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1.
We consider the problem of strange-star (SS) radiation. The bare quark SS surface and electrons on the stellar surface generate an electric field that is strong enough for electron-positron pairs to be produced from a vacuum at a nonzero temperature. The luminosity in pairs is assumed to be within ?1049 erg s?1 from a surface with a characteristic radius of 10 km. We consider the energy transfer from pairs to photons by taking into account the well-studied reactions between e, e +, γ and obtain a change in the photon spectrum with luminosity. Our analysis is restricted to the spherically symmetric case. The magnetic field is disregarded. To solve the problem, we developed a new numerical method of integrating the Boltzmann kinetic equations for pairs and photons. This method is used to calculate the problem up to a luminosity of 1042 erg s?1 This region is difficult to investigate when the optical path for pairs or photons is considerably larger than unity but the two optical depths are not simultaneously much larger than unity (when hydrodynamics with heat conduction is applicable). It turns out that the mean photon energy is approximately equal to $\bar \in _\gamma \approx m_e c^2$ (the annihilation line for pairs) at a modest luminosity, L?1×1037 erg s?1, and decreases to ≈210 keV at L?1038 erg s?1. Hydrodynamic estimates point to an increase in the mean energy $\bar \in _\gamma$ to 1 MeV as the luminosity further increases to L?1049 erg s?1. Our calculations may prove to be useful in interpreting soft gamma repeaters (SGRs) and are of methodological interest.  相似文献   

2.
The distributionsf(z) of the redshifts for active galaxies (Seyfert galaxies, radio galaxies, and quasars) have been studied. Some statistically-significant maxima and minima are observed in the distributionsf(z) for these objects. The significance of peaks and gaps increases for the brighter objects, for which the samples are more complete. The clustering of the Seyfert galaxies is significantly different from that of the nearby normal galaxies. The distributionf(z) for the radio galaxies is similar to the analogous distribution for the galaxy clusters. Three of the five peaks in the distributionf(z) for the radio quasars may be caused by the selection effects. Two peaks within the intervalsz (0.5, 0.7) and (1.0, 1.1) are probably real. The corresponding scales of the QSO clustering along the line-of-sight are about 100h –1 Mpc (h is the Hubble constant in the units of 75 km s–1 Mpc–1). The possibility of some global quasi-periodical cycles for the processes of activity is discussed. The period of a cycle for the Seyfert and radio galaxies is about 1×108 years that corresponds to the distances of about 30h –1 Mpc between the shells.  相似文献   

3.
We investigate the relationship between the present-day optical luminosity function of galaxies and the X-ray luminosity function of Seyfert 1s to determine the fraction of galaxies that host Seyfert 1 nuclei and their Eddington ratios. The local type 1 active galactic nuclei (AGN) X-ray luminosity function is well reproduced if ∼1 per cent of all galaxies are type 1 Seyferts which have Eddington ratios of ∼10−3. However, in such a model the X-ray luminosity function is completely dominated by AGN in E and S0 galaxies, contrary to the observed mix of Seyfert host galaxies. To obtain a plausible mix of AGN host galaxy morphologies requires that the most massive black holes in E and S0 galaxies accrete with lower Eddington ratios, or have a lower incidence of Seyfert activity, than the central black holes of later-type galaxies.  相似文献   

4.
We examine the XMM X-ray spectrum of the low-ionisation nuclear emission-line region (LINER)-AGN NGC 7213, which is best fit with a power law, Kα emission lines from Fe i, Fe xxv and Fe xxvi and a soft X-ray collisionally ionised thermal plasma with kT = 0.18+0.03−0.01 keV. We find a luminosity of 7× 10−4 LEdd, and a lack of soft X-ray excess emission, suggesting a truncated accretion disc. NGC 7213 has intermediate X-ray spectral properties, between those of the weak AGN found in the LINER M 81 and higher luminosity Seyfert galaxies. This supports the notion of a continuous sequence of X-ray properties from the Galactic Centre through LINER galaxies to Seyferts, likely determined by the amount of material available for accretion in the central regions. This work is based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).  相似文献   

