Search for GRB counterparts: non-optical

The present status of the search for counterparts of gamma-ray bursts is given. particular emphasis will be put on the search for flaring counterparts, i.e. emission during or shortly after the gamma-ray emission. In view of a separate review on optical counterparts I will concentrate on GeV/TeV, X-ray, radio and neutrino searches. (orig.)Available from TIB Hannover: RN 9303(327) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Discovery of a giant and luminous X-ray outburst from the optically inactive galaxy pair RX J1242.6-1119

We report the discovery of large-amplitude X-ray variability from the direction of the previously unknown, optically inactive galaxy pair RX J1242.6-1119. The X-ray source shows variability by a factor >or#approx# 20 between the ROSAT all-sky survey and a later pointed observation separated by #propor to# 1.5 yr. Its spectrum is extremely soft with photon index #GAMMA#_x#approx =# -5, among the steepest ever observed among galaxies. Based on the redshift derived from the optical spectra, z = 0.05, the source's intrinsic luminosity is large, L_x >or#approx# 10"4"3 erg s"-"1. Surprisingly, the optical spectra of both galaxies are characterized by absorption lines and do not show signs of (Seyfert) activity. This makes RX J1242-11 the third candidate for giant-amplitude variability in an otherwise non-active galaxy, the first two being NGC 4552 (in the UV: Renzini et al. 1995) and NGC 5905 (in X-rays: Bade et al. 1996, Komossa and Bade 1999). Several mechanisms to explain this unexpected and peculiar behavior are investigated. The most likely one seems to be an accretion event onto an otherwise dormant supermassive black hole (SMBH), e.g., by a tidal disruption eventSIGLEAvailable from TIB Hannover: RN 9303(472) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

The complex X-ray spectra of active galaxies with warm absorbers. Warm absorbers in Narrow-Line Seyfert 1 galaxies

SIGLEAvailable from TIB Hannover: RN 9303(453) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

A large amplitude flaring dMe star in the 1978 October 6B #gamma#-ray burst error box

Spectroscopic observations provide evidence that the optical transient object observed in 1966 on archival plates of Sonneberg Observatory is a B 18.5 dMe star. For an assumed flare duration of 40 min. (or longer) the flare amplitude was #DELTA#m_B #approx# 5.2 mag. If the recorded event was belonging to the class of 'fast' flares its amplitude could have reached 7-9 mag. We estimate a lower limit for the optical flare energy release of 10"3"5 (d/100 pc)"2 erg/s. We discuss the positional coincidence of this large amplitude flaring star with the error box of the #gamma#-ray burst 1978 October 6B and conclude that the flare star is probably not related to the #gamma#-ray burst. The fact that no other optical flare was found from this object restricts their frequency to be less than 7 x 10"-"4 h"-"1 for amplitudes (in B) greater than 4.5 mag. Nevertheless, large amplitude flares constitute a serious background problem for the wide field search for possible optical counterparts of #gamma#-ray bursters. (orig.)SIGLEAvailable from TIB Hannover: RN 9303(295) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Anwendung der Maximum Entropie Methode zur Bildrekonstruktion sowie Auswertung und Interpretation der Daten von Kosmischen Bursts und Solaren Flares fuer die GRO-Experimente COMPTEL und EGRET Schlussbericht

SIGLEAvailable from TIB Hannover: DtF QN1(59,39) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany); DLR Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Bonn (Germany)DEGerman

ROSAT HRI discovery of luminous extended X-ray emission in NGC 6240

We report the detection of luminous extended X-ray emission in NGC 6240 on the basis of ROSAT HRI observations of this ultraluminous IR galaxy. The spatial structure and temporal behavior of the X-ray source were analyzed. We find that >or#approx#70% of the soft X-ray emission is extended beyond a radius of 5''. Strong emission can be traced out to a radius of 20'' and weaker emission extends out to #propor to#50''. With a luminosity of at least L_x#approx =#10"4"2 erg/s this makes NGC 6240 one of the most luminous X-ray emitters in extended emission known. Evidence for a nuclear compact variable component is indicated by a drop of 32% in the HRI count rate as compared to the PSPC data taken one year earlier. No short-timescale variability is detected. The HRI data, which represent the first high-resolution study of the X-ray emission from NGC 6240, complement previous spectral fits to ROSAT PSPC data that suggested a two-component model consisting of thermal emission from shocked gas immersed in a starburst wind plus a powerlaw source attributed to scattered light from an obscured AGN. We discuss several models to account for the extended and compact emission. Although pushed to its limits the starburst outflow model is tenable for the essential part of the extended emission. For the AGN-type component we propose a model consisting of a near-nuclear 'warm scatterer' that explains the apparent fading of the X-ray flux within a year as well as the strong FeK#alpha# complex seen in an ASCA spectrum. (orig.)Available from TIB Hannover: RN 9303(435) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Four new active galaxies with steep soft X-ray spectra

We have discovered four AGN in the ROSAT all-sky-survey data with very steep X-ray spectra. We apply several models to these X-ray spectra with emphasis on warm absorber models which give an adequate description of the data. We report on the follow-up optical and radio observations which allow the identification of three of these objects as Narrow Line Seyfert 1 galaxies, and the fourth as BL Lac object. We have measured small FWHM H#beta# lines, strong FeII emission and weak [OIII] emission in the three Narrow Line Seyfert 1 galaxies, in line with known correlations with respect to the steepness of the X-ray spectra. We have discovered strong optical variability in the BL Lac object and two of the Seyfert galaxies using photographic plates of the Sonneberg Observatory field patrol. We finally discuss the statistical implications of our search algorithm on the expected number density of soft X-ray selected AGN and conclude that up to 30% of X-ray selected AGN might have supersoft X-ray spectra. (orig.)Available from TIB Hannover: RN 9303(342) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

The giant-amplitude X-ray outburst in NGC 5905 - a tidal disruption event? The ROSAT view of NGC 1365: core emission, the highly variable source NGC 1365-X1, and alignments of surrounding X-ray sources. Properties of warm absorbers in active galaxies. The ULIRG NGC 6240: luminous extended X-ray emission and evidence for an AGN

SIGLEAvailable from TIB Hannover: RN 9303(448) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Search for quiescent X-rays from GRB sources

SIGLEAvailable from TIB Hannover: RN 9303(274) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Near-simultaneous ROSAT and Ginga observations of the 1991 X-ray transient in Musca

During its All-Sky-Survey ROSAT has observed the Musca 1991 X-ray transient on January 24/25, two weeks after outburst, for about 170 s. The intensity was found to be nearly 6 Crab in the ROSAT band. A combined fit of ROSAT and Ginga data from 1991 January 25 with a multitemperature disk blackbody model plus a power law component results in a maximal temperature of the disk of about kT=0.96 keV at an absorbing column of N_H=2.2x10"2"1 cm"-"2. With the knowledge of the mass function f(M)=3.1 M_sun from optical observations we derive a minimum distance to the black hole binary of at least 4-5 kpc. Including the accretion disk inclination angle of i=26 #+-#25 determined from the shape of the positron annihilation line, and the quiescent optical brightness together with the most probable spectral type of the companion we drive a black hole mass of M=(6#+-#1.5) M_sun and a distance of about (11#+-#3) kpc. (orig.)Available from TIB Hannover: RN 9303(273) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman