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Is Every One LINER Dense at Its Core? a X Is Every One LINER Dense at Its Core? A X-Ray Spectroscopy Study of LINERs as Observed by XMM-Newton Adam Andrews (920310) [email protected] Department of Physics Royal Institute of Technology (KTH) Supervisor: Serena Falocco November 22, 2017 Typeset in LATEX ISRN KTH/FYS/{{17:68{{SE ISSN 0280-316X TRITA-FYS 2017:68 ©Adam Andrews, 2017 Abstract Active Galactic Nuclei (AGN) emit high luminosity in nearly all wavelength bands; they have a characteristic X-ray spectrum and can be modelled as accreting Super Massive Black Holes (SMBH). Low-Ionization Nuclear Emission-line Regions (LINERs) are an- other type of galactic nuclei. The aim of this project is to study the X-ray spectra of two LINERs (NGC 1052 and NGC 1961) in order to find any evidence of AGN presence. Data from the XMM-Newton is reduced and processed, utilizing xspec to select and fit models applied to the data, in order to test their statistical significance. The results show that NGC 1052 exhibits clear AGN features in the X-ray band, including a power-law, clear Fe-emission line, reflected emission and variability, as well as starburst presence. The NGC 1961 data displays a power-law and starburst emission; the time span of the observations denies us the possibility of testing for variability. The temperature and the photon index of NGC 1052 are consistent with the values in the literature, as well as our findings of variability. In NGC 1961, we find clear evidence for a hot plasma and pri- mary emission, and also the possibility of another plasma structure, which is supported by other studies on the object. Improvements and further investigations are discussed, mainly focused on expanding the data sets and using this project as a stepping stone for further research. Contents 1 Introduction and Theory 2 1.1 Aim ................................................ 2 1.2 History of HE Astrophysics and Background . 2 1.3 AGNs and the Unified Model . 3 1.3.1 Type I and Type II . 4 1.3.2 Radio Loud and Radio Quiet . 5 1.4 X-Ray Spectra of AGNs . 6 1.5 The LINER-model, NGC 1052 and NGC 1961 . 9 2 Method and Instrumentation 13 2.1 Instrumentation and Software . 13 2.2 Data Reduction Procedure . 15 2.3 Quality of the Data . 16 2.4 Data Analysis . 17 2.5 Model Selection . 19 2.5.1 NGC 1052 . 19 2.5.2 NGC 1961 . 21 3 Processed Data and Results 22 3.1 Data Extraction Procedure . 22 3.2 Spectral Data Plots . 22 3.3 Spectral Fitting . 24 3.3.1 NGC1052 . 24 3.3.2 NGC1961 . 27 3.4 Contour Plots . 29 4 Discussion and Conclusion 32 4.1 NGC 1052 . 32 4.2 NGC 1961 . 34 4.3 Variability . 35 4.4 Summary . 35 5 Evaluation and Extensions 37 5.1 Strengths . 37 5.2 Improvements . 37 5.3 Other Possible Investigations . 38 5.4 Future Work . 39 6 Acknowledgments 40 7 Appendix 43 7.1 Images of Plates . 43 Bibliography 44 1 Chapter 1 Introduction and Theory 1.1 Aim The aim of this study is to investigate the X-ray spectra of the two LINERs NGC 1052 and NGC 1961. By studying this range in the electromagnetic spectrum, we wish to apply theoretical models to the data to test for AGN presence: power-law emission, soft excess, Compton reflection, broad and narrow iron lines and variability. In addition, we search for any signs of starburst activity and host galaxy emission. 1.2 History of HE Astrophysics and Background Although astronomy has existed since the dawn of mankind, high-energy astrophysics was not possible until approximately 50 years ago. This is mainly due to the fact that the atmosphere absorbs most X-rays, and in order to observe non-terrestrial high-energy photons, instruments would be required to be placed above the atmosphere. The first mission to successfully detect extrasolar X-rays was the OSO-3 satellite, launched in 1967 by NASA. OSO-3 was able to detect the strong X-ray source of Scorpius X-1 [63]. In order to circumvent the absorption of high-energy photons by the atmosphere, the project demonstrated that new information could be attained by high-altitude detectors [61]. As a result of this expedition, the 1970s witnessed several groundbreaking research projects aimed at observing the X-ray sky of the universe. More specifically, instead of using rockets to lift scientific equipment to a sufficient altitude, satellites were used to carry these X-ray detectors. Projects included Uhuru, Ariel-5, SAS-3, OSO-8, and HEAO-1, which together greatly advanced X-ray astrophysics and lifted the area into mainstream astronomy. It was hypothesized around this time that most of the X-ray sources were neutron star binaries, with \normal" stars accreting onto a neutron star and thus producing X-ray radiation. These systems were