5.
In 1968–2005 different observers (mainly, one of the authors—V.M. Lyuty) performed numerous measurements of luminosity of the nucleus of the Seyfert galaxy NGC 4151. It is shown that (a) luminosity of the object pulsated over 38 years with a period of 160.0106(7) min coinciding, within the error limits, with the well-known period P 0 = 160.0101(2) min of the enigmatic “solar” pulsations, and (b) when registering oscillations of luminosity of NGC 4151 nucleus with the P 0 period, time moments of observations must be reduced to the earth instead of the sun, i.e., to the reference frame of the observer. The coherent P 0 oscillation is characterized, therefore, by invariability of both frequency and phase with respect to redshift z and the earth’s orbital motion, respectively. From these results it, thus, follows that the coherent P 0 oscillation seems to be of a true cosmological origin. The P 0 period itself might represent a course of the “cosmic clock” related to the existence of an absolute time of the Universe in Newton’s comprehension.  相似文献   

6.
The rapid and seemingly random fluctuations in X-ray luminosity of Seyfert galaxies provided early support for the standard model in which Seyferts are powered by a supermassive black hole fed from an accretion disc. However, since EXOSAT there has been little opportunity to advance our understanding of the most rapid X-ray variability. Observations with XMM-Newton have changed this. We discuss some recent results obtained from XMM-Newton observations of Seyfert 1 galaxies. Particular attention will be given to the remarkable similarity found between the timing properties of Seyferts and black hole X-ray binaries, including the power spectrum and the cross spectrum (time delays and coherence), and their implications for the physical processes at work in Seyferts.  相似文献   

7.
Galaxies of redshiftz ≲ 1000 km s−1 are investigated. In the South Galactic Hemisphere there are two large concentrations of these galaxies. One is in the direction of the centre of the Local Group, roughly aligned with M 31 and M 33. The other concentration is centred almost 80 degrees away on the sky and involves the next nearest galaxies to the Local Group, NGC 55, NGC 300 and NGC 253. The large scale and isolation of these concentrations, and the continuity of their redshifts require that they are all galaxies at the same, relatively close distance of the brightest group members. The fainter members of the group have higher redshifts, mimicking to some extent a Hubble relation. But if they are all at the same average distance the higher redshifts must be due to a cause other than velocity. The redshifts of the galaxies in the central areas of these groups all obey a quantization interval of δcz0 = 72.4 kms−1. This is the same quantization found by William Tifft, and later by others, in all physical groups and pairs which have been tested. The quantization discovered here, however, extends over a larger interval in redshift than heretofore encountered. The majority of redshifts used in the present analysis are accurate to ± 8 km s−1. The deviation of those redshifts from multiples of 72.4 km s-1 averages ±8.2 km s−1. The astonishing result, however, is that for those redshifts which are known more accurately, the deviation from modulo 72.4 drops to a value between 3 and 4 km s−1! The amount of relative velocity allowed these galaxies is therefore implied to be less than this extremely small value.  相似文献   

8.
High-resolution Chandra and XMM-Newton X-ray spectroscopic studies of stellar and supermassive black holes have revealed that these phenomenologically different systems share many common physical characteristics. The observed outflows in the micro-quasar GRS 1915+105, the Seyfert 1 galaxy MCG–6-30-15 and the Seyfert 2 galaxy IRAS 18325-5926 are the focus of this proceeding.  相似文献   

9.
On the basis of a radio index-surface brightness diagram recently published, the luminosity function and the luminosity diameter function are obtained. The uncertainties due to the incompleteness of the sample are of the same order as the statistical uncertainties. The luminosity function differs considerably from a simple power law and supports the distinction of two populations. The density of the weak population (P<1035 W Hz−1 ster−1 at 1400 MHz) follows nearly a power law in P and increases towards small diameters at least down to I kpc. The density of the strong population (the high luminosity and small diameter part of which is occupied by the quasars) has a maximum between 1025 and 1028 W Hz−1 ster−1 and around 100 kpc. A strong evolution effect is clearly present and is in a good agreement with the models obtained from the log N-log S counts.  相似文献   

