70 results on '"Megan Argo"'
Search Results
2. Trialling the use of generative adversarial networks for efficient identification of radio frequency interference
- Author
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Jacob Brooks and Megan Argo
- Published
- 2023
3. When aliens land
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Steven Gulberg, Steve Miller, Megan Argo, Jarita Holbrook, Alejandro Lopez, Javier Mejuto, and Annette Lee
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Geophysics ,Geochemistry and Petrology ,Astronomy and Astrophysics - Abstract
Lead author Steven Gullberg reports with colleagues on a new joint initiative to acknowledge and respect Indigenous sensitivities where observatories have been built upon sacred grounds
- Published
- 2023
4. LeMMINGs - II. The e-MERLIN legacy survey of nearby galaxies. The deepest radio view of the Palomar sample on parsec scale
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David A. Green, Elmar Körding, Susanne Aalto, David R. Williams, Bililign T. Dullo, Alison B. Peck, Ranieri D. Baldi, C. Romero-Cañizales, Willem A. Baan, I. M. McHardy, Megan Argo, Eskil Varenius, Antxon Alberdi, Miguel A. Pérez-Torres, Payaswini Saikia, Francesca Panessa, Stephane Corbel, John S. Gallagher, Martin Ward, R. C. Kennicutt, George J. Bendo, Jeremy Yates, Francesco Shankar, P. Uttley, Hans-Rainer Klöckner, Ralph Spencer, T. J. Maccarone, Johan H. Knapen, Ian R. Stevens, Danielle Fenech, T. W. B. Muxlow, C. G. Mundell, Robert Beswick, Elias Brinks, Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Unité Scientifique de la Station de Nançay (USN), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Ministerio de Ciencia, Innovación y Universidades (España), Comunidad de Madrid, Universidad Complutense de Madrid, University of Bath, University of Wisconsin-Madison, European Commission, Green, David [0000-0003-3189-9998], Apollo - University of Cambridge Repository, Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), and Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)
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Astrofísica ,active [Galaxies] ,galaxies: jet ,media_common.quotation_subject ,Astronomy ,galaxies: active ,FOS: Physical sciences ,Scale (descriptive set theory) ,Astrophysics ,F500 ,galaxies [Radio continuum] ,01 natural sciences ,jet [Galaxies] ,star formation [Galaxies] ,Spectral line ,Parsec ,0103 physical sciences ,010303 astronomy & astrophysics ,MERLIN ,media_common ,Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,radio continuum: galaxies ,010308 nuclear & particles physics ,Astronomy and Astrophysics ,Sample (graphics) ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Universe ,Astronomía ,Space and Planetary Science ,nuclei [Galaxies] ,Astrophysics of Galaxies (astro-ph.GA) ,galaxies: star formation ,galaxies: nuclei ,Astrophysics - High Energy Astrophysical Phenomena ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] ,Data release - Abstract
Full list of authors: Baldi, R. D.; Williams, D. R. A.; McHardy, I. M.; Beswick, R. J.; Brinks, E.; Dullo, B. T.; Knapen, J. H.; Argo, M. K.; Aalto, S.; Alberdi, A.; Baan, W. A.; Bendo, G. J.; Corbel, S.; Fenech, D. M.; Gallagher, J. S.; Green, D. A.; Kennicutt, R. C.; Klöckner, H. -R.; Körding, E.; Maccarone, T. J.; Muxlow, T. W. B.; Mundell, C. G.; Panessa, F.; Peck, A. B.; Pérez-Torres, M. A.; Romero-Cañizales, C.; Saikia, P.; Shankar, F.; Spencer, R. E.; Stevens, I. R.; Varenius, E.; Ward, M. J.; Yates, J.; Uttley, P., We present the second data release of high-resolution (≤0.2 arcsec) 1.5-GHz radio images of 177 nearby galaxies from the Palomar sample, observed with the e-MERLIN array, as part of the Legacy e-MERLIN Multi-band Imaging of Nearby Galaxies Sample (LeMMINGs) survey. Together with the 103 targets of the first LeMMINGs data release, this represents a complete sample of 280 local active (LINER and Seyfert) and inactive galaxies (H ii galaxies and absorption line galaxies, ALG). This large program is the deepest radio survey of the local Universe, ≳1017.6 W Hz-1, regardless of the host and nuclear type: we detect radio emission ≳0.25 mJy beam-1 for 125/280 galaxies (44.6 per cent) with sizes of typically ≲100 pc. Of those 125, 106 targets show a core which coincides within 1.2 arcsec with the optical nucleus. Although we observed mostly cores, around one third of the detected galaxies features jetted morphologies. The detected radio core luminosities of the sample range between ∼1034 and 1040 erg s-1. LINERs and Seyferts are the most luminous sources, whereas H ii galaxies are the least. LINERs show FR I-like core-brightened radio structures while Seyferts reveal the highest fraction of symmetric morphologies. The majority of H ii galaxies have single radio core or complex extended structures, which probably conceal a nuclear starburst and/or a weak active nucleus (seven of them show clear jets). ALGs, which are typically found in evolved ellipticals, although the least numerous, exhibit on average the most luminous radio structures, similar to LINERs. © 2020 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society., The authors thank the anonymous referee for his/her helpful comments to improve the manuscript. AA and MAPT acknowledge support from the Spanish MCIU through grant PGC2018-098915-B-C21 and from the State Agency for Research of the Spanish MCIU through the 'Center of Excellence Severo Ochoa' award for the Instituto de Astrof ' isica de Andalucia (SEV-2017-0709). BTD acknowledges support from a Spanish postdoctoral fellowship 'Ayudas 1265 para la atraccion del talento investigador. Modalidad 2: jovenes investigadores.' funded by Comunidad de Madrid under grant number 2016-T2/TIC-2039. BTD also acknowledges support from grant 'Ayudas para la realizaci on de proyectos de I + D para jovenes doctores 2019.' funded by Comunidad de Madrid and Universidad Complutense de Madrid under grant number PR65/19-22417. JHK acknowledges financial support from the European Union's Horizon 2020 research and innovation programme under Marie Sklodowska-Curie grant agreement No. 721463 to the SUNDIAL ITN network, from the State Research Agency (AEI-MCINN) of the Spanish Ministry of Science and Innovation under the grant 'The structure and evolution of galaxies and their central regions' with reference PID2019-105602GB-I00/10.13039/501100011033, and from IAC project P/300724, financed by the Ministry of Science and Innovation, through the State Budget and by the Canary Islands Department of Economy, Knowledge and Employment, through the Regional Budget of the Autonomous Community. JSG thanks the University of Wisconsin-Madison and its Foundation for support of this research through his Rupple Bascom Professorship. FS acknowledges partial support from a Leverhulme Trust Research fellowship. CGM acknowledges support from the University of Bath and Jim and Hiroko Sherwin. e-MERLIN is a National Facility operated by the University of Manchester at Jodrell Bank Observatory on behalf of STFC, part of UK Research and Innovation.
