In the 1980's some of the first systematic photometric studies established that Seyfert galaxies are variable on typical timescales of months. In some instances the luminosity, and even some of the spectral characteristics have changed dramatically over the years. In contrast, other AGN also classified as broad-line Seyferts have proved to be much more photometrically stable. The paper presents re-observations of several AGN obtained at SAAO in 2016-2017. These are used with other recent data to highlight a potential correlation between the spectral characteristics and the variability pattern. The significance of this correlation is briefly explored.
{"title":"Some things change, some don’t. An exploration of Seyfert galaxy luminosity changes over a generation","authors":"H. Winkler","doi":"10.22323/1.319.0011","DOIUrl":"https://doi.org/10.22323/1.319.0011","url":null,"abstract":"In the 1980's some of the first systematic photometric studies established that Seyfert galaxies are variable on typical timescales of months. In some instances the luminosity, and even some of the spectral characteristics have changed dramatically over the years. In contrast, other AGN also classified as broad-line Seyferts have proved to be much more photometrically stable. The paper presents re-observations of several AGN obtained at SAAO in 2016-2017. These are used with other recent data to highlight a potential correlation between the spectral characteristics and the variability pattern. The significance of this correlation is briefly explored.","PeriodicalId":366250,"journal":{"name":"Proceedings of 5th Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA2017)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128652752","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Galaxy clusters are expected to be dominated by a component of Dark Matter (DM) of unknown nature. The annihilation of DM particles in a galaxy cluster can produce relativistic electrons and gamma rays, that can be used to test the properties of the DM particles and of the cluster itself. Gravitational lensing measures provide the spatial DM distribution in a cluster, and can be used to build detailed models to estimate the contribution of DM-produced electrons to the non-thermal diffuse emission observed in some galaxy clusters. Therefore putting together the information derived from radio and gravitational lensing measures in galaxy clusters can provide important information about the properties of DM and the physics of clusters. We apply this technique to two galaxy clusters where radio and gravitational lensing measurements are available. In the Bullet cluster a contribution of the DM to the diffuse radio emission is possible because of the spectral changes visible in the overall spectrum, that suggest that more than one component can be present; to better constrain this possibility information on the spectrum of the diffuse radio emission in smaller regions of the cluster is necessary. In the Coma cluster the distribution of the DM sub-halos closely resembles the radio halo surface brightness shape, and the overall radio halo spectrum is well reproduced by a DM model for the observed properties of the magnetic field, without violating the gamma ray upper limits in the cluster; however, there are open issues, like the values of the annihilation cross section and of the substructures boosting factor. On the basis of these results, we conclude that the combination of radio and gravitational lensing studies of galaxy clusters appears to be a very promising way to obtain information about the physics of galaxy clusters and the DM properties. Present results suggest that a contribution from DM to the total diffuse radio emission can be important, but require to study in detail the spectrum of the diffuse radio emission obtained in smaller regions of the clusters, and to have good contraints on the components of baryonic origin. The application of this technique to a higher number of clusters will be important to obtain better information and solve some open issues.
{"title":"Studying the dark matter annihilation in galaxy clusters through radio and gravitational lensing measures","authors":"P. Marchegiani, S. Colafrancesco","doi":"10.22323/1.319.0006","DOIUrl":"https://doi.org/10.22323/1.319.0006","url":null,"abstract":"Galaxy clusters are expected to be dominated by a component of Dark Matter (DM) of unknown nature. The annihilation of DM particles in a galaxy cluster can produce relativistic electrons and gamma rays, that can be used to test the properties of the DM particles and of the cluster itself. Gravitational lensing measures provide the spatial DM distribution in a cluster, and can be used to build detailed models to estimate the contribution of DM-produced electrons to the non-thermal diffuse emission observed in some galaxy clusters. Therefore putting together the information derived from radio and gravitational lensing measures in galaxy clusters can provide important information about the properties of DM and the physics of clusters. \u0000We apply this technique to two galaxy clusters where radio and gravitational lensing measurements are available. In the Bullet cluster a contribution of the DM to the diffuse radio emission is possible because of the spectral changes visible in the overall spectrum, that suggest that more than one component can be present; to better constrain this possibility information on the spectrum of the diffuse radio emission in smaller regions of the cluster is necessary. In the Coma cluster the distribution of the DM sub-halos closely resembles the radio halo surface brightness shape, and the overall radio halo spectrum is well reproduced by a DM model for the observed properties of the magnetic field, without violating the gamma ray upper limits in the cluster; however, there are open issues, like the values of the annihilation cross section and of the substructures boosting factor. \u0000On the basis of these results, we conclude that the combination of radio and gravitational lensing studies of galaxy clusters appears to be a very promising way to obtain information about the physics of galaxy clusters and the DM properties. Present results suggest that a contribution from DM to the total diffuse radio emission can be important, but require to study in detail the spectrum of the diffuse radio emission obtained in smaller regions of the clusters, and to have good contraints on the components of baryonic origin. The application of this technique to a higher number of clusters will be important to obtain better information and solve some open issues.","PeriodicalId":366250,"journal":{"name":"Proceedings of 5th Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA2017)","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130348695","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We review LIGO and VIRGO detection events reported so far, as well as future prospects. We also review the prospects for gravitational wave measurements, but in lower frequency bands, from pulsar timing arrays, and from the space system LISA.
{"title":"Current status of gravitational wave observations","authors":"N. Bishop","doi":"10.22323/1.319.0001","DOIUrl":"https://doi.org/10.22323/1.319.0001","url":null,"abstract":"We review LIGO and VIRGO detection events reported so far, as well as future prospects. We also review the prospects for gravitational wave measurements, but in lower frequency bands, from pulsar timing arrays, and from the space system LISA.","PeriodicalId":366250,"journal":{"name":"Proceedings of 5th Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA2017)","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115806223","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In pursuit of understanding the early Universe and early processes occurring particularly in the Dark Ages (DA) and the Epoch of Reionization (EoR), it is vital that a suitable probe is identified. Probing these epochs will be useful in studies of the origin of first galaxies and most importantly formation of early black-holes. Over the past decade numerous probes have been proposed, with one of the most promising being the SZE-21cm, a specific form of the Sunyaev-Zeldovich effect (SZE) produced when photons of the 21cm background are inverse Compton up-scattered by electrons residing in hot plasma of cosmic structures such as galaxy clusters and active radio galaxies. The SZE-21cm is calculated in a full relativistic approach of the scattering processes of the CMB photons modified by the cosmological redshifted 21cm background in the hot intra-cluster medium of galaxy clusters capturing effects induced by relativistic corrections to this scattering and by multiple scattering effects. We apply image differencing techniques to simulated radio observations of galaxy clusters using the redshifted 21cm background, we conduct this making use of the public semi-numeric code 21cmFAST. We are able to achieve subtraction of contaminating foregrounds through pixel by pixel operations on the data retrieved from our simulated data cubes. We demonstrate that SZE-21cm can be recovered through differential observations of the 21cm background.
{"title":"Analysis of differential observations of the cosmological radio background : studying the SZE-21cm","authors":"C. Takalana, S. Colafrancesco, P. Marchegiani","doi":"10.22323/1.319.0008","DOIUrl":"https://doi.org/10.22323/1.319.0008","url":null,"abstract":"In pursuit of understanding the early Universe and early processes occurring particularly in the Dark Ages (DA) and the Epoch of Reionization (EoR), it is vital that a suitable probe is identified. Probing these epochs will be useful in studies of the origin of first galaxies and most importantly formation of early black-holes. Over the past decade numerous probes have been proposed, with one of the most promising being the SZE-21cm, a specific form of the Sunyaev-Zeldovich effect (SZE) produced when photons of the 21cm background are inverse Compton up-scattered by electrons residing in hot plasma of cosmic structures such as galaxy clusters and active radio galaxies. The SZE-21cm is calculated in a full relativistic approach of the scattering processes of the CMB photons modified by the cosmological redshifted 21cm background in the hot intra-cluster medium of galaxy clusters capturing effects induced by relativistic corrections to this scattering and by multiple scattering effects. We apply image differencing techniques to simulated radio observations of galaxy clusters using the redshifted 21cm background, we conduct this making use of the public semi-numeric code 21cmFAST. We are able to achieve subtraction of contaminating foregrounds through pixel by pixel operations on the data retrieved from our simulated data cubes. We demonstrate that SZE-21cm can be recovered through differential observations of the 21cm background.","PeriodicalId":366250,"journal":{"name":"Proceedings of 5th Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA2017)","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127164536","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Madala hypothesis was formulated to explain anomalies in LHC data from run-1. Subsequently, these anomalies have endured into run-2 and been strengthened. This makes the analysis of the proposal highly pertinent, and, since some of the properties of the model are beyond the reach of current collider data it is also important to determine alternative means of analysis. Here, we examine the consequences of WIMPs linked to the Madala hypothesis providing a dark matter candidate and annihilating in the galactic centre of the Milky-Way and the Andromeda galaxy. These targets have been observed to have similar gamma-ray spectra by Fermi-LAT and their emissions have been widely discussed in terms of dark matter annihilation in the literature. We show that, when the decay branchings of the hidden-sector mediator in the Madala hypothesis are assumed Higgs-like, the emissions of Andromeda and the Milky-Way are not compatible with both being produced by dark matter annihilation, apart from when a steeply contracted NFW profile is assumed for the halos or the WIMP has a mass above 1 TeV. Additionally, similar results are displayed for a wide variety of model independent cases