10.
We present the latest results from a multi-epoch timing and spectral study of the Transient Anomalous X-ray Pulsar XTE J1810–197. We have acquired seven observations of this pulsar with the Newton X-ray Multi-mirror Mission (XMM-Newton) over the course of two and a half years, to follow the spectral evolution as the source fades from outburst. The spectrum is arguably best characterized by a two-temperature blackbody whose luminosities are decreasing exponentially with τ 1=870 d and τ 2=280 d, respectively. The temperatures of these components are currently cooling at a rate of 22% per year from a nearly constant value recorded at earlier epochs of kT 1=0.25 keV and kT 2=0.67 keV, respectively. The new data show that the temperature T 1 and luminosity of that component have nearly returned to their historic quiescent levels and that its pulsed fraction, which has steadily decreased with time, is now consistent with the previous lack of detected pulsations in quiescence. We also summarize the detections of radio emission from XTE J1810–197, the first confirmed for any AXP. We consider possible models for the emission geometry and mechanisms of XTE J1810–197. XMM-Newton is an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. This research is supported by XMM-Newton grant NNG05GJ61G and NASA ADP grant ADP04-0059-0024.  相似文献   

11.
A statistical analysis of 87 optical selected quasars and 30 type I Seyfert galaxies is carried out in this paper. Using a quasi-Monte-Carlo method, the relation between the 2 keV monochromatic X-ray luminosity 1X and ∼2500A monochromatic ultraviolet luminosity is calculated and the result is: 1x ∝ 10bp, b = 0.93 ± 0.18 when the accretion rate ⪡ cr, and b = 0.28 ± 0.18 when > cr.A detailed semi-quantitative physical discussion of our results ruled out many available radiative mechanisms. We conclude that the most plausible dominant radiation in the band from 2500A UV to 2 keV soft X-ray is non-thermal synchrotron radiation. We discuss that when the accretion rate is growing, most of the X radiation is dragged into the black hole (the dragging effect). This is the main reason why the X-ray luminosity increases much more slowly with M than does the UV luminosity.Finally, in the context of pure luminosity evolution, we have obtained that 1x evolves more slowly than does 10p.  相似文献   

12.
We analyse the scaling of the X-ray power density spectra with the mass of the black hole in the examples of Cyg X-1 and the Seyfert 1 galaxy NGC 5548. We show that the high-frequency tail of the power density spectrum can be successfully used for the determination of the black hole mass. We determine the masses of the black holes in six broad-line Seyfert 1 galaxies, five narrow-line Seyfert 1 galaxies and two quasi-stellar objects (QSOs) using the available power density spectra. The proposed scaling is clearly appropriate for other Seyfert galaxies and QSOs. In all but one of the normal Seyferts, the resulting luminosity to Eddington luminosity ratio is smaller than 0.15, with the source MCG -6-15-30 being an exception. The applicability of the same scaling to a narrow-line Seyfert 1 is less clear and there may be a systematic shift between the power spectra of NLS1 and S1 galaxies of the same mass, leading to underestimation of the black hole mass. However, both the method based on variability and the method based on spectral fitting show that those galaxies have relatively low masses and a high luminosity to Eddington luminosity ratio, supporting the view of those objects as analogues of galactic sources in their high, soft or very high state, based on the overall spectral shape. The bulge masses of their host galaxies are similar to that of normal Seyfert galaxies, so they do not follow the black hole mass–bulge mass relation for Seyfert galaxies, being evolutionarily less advanced, as suggested by Mathur. The bulge mass–black hole mass relation in our sample is consistent with being linear, with the black hole to bulge ratio ∼0.03 per cent, similar to Wandel and Laor for low-mass objects, but significantly shifted from the relation of Magorrian et al. and McLure & Dunlop.  相似文献   

13.
The relationships between the monochromatic luminosity of Seyfert galaxies at frequencies of 0.408, 1.49, and 4.85 GHz and the integrated luminosity in the far infrared (IR) range are investigated. At all radio frequencies they are linear and equally close. Some Seyfert galaxies, of morphological types S0/a, E, and S0, have a far higher radio luminosity than Seyfert spiral galaxies with the same IR luminosity. Most of them are found to have compact central radio components. Seyfert spiral galaxies follow the same relationship between radio and IR emission as non-Seyfert spiral galaxies. The relationships between radio and IR luminosity for the individual groups of galaxies of spectral types Sy 1-Sy 1.5 and Sy 1.8-Sy 2 are also linear.  相似文献   