- Published
- 2021
5. AT 2018cow VLBI: no long-lived relativistic outflow
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Michael Bietenholz, Giacomo Terreran, Dan Milisavljevic, Kate D. Alexander, Edo Berger, Tarraneh Eftekhari, Megan Argo, Raffaella Margutti, Norbert Bartel, and Deanne L. Coppejans
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High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,F990 ,Jet (fluid) ,Proper motion ,010308 nuclear & particles physics ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,01 natural sciences ,Luminosity ,Tidal disruption event ,Supernova ,Space and Planetary Science ,0103 physical sciences ,Very-long-baseline interferometry ,Outflow ,Astrophysics - High Energy Astrophysical Phenomena ,Ejecta ,010303 astronomy & astrophysics - Abstract
We report on VLBI observations of the fast and blue optical transient (FBOT), AT 2018cow. At ~62 Mpc, AT 2018cow is the first relatively nearby FBOT. The nature of AT 2018cow is not clear, although various hypotheses from a tidal disruption event to different kinds of supernovae have been suggested. It had a very fast rise time (3.5 d) and an almost featureless blue spectrum although high photospheric velocities (40,000 km s$^{-1}$) were suggested early on. The X-ray luminosity was very high, ~$1.4 \times 10^{43}$ erg s$^{-1}$, larger than those of ordinary SNe, and more consistent with those of SNe associated with gamma-ray bursts. Variable hard X-ray emission hints at a long-lived "central engine." It was also fairly radio luminous, with a peak 8.4-GHz spectral luminosity of ~$4 \times 10^{28}$ erg s$^{-1}$ Hz$^{-1}$, allowing us to make VLBI observations at ages between 22 and 287 d. We do not resolve AT 2018cow. Assuming a circularly symmetric source, our observations constrain the average apparent expansion velocity to be, Accepted for publication in MNRAS 3 figurs]es
- Published
- 2019
6. The Radio Luminosity-Risetime Function of Core-Collapse Supernovae
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Michael Bietenholz, Megan Argo, Alicia M. Soderberg, R. Dua, Stuart D. Ryder, and Norbert Bartel
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Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,010504 meteorology & atmospheric sciences ,F510 ,Radio flux ,FOS: Physical sciences ,Astronomy and Astrophysics ,Function (mathematics) ,Astrophysics ,01 natural sciences ,Standard deviation ,Luminosity ,Supernova ,Space and Planetary Science ,0103 physical sciences ,Astrophysics - High Energy Astrophysical Phenomena ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences - Abstract
We assemble a large set of 2-10 GHz radio flux density measurements and upper limits of 294 different supernovae (SNe), from the literature and our own and archival data. Only 31% of the SNe were detected. We characterize the SN lightcurves near the peak using a two-parameter model, with $t_{\rm pk}$ being the time to rise to a peak and $L_{\rm pk}$ the spectral luminosity at that peak. Over all SNe in our sample at $D, Accepted for publication in the Astrophysical Journal 15 Figures, 4 Tables; Full version of Table 1 in ancillary files. Minor revisions only from version 1
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- 2021
7. LeMMINGs III. The e-MERLIN legacy survey of the Palomar sample: exploring the origin of nuclear radio emission in active and inactive galaxies through the [O III] - radio connection
- Author
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George J. Bendo, J. M. Marcaide, Ivan Marti-Vidal, Lorenzo Zanisi, Payaswini Saikia, Ranieri D. Baldi, Francesco Shankar, C. Romero-Cañizales, Elmar Körding, Isaac Mutie, Elias Brinks, Robert Beswick, Carole Mundell, Willem A. Baan, David A. Green, Antonio Alberdi, Susanne Aalto, S. Corbel, Bililign T. Dullo, Hans-Rainer Klöckner, Danielle Fenech, Ralph Spencer, Ian R. Stevens, T. J. Maccarone, Martin Ward, Megan Argo, D. J. Saikia, Miguel A. Pérez-Torres, P. Uttley, M. Pahari, Francesca Panessa, I. M. McHardy, Johan H. Knapen, David R. Williams, High Energy Astrophys. & Astropart. Phys (API, FNWI), European Commission, Ministerio de Ciencia e Innovación (España), Ministerio de Ciencia, Innovación y Universidades (España), Comunidad de Madrid, Generalitat Valenciana, Baldi, RD [0000-0002-1824-0411], Romero-Cañizales, C [0000-0001-6301-9073], Martí-Vidal, I [0000-0003-3708-9611], Apollo - University of Cambridge Repository, Unité Scientifique de la Station de Nançay (USN), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)
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Astrofísica ,Active galactic nucleus ,Astronomy ,Astrophysics::High Energy Astrophysical Phenomena ,nuclei [galaxies] ,jets [galaxies] ,Doubly ionized oxygen ,FOS: Physical sciences ,Astrophysics ,F500 ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Radio continuum: galaxies ,Luminosity ,Astrophysical jet ,Subatomic Physics ,0103 physical sciences ,Astronomy, Astrophysics and Cosmology ,Astrophysics::Solar and Stellar Astrophysics ,Connection (algebraic framework) ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Galaxies: nuclei ,Astronomia Observacions ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,[SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph] ,Galaxies: star formation ,010308 nuclear & particles physics ,Astronomy and Astrophysics ,Galaxies: active ,Astrophysics - Astrophysics of Galaxies ,galaxies [radio continuum] ,Accretion (astrophysics) ,Galaxy ,[SDU]Sciences of the Universe [physics] ,Meteorology and Atmospheric Sciences ,Space and Planetary Science ,Galaxies: jets ,Astrophysics of Galaxies (astro-ph.GA) ,active [galaxies] ,Production (computer science) ,star formation [galaxies] ,Astrophysics - High Energy Astrophysical Phenomena - Abstract