{"title":"Gamma rays and the LHC inspired dark matter","authors":"G. Beck, S. Colafrancesco","doi":"10.22323/1.319.0030","DOIUrl":"https://doi.org/10.22323/1.319.0030","url":null,"abstract":"The Madala hypothesis was formulated to explain anomalies in LHC data from run-1. Subsequently, these anomalies have endured into run-2 and been strengthened. This makes the analysis of the proposal highly pertinent, and, since some of the properties of the model are beyond the reach of current collider data it is also important to determine alternative means of analysis. Here, we examine the consequences of WIMPs linked to the Madala hypothesis providing a dark matter candidate and annihilating in the galactic centre of the Milky-Way and the Andromeda galaxy. These targets have been observed to have similar gamma-ray spectra by Fermi-LAT and their emissions have been widely discussed in terms of dark matter annihilation in the literature. \u0000We show that, when the decay branchings of the hidden-sector mediator in the Madala hypothesis are assumed Higgs-like, the emissions of Andromeda and the Milky-Way are not compatible with both being produced by dark matter annihilation, apart from when a steeply contracted NFW profile is assumed for the halos or the WIMP has a mass above 1 TeV. Additionally, similar results are displayed for a wide variety of model independent cases","PeriodicalId":366250,"journal":{"name":"Proceedings of 5th Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA2017)","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116621675","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tiaan Bezuidenhout, C. Venter, A. Seyffert, A. Harding
The Large Area Telescope aboard the Fermi spacecraft has detected more than 200 $gamma$-ray pulsars since its launch in 2008. By concurrently fitting standard geometric model light curves onto Fermi and radio data, researchers have constrained the inclination and observer angles of a number of pulsars. At first this was done by comparing observed and modelled light curves by eye, and later via statistical approaches. We fit modelled light curves of 16 pulsars to radio and $gamma$-ray data by optimising a custom test statistic that we have developed for combining light curves across the two wavebands, taking their disparate errors into account. We present geometrical constraints found using this process, and compare them with results found by eye or using other statistical methods.
{"title":"Assessment of a statistical approach towards constraining pulsar geometry via multiband light curve fitting","authors":"Tiaan Bezuidenhout, C. Venter, A. Seyffert, A. Harding","doi":"10.22323/1.319.0018","DOIUrl":"https://doi.org/10.22323/1.319.0018","url":null,"abstract":"The Large Area Telescope aboard the Fermi spacecraft has detected more than 200 $gamma$-ray pulsars \u0000since its launch in 2008. By concurrently fitting standard geometric model light curves onto Fermi \u0000and radio data, researchers have constrained the inclination and observer angles of a number of \u0000pulsars. At first this was done by comparing observed and modelled light curves by eye, and later \u0000via statistical approaches. We fit modelled light curves of 16 pulsars to radio and $gamma$-ray data by \u0000optimising a custom test statistic that we have developed for combining light curves across the \u0000two wavebands, taking their disparate errors into account. We present geometrical constraints \u0000found using this process, and compare them with results found by eye or using other statistical \u0000methods.","PeriodicalId":366250,"journal":{"name":"Proceedings of 5th Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA2017)","volume":"65 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126841763","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Colliding-wind binaries have long been thought to accelerate particles in the shocked wind. Recent detection of a hard $gamma$-ray spectrum by the Fermi-LAT from $eta$ Carinae hints to the presence of a hadronic component dominating in the $approx 10$-300 GeV range, presumably from protons accelerated in the shocks and interacting ($pp$) with particles in the wind. Neutrinos are naturally produced in $pp$ interactions and emitted together with $gamma$ rays. Detection of this multi-messenger signal can be very powerful to probe characteristics of the hadronic $gamma$-ray component as well as particle accleration. We show that detection of high-energy neutrinos from $eta$ Carinae by neutrino telescopes can probe the maximum shock-accelerated proton energy in the $gtrsim 0.1$ PeV range.
