolution (comparable to that of HST), full wavelength coverage, and high sensitivity (approaching the fundamental limit imposed by photon counting statistics) will motivate the development of far-IR and submillimeter space interferometry using cold telescopes and incoherent detector arrays. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58629

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Although the richness of the millimeter/submillimeter sky has been known for the last two decades, precision imaging of the sky has been impossible at all but the longest wavelengths. The Millimeter Array (MMA) will consist of 36 precision 10m antennas located above 5000m altitude in the Atacama Desert of Chile. It will apply aperture synthesis techniques for precision imaging of the cool thermal sky, particularly those objects which can now only be studied in the far infrared with coarse angular resolution. The MMA will offer unprecedented sensitivity–it will image a galaxy with the dust mass of the Milky Way atz=1in one minute. The images the MMA will produce of this and highzsystems will be high resolution images: the MMA will offer unprecedented angular resolution for imaging cool matter, providing images at a few hundredths arcsecond resolution. The MMA provides extinction-free spectroscopy of dusty highzsystems. The MMA is currently under development; construction is scheduled to begin in 2001 with operations scheduled to begin in 2008. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58651

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The US-Japanese ASTRO-E observatory, is scheduled to be launched in early 2000. ASTRO-E carries four X-ray CCD detectors and a hard X-ray detector. The CCDs are located at the focus of grazing incidence X-ray mirrors and will primarily provide imaging over 0.4–12 keV bandpass. ASTRO-E also carries the XRS microcalorimeter X-ray detector. A platinum X-ray mirror will focus X-rays onto a 32-element array of microcalorimeter pixels for high-throughput, high-resolution spectroscopy with limited spatial resolution. The mean measured energy resolution of the XRS flight model detector is about 12 eV at 6 keV for the nominal operating temperature of 65 mK. We present results from our calibration of the XRS flight model detector. We describe the methods used to determine the spectral redistribution of the detector and the overall detection efficiency. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58630

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The Constellation X-ray Mission is a high throughput X-ray facility emphasizing observations at high spectral resolution(E/&Dgr;E∼300–3000),and broad energy bandpass (0.25–40 keV). Constellation-X will provide a factor of nearly 100 increase in sensitivity over current high resolution X-ray spectroscopy missions. It is the X-ray astronomy equivalent of large ground-based optical telescopes such as the Keck Observatory and the ESO Very Large Telescope. When observations commence toward the end of next decade, Constellation-X will address many fundamental astrophysics questions such as: the formation and evolution of clusters of galaxies; constraining the baryon content of the Universe; determining the spin and mass of supermassive black holes in AGN; and probing strong gravity in the vicinity of black holes. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58631

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We present the results of a survey of archival data and catalogued objects in the region around the Southern Hubble Deep Field (HDF-South). The survey encompasses NASA mission logs, astronomical catalogs, and journal tables. The HDF-South (HDF-S) has been the focus of a dedicated HST observing campaign during October 1998. Many astrophysically interesting objects in the vicinity of the HDF-S, including quasars and clusters of galaxies, have been catalogued and observed at a wide range of wavelengths. The byproducts of this and similar user-selected surveys of archival data can be used to study classes of objects that may potentially be represented among the faint objects discovered within the HDF-S. This survey was conducted using a suite of new data search, browse, and visualization tools available at the NASA ADC (Astronomical Data Center: http://adc.gafc.nasa.gov/). ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58632

出版商:AIP    

年代:1999

数据来源: AIP