Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEvidence for a Black Hole and Accretion Disk in the LINER NGC 4203
85
0
0.0
(
0
)
Authors
Joseph C. Shields
Ask ChatGPT about the research
No Arabic abstract
We present spectroscopic observations from the Hubble Space Telescope that reveal for the first time the presence of a broad pedestal of Balmer-line emission in the LINER galaxy NGC 4203. The emission-line profile is suggestive of a relativistic accretion disk, and is reminiscent of double-peaked transient Balmer emission observed in a handful of other LINERs. The very broad line emission thus constitutes clear qualitative evidence for a black hole, and spatially resolved narrow-line emission in NGC 4203 can be used to constrain its mass, with M_BH less than 6 x 10^6 solar masses at 99.7% confidence. This value implies a ratio of black-hole mass to bulge mass of less than approximately 7 x 10^-4 in NGC 4203, which is less by a factor of ~3 - 9 than the mean ratio obtained for other galaxies. The availability of an independent constraint on central black-hole mass makes NGC4203 an important testbed for probing the physics of weak active galactic nuclei. Assuming M_BH near the detection limit, the ratio of observed luminosity to the Eddington luminosity is approximately 10^-4. This value is consistent with advection-dominated accretion, and hence with scenarios in which an ion torus irradiates an outer accretion disk that produces the observed double-peaked line emission. Follow-up observations will make it possible to improve the black-hole mass estimate and study variability in the nuclear emission.
rate research
Read More
We present observations of the double-peaked broad H$alpha$ profile emitted by the active nucleus of NGC 7213 using the the Gemini South Telescope in 13 epochs between 2011 September 27 and 2013 July 23. This is the first time that the double-peaked line profile of this nucleus -- typical of gas emission from the outer parts of an accretion disk surrounding a supermassive black hole (SMBH) -- is reported to vary. From the analysis of the line profiles we find two variability timescales: (1) the shortest one, between 7 and 28 days, is consistent with the light travel time between the ionizing source and the part of the disk emitting the line; and (2) a longer one of $gtrsim 3$ months corresponding to variations in the relative intensity of the blue and red sides of the profile, which can be identified with the dynamical timescale of this outer part of the the accretion disk. We modeled the line profiles as due to emission from a region between $approx$ 300 and 3000 gravitational radii of a relativistic, Keplerian accretion disk surrounding the SMBH. Superposed on the disk emissivity, the model includes an asymmetric feature in the shape of a spiral arm with a rotation period of $approx$ 21 months, which reproduces the variations in the relative intensity of the blue and red sides of the profile. Besides these variations, the $rms$ variation profile reveals the presence of another variable component in the broad line, with smaller velocity width W$_{68}$ (the width of the profile corresponding to 68$%$ of the flux) of $sim 2100$ km s$^{-1}$.
The broad-line radio galaxy 3C120 is a powerful source of both X-ray and radio emission including superluminal jet outflows. We report on our reanalysis of 160 ks of Suzaku data taken in 2006, previously examined by Kataoka et al. (2007). Spectral fits to the XIS and HXD/PIN data over a range of 0.7-45 keV reveal a well-defined iron K line complex with a narrow Ka core and relativistically broadened features consistent with emission from the inner regions of the accretion disk. Furthermore, the inner region of the disk appears to be truncated with an inner radius of r_in = 11.7^{+3.5}_{-5.2} r_g. If we assume that fluorescent iron line features terminate at the inner-most stable circular orbit (ISCO), we measure a black hole spin of a < -0.1 at a 90% confidence level. A rapidly spinning prograde black hole (a > 0.8) can be ruled out at the 99% confidence level. Alternatively, the disk may be truncated well outside of the ISCO of a rapid prograde hole. The most compelling scenario is the possibility that the inner regions of the disk were destroyed/ejected by catastrophic instabilities just prior to the time these observations were made.
The stellar kinematics of the dwarf elliptical galaxy NGC 4486B have been measured in seeing sigma_* = .22 arcsec with the Canada-France-Hawaii Telescope. Lauer et al. 1996, ApJ, 471, L79 have shown that NGC 4486B is similar to M31 in having a double nucleus. We show that it also resembles M31 in its kinematics. The velocity dispersion gradient is very steep: sigma increases from 116 +- 6 km/s at r = 2 - 6 to 281 +- 11 km/s at the center. This is much higher than expected for an elliptical galaxy of absolute magnitude M_B = -16.8: NGC 4486B is far above the scatter in the Faber-Jackson correlation between sigma and bulge luminosity. Therefore the King core mass-to-light ratio, M/L_V = 20, is unusually high compared with normal values for old stellar populations. We construct dynamical models with isotropic velocity dispersions and show that they reproduce black hole (BH) masses derived by more detailed methods. We also fit axisymmetric, three-integral models. Isotropic models imply that NGC 4486B contains a central dark object, probably a BH, of mass M_BH = 6^{+3}_{-2} x 10^8 M_sun. However, anisotropic models fit the data without a BH if the ratio of radial to azimuthal dispersions is ~ 2 at 1. Therefore this is a less strong BH detection than the ones in M31, M32, and NGC 3115. A 6 x 10^8 M_sun BH is 9 % of the mass M_bulge in stars; even if M_BH is smaller than the isotropic value, M_BH/M_bulge is likely to be unusually large. Double nuclei are a puzzle because the dynamical friction timescales for self-gravitating star clusters in orbit around each other are short. Since both M31 and NGC 4486B contain central dark objects, our results support models in which the survival of double nuclei is connected with the presence of a BH (e. g., Tremaine 1995, AJ, 110, 628).
The nucleus of the Seyfert galaxy NGC 1068 is believed to host a supermassive black hole. Evidence for the presence of a massive central object is provided by water maser emission, which displays a linear pattern in the sky, suggestive of a rotating disk. The rotating disk hypothesis is further strengthened by the declining shape of the derived rotation curve. Similar maser emission from NGC 4258 has led to a reliable estimate of the mass of the central black hole, because in this case the rotation curve is Keplerian. In the case of NGC 1068 the rotation curve traced by the water maser is non-Keplerian. In this paper we provide an interpretation of the non-Keplerian rotation in NGC 1068 by means of a self-gravitating accretion disk model. We obtain a good fit to the available data and derive a black hole mass M_{bh}=(8.0pm 0.3) 10^6M_{sun}. The resulting disk mass is comparable to the black hole mass. As an interesting by-product of our fitting procedure, we are able to estimate the viscosity parameter, which turns out to be alphaapprox 10^{-2}, in line with some theoretical expectations.
Models of jet production in black hole systems suggest that the properties of the accretion disk - such as its mass accretion rate, inner radius, and emergent magnetic field - should drive and modulate the production of relativistic jets. Stellar-mass black holes in the low/hard state are an excellent laboratory in which to study disk-jet connections, but few coordinated observations are made using spectrometers that can incisively probe the inner disk. We report on a series of 20 Suzaku observations of Cygnus X-1 made in the jet-producing low/hard state. Contemporaneous radio monitoring was done using the Arcminute MicroKelvin Array radio telescope. Two important and simple results are obtained: (1) the jet (as traced by radio flux) does not appear to be modulated by changes in the inner radius of the accretion disk; and (2) the jet is sensitive to disk properties, including its flux, temperature, and ionization. Some more complex results may reveal aspects of a coupled disk-corona-jet system. A positive correlation between the reflected X-ray flux and radio flux may represent specific support for a plasma ejection model of the corona, wherein the base of a jet produces hard X-ray emission. Within the framework of the plasma ejection model, the spectra suggest a jet base with v/c ~ 0.3, or the escape velocity for a vertical height of z ~ 20 GM/c^2 above the black hole. The detailed results of X-ray disk continuum and reflection modeling also suggest a height of z ~ 20 GM/c^2 for hard X-ray production above a black hole, with a spin in the range 0.6 < a < 0.99. This height agrees with X-ray time lags recently found in Cygnus X-1. The overall picture that emerges from this study is broadly consistent with some jet-focused models for black hole spectral energy distributions in which a relativistic plasma is accelerated at z = 10-100 GM/c^2.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