dubbed \X-ray binaries", and the mass of the heavier object could be studied and calculated. A few percent of galactic centra contained X-ray sources as well, which were called Active Galactic Nuclei. It is now known that these AGNs and some of the X-ray binaries contain black holes as their central engine [61]. Current projects aiming at studying and understanding X-ray sources throughout the universe include Chandra X-ray Observatory (CXO, launched in 1999), Suzaku (2005), X-ray Multi-Mirror Mission (XMM-Newton) (1999), as well as NUclear Spectroscopic 2 Telescopic ARray (NuSTAR, 2012). As this thesis will use data from the XMM-Newton Science Archive, it will not consider the other projects as much [61]. Figure 1.1: The XMM-Newton (Source: NASA) 1.3 AGNs and the Unified Model As a result of the study of astrophysical objects in X-ray spectra, new ways to explore the universe emerged. Since X-rays are linked to very hot or energetic processes, mechanisms close to extremely compact objects were viewed in a new light. Also, X-ray radiation allowed physicists to reach farther out into the universe, making never-before-seen objects observable. Furthermore, X-rays have an intrinsic ability to penetrate many materials, allowing us to probe closer to the sources [19]. Typically, the main action behind X-ray production is accretion, thus compact objects can be studied, especially in their inner regions, with X-ray spectroscopy [77]. In addition, these processes allow us to understand specifically one type of object, namely Active Galactic Nuclei (AGNs). Usually, AGNs are said to consist of a galaxy core containing a SMBH (> 105M ) with the constraint on the Eddington ratio LAGN = 0:5, LEdd where LAGN is the bolometric luminosity. Moreover, AGNs usually include a mixture of several structure components. These include an accretion disk, a hot cloud of plasma surrounding the accretion disk (known as the hot corona), high velocity gas clouds known as the Broad-Line Region (BLR), a dusty torus, lower velocity gas clouds known as the Narrow-Line Region (NLR), as well as a central jet. Figure 1.2 shows an AGN and its system consisting of the aforementioned components [26]. 3 Figure 1.2: The structure of an AGN (Source: NASA) There is no single definitive observational feature of AGN, but rather a mixture of traits. These include radio continuum emission, optical continuum and line emissions (narrow and broad), X-ray continuum and X-ray line emissions. The continuum emissions are typically emitted from the accretion disk, the hot corona and the jet. We will not further develop the non-X-ray features of AGNs in this report, but rather refer to Krolik and his summary [77]. Due to these general traits of the spectrum, a plethora of categories have emerged to handle all combinations of observational characteristics available. In broad terms, AGNs can be organized as being Type I, Type II, radio-loud or radio-quiet. A Type I AGN has broad and narrow optical lines while a Type II AGN has only narrow optical lines. Radio-loud implies a high ratio of fluxes in radio to optical emission, while radio-quiet has a larger flux in the optical range than radio. Additionally, a Unified Model has been proposed in order to organize all these variations under one parameter. We will see that all AGNs can be explained as variations in a single variable, namely the orientation of the accretion disk [56] [26] [55]. 1.3.1 Type I and Type II Through the observational evidence of (optical) broad line emissions, we characterize AGNs as either Type I or Type II. When discussing the structure, we designated the BLR and the NLR as Keplerian velocity gas clouds and low velocity gas clouds. Basi- cally, Keplerian velocities broaden the optical emission lines, while the relatively narrow emission lines emanate from the NLR. This is because the BLR is closer to the SMBH, thus experiencing a much stronger gravitational force. Important to realize, the reason we can express this difference via the Unified Model as mere orientation differences, is due to the possibility of the BLR being blocked by the dusty torus. If the torus lies in the line of sight between the observer and the BLR, we cannot possibly detect the broadened optical lines directly. However, in some cases, the broadened optical lines are detected via polarized light. This indicates that photons have been scattered after leaving the BLR, and these galaxies are thus defined as Type II AGNs. The broader emission lines in the optical spectra are used to discriminate between Type I AGNs and Type II AGNs. The difference between Type I and Type II AGNs can be clearly displayed in the optical band.
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