Full list of authors: Baldi, R. D.; Williams, D. R. A.; Beswick, R. J.; McHardy, I.; Dullo, B. T.; Knapen, J. H.; Zanisi, L.; Argo, M. K.; Aalto, S.; Alberdi, A.; Baan, W. A.; Bendo, G. J.; Fenech, D. M.; Green, D. A.; Klöckner, H. -R.; Körding, E.; Maccarone, T. J.; Marcaide, J. M.; Mutie, I.; Panessa, F.; Pérez-Torres, M. A.; Romero-Cañizales, C.; Saikia, D. J.; Saikia, P.; Shankar, F.; Spencer, R. E.; Stevens, I. R.; Uttley, P.; Brinks, E.; Corbel, S.; Martí-Vidal, I.; Mundell, C. G.; Pahari, M.; Ward, M. J., What determines the nuclear radio emission in local galaxies? To address this question, we combine optical [O iii] line emission, robust black hole (BH) mass estimates, and high-resolution e-MERLIN 1.5-GHz data, from the LeMMINGs survey, of a statistically complete sample of 280 nearby optically active (LINER and Seyfert) and inactive [H ii and absorption line galaxies (ALGs)] galaxies. Using [O iii] luminosity (L[O III]) as a proxy for the accretion power, local galaxies follow distinct sequences in the optical-radio planes of BH activity, which suggest different origins of the nuclear radio emission for the optical classes. The 1.5-GHz radio luminosity of their parsec-scale cores (Lcore) is found to scale with BH mass (MBH) and [O iii] luminosity. Below MBH ∼106.5 M⊙, stellar processes from non-jetted H ii galaxies dominate with Lcore ∝ MBH0.61 ± 0.33 and Lcore ∝ L[O III]0.79 ± 0.30. Above MBH ∼106.5 M⊙, accretion-driven processes dominate with Lcore ∝ MBH1.5-1.65 and Lcore ∝ L[O III]0.99-1.31 for active galaxies: radio-quiet/loud LINERs, Seyferts, and jetted H ii galaxies always display (although low) signatures of radio-emitting BH activity, with L1.5 GHz ≳ 1019.8 W Hz-1 and MBH ≳ 107 M⊙, on a broad range of Eddington-scaled accretion rates (m). Radio-quiet and radio-loud LINERs are powered by low-m discs launching sub-relativistic and relativistic jets, respectively. Low-power slow jets and disc/corona winds from moderately high to high-m discs account for the compact and edge-brightened jets of Seyferts, respectively. Jetted H ii galaxies may host weakly active BHs. Fuel-starved BHs and recurrent activity account for ALG properties. In conclusion, specific accretion-ejection states of active BHs determine the radio production and the optical classification of local active galaxies. © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society., This research was supported by a Newton Fund project, DARA (Development in Africa with Radio Astronomy), and awarded by the UK’s Science and Technology Facilities Council (STFC) – grant reference ST/R001103/1. This research was supported by European Commission Horizon 2020 Research and Innovation Programme under grant agreement No. 730884 (JUMPING JIVE). FS acknowledges support from a Leverhulme Trust Research Fellowship. JHK acknowledges support from the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement no. 721463 to the SUNDIAL ITN network, from the State Research Agency (AEI) of the Spanish Ministry of Science and Innovation and the European Regional Development Fund (FEDER) under the grant with reference PID2019-105602GB-I00, and from IAC project P/300724, financed by the Ministry of Science and Innovation, through the State Budget and by the Canary Islands Department of Economy, Knowledge and Employment, through the Regional Budget of the Autonomous Community. IMV thanks the Generalitat Valenciana (funding from the GenT Project CIDEGENT/2018/021) and the MICINN (funding from the Research Project PID2019-108995GB-C22). AA and MAPT acknowledge support from the Spanish MCIU through grant PGC2018-098915-B-C21 and from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award for the Instituto de Astrofìsica de Andalucìa (SEV-2017-0709). BTD acknowledges financial support from grant ‘Ayudas para la realización de proyectos de I + D para jóvenes doctores 2019’ funded by Comunidad de Madrid and Universidad Complutense de Madrid under grant no. PR65/19-22417.
- Published
- 2021
8. The curious activity in the nucleus of NGC 4151:Jet interaction causing variability?
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David R. Williams, Ian M. McHardy, Johan H. Knapen, Jonathan Westcott, Elias Brinks, T. W. B. Muxlow, Carole Mundell, Mayukh Pahari, Robert Beswick, D Fenech, J. Moldon, Bililign T. Dullo, D. May, Francesca Panessa, Megan Argo, Gabriele Bruni, Ranieri D. Baldi, University of Southampton, Oxford Hintze Centre for Astrophysical Surveys (UK), European Commission, Leverhulme Trust, Science and Technology Facilities Council (UK), Agenzia Spaziale Italiana, Ministerio de Ciencia, Innovación y Universidades (España), Gobierno de Canarias, Fundación BBVA, and Royal Society (UK)
- Subjects
Galaxies: Seyfert ,F520 ,F521 ,Center of excellence ,European Regional Development Fund ,jets [galaxies] ,nuclei [galaxies] ,Library science ,FOS: Physical sciences ,01 natural sciences ,Seyfert [galaxies] ,emission lines [quasars] ,0103 physical sciences ,media_common.cataloged_instance ,Galaxies: individual: NGC 4151 ,European union ,010303 astronomy & astrophysics ,Active [galaxies] ,MERLIN ,media_common ,Galaxies: nuclei ,Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Quasars: emission lines ,010308 nuclear & particles physics ,Astronomy and Astrophysics ,Galaxies: active ,Astrophysics - Astrophysics of Galaxies ,individual: NGC 4151 [galaxies] ,Scholarship ,State agency ,Galaxies: jets ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Christian ministry ,Astrophysics - High Energy Astrophysical Phenomena - Abstract
A key characteristic of many active galactic nuclei (AGN) is their variability, but its origin is poorly understood, especially in the radio domain. Williams et al. (2017) reported a ∼50 per cent increase in peak flux density of the AGN in the Seyfert galaxy NGC 4151 at 1.5 GHz with the e-MERLIN array. We present new high resolution e-MERLIN observations at 5 GHz and compare these to archival MERLIN observations to investigate the reported variability. Our new observations allow us to probe the nuclear region at a factor three times higher-resolution than the previous e-MERLIN study. We separate the core component, C4, into three separate components: C4W, C4E and X. The AGN is thought to reside in component C4W, but this component has remained constant between epochs within uncertainties. However, we find that the Eastern-most component, C4E, has increased in peak flux density from 19.35±1.10 to 37.09±1.86 mJy/beam, representing a 8.2σ increase on the MERLIN observations. We attribute this peak flux density increase to continued interaction between the jet and the emission line region (ELR), observed for the first time in a low-luminosity AGN such as NGC 4151. We identify discrete resolved components at 5 GHz along the jet axis, which we interpret as areas of jet-ELR interaction.© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society, We thank the anonymous reviewer for their comments and revisions, which greatly improved the quality of this manuscript. We acknowledge funding from the Mayflower Scholarship from the University of Southampton afforded to DW to complete this work. This work was supported by the Oxford Centre for Astrophysical Surveys, which is funded through generous support from the Hintze Family Charitable Foundation. The research leading to these results has received funding from the European Union’s Horizon 2020 Programme under the AHEAD project (grant agreement no. 654215). This publication has also received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 730562 [RadioNet]. IMcH thanks the Royal Society for the award of a Royal Society Leverhulme Trust Senior Research Fellowship. RDB and IMcH also acknowledge the support of STFC under grant [ST/M001326/1]. FP acknowledges support from grant PRIN-INAF SKA-CTA 2016. GB acknowledges financial support under the INTEGRAL ASI-INAF agreement 2013-025-R1 and under the INTEGRAL ASI-INAF agreement 2019-35-HH.0. JHK acknowledges financial support from the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement no. 721463 to the SUNDIAL ITN network, and from the Spanish Ministry of Science, Innovation and Universities (MCIU) and the European Regional Development Fund (FEDER) under the grant with reference AYA2016-76219-P, from IAC project P/300724, financed by the Ministry of Science, Innovation and Universities, through the State Budget and by the Canary Islands Department of Economy, Knowledge and Employment, through the Regional Budget of the Autonomous Community, and from the Fundacion BBVA under ´ its 2017 programme of assistance to scientific research groups, for the project ‘Using machine-learning techniques to drag galaxies from the noise in deep imaging’. DMF wishes to acknowledge funding from an STFC Q10 consolidated grant [ST/M001334/1]. EB and JW acknowledge support from the UK’s Science and Technology Facilities Council grant numbers [ST/M503514/1] and [ST/M001008/1], respectively. JM acknowledges financial support from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award to the Instituto de Astrof´ısica de Andaluc´ıa (SEV-2017-0709) and from the grant RTI2018-096228-B-C31 (MICIU/FEDER, EU). CGM acknowledges financial support from STFC. We also acknowledge Jodrell Bank Centre for Astrophysics, which is funded by the STFC. eMERLIN and formerly, MERLIN, is a National Facility operated by the University of Manchester at Jodrell Bank Observatory on behalf of STFC. MP acknowledges the support from the Royal Society Newton International Fellowship.
- Published
- 2020
9. Searching for obscured AGN in z ~ 2 submillimetre galaxies
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Isabella Prandoni, Hai-Bo Chen, T. W. B. Muxlow, Megan Argo, I. M. McHardy, M. A. Garrett, D. Guidetti, Peter Barthel, Robert Beswick, S. Chi, David M. Alexander, Ian Smail, M. Bondi, Alasdair Thomson, Nicholas Wrigley, and J. F. Radcliffe
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European VLBI Network ,Active galactic nucleus ,85A15 ,media_common.quotation_subject ,Population ,FOS: Physical sciences ,Astrophysics ,01 natural sciences ,0103 physical sciences ,Very-long-baseline interferometry ,education ,010303 astronomy & astrophysics ,media_common ,Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,education.field_of_study ,F990 ,010308 nuclear & particles physics ,Astronomy and Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Universe ,Redshift ,Space and Planetary Science ,Brightness temperature ,Astrophysics of Galaxies (astro-ph.GA) ,Astrophysics - High Energy Astrophysical Phenomena - Abstract
Submillimetre-selected galaxies (SMGs) at high redshift ($z$ $\sim$ 2) are potential host galaxies of active galactic nuclei (AGN). If the local Universe is a good guide, $\sim$ 50$\%$ of the obscured AGN amongst the SMG population could be missed even in the deepest X-ray surveys. Radio observations are insensitive to obscuration; therefore, very long baseline interferometry (VLBI) can be used as a tool to identify AGN in obscured systems. A well-established upper limit to the brightness temperature of 10$^5$ K exists in star-forming systems, thus VLBI observations can distinguish AGN from star-forming systems via brightness temperature measurements. We present 1.6 GHz European VLBI Network (EVN) observations of four SMGs (with measured redshifts) to search for evidence of compact radio components associated with AGN cores. For two of the sources, e-MERLIN images are also presented. Out of the four SMGs observed, we detect one source, J123555.14, that has an integrated EVN flux density of 201 $\pm$ 15.2 $\mu$Jy, corresponding to a brightness temperature of 5.2 $\pm$ 0.7 $\times$ 10$^5$ K. We therefore identify that the radio emission from J123555.14 is associated with an AGN. We do not detect compact radio emission from a possible AGN in the remaining sources (J123600.10, J131225.73, and J163650.43). In the case of J131225.73, this is particularly surprising, and the data suggest that this may be an extended, jet-dominated AGN that is resolved by VLBI. Since the morphology of the faint radio source population is still largely unknown at these scales, it is possible that with a $\sim$ 10 mas resolution, VLBI misses (or resolves) many radio AGN extended on kiloparsec scales., Comment: 11 pages, 5 figures
- Published
- 2020
10. The Deepest Radio Observations of Nearby SNe Ia:Constraining Progenitor Types and Optimizing Future Surveys
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Stuart D. Ryder, Antxon Alberdi, Erik C. Kool, Robert Beswick, Megan Argo, Miguel A. Pérez-Torres, Peter Lundqvist, Esha Kundu, C. I. Bjornsson, Javier Moldon, Swedish Research Council, Ministerio de Ciencia, Innovación y Universidades (España), Ministerio de Economía y Competitividad (España), European Commission, and Australian Government
- Subjects
Physics ,Solar mass ,Energy distribution ,010504 meteorology & atmospheric sciences ,Astronomy and Astrophysics ,Astrophysics ,Type (model theory) ,7. Clean energy ,01 natural sciences ,law.invention ,Telescope ,Supernova ,Space and Planetary Science ,law ,0103 physical sciences ,Radio frequency ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences - Abstract