{"title":"Eta Carinae: A multi-messenger source","authors":"S. Razzaque","doi":"10.22323/1.319.0039","DOIUrl":"https://doi.org/10.22323/1.319.0039","url":null,"abstract":"Colliding-wind binaries have long been thought to accelerate particles in the shocked wind. Recent detection of a hard $gamma$-ray spectrum by the Fermi-LAT from $eta$ Carinae hints to the presence of a hadronic component dominating in the $approx 10$-300 GeV range, presumably from protons accelerated in the shocks and interacting ($pp$) with particles in the wind. Neutrinos are naturally produced in $pp$ interactions and emitted together with $gamma$ rays. Detection of this multi-messenger signal can be very powerful to probe characteristics of the hadronic $gamma$-ray component as well as particle accleration. We show that detection of high-energy neutrinos from $eta$ Carinae by neutrino telescopes can probe the maximum shock-accelerated proton energy in the $gtrsim 0.1$ PeV range.","PeriodicalId":366250,"journal":{"name":"Proceedings of 5th Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA2017)","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133501236","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Electromagnetic radiation is known to be associated with certain gravitational waves events, i.e. the collision of binary neutron stars. Establishing this connection is non-trivial. However, if electromagnetic counterparts could be produced by directly converting gravitons into photons, then a simple smoking gun test exists linking the two events. This model uses the general and conversion mechanism discussed by Raffelt and Stodolsky. Furthermore, because this mechanism is generic to the symmetries of general relativity and the standard model and because it assumes a quantised gravitational field, we may probe both the existence of the graviton and the scale at which quantum gravity effects (and thus very high-energy phenomena) become relevant using simple low-energy experiments.
{"title":"Using Gravitational Wave Observations to Probe Quantum Gravity","authors":"J. Tarrant, S. Colafrancesco","doi":"10.22323/1.319.0027","DOIUrl":"https://doi.org/10.22323/1.319.0027","url":null,"abstract":"Electromagnetic radiation is known to be associated with certain gravitational waves events, i.e. the collision of binary neutron stars. Establishing this connection is non-trivial. However, if electromagnetic counterparts could be produced by directly converting gravitons into photons, then a simple smoking gun test exists linking the two events. This model uses the general and conversion mechanism discussed by Raffelt and Stodolsky. Furthermore, because this mechanism is generic to the symmetries of general relativity and the standard model and because it assumes a quantised gravitational field, we may probe both the existence of the graviton and the scale at which quantum gravity effects (and thus very high-energy phenomena) become relevant using simple low-energy experiments.","PeriodicalId":366250,"journal":{"name":"Proceedings of 5th Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA2017)","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115764410","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fermi Large Area Telescope data reveal an excess of GeV gamma rays from the direction of the Galactic Center and bulge. Several explanations have been proposed for this excess including an unresolved population of millisecond pulsars (MSPs) and self-annihilating dark matter. It has been claimed that a key discriminant for or against the MSP explanation can be extracted from the properties of the luminosity function describing this source population. Specifically, is the luminosity function of the putative MSPs in the Galactic Center consistent with that characterizing the resolved MSPs in the Galactic disk? To investigate this we have used a Bayesian Markov Chain Monte Carlo to evaluate the posterior distribution of the parameters of the MSP luminosity function describing both resolved MSPs and the Galactic Center excess. At variance with some other claims, our analysis reveals that, within current uncertainties, both data sets can be well fit with the same luminosity function.