14.
Sinusoidal variations in bothV - andB-bands were detected in some flare stars of the UV Ceti type outside of flares. This detection has confirmed the light variation detection in Johnson'sV -band in EV Lac at quiet-state luminosity by Pettersen (1980) with a cyclic period equals about 4 . d 378 and an amplitude of about 0 . m 07. An interpretation of these short cyclic periods is that they are due to intensity modulations from a photospheric spot group as a result of stellar equatorial rotations. A short period of 14 days with an amplitude of 0 . m 099 was detected inB-band in AD Leo. For the two flare stars, BD+55° 1823 and DO Cep in bothV- andB-bands, cyclic periods of more than 3 days and less than 17 days with amplitudes more than 0 . m 090 and less than 0 . m 250 have been registered. A significant contribution has been found in the flare star EV Lac in bothV- andB-bands at its quiescent-state luminosity where the detected cyclic periods are agreed with that which was detected by Pettersen (1980) in the same flare star in Johnson'sV-band, about 4 days. Furthermore, we found the same cyclic period in the colour index,B - V (about 4 days) which strengthens starspot phenomenon. This colour index period could not be detected by Pettersen (1980).  相似文献   

15.
New and existing photometry for the G0 Ia supergiant HD 18391 is analyzed in order to confirm the nature of the variability previously detected in the star, which lies off the hot edge of the Cepheid instability strip. Small‐amplitude variability at a level of δV = 0.016 ± 0.002 is indicated, with a period of P = 123d.04 ± 0d.06. A weaker second signal may be present at P = 177d.84 ± 0d.18 with δV = 0.007 ± 0.002, likely corresponding to fundamental mode pulsation if the primary signal represents overtone pulsation (123.04/177.84 = 0.69). The star, with a spectroscopic reddening of EB–V = 1.02 ± 0.003, is associated with heavily‐reddened B‐type stars in its immediate vicinity that appear to be outlying members of an anonymous young cluster centered ∼10′ to the west and 1661 ± 73 pc distant. The cluster has nuclear and coronal radii of rn = 3.5′ and Rc = 14′, respectively, while the parameters for HD 18391 derived from membership in the cluster with its outlying B stars are consistent with those implied by its Cepheid‐like pulsation, provided that it follows the semi‐period‐luminosity relation expected of such objects. Its inferred luminosity as a cluster member is MV = –7.76 ± 0.10, its age (9 ± 1) × 106 years, and its evolutionary mass ∼19 M⊙. HD 18391 is not a classical Cepheid, yet it follows the Cepheid period‐luminosity relation closely, much like another Cepheid impostor, V810 Cen (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

16.
A major legacy of the EGRET experiment aboard the Compton Gamma-Ray Observatory (CGRO) is the detection of a large number of unidentified Gamma-ray sources. Out of the 271 EGRET sources are 170 not identified yet [Hartman et al. ApJS (123) (1999) 79]. To provide additional information on these unidentified EGRET sources, we derived simultaneous MeV fluxes or flux limits for each source by analyzing the contemporaneous COMPTEL data. Then we compare these MeV fluxes to the extrapolations of the published EGRET spectra. Our results can be grouped into 4 categories [Zhang et al. A&A (421) (2004) 983]: (1) non-constraining upper limits (∼120 sources), (2) hints (> 2 sigma) or detections with consistent MeV fluxes (∼16 sources), (3) enhanced MeV emission (2 sources), and (4) constraining MeV flux limits, requiring a spectral break (∼22 sources). In summary, for about 40 of the unidentified EGRET sources we can provide supplementary spectral information in the neighboring gamma-ray band, which – together with other source parameters – might provide clues to the underlying source nature.  相似文献   

