摘要:

A 50.4 ksec PSPC image of the nearby spiral galaxy M33 reveals 35 sources with 15 arcmin of the nucleus brighter than 1.3×1036ergs s−1. The bright sources that had been detected within Einstein in the same region are still visible. Several ROSAT sources are time variable, but the brightest source, the nuclear source, appears constant over the duration of our observations.The bulk of the sources in the galaxy are associated with Pop I tracers, and both the northern and the southern spiral arms of M33 are readily apparent in the image. There is additional diffuse (or unresolved source) emission throughout the inner portions of M33. There are 12 sources in the image that lie within 30 arcsec of optically‐identified supernova remnants in M33. The spectra of these sources are soft compared to other sources of comparable brightness, and therefore it is likely that most of these sources are supernova remnants. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46681

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have examined the archival ROSAT Position Sensitive Proportional Counter and the High Resolution Imager images of the galaxy M101 to study the x−ray properties of its giant H iiregions. All five giant H iiregions, NGC 5447, 5455, 5461, 5462 and 5471, show x‐ray emission. By observing their basic properties, such as size, hardness ratio and estimated luminosity, and by comparisons with better‐known regions in the LMC, we suggest possible mechanisms for the sources of the x‐ray emission. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46682

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Our 35 ksec ROSAT HRI observation of M33 reveals 37 X‐ray sources stronger than about 2.3&sgr;. Eight of the sources are coincident with supernova remnants, four are coincident with giant HII regions, and three are coincident with HI holes. M33 X‐7 is a compact accreting eclipsing binary, similar to binary X‐ray sources detected in the Galaxy. Our ROSAT data confirm the binary interpretation and allow us to measure the period to an accuracy of 0.001%. The nuclear source, M33 X‐8, is not found to be variable in the ROSAT HRI observations, although it varied as much as 40% betweenEinsteinHRI observations. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46683

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Multi−wavelength observations have been made of the interacting galaxy system Arp 270 (=NGC3395/96). A comparison is made between recently obtained ROSAT PSPC observations and optical and near‐infrared images of the system, as well as 21 cm HI observations made at the VLA. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46684

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The elliptical galaxy NGC1407 is the brightest member of the Eridanus group of galaxies. A 22,000 sec ROSAT PSPC pointing centered on NGC 1407 shows that it is embedded in a flattened distribution of gas (with axial ratio 2:1) extending to at least 120 kpc (25′) from the galaxy along the major axis (adopting the surface‐brightness‐fluctuation distance to NGC 1407 to 16.4 Mpc). The hot gas extends 11–22 times further than the optical effective radius of NGC1407, so it is likely that at least some of the gas belongs to the group rather than NGC1407, so it is likely that at least some of the gas belongs to the group rather than NGC1407 itself. Outside a central cooler region, indicative of cooling flow, the gas is roughly isothermal (perhaps declinining slowly outward) with temperature of ∼1 keV. The mass‐to‐light ratio isM/LB≊70 within 70 kpc of the galaxy, which implies that ∼85% of the enclosed mass is dark.

ISSN:0094-243X    

DOI:10.1063/1.46685

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We present our preliminary analysis of a 24 ksec PSPC observation of the NGC 3607 group of galaxies. There is no evidence of extended group emission more than 50 kpc from the brightest galaxy in the group. The x‐ray emission from the vicinity of NGC 3607 is asymmetric and is dominated by a 0.4 keV plasma, but shows evidence of an additional hard component. Possible origins for the spatial structure and the hard spectral component are discussed. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46686

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

This Seyfert galaxy has a helically twisted, bisymmetric nuclear jet that flows mostly in the gas disk. Our ROSAT results are: 1) The jet dominates the soft x‐ray emission. After correcting pointing‐errors of up to ±6″ in our 25 ksec HRL exposure, we find that the SE jet branch is spatially unresolved in width along much of its 2″5length. The NW branch is more diffuse, and the extensive radio ‘‘plateaus’’ also emit x‐rays. 2) The jet spectrum from the 6.5 ksec PSPC archival exposure is noisy, but is best fit as a Raymond‐Smith plasma withkT=0.30 keV, logNH≊20.0 cm−2, and luminosity 1.6×1040ergs s−1between 0.1 and 2.4 keV.Gas at this temperature can arise from shock speeds of 350–500 km s−1(depending on preshock excitation), and may have been entrained as the jet scrapes along molecular clouds. The gaseous excitation and radial velocities from our published optical, emission‐line spectra of the jet are consistent with these shock speeds if gas flows along helical paths. The PSPC spectral fit is poor above 0.6 keV. An additional hard component is required that peaks near the nucleus. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46687

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Although cooling flows make the centers of rich clusters inherently interesting, most of a cluster’s gas mass is found at large radii. Moreover, this gas may still be infalling and may not be in equilibrium. Therefore, a study of this extended gas through its X‐ray emission may provide answers to such problems as the distribution of total mass within a cluster, the relationship between clusters and superclusters, and the intereaction between the cluster gas and its member galaxies.Four pointed observations were made of the Perseus cluster using the ROSAT PSPC. Each observation was located 50 arcmin (1.6 Mpc at Ho=50 km/s/Mpc) from the cluster center (NGC 1275), and the observations are spaced evenly in azimuth. We report here on the construction of a mosaic of images from these observations. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46688

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We present PSPC observations of two rich Abell clusters in the Shapley Supercluster, richest known concentration of galaxies in the local Universe. We measure temperature and density profiles for the X‐ray emitting intracluster gas in each cluster. We also highlight details of our data reduction process which we have found to be useful, such as the use of high resolution energy‐dependent exposure maps generated by recently‐released IDL routines. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46689

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Using the surface brightness distribution from the ROSAT PSPC and the Ginga broad‐beam temperature, we derive a range of acceptable potentials for the cluster A1689. The faint optical arcs observed in A1689 lie at radii which are too large to be produced by simple smooth potentials, consistent with the X‐ray data and with plausible elongation along the line‐of‐sight. They thus reflect superposition or substructure.Although the x‐ray observations show no evidence of substructure, the cluster velocity dispersion is too large to be due to a single cluster with the gas temperature and mass measured through the X‐ray observations. The galaxy radial velocity data then suggest the superposition of one or more subclusters directly along the line‐of‐sight to the primary A1689 cluster.The cooling flow region in the cluster core is well resolved by the PSPC. Spectral fitting of the inner 1′ shows emission from gas cooler than the broad‐beam temperature, and consistent with a massive cooling flow of ≊500M⊙yr−1, in agreement with the mass deposition rate found from a deprojection analysis of the imaging data. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46690

出版商:AIP    

年代:1994

数据来源: AIP