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NGC 6418



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Radio emission from AGN detected by the VLA FIRST survey
Using the most recent (April 2003) version of the VLA FIRST survey radiocatalog, we have searched for radio emission from >2800 AGN takenfrom the most recent (2001) version of the Veron-Cetty and Veron AGNcatalog. These AGN lie in the ˜9033 square degrees of sky alreadycovered by the VLA FIRST survey. Our work has resulted in positivedetection of radio emission from 775 AGN of which 214 are new detectionsat radio wavelengths.Tables 3 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/35

Search for an optical counterpart of the COMPTEL source GRO J1753+57.
In November 1992, COMPTEL discovered the unusual and highly variablesource GRO J1753+57. There are no obvious candidates for counterparts inother wavebands, such as a bright radio loud AGN. A thorough search ofradio and NGC sources was undertaken to identify possible counterparts.Two potentially interesting objects were found, NGC 6454 and NGC 6474,but they exhibit only limited optical variability and core emission,contrarily to what would be expected from known extragalacticγ-ray sources. Supportive evidence for the elliptical galaxy NGC6454 comes from previous radio and X-ray measurements.

Active galaxies observed during the Extreme Ultraviolet Explorer all-sky survey
We present observations of active galactic nuclei (AGNs) obtained withthe Extreme Ultraviolet Explorer (EUVE) during the all-sky survey. Atotal of 13 sources were detected at a significance of 2.5 sigma orbetter: seven Seyfert galaxies, five BL Lac objects, and one quasar. Thefraction of BL Lac objects is higher in our sample than in hard X-raysurveys but is consistent with the soft X-ray Einstein Slew Survey,indicating that the main reason for the large number of BL Lac objectsin the extreme ultraviolet (EUV) and soft X-ray bands is their steeperX-ray spectra. We show that the number of AGNs observed in both the EUVEand ROSAT Wide Field Camera surveys can readily be explained bymodelling the EUV spectra with a simple power law in the case of BL Lacobjects and with an additional EUV excess in the case of Seyferts andquasars. Allowing for cold matter absorption in Seyfert galaxy hostsdrive up the inferred average continuum slope to 2.0 +/- 0.5 (at 90%confidence), compared to a slope of 1.0 usually found from soft X-raydata. If Seyfert galaxies without EUV excesses form a significantfraction of the population, then the average spectrum of those withbumps should be even steeper. We place a conservative limit on neutralgas in BL Lac objects: NH less than 1020/sq cm.

The detection of an unidentified variable gamma-ray source by COMPTEL.
We report the detection of an unidentified, high galactic latitude,γ-ray source (GRO J1753+57) by the COMPTEL instrument onboard theCompton Gamma-ray Observatory. The source was clearly detected duringobservations in November 1992 and had a flux in the 1-3MeV band ofapproximately half that of the Crab. All other observations of thisregion by COMPTEL only yield upper limits, or marginal detections,showing that this source is highly variable on a timescale of weeks.Possible counterparts are discussed.

Twenty-two emission-line AGNs from the HEAO-1 X-ray survey
We report 22 emission-line AGN as bright, hard X-ray sources. All ofthem appear to be new classifications with the exception of one peculiarIRAS source which is a known quasar and has no published spectrum. Thissample exhibits a rich diversity in optical spectral properties andluminosities, ranging from a powerful broad-absorption-line quasar to aweak nucleus embedded in a nearby NGC galaxy. Two cases confer X-rayluminosities in excess of 10 exp 47 erg/s. However, there is a degree ofuncertainty in the X-ray identification for the AGN fainter than V about16.5. Optically, several AGN exhibit very strong Fe II emission. OneSeyfert galaxy with substantial radio flux is an exception to the commonassociation of strong Fe II emission and radio-quiet AGN. The previouslyrecognized IRAS quasar shows extreme velocities in the profiles of theforbidden lines; the 0 III pair is broadened to the point that the linesare blended. Several of these AGN show evidence of intrinsicobscuration, illustrating the effectiveness of hard X-ray surveys inlocating AGN through high column density.

HI observations of galaxies in nearby Zwicky clusters
The results of a long term project of H I observations of galaxieswithin the boundaries of nearby Zwicky clusters are presented. Thedetection rate is rather low (233 out of 618, i.e., 38 percent) ascompared to other surveys carried out recently. Most of the radialvelocities of the detected galaxies are new determinations. The largespread in radial velocities for many of these clusters is a strongindication for the presence of several foreground and/or backgroundgalaxies.

An intermediate-sensitivity survey at high Galactic latitude with HEAO A-1
A 314 square degree region of sky at high galactic latitude was mappedin 0.5-20 keV X-rays using summed data from the HEAO A-1 experiment. 21sources are detected above a 5 sigma threshold corresponding to alimiting flux of about 0.2 UFU. This limit is at a decade intermediateto those achieved in the full-sky surveys, Uhuru, Ariel 5, and the HEAOA-2 experiment, and to those achieved in the Einstein partial-skysurveys. The HEAO A-1 detectors also complement these other instrumentsin terms of spectral response characteristics. A table of sourceintensities and positional error boxes for the 21 source detections ispresented. A graphical representation of the positional error boxes isalso presented. Identifications for 14 sources are proposed. Anumber-flux curve representing all high galactic latitude X-ray sourcesdetected with HEAO A-1 has been constructed. The number-flux curveappears to be consistent with d log N/d log S = -1.5.

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Observation and Astrometry data

Right ascension:17h38m09.30s
Aparent dimensions:0.525′ × 0.407′

Catalogs and designations:
Proper Names   (Edit)
NGC 2000.0NGC 6418

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