The Extremes of AGN Variability Komossa, S.; Grupe, D.; Schartel, N. ...
Proceedings of the International Astronomical Union,
09/2016, Letnik:
12, Številka:
S324
Journal Article
Recenzirano
We present results from our ongoing monitoring programs aimed at identifying and understanding Active Galactic Nuclei (AGN) in extreme flux and spectral states. Observations of AGN in extreme states ...can reveal the nature of the inner accretion flow, the physics of matter under strong gravity, and they provide insight on the properties of ionized absorbers and outflows launched near supermassive black holes (SMBHs). We present new results from our long-term monitoring of IC 3599, WPVS007, and Mrk 335, multi-wavelength follow-ups of the newly identified changing-look AGN HE 1136–2304, and UV–X-ray follow-ups of the binary SMBH candidate OJ 287 after its 2015 optical maximum, now in a new optical-X-ray–high-state.
ABSTRACT In this work, we present the results of a detailed X-ray spectral analysis of the brightest active galactic nuclei (AGNs) detected in the XMM–Newton 1.75 Ms Ultra Narrow Deep Field. We ...analysed 23 AGNs that have a luminosity range of $\sim 10^{42} {\!-\!} 10^{46}\, \rm {erg}\, \rm {s}^{-1}$ in the $2 {\!-\!} 10\, \rm {keV}$ energy band, redshifts up to 2.66, and $\sim 10\,000$ X-ray photon counts in the $0.3{ \!-\! }10\, \rm {keV}$ energy band. Our analysis confirms the ‘Iwasawa–Taniguchi effect,’ an anticorrelation between the X-ray luminosity ($L_x$) and the Fe–k$\alpha$ equivalent width (${\rm EW}_{\rm Fe}$) possibly associated with the decreasing of the torus covering factor as the AGN luminosity increases. We investigated the relationship among black hole mass ($M_{\rm BH}$), $L_x$, and X-ray variability, quantified by the Normalized Excess Variance ($\sigma ^2_{\rm rms}$). Our analysis suggest an anticorrelation in both $M_{\rm BH} - \sigma ^2_{\rm rms}$ and $L_x- \sigma ^2_{\rm rms}$ relations. The first is described as $\sigma ^2_{\rm rms} \propto M^{-0.26 \pm 0.05}_{\rm BH}$, while the second presents a similar trend with $\sigma ^2_{\rm rms} \propto L_{x}^{-0.31 \pm 0.04}$. These results support the idea that the luminosity–variability anticorrelation is a byproduct of an intrinsic relationship between the BH mass and the X-ray variability, through the size of the emitting region. Finally, we found a strong correlation among the Eddington ratio ($\lambda _{\rm Edd}$), the hard X-ray photon index ($\Gamma$), and the illumination factor $\log (A)$, which is related to the ratio between the number of Compton scattered photons and the number of seed photons. The $\log (\lambda _{\rm Edd})-\Gamma -\log (A)$ plane could arise naturally from the connection between the accretion flow and the hot corona.
We present a detailed analysis of the Chandra High Energy Transmission Grating Spectrometer (HETGS) and XMM-Newton high-resolution spectra of the bright Seyfert 1 galaxy, Mrk 290.
The Chandra HETGS ...spectra reveal complex absorption features that can be best described by a combination of three ionized absorbers. The outflow velocities of these warm absorbers are about 450 km s−1, consistent with the three absorption components found in a previous far-UV study. The ionizing continuum of Mrk 290 fluctuated by a factor of 1.4 during Chandra observations on a time-scale of 17 d. Using the response in opacity of the three absorbers to this fluctuation, we put a lower limit on the distance from the ionizing source of 0.9 pc for the medium ionized absorber and an upper limit on a distance of 2.5 pc for the lowest ionized absorber. The three ionization components lie on the stable branch of the thermal equilibrium curve, indicating roughly the same gas pressure. Therefore, the thermal wind from the torus is most likely the origin of warm absorbing gas in Mrk 290.
During the XMM-Newton observation, the ionizing luminosity was 50 per cent lower compared to that in the Chandra observation. The Reflection Grating Spectrometer spectrum is well fitted by a two-phase warm absorber, with several additional absorption lines attributed to a Galactic high-velocity cloud, complex C. Neither the ionization parameter ξ nor the column density N
H of the two absorbing components varied significantly, compared to the results from Chandra observations. The outflow velocities of both components were 1260 km s−1. We suggest that an entirely new warm absorber from the torus passed through our line of sight.
Assuming the torus wind model, the estimated mass outflow rate is ∼0.1 M⊙ per year while the nuclear accretion rate is ∼0.04 M⊙ per year. The O vii and Ne ix forbidden lines are the most prominent soft X-ray emission lines, with a mean redshift of 700 km s−1 relative to the systematic velocity. There seems to be no relation between emission lines and warm absorbers.