We report deep radio observations of nearby Type Ia supernovae (SNe Ia) with the electronic Multi-Element Radio Linked Interferometer Network and the Australia Telescope Compact Array. No detections were made. With standard assumptions for the energy densities of relativistic electrons going into a power-law energy distribution and the magnetic field strength ( e = B = 0.1), we arrive at upper limits on mass-loss rate for the progenitor system of SN 2013dy (SN 2016coj, SN 2018gv, SN 2018pv, SN 2019np) of, where v w is the wind speed of the mass loss. To SN 2016coj, SN 2018gv, SN 2018pv, and SN 2019np we add radio data for 17 other nearby SNe Ia and model their nondetections. With the same model as described, all 21 SNe Ia have. We compare those limits with the expected mass-loss rates in different single-degenerate progenitor scenarios. We also discuss how information on e and B can be obtained from late observations of SNe Ia and the youngest SN Ia remnant detected in radio, G1.9+0.3, as well as stripped-envelope core-collapse SNe. We highlight SN 2011dh and argue for e ≈ 0.1 and B ≈ 0.0033. Finally, we discuss strategies to observe at radio frequencies to maximize the chance of detection, given the time since explosion, the distance to the SN, and the telescope sensitivity. © 2020. The American Astronomical Society. All rights reserved., We thank Subo Dong for sharing data for SN.2018gv and SN 2018pv prior to publication, Stephen Reynolds for discussions and comments on an early version of the manuscript, and Nancy Elias-Rosa for discussions on SN.2019np. P. L. acknowledges support from the Swedish Research Council, and M.P.T. acknowledges financial support from the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709) and through the MINECO grants AYA2012-38491-C02-02 and AYA2015-63939-C2-1-P. J.M. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709) and from the grant RTI2018-096228-B-C31 (MICIU/FEDER, EU). The research leading to these results has received funding from the European Commission Horizon 2020 Research and Innovation Programme under grant agreement No. 730562 (RadioNet). The electronic Multi-Element Radio Linked Interferometer Network (e-MERLIN) is the UK's facility for high-resolution radio astronomy observations, operated by the University of Manchester for the Science and Technology Facilities Council (STFC). The Australia Telescope Compact Array (ATCA) is part of the Australia Telescope National Facility, which is funded by the Australian Government for operation as a National Facility managed by CSIRO. The ATCA data reported here were obtained under program C1303 (P.I. P. Lundqvist). This research has made use of the NASA Astrophysics Data System (ADS) Bibliographic Services and the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
- Published
- 2020
11. Spatially resolving the OH masers in M82
- Author
-
Megan Argo
- Subjects
Physics ,Space and Planetary Science ,law ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Maser ,Astrophysics::Galaxy Astrophysics ,law.invention - Abstract
With luminosities between those of typical Galactic OH masers and more distant OH megamasers, the masers in the nearby galaxy M82 are an interesting population which can be used to probe the physical conditions in the central starburst region of this irregular galaxy. Following on from previous low spatial resolution studies, here we present the initial results of two high-resolution observations separated by eight years. We find that some of the maser spots are resolved into multiple spatial components when observed with the EVN, as predicted by our previous studies, but that significantly less flux is recovered that that seen with the previous VLA observations. We conclude that some of this flux difference is likely due to variability but that, in common with the results seen in Arp220, there may also be a significant diffuse component.
- Published
- 2017
12. Searching for intermediate-mass black holes in NGC3310
- Author
-
Joseph Coppola, Timothy P.L. Roberts, Hannah P. Earnshaw, Mar Mezcua, and Megan Argo
- Subjects
Physics ,Supernova ,Spiral galaxy ,Coincident ,Astrophysics of Galaxies (astro-ph.GA) ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Astrophysics::Galaxy Astrophysics ,MERLIN ,Luminosity - Abstract
Intermediate-mass black holes are theoretically predicted but observationally elusive, and evidence for them is often indirect. The nearby face-on spiral galaxy NGC3310 has hosted many supernovae in recent history, and recent Chandra observations have shown a group of strong off-nuclear X-ray sources that are coincident with radio emission seen in archival VLA and MERLIN observations. Their luminosity, spectrum and off-nuclear location make these sources excellent IMBH candidates. To investigate this possibility, we used combined EVN/e-MERLIN observations at both 1.4 and 5 GHz to look for compact radio emission and evidence of jet activity. We detect a compact radio source within one arcsecond of a Chandra source with an estimated mass ${\rm M}_{\rm BH}\sim3\times10^4 {\rm M}_{\odot}$., Comment: Six pages, two figures. Contributed talk at the EVN Symposium, Granada, Spain, October 2018, to be published in POS
- Published
- 2019
13. Radio jets in NGC 4151: Where eMERLIN meets HST
- Author
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I. M. McHardy, Jonathan Westcott, Elias Brinks, H. Rampadarath, Francesca Panessa, Carole Mundell, Bililign T. Dullo, David R. Williams, Ranieri D. Baldi, Johan H. Knapen, Robert Beswick, Megan Argo, T. W. B. Muxlow, Danielle Fenech, ITA, GBR, and ESP
- Subjects
Physics ,Seyfert [Galaxies] ,active [Galaxies] ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astronomy and Astrophysics ,F500 ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Astrophysics - Astrophysics of Galaxies ,emission lines [Quasars] ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,nuclei [Galaxies] ,0103 physical sciences ,individual: NGC 4151 [Galaxies] ,jets [Galaxies] ,010303 astronomy & astrophysics ,Classics ,Astrophysics::Galaxy Astrophysics - Abstract
We present high-sensitivity eMERLIN radio images of the Seyfert galaxy NGC 4151 at 1.5 GHz. We compare the new eMERLIN images to those from archival MERLIN observations in 1993 to determine the change in jet morphology in the 22 years between observations. We report an increase by almost a factor of 2 in the peak flux density of the central core component, C4, thought to host the black hole, but a probable decrease in some other components, possibly due to adiabatic expansion. The core flux increase indicates an AGN which is currently active and feeding the jet. We detect no significant motion in 22 years between C4 and the component C3, which is unresolved in the eMERLIN image. We present a spectral index image made within the 512 MHz band of the 1.5 GHz observations. The spectrum of the core, C4, is flatter than that of other components further out in the jet. We use HST emission line images (H$\alpha$, [O III] and [O II]) to study the connection between the jet and the emission line region. Based on the changing emission line ratios away from the core and comparison with the eMERLIN radio jet, we conclude that photoionisation from the central AGN is responsible for the observed emission line properties further than 4" (360 pc) from the core, C4. Within this region, several evidences (radio-line co-spatiality, low [O III]/H$\alpha$ and estimated fast shocks) suggest additional ionisation from the jet., Comment: 13 pages, 8 figures, 2 tables. Accepted to MNRAS: MN-17-2603-MJ.R1