17.
The computational algorithm to determine the the proper motions of Zirconium stars on the basis of catalogues “Carte du Ciel” and on the recent photographic observations carried out with the 70cm Abastumani meniscus telescope is presented. It allowed to determine the proper motions of 288 stars in the region around α Per with a rms error of ± 0,004 arcsec/yr. Applying the method proper motions of 74 Zirconium stars and 146 control stars have been obtained. The error of proper motions obtained for the North Zone (δ > −2°) 109 AGK3 control stars is ± 0.006 arcsec/yr. On the basis of proper motins absolute magnitudes were separately calculated for the MCLPZS and LASZS. For the MCLPZS the average absolute visual magnitude at maximum, corresponding to the mean period of P = 350 days, equals −3ϕm.9. For the LASZS the mean absolute visual magnitude, corresponding to the apparent median ones equals −1ϕm.9. Low luminosity (Mv = −1ϕmϕ9) Zirconium stars escape rather far (at a distance of up to 2 kpc) to the South from the Galactic plane into the region l ∼ 240 – 260°, where its assumed to be a connection with the Large Magellanic Cloud (LMC) begins to appear. Low luminosity Zirconium stars are weakly correlated with position of the Galaxy spiral arms. The MCLPZS show a somewhat other distribution.  相似文献   

18.
Summary. This paper reviews the physical state of stars and Interstellar Matter in the Galactic Bulge (radius kpc from the dynamical center of the Galaxy), in the Nuclear Bulge (kpc) and in the Sgr A Radio and GMC Complex, i.e. the central \,pc of our Galaxy. The Galactic Bulge is devoid of cold Interstellar Matter and consists mainly of old stars, while the Nuclear Bulge accounts for of the mass of all of the Interstellar Matter in the Galaxy. A similar ratio holds for the formation rate of medium and high mass stars in Bulge and Disk. The metal abundance of the Interstellar Matter in the Galactic Bulge is found to be . The H-to-CO conversion factors to be applied to molecular gas in the Central Region are by factors 3 (Arimoto et al. 1996) to 10 (Sodroski et al. 1995) lower than in the solar vicinity. Hence, most H masses derived for the Central Region appear to be considerably overestimated. The Nuclear Bulge is pervaded by a thermal plasma (K) which is responsible for the diffuse free-free emission. Lyman continuum photon and dust IR luminosity of the Nuclear Bulge again account for of the respective total luminosities of the Galaxy. Magnetic fields in the Nuclear Bulge are strong (up to mG) as compared with the Galactic Disk (a few tens of G). The field lines are oriented parallel to the galactic plane inside giant molecular clouds and perpendicular to the plane in the intercloud medium. The compact source Sgr A* is close to or at the dynamical center of the Galaxy. Its radio spectrum with a high frequency cut-off at GHz, a low frequency turnover at GHz and a flux density dependence in between can be explained by synchrotron emission from quasi-monoenergetic relativistic electrons. Due to an extinction between Sun and Galactic Center corresponding to , an intrinsic weakness of this source in the near infrared, and a strong background emission from warm dust there are only upper limits available for the flux density of Sgr A* in the far, mid and near infrared and X-ray regime. The size of Sgr A* in the radio regime is cm, its dereddened K-band flux density is mJy, its luminosity has upper limits of (if radiation comes from an Accretion Disk) and (if black-body radiation from an object with a single temperature of K is assumed). If anyone of the soft X-ray sources detected by ROSAT actually coincides with Sgr A*, its X-ray luminosity would be less than a few . With a dark mass of Sgr A* is the best candidate for a starving black hole, although there are no observational indications for the presence of a (Standard) Accretion Disk. While the radio/IR spectrum of Sgr A* is purely nonthermal, the spectrum integrated over the central parsec resembles that of a Seyfert galaxy. Sgr A* is embedded in the Hii region Sgr A West with part of the ionized gas forming a minispiral. Sgr A West is surrounded by the Circum Nuclear Disk, an irregular shaped assembly of molecular gas which extends from pc and rotates around the Galactic Center with an estimated dynamical time scale of \,yr. The total luminosity of of the central parsec is due to the radiation of early-type stars of which have now been directly identified as luminous blue supergiants. It is still debated, however, if these stars can also account for all of the ionization of Sgr A West. In addition, the central parsec contains red giants, AGB stars, and a few super giants of which the brightest are now identified by direct imaging. These stars – together with a few million low mass main sequence stars – account for the bulk of the 2.2\,m emission. The spatial distributions of the three stellar populations in the central pc are remarkably different. Sgr A* is – along the line-of-sight – presumably located close to the center of the Hii region Sgr A West, which in turn is located in front of the extended (pc) synchrotron source Sgr A East, which appears to be the remnant of a gigantic explosion (of the order of the energy of a single supernova explosion) which took place yr ago inside the GMC Sgr A East Core. X-ray observations show within pc a pervasive hot (keV) plasma of expansion age of yr. Both phenomena – as well as the formation of the Circum Nuclear Disk – may have the same origin. Influx of material is observed within the Nuclear Bulge on all distance scales. In the Nuclear Bulge (pc) as well as in the Circum Nuclear Disk (pc) inflow towards the Galactic Center occurs primarily in the galactic plane and amounts to a few . The accretion rate into the central Black Hole, deduced from the luminosity of Sgr A*, however, appears to be lower by at least five orders of magnitude (assuming standard disk accretion). But in an equilibrium state only part of the infalling mass which is not accreted by the Black Hole can be consumed by star formation. A mass inflow rate varying with time is a more natural explanation. Comparing the physical state of the Center of our Galaxy with that of Active Galactic Nuclei derived from observations and modelling, we find that most of the basic characteristics of an AGN are also present in the Galactic Center. Lacking are, however, both the evidence for a standard Accretion Disk and a hard UV spectrum with accompanying high excitation emission lines in the Galactic Center which are characteristic for AGN. The luminosity of the central parsec, , amounts to only of the total luminosity of the Galaxy of . Seen from a distance of M31 (kpc) with an angular resolution of (corresponding to a linear size of pc) the Center of our Galaxy would appear as a mildly active nucleus with some starburst activity and would probably be classified as a weak Seyfert galaxy. The synchrotron spectrum of Sgr A*, however, would be completely masked by reprocessed stellar light (i.e. free-free and dust emission). Received: October 21, 1996  相似文献   

