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Register a new userA NuSTAR census of coronal parameters in Seyfert galaxies
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We discuss the results on the hot corona parameters of Active Galactic Nuclei that have been recently measured with NuSTAR. The values taken from the literature of a sample of nineteen bright Seyfert galaxies are analysed. Aims. The aim of this work is to look for correlations between coronal parameters, such as the photon index and cutoff energy (when a phenomenological model is adopted) or the optical depth and temperature (when a Comptonization model is used), with other parameters of the systems like the black hole mass or the Eddington ratio. We analysed the coronal parameters of the nineteen unobscured, bright Seyfert galaxies that are present in the Swift-BAT 70 months catalogue and that have been observed by NuSTAR, alone or simultaneously with others X-rays observatories such as Swift, Suzaku or XMM-Newton. We found an anti-correlation with a significance level > 98% between the coronal optical depth and the coronal temperature of our sample. On the other hand, no correlation between the above parameters and the black hole mass, the accretion rate and the intrinsic spectral slope of the sources is found.
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Narrow line Seyfert 1 (NLSy1) galaxies constitute a class of active galactic nuclei characterized by the full width at half maximum (FWHM) of the H$beta$ broad emission line < 2000 km/s and the flux ratio of [O III] to H$beta$ < 3. Their properties are not well understood since only a few NLSy1 galaxies were known earlier. We have studied various properties of NLSy1 galaxies using an enlarged sample and compared them with the conventional broad-line Seyfert 1 (BLSy1) galaxies. Both the sample of sources have z $le$ 0.8 and their optical spectra from SDSS-DR12 that are used to derive various physical parameters have a median signal to noise (S/N) ratio >10 per pixel. Strong correlations between the H$beta$ and H$alpha$ emission lines are found both in the FWHM and flux. The nuclear continuum luminosity is found to be strongly correlated with the luminosity of H$beta$, H$alpha$ and [O III] emission lines. The black hole mass in NLSy1 galaxies is lower compared to their broad line counterparts. Compared to BLSy1 galaxies, NLSy1 galaxies have a stronger FeII emission and a higher Eddington ratio that place them in the extreme upper right corner of the $R_{4570}$ - $xi_{Edd}$ diagram. The distribution of the radio-loudness parameter (R) in NLSy1 galaxies drops rapidly at R > 10 compared to the BLSy1 galaxies that have powerful radio jets. The soft X-ray photon index in NLSy1 galaxies is on average higher (2.9 $pm$ 0.9) than BLSy1 galaxies (2.4 $pm$ 0.8). It is anti-correlated with the H$beta$ width but correlated with the Fe II strength. NLSy1 galaxies on average have a lower amplitude of optical variability compared to their broad lines counterparts. These results suggest Eddington ratio as the main parameter that drives optical variability in these sources.
The Active Galactic Nuclei (AGN) produce copious amounts of X-rays through the corona that is the hot gas that lies close to the accretion disk. The temperature of the corona can be accurately determined by the cut-off signature in the X-ray spectrum. Owing to the large temperatures of the corona, observations well above 10 keV are necessary. Here, we explore the NuSTAR observations of 118 Gehrels/Swift selected Seyfert 1 AGN. We model the spectrum using a single power-law with an exponential cut-off modified by neutral and ionised absorption as well as a reflection component. We find secure spectral cut-off estimates in 62 sources while for the remaining ones we derive only lower limits. The mean value is 103 keV with a skewed distribution towards large energies with large dispersion. When we consider the lower limits using survival analysis techniques, the mean cut-off energy becomes significantly larger, about 200 keV. Because of various limitations (e.g. limited spectral passband, photon statistics, model degeneracies) we perform extensive simulations to explore the underlying spectral cut-off distribution. We find that an intrinsic spectral cut-off distribution which has a Maxwell-Boltzmann shape with a mean value in the range of 160 - 200 keV can reproduce sufficiently well the observations. Finally, our spectral analysis places very stringent constraints on both the photon index (Gamma=1.77+/-0.01) as well as on the reflection component (R=0.69+/-0.04) of the Seyfert 1 population. From the values of the spectral cut-off and the photon-index we deduce that the mean optical depth of the AGN corona is approximately tau=1.82+/-0.14 and its mean temperature approximately kT=65+/-10 keV.