- Published
- 2018
14. Jets, Arcs and Shocks: NGC 5195 at radio wavelengths
- Author
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Ranieri D. Baldi, Eric M. Schlegel, Robert Beswick, Roberto Soria, C.K. Lacey, I. M. McHardy, Gaelle Dumas, T. W. B. Muxlow, Megan Argo, David R. Williams, Ryan Urquhart, Murray Brightman, H. Rampadarath, Institut de RadioAstronomie Millimétrique ( IRAM ), Centre National de la Recherche Scientifique ( CNRS ), Institut de RadioAstronomie Millimétrique (IRAM), and Centre National de la Recherche Scientifique (CNRS)
- Subjects
Active galactic nucleus ,active [Galaxies] ,[ PHYS.ASTR ] Physics [physics]/Astrophysics [astro-ph] ,Astrophysics::High Energy Astrophysical Phenomena ,galaxies: active ,FOS: Physical sciences ,techniques: radar astronomy ,galaxies [Radio continuum] ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,F500 ,01 natural sciences ,symbols.namesake ,0103 physical sciences ,Very-long-baseline interferometry ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,radio continuum: galaxies ,Physics ,radio astronomy [techniques] ,Supermassive black hole ,galaxies: individual: NGC 5195 ,Individual (NGC 5195) [Galaxies] ,010308 nuclear & particles physics ,Star formation ,Balmer series ,Astronomy and Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Accretion (astrophysics) ,galaxies [X-rays] ,X-rays: galaxies ,techniques: interferometric ,13. Climate action ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,interferometric ,symbols ,Astrophysics - High Energy Astrophysical Phenomena ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] ,Order of magnitude - Abstract
We studied the nearby, interacting galaxy NGC 5195 (M51b) in the radio, optical and X-ray bands. We mapped the extended, low-surface-brightness features of its radio-continuum emission; determined the energy content of its complex structure of shock-ionized gas; constrained the current activity level of its supermassive nuclear black hole. In particular, we combined data from the European Very Long Baseline Interferometry Network (~1-pc scale), from our new e-MERLIN observations (~10-pc scale), and from the Very Large Array (~100-1000-pc scale), to obtain a global picture of energy injection in this galaxy. We put an upper limit to the luminosity of the (undetected) flat-spectrum radio core. We find steep-spectrum, extended emission within 10 pc of the nuclear position, consistent with optically-thin synchrotron emission from nuclear star formation or from an outflow powered by an active galactic nucleus (AGN). A linear spur of radio emission juts out of the nuclear source towards the kpc-scale arcs (detected in radio, Halpha and X-ray bands). From the size, shock velocity, and Balmer line luminosity of the kpc-scale bubble, we estimate that it was inflated by a long-term-average mechanical power ~3-6 x 10^{41} erg/s over the last 3-6 Myr. This is an order of magnitude more power than can be provided by the current level of star formation, and by the current accretion power of the supermassive black hole. We argue that a jet-inflated bubble scenario associated with previous episodes of AGN activity is the most likely explanation for the kpc-scale structures., Comment: 16 pages, 7 figures. Accepted by MNRAS on 2017 Feb 12
- Published
- 2018
15. The nuclear activity and central structure of the elliptical galaxy NGC 5322
- Author
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Johan H. Knapen, George J. Bendo, Ranieri D. Baldi, Megan Argo, Jonathan Westcott, David R. Williams, Ian M. McHardy, Robert Beswick, Bililign T. Dullo, and T. W. B. Muxlow
- Subjects
Stellar mass ,Astrophysics::High Energy Astrophysical Phenomena ,nuclei [galaxies] ,FOS: Physical sciences ,galaxies [Radio continuum] ,Astrophysics ,F500 ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Surface brightness ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Physics ,010308 nuclear & particles physics ,Star formation ,Astronomy and Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Accretion (astrophysics) ,Galaxy ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Brightness temperature ,photometry [galaxies] ,structure [galaxies] ,Elliptical galaxy ,Halo ,Astrophysics::Earth and Planetary Astrophysics ,elliptical and lenticular, cD [galaxies] - Abstract
We have analysed a new high-resolution e-MERLIN 1.5 GHz radio continuum map together with $HST$ and SDSS imaging of NGC 5322, an elliptical galaxy hosting radio jets, aiming to understand the galaxy's central structure and its connection to the nuclear activity. We decomposed the composite $HST$ + SDSS surface brightness profile of the galaxy into an inner stellar disc, a spheroid, and an outer stellar halo. Past works showed that this embedded disc counter-rotates rapidly with respect to the spheroid. The $HST$ images reveal an edge-on nuclear dust disc across the centre, aligned along the major-axis of the galaxy and nearly perpendicular to the radio jets. After careful masking of this dust disc, we find a central stellar mass deficit $M_{\rm def}$ in the spheroid, scoured by SMBH binaries with final mass $M_{\rm BH}$ such that $M_{\rm def}/M_{\rm BH} \sim 1.3 - 3.4$. We propose a three-phase formation scenario for NGC 5322 where a few ($2-7$) "dry" major mergers involving SMBHs built the spheroid with a depleted core. The cannibalism of a gas-rich satellite subsequently creates the faint counter-rotating disc and funnels gaseous material directly onto the AGN, powering the radio core with a brightness temperature of $T_{\rm B,core} \sim 4.5 \times 10^{7}$ K and the low-power radio jets ($P_{\rm jets}\sim 7.04 \times 10^{20}$ W Hz$^{-1}$) which extend $\sim 1.6$ kpc. The outer halo can later grow via minor mergers and the accretion of tidal debris. The low-luminosity AGN/jet-driven feedback may have quenched the late-time nuclear star formation promptly, which could otherwise have replenished the depleted core., 14 pages, 5 figures, accepted for publication in MNRAS
- Published
- 2018
16. A new period of activity in the core of NGC 660
- Author
-
Robert Beswick, Megan Argo, Ilse van Bemmel, and S. Connolly
- Subjects