{"title":"Resolved Millisecond Pulsars are Consistent with the Galactic Center Excess (Invited Talk)","authors":"C. Gordon, H. Ploeg, R. Crocker, O. Macias","doi":"10.22323/1.319.0020","DOIUrl":"https://doi.org/10.22323/1.319.0020","url":null,"abstract":"Fermi Large Area Telescope data reveal an excess of GeV gamma rays from the direction of the Galactic Center and bulge. Several explanations have been proposed for this excess including an unresolved population of millisecond pulsars (MSPs) and self-annihilating dark matter. It has been claimed that a key discriminant for or against the MSP explanation can be extracted from the properties of the luminosity function describing this source population. Specifically, is the luminosity function of the putative MSPs in the Galactic Center consistent with that characterizing the resolved MSPs in the Galactic disk? To investigate this we have used a Bayesian Markov Chain Monte Carlo to evaluate the posterior distribution of the parameters of the MSP luminosity function describing both resolved MSPs and the Galactic Center excess. At variance with some other claims, our analysis reveals that, within current uncertainties, both data sets can be well fit with the same luminosity function.","PeriodicalId":366250,"journal":{"name":"Proceedings of 5th Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA2017)","volume":"76 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126162048","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Most radio-loud AGN are associated with jet-like structures that can extend over hundreds of kiloparsecs. These jets are a source of variable emission that covers most of the electromagnetic spectrum. The dominant component of the emission is produced through non-thermal processes like synchrotron radiation. In this study we investigate the contribution of hydrodynamic instabilities to the long term variability observed within these sources. This is done by undertaking 3D hydrodynamic simulations of a relativistic jet that is evolved with time. The simulation is constructed with the hydrodynamic code PLUTO and consists of a rectangular grid, spanning $256times256times512$ cells. The environment contains a uniform background medium into which less dense jet material is injected, at a Lorentz factor of 10. We have developed a post-processing code in order to determine the synchrotron emission that will be produced by this environment and calculate intensity maps at arbitrary viewing angles with respect to the hydrodynamic environment. In this code we assume that the emission is produced by non-thermal electrons in a power-law distribution and take into account geometric and relativistic effects. The resulting intensity maps show a similar large scale morphology to that of FR II type AGN, containing a central relativistic beam surrounded by lobe structures. The results also show the formation of time dependent structures, such as knots and blobs, due to hydrodynamic instabilities. It was found that these structures may cause a variation of up to $10%$ in the total intensity.
{"title":"Hydrodynamic instabilities as a source of variability in AGN jets.","authors":"I. V. D. Westhuizen, B. V. Soelen, P. Meintjes","doi":"10.22323/1.319.0012","DOIUrl":"https://doi.org/10.22323/1.319.0012","url":null,"abstract":"Most radio-loud AGN are associated with jet-like structures that can extend over hundreds of kiloparsecs. These jets are a source of variable emission that covers most of the electromagnetic spectrum. The dominant component of the emission is produced through non-thermal processes like synchrotron radiation. In this study we investigate the contribution of hydrodynamic instabilities to the long term variability observed within these sources. This is done by undertaking 3D hydrodynamic simulations of a relativistic jet that is evolved with time. The simulation is constructed with the hydrodynamic code PLUTO and consists of a rectangular grid, spanning $256times256times512$ cells. The environment contains a uniform background medium into which less dense jet material is injected, at a Lorentz factor of 10. We have developed a post-processing code in order to determine the synchrotron emission that will be produced by this environment and calculate intensity maps at arbitrary viewing angles with respect to the hydrodynamic environment. In this code we assume that the emission is produced by non-thermal electrons in a power-law distribution and take into account geometric and relativistic effects. The resulting intensity maps show a similar large scale morphology to that of FR II type AGN, containing a central relativistic beam surrounded by lobe structures. The results also show the formation of time dependent structures, such as knots and blobs, due to hydrodynamic instabilities. It was found that these structures may cause a variation of up to $10%$ in the total intensity.","PeriodicalId":366250,"journal":{"name":"Proceedings of 5th Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA2017)","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116851487","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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