We present measurement of the cut-off energy, a proxy for the temperature of the corona in the nuclear continuum of the Seyfert 1 galaxy 3C 120 using $sim$120 ks of observation from ${it NuSTAR}$. The quality broad band spectrum from 3$-$79 keV has enabled us to measure the Compton reflection component (R) and to constrain the temperature of the coronal plasma. Fitting one of the advanced Comptonization models, ${it compPS}$ to the observed broad band spectrum we derived the kinetic temperature of the electrons in the corona to be $kT_e = 25 pm 2$ keV with Compton ${it y}$ parameter of $y = 2.2 pm 0.1$ for a slab geometry and $kT_e = 26_{-0}^{+2}$ keV with a $y$ of $2.99_{-0.18}^{+2.99}$ assuming a spherical geometry. We noticed excess emission from $sim$10$-$35 keV arising due to Compton reflection and a broad Fe $Kalpha$ line at 6.43 keV with an equivalent width of 60 $pm$ 5 eV. The variations in count rates in the soft (3$-$10 keV) band is found to be more compared to the hard (10$-$79 keV) band with mean fractional variability amplitudes of 0.065$pm$0.002 and 0.052$pm$0.003 for the soft and hard bands respectively. 3C 120 is known to have a strong jet, however, our results indicate that it is either dormant or its contribution if any to the X-ray emission is negligible during the epoch of ${it NuSTAR}$ observation.
The fundamental nature and extent of the coronal line region (CLR), which may serve as a vital tracer for Active Galactic Nucleus (AGN) activity, remain unresolved. Previous studies suggest that the CLR is produced by AGN-driven outflows and occupies a distinct region between the broad line region and the narrow line region, which places it tens to hundreds of parsecs from the galactic center. Here, we investigate 10 coronal line (CL; ionization potential $ge$ 100 eV) emitting galaxies from the SDSS-IV MaNGA catalog with emission from one or more CLs detected at $ge$ $5{sigma}$ above the continuum in at least 10 spaxels - the largest such MaNGA catalog. We find that the CLR is far more extended, reaching out to 1.3 - 23 kpc from the galactic center. We cross-match our sample of 10 CL galaxies with the largest existing MaNGA AGN catalog and identify 7 in it; two of the remaining three are galaxy mergers and the final one is an AGN candidate. Further, we measure the average CLR electron temperatures to range between 12,331 K - 22,530 K, slightly above the typical threshold for pure AGN photoionization ($sim$ 20,000 K) and indicative of shocks (e.g., merger-induced or from supernova remnants) in the CLR. We reason that ionizing photons emitted by the central continuum source (i.e. AGN photoionization) primarily generate the CLs, and that energetic shocks are an additional ionization mechanism that likely produce the most extended CLRs we measure.
Nearby galaxy surveys have long classified X-ray binaries (XRBs) by the mass category of their donor stars (high-mass and low-mass). The NuSTAR observatory, which provides imaging data at E $>10$ keV, has enabled the classification of extragalactic XRBs by their compact object type: neutron star (NS) or black hole (BH). We analyzed NuSTAR/Chandra/XMM-Newton observations from a NuSTAR-selected sample of 12 galaxies within 5 Mpc having stellar masses ($M_{star}$) $10^{7-11}$ $M_{odot}$ and star formation rates (SFR) $approx0.01-15$ $M_{odot}$ yr$^{-1}$. We detect 128 NuSTAR sources to a sensitivity of $approx10^{38}$ erg s$^{-1}$. Using NuSTAR color-intensity and color-color diagrams we classify 43 of these sources as candidate NS and 47 as candidate BH. We further subdivide BH by accretion states (soft, intermediate, and hard) and NS by weak (Z/Atoll) and strong (accreting pulsar) magnetic field. Using 8 normal (Milky Way-type) galaxies in the sample, we confirm the relation between SFR and galaxy X-ray point source luminosity in the 4-25 and 12-25 keV energy bands. We also constrain galaxy X-ray point source luminosity using the relation $L_{rm{X}}=alpha M_{star}+betatext{SFR}$, finding agreement with previous work. The XLF of all sources in the 4-25 and 12-25 keV energy bands matches with the $alpha=1.6$ slope for high-mass XRBs. We find that NS XLFs suggest a decline beginning at the Eddington limit for a 1.4 $M_{odot}$ NS, whereas the BH fraction shows an approximate monotonic increase in the 4-25 and 12-25keV energy bands. We calculate the overall ratio of BH to NS to be $approx1$ for 4-25 keV and $approx2$ for 12-25 keV.
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