Physics ,European VLBI Network ,Active galactic nucleus ,Astrophysics::High Energy Astrophysical Phenomena ,Continuum (design consultancy) ,FOS: Physical sciences ,Astronomy ,Astronomy and Astrophysics ,F500 ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Polar-ring galaxy ,Galaxy ,X-shaped radio galaxy ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Spectral energy distribution ,Angular resolution ,Astrophysics::Galaxy Astrophysics - Abstract
The core of the nearby galaxy NGC660 has recently undergone a spectacular radio outburst; using a combination of archival radio and Chandra X-ray data, together with new observations, the nature of this event is investigated. Radio observations made using e-MERLIN in mid-2013 show a new compact and extremely bright continuum source at the centre of the galaxy. High angular resolution observations carried out with the European VLBI Network show an obvious jet-like feature to the north east and evidence of a weak extension to the west, possibly a counter-jet. We also examine high angular resolution HI spectra of these new sources, and the radio spectral energy distribution using the new wide-band capabilities of e-MERLIN. We compare the properties of the new object with possible explanations, concluding that we are seeing a period of new AGN activity in the core of this polar ring galaxy., 9 pages, 7 figures. Accepted for publication in MNRAS
- Published
- 2015
17. A high-resolution wide-field radio survey of M51
- Author
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Roberto Soria, Megan Argo, Steven Tingay, H. Rampadarath, Cormac Reynolds, John Morgan, and Gaelle Dumas
- Subjects
Physics ,European VLBI Network ,Radio galaxy ,Astrophysics::High Energy Astrophysical Phenomena ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Wide field ,Galaxy ,Wavelength ,Supernova ,Space and Planetary Science ,Hubble space telescope ,Hotspot (geology) ,Astrophysics::Galaxy Astrophysics - Abstract
We present the highest resolution, wide-field radio survey of a nearby face-on starforming galaxy to date. The multi-phase centre technique is used to survey the entire disk of M51 (77 square arc minutes) at a maximum resolution of 5 milli-arcseconds on a single 8 hr pointing with the European VLBI Network at 18 cm. In total, 7 billion pixels were imaged using 192 phase centres that resulted in the detection of six sources: the Seyfert nucleus, the supernova SN 2011dh, and four background AGNs. Using the wealth of archival data available in the radio (MERLIN and the VLA), optical (Hubble Space Telescope) and X-rays (Chandra) the properties of the individual sources were investigated in detail. The combined multi-wavelength observations reveal a very complex and puzzling core region that includes a low-luminosity parsec scale core-jet structure typical of AGNs, with evidence for a lateral shift corresponding to 0.27c. Furthermore, there is evidence for a fossil radio hotspot located 1.44 kpc from the Seyfert nucleus that may have resulted from a previous ejection cycle. Our study provides measures of the supernova and star-formation rates that are comparable to independent studies at other wavelengths, and places further limits on the radio and X-ray luminosity evolution of the supernovae SN 1994I, SN 2005cs and SN 2011dh. The radio images of background AGN reveal complex morphologies that are indicative of powerful radio galaxies, and confirmed via the X-ray and optical properties.
- Published
- 2015
18. A high-resolution radio continuum study of the dwarf irregular galaxy IC 10
- Author
-
I. M. McHardy, David R. Williams, Volker Heesen, Danielle Fenech, Daniel J. Smith, Robert Beswick, Megan Argo, Jonathan Westcott, Elias Brinks, and Ranieri D. Baldi
- Subjects
HII regions ,dwarf [galaxies] ,Astrophysics::High Energy Astrophysical Phenomena ,High resolution ,FOS: Physical sciences ,F500 ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,0103 physical sciences ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Dwarf galaxy ,Physics ,ISM [galaxies] ,Continuum (measurement) ,010308 nuclear & particles physics ,supernova remnants [ISM] ,high angular resolution [techniques] ,Astronomy ,Astronomy and Astrophysics ,Thermal emission ,Astrophysics - Astrophysics of Galaxies ,interferometric [techniques] ,Supernova ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Irregular galaxy - Abstract
We present high-resolution e-MERLIN radio continuum maps of the Dwarf Irregular galaxy IC10 at 1.5GHz and 5GHz. We detect 11 compact sources at 1.5GHz, 5 of which have complementary detections at 5GHz. We classify 3 extended sources as compact H{\sc ii} regions within IC10, 5 sources as contaminating background galaxies and identify 3 sources which require additional observations to classify. We do not expect that any of these 3 sources are Supernova Remnants as they will likely be resolved out at the assumed distance of IC10 (0.7Mpc). We correct integrated flux densities of IC10 from the literature for contamination by unrelated background sources and obtain updated flux density measurements of $354\pm11$\,mJy at 1.5GHz and $199\pm9$\,mJy at 4.85GHz. The background contamination does not contribute significantly to the overall radio emission from IC10, so previous analysis concerning its integrated radio properties remain valid., Comment: 15 pages, 7 Figures, 5 Tables, Accepted for publication in MNRAS
- Published
- 2017
19. Unveiling the AGN in IC 883: discovery of a parsec-scale radio jet
- Author
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Antxon Alberdi, Franz E. Bauer, Rubén Herrero-Illana, Robert Beswick, Stuart D. Ryder, C. Romero-Canizales, Andreas Efstathiou, Patricia Arevalo, Seppo Mattila, T. W. B. Muxlow, Claudio Ricci, John Conway, M. Bondi, Megan Argo, Miguel A. Pérez-Torres, Ministerio de Economía y Competitividad (España), Ministry of Economy, Development and Tourism (Greece), Comisión Nacional de Investigación Científica y Tecnológica (Chile), and European Commission
- Subjects
Active galactic nucleus ,Proper motion ,active [Galaxies] ,Radio galaxy ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,galaxies [Radio continuum] ,F500 ,01 natural sciences ,Radio continuum: galaxies ,Luminosity ,individual: IC 883 [Galaxies] ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Astronomy, Astrophysics and Cosmology ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Galaxies: nuclei ,Luminosity function (astronomy) ,Luminous infrared galaxy ,Physics ,ta115 ,010308 nuclear & particles physics ,Star formation ,Astronomy ,Astronomy and Astrophysics ,Galaxies: active ,Astrophysics - Astrophysics of Galaxies ,galaxies [X-rays] ,X-rays: galaxies ,Supernova ,Galaxies: jets ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Galaxies: individual: IC 883 ,nuclei [Galaxies] ,jets [Galaxies] - Abstract