19.
A number of studies have shown that the visibility of scattered broad emission lines in Seyfert 2 galaxies is strongly dependent on the IRAS     flux ratio, where those Seyfert 2 galaxies with 'warm' IRAS colours show polarized broad line emission. It is now clear that this effect is owing to the increasing dominance of the galactic rather than the active galactic nucleus (AGN) emission at 60 μm in less-luminous 'cool' Seyfert 2 galaxies. However, we present evidence that the 25-μm emission is a good measure of the AGN luminosity for most Seyfert 2 galaxies. Using this result, we show that the visibility of scattered broad line emission has a dependence on the AGN luminosity. The observations can be interpreted self-consistently if the scaleheight of the scattering zone varies with central source luminosity whilst the scaleheight of the obscuring torus is approximately constant.  相似文献   

20.
We use optical and infrared imaging data of a complete hard X-ray selected sample of AGN to investigate the host galaxies of nearby Seyfert 1 nuclei. We disentangle the emission due to the unresolved point source and the resolved host galaxy by means of luminosity profile fitting. The stellar colours in the nucleus are redder inB — V andV — K than in normal spiral bulges or current stellar evolutionary models, probably due to dust obscuration.J — H colour is quite normal butH — K usually very red, probably indicating a large contribution from reradiating hot dust to the IR colours. No significant difference in IR colours oi the stellar component is found with respect to a comparison sample of Liners and starbursts, except that the reradiating dust in Seyferts tends to be hotter and lie closer to the nucleus.B — V colour gets slightly bluer towards the nucleus, whereasV — K andJ — K have red gradients.B — V andJ — K gradients are not correlated and are likely to be caused by different mechanisms. There is a clear correlation between the AGN and host luminosity. Finally, we present optical colour ratio maps of two Seyfert nuclei, NGC 3227 and NGC 7469. The blue, ringlike or elongated structure in the maps and its correspondence with molecular CO geometry is interpreted as evidence for circumnuclear star formation in these AGN.  相似文献   

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