The Crab Nebula is the brightest TeV gamma-ray source in the sky and has been used for the past 25 years as a reference source in TeV astronomy, for calibration and verification of new TeV ...instruments. The High Altitude Water Cherenkov Observatory (HAWC), completed in early 2015, has been used to observe the Crab Nebula at high significance across nearly the full spectrum of energies to which HAWC is sensitive. HAWC is unique for its wide field of view, nearly 2 sr at any instant, and its high-energy reach, up to 100 TeV. HAWC's sensitivity improves with the gamma-ray energy. Above ∼1 TeV the sensitivity is driven by the best background rejection and angular resolution ever achieved for a wide-field ground array. We present a time-integrated analysis of the Crab using 507 live days of HAWC data from 2014 November to 2016 June. The spectrum of the Crab is fit to a function of the form . The data is well fitted with values of = 2.63 0.03, β = 0.15 0.03, and when E0 is fixed at 7 TeV and the fit applies between 1 and 37 TeV. Study of the systematic errors in this HAWC measurement is discussed and estimated to be 50% in the photon flux between 1 and 37 TeV. Confirmation of the Crab flux serves to establish the HAWC instrument's sensitivity for surveys of the sky. The HAWC all-sky survey will be the deepest survey of the northern sky ever conducted in the multi-TeV band.
Context. Markarian 509 and Markarian 841 are two bright Seyfert 1 galaxies with X-ray spectra characterised by a strong soft excess and a variable Fe Kα line, as shown by several X-ray observatories ...in the past. Aims. We report an analysis and modelling of new Suzaku observations of these sources, taken between April and November, 2006, for Mrk 509, and between January and July, 2007, for Mrk 841, for a total exposure time of ≈ 100 ks each. Data from XIS and HXD/PIN instruments, going from 0.5 to 60 keV, represent the highest spectral resolution simultaneous broad-band X-ray spectrum for these objects, and provide the strongest constraints yet on the origin of the soft excess emission. Methods. We fitted the broad-band spectrum of both sources with a double Comptonisation model, adding neutral reflection from distant material and a two-phase warm absorber. We then studied the two competing models developed to explain the soft excess in terms of atomic processes: a blurred ionised disc reflection and an ionised absorption by a high velocity material. Results. When fitting the data in the 3–10 keV range with a power law spectrum, and extrapolating this result to low energies, a soft excess is clearly observed below 2 keV, although its strength is weak compared to previous observations of both sources. A moderate hard excess is seen at energies higher than 10 keV, together with a neutral Fe Kα narrow emission line at E0 ≈ 6.4 keV and a broad Fe emission line. For Mrk 509, the broad Fe emission line is required in all the three physical models to ensure a good fit to the data: this finding suggests that the blurred reflection model correctly describes the soft excess, but that it underestimates the broad Fe emission line. For the smeared absorption model, this suggests instead that the continuum spectrum absorbed by the outflowing gas should indeed contain a reflected component. For Mrk 841, all three models that we tested provide a good fit to the data, and we cannot rule out any of them. A broad emission line is required in the double Comptonisation and smeared absorption models, while the blurred reflection model consistently fits the broad-band spectrum, without adding any extra emission-line component.
SS 433 is a binary system containing a supergiant star that is overflowing its Roche lobe with matter accreting onto a compact object (either a black hole or neutron star)
. Two jets of ionized ...matter with a bulk velocity of approximately 0.26c (where c is the speed of light in vacuum) extend from the binary, perpendicular to the line of sight, and terminate inside W50, a supernova remnant that is being distorted by the jets
. SS 433 differs from other microquasars (small-scale versions of quasars that are present within our own Galaxy) in that the accretion is believed to be super-Eddington
, and the luminosity of the system is about 10
ergs per second
. The lobes of W50 in which the jets terminate, about 40 parsecs from the central source, are expected to accelerate charged particles, and indeed radio and X-ray emission consistent with electron synchrotron emission in a magnetic field have been observed
. At higher energies (greater than 100 gigaelectronvolts), the particle fluxes of γ-rays from X-ray hotspots around SS 433 have been reported as flux upper limits
. In this energy regime, it has been unclear whether the emission is dominated by electrons that are interacting with photons from the cosmic microwave background through inverse-Compton scattering or by protons that are interacting with the ambient gas. Here we report teraelectronvolt γ-ray observations of the SS 433/W50 system that spatially resolve the lobes. The teraelectronvolt emission is localized to structures in the lobes, far from the centre of the system where the jets are formed. We have measured photon energies of at least 25 teraelectronvolts, and these are certainly not Doppler-boosted, because of the viewing geometry. We conclude that the emission-from radio to teraelectronvolt energies-is consistent with a single population of electrons with energies extending to at least hundreds of teraelectronvolts in a magnetic field of about 16 microgauss.