Romero-Canizales, C. et. al., IC 883 is a luminous infrared galaxy (LIRG) classified as a starburst- active galactic nucleus (AGN) composite. In a previous study, we detected a low- luminosity AGN (LLAGN) radio candidate. Here, we report on our radio follow- up at three frequencies that provides direct and unequivocal evidence of the AGN activity in IC 883. Our analysis of archival X-ray data, together with the detection of a transient radio source with luminosity typical of bright supernovae, gives further evidence of the ongoing star formation activity, which dominates the energetics of the system. At sub- parsec scales, the radio nucleus has a core-jet morphology with the jet being a newly ejected component showing a subluminal proper motion of 0.6-1 c. The AGN contributes less than 2 per cent of the total IR luminosity of the system. The corresponding Eddington factor is similar to 10(-3), suggesting this is a low-accretion rate engine, as often found in LLAGNs. However, its high bolometric luminosity (similar to 10(44) erg s(-1)) agrees better with a normal AGN. This apparent discrepancy may just be an indication of the transition nature of the nucleus from a system dominated by star formation, to an AGN-dominated system. The nucleus has a strongly inverted spectrum and a turnover at similar to 4.4 GHz, thus qualifying as a candidate for the least luminous (L(5.0)GHz similar to 6.3 x 10(28) erg s(-1) Hz(-1)) and one of the youngest (similar to 3 x 10(3) yr) gigahertz-peaked spectrum (GPS) sources. If the GPS origin for the IC 883 nucleus is confirmed, then advanced mergers in the LIRG category are potentially key environments to unveil the evolution of GPS sources into more powerful radio galaxies. © 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society., We acknowledge financial support by the Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS, Chile (CR-C, FEB), from CONICYT through FONDECYT grants 3150238 (CR-C), 1140304 (PA), 1141218 and 1151408, from the CONICYT-Chile grants 'EMBIGGEN' Anillo ACT1101, Basal-CATA PFB-06/2007 and the China-CONICYT fellowship (CR, FEB), as well as funding from the SpanishMinistry of Economy and Competitiveness under grants AYA2012-38491CO2-02 and AYA2015-63939-C2-1-P, which are partly funded by the FEDER programme (AA, MAP-T, RH-I). The European VLBI Network is a joint facility of independent European, African, Asian and North American radio astronomy institutes. Scientific results from data presented in this publication are derived from the EVN project code ER030. The research leading to these results has received funding from the European Commission Seventh Framework Programme (FP/2007-2013) under grant agreement no. 283393 (RadioNet3). The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
- Published
- 2017
20. The peculiar mass-loss history of SN 2014C as revealed through AMI radio observations
- Author
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Y. C. Perrott, M. L. Pretorius, Rob Fender, Assaf Horesh, David Titterington, Richard M. Plotkin, G. E. Anderson, Megan Argo, Miguel A. Pérez-Torres, Kunal Mooley, Tim D. Staley, A. Rushton, Paul Hancock, Clare Rumsey, and Robert Beswick
- Subjects
High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,010308 nuclear & particles physics ,Arcminute Microkelvin Imager ,FOS: Physical sciences ,Flux ,Astronomy ,Astronomy and Astrophysics ,F500 ,Astrophysics ,Light curve ,01 natural sciences ,Synchrotron ,law.invention ,Interferometry ,Supernova ,13. Climate action ,Space and Planetary Science ,law ,0103 physical sciences ,Very-long-baseline interferometry ,Astrophysics - High Energy Astrophysical Phenomena ,Absorption (electromagnetic radiation) ,010303 astronomy & astrophysics - Abstract
We present a radio light curve of supernova (SN) 2014C taken with the Arcminute Microkelvin Imager (AMI) Large Array at 15.7 GHz. Optical observations presented by Milisavljevic et al. demonstrated that SN 2014C metamorphosed from a stripped-envelope Type Ib SN into a strongly interacting Type IIn SN within 1 year. The AMI light curve clearly shows two distinct radio peaks, the second being a factor of 4 times more luminous than the first peak. This double bump morphology indicates two distinct phases of mass-loss from the progenitor star with the transition between density regimes occurring at 100-200 days. This reinforces the interpretation that SN 2014C exploded in a low density region before encountering a dense Hydrogen-rich shell of circumstellar material that was likely ejected by the progenitor prior to the explosion. The AMI flux measurements of the first light curve bump are the only reported observations taken within ~50 to ~125 days post-explosion, before the blast-wave encountered the Hydrogen shell. Simplistic synchrotron self-absorption (SSA) and free-free absorption (FFA) modelling suggest that some physical properties of SN 2014C, such as the mass-loss rate, are consistent with the properties of other Type Ibc and IIn SNe. However, our single frequency data does not allow us to distinguish between these two models, which implies they are likely too simplistic to describe the complex environment surrounding this event. Lastly, we present the precise radio location of SN 2014C obtained with eMERLIN, which will be useful for future VLBI observations of the SN., 19 pages, 11 figures, 3 tables, accepted for publication in MNRAS
- Published
- 2017
21. The eMERGE Survey - I: Very Large Array 5.5 GHz observations of the GOODS-North Field
- Author
-
Ian Smail, M. Bondi, Alasdair Thomson, Robert Beswick, I. M. McHardy, Megan Argo, Jack Radcliffe, Nicholas Wrigley, D. Guidetti, T. W. B. Muxlow, Isabella Prandoni, and Astronomy
- Subjects
ACTIVE GALACTIC NUCLEI ,Active galactic nucleus ,Hubble Deep Field ,DEEP FIELD ,Astrophysics::High Energy Astrophysical Phenomena ,galaxies: active ,FOS: Physical sciences ,Flux ,galaxies: starburst ,Astrophysics ,F500 ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Jansky ,SUPERMASSIVE BLACK-HOLES ,0103 physical sciences ,OPTICAL IDENTIFICATIONS ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Physics ,radio continuum: galaxies ,Supermassive black hole ,010308 nuclear & particles physics ,HUBBLE-DEEP ,Astronomy ,Astronomy and Astrophysics ,STAR-FORMATION HISTORY ,Astrophysics - Astrophysics of Galaxies ,Redshift ,Galaxy ,ADVECTION-DOMINATED ACCRