30 research outputs found
A Transition Mass for Black Holes to Show Broad Emission Lines
Although the supermassive (AGN) and stellar mass (BHBs) black holes have many properties in common, the broad emission lines (BELs) are exclusively signatures of the active galactic nuclei (AGN). Based on the detection of these lines from Sloan Digital Sky Survey (SDSS) data bases, there seems to be no AGN with mass MBH ≲ 105 M⊙. In this paper, we investigate if such low-mass black holes are really non-existent or they are undetected because the BELs in them are not produced efficiently. Using the ionizing spectral energy distribution for a wide range of black hole mass, 10–109 M⊙, spanning black hole X-ray binaries (BHBs) to AGN, we calculate the equivalent widths (EWs) of ultraviolet and optical lines Lyα 1216 Å, Hβ 4861 Å, C IV 1549 Å and Mg II 2798 Å. The LOC (locally optimally emitting cloud) model has been used to describe the broad emission-line region (BELR) for the calculations. We find that the hardening of the SED shape with decreasing mass do not decrease the BEL EWs. However, finite size of the BELR, as measured by the line widths, which is controlled by the mass of the black hole, regulates the production of these emission lines. There seems to be a peak in the EWs of the emission lines for typical AGN black holes of ∼108 M⊙, below which the lines become intrinsically fainter with a sharp fall-off below ∼106 M⊙. This may be the cause of the absence of low-mass AGN in SDSS
The Influence of Soft Spectral Components on the Structure and Stability of Warm Absorbers in Active Galactic Nuclei
The radiation from the central regions of active galactic nuclei, including that from the accretion disc surrounding the black hole, is likely to peak in the extreme-ultraviolet ∼13–100 eV. However, due to Galactic absorption, we are limited to constrain the physical properties, i.e. the black hole mass and the accretion rate, from what observations we have below ∼10 eV or above ∼100 eV. In this paper, we predict the thermal and ionization states of warm absorbers as a function of the shape of the unobservable continuum. In particular we model an accretion disc at kTin∼ 10 eV and a soft excess at kTse∼ 150 eV. The warm absorber, which is the highly ionized gas along the line of sight to the continuum, shows signatures in the ∼0.3–2 keV energy range consisting of numerous absorption lines and edges of various ions, some of the prominent ones being H- and He-like oxygen, neon, magnesium and silicon. We find that the properties of the warm absorber are significantly influenced by the changes in the temperature of the accretion disc, as well as by the strength of the soft excess, as they affect the optical depth particularly for iron and oxygen. These trends may help develop a method of characterizing the shape of the unobservable continuum and the occurrence of warm absorbers
The evolution of GX 339-4 in the low-hard state as seen by NuSTAR and Swift
We analyze eleven NuSTAR and Swift observations of the black hole X-ray
binary GX 339-4 in the hard state, six of which were taken during the end of
the 2015 outburst, five during a failed outburst in 2013. These observations
cover luminosities from 0.5%-5% of the Eddington luminosity. Implementing the
most recent version of the reflection model relxillCp, we perform simultaneous
spectral fits on both datasets to track the evolution of the properties in the
accretion disk including the inner edge radius, the ionization, and temperature
of the thermal emission. We also constrain the photon index and electron
temperature of the primary source (the "corona"). We find the disk becomes more
truncated when the luminosity decreases, and observe a maximum truncation
radius of . We also explore a self-consistent model under the framework
of coronal Comptonization, and find consistent results regarding the disk
truncation in the 2015 data, providing a more physical preferred fit for the
2013 observations.Comment: 15 pages, 8 figures, 6 tables, accepted for publication in The
Astrophysical Journa
Dielectronic recombination and stability of warm gas in AGN
Understanding the thermal equilibrium (stability) curve may offer insights
into the nature of the warm absorbers often found in active galactic nuclei.
Its shape is determined by factors like the spectrum of the ionizing continuum
and the chemical composition of the gas. We find that the stability curves
obtained under the same set of the above mentioned physical factors, but using
recently derived dielectronic recombination rates, give significantly different
results, especially in the regions corresponding to warm absorbers, leading to
different physical predictions. Using the current rates we find a larger
probability of having thermally stable warm absorber at 10^5 \kel than
previous predictions and also a greater possibility for its multiphase nature.
the results obtained with the current dielectronic recombination rate
coefficients are more reliable because the warm absorber models along the
stability curve have computed coefficient values, whereas previous calculations
relied on guessed averages for the same due to lack of available data.Comment: 5 pages, 3 figures, Accepted for publication in MNRAS Letters. The
definitive version is available at
http://www3.interscience.wiley.com/cgi-bin/hom