We present TeV gamma-ray observations of the Crab Nebula, the standard reference source in ground-based gamma-ray astronomy, using data from the High Altitude Water Cherenkov (HAWC) Gamma-Ray ...Observatory. In this analysis we use two independent energy estimation methods that utilize extensive air shower variables such as the core position, shower angle, and shower lateral energy distribution. In contrast, the previously published HAWC energy spectrum roughly estimated the shower energy with only the number of photomultipliers triggered. This new methodology yields a much-improved energy resolution over the previous analysis and extends HAWC's ability to accurately measure gamma-ray energies well beyond 100 TeV. The energy spectrum of the Crab Nebula is well fit to a log-parabola shape with emission up to at least 100 TeV. For the first estimator, a ground parameter that utilizes fits to the lateral distribution function to measure the charge density 40 m from the shower axis, the best-fit values are (TeV cm2 s)−1, , and . For the second estimator, a neural network that uses the charge distribution in annuli around the core and other variables, these values are (TeV cm2 s)−1, , and β = 0.06 0.01 0.02. The first set of uncertainties is statistical; the second set is systematic. Both methods yield compatible results. These measurements are the highest-energy observation of a gamma-ray source to date.
Context.Mrk 841 is a bright Seyfert 1 galaxy known to harbor a strong soft excess and a variable Kα iron line. Historical UV, X and γ-rays observations show clear variation of its spectrum in flux ...and in shape on a monthly time scale. Aims.Mrk 841 has been observed during 3 different periods (January 2001, January 2005 and July 2005) by XMM-Newton for a total cumulated exposure time of ~108 ks. We present in this paper a broad band spectral analysis of the complete EPIC-pn data sets. These are the best observations so far for the study of the soft excess and iron line complex in this source. Methods.We use different methods of data analysis including model-independent methods (spectral ratios, rms, ...) as well as model fitting. We were able to test two different models for the soft excess, a relativistically blurred photoionized reflection (REF model) and a relativistically smeared ionized absorption (ABS model). The continuum is modeled by a simple cut-off power law and we also add a neutral reflection. Results.These observations confirm the presence of a soft excess and iron line and reveal extreme and puzzling spectral and temporal behaviors. The 0.5–3 keV soft X-ray flux decreases by a factor 3 between 2001 and 2005 and the line shape appears to be a mixture of broad and narrow components, the former being variable on small (ks) time scale while the later is consistent with being constant. The 2–10 keV spectrum also hardens between 2001 and 2005. We succeed in describing this complex broad-band 0.5–10 keV spectral variability using either REF or ABS to fit the soft excess. Both models give statistically equivalent results even including simultaneous BeppoSAX data up to 200 keV. Both models are consistent with the presence of remote reflection characterized by a constant narrow component in the data. However they differ in the presence of a broad line component present in REF but not needed in ABS. Consequently the physical interpretation of the line profile variability is quite different, resulting from the variability of the broad line component in REF and from the variability of the absorbing medium in ABS. This study also reveals the sporadic presence of relativistically redshifted narrow iron lines, one of them being detected at 4.8 keV in the EPIC-pn instruments at more than 98.5% confidence level. If interpreted as the blue horn of a relativistically distorted neutral iron line, the large redshift implies the presence of a Kerr black hole.
The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a wide field of view observatory sensitive to 500 GeV-100 TeV gamma-rays and cosmic rays. It can also perform diverse indirect ...searches for dark matter annihilation and decay. Among the most promising targets for the indirect detection of dark matter are dwarf spheroidal galaxies. These objects are expected to have few astrophysical sources of gamma-rays but high dark matter content, making them ideal candidates for an indirect dark matter detection with gamma-rays. Here we present individual limits on the annihilation cross section and decay lifetime for 15 dwarf spheroidal galaxies within the field of view, as well as their combined limit. These are the first limits on the annihilation cross section and decay lifetime using data collected with HAWC. We also present the HAWC flux upper limits of the 15 dwarf spheroidal galaxies in half-decade energy bins.
We present the detection of very-high-energy gamma-ray emission above 100 TeV from HAWC J2227+610 with the High-Altitude Water Cherenov Gamma-Ray Observatory (HAWC) observatory. Combining our ...observations with previously published results by the Very Energetic Radiation Imaging Telescope Array System (VERTIAS), we interpret the gamma-ray emission from HAWC J2227+610 as emission from protons with a lower limit in their cutoff energy of 800 TeV. The most likely source of the protons is the associated supernova remnant G106.3+2.7, making it a good candidate for a Galactic PeVatron. However, a purely leptonic origin of the observed emission cannot be excluded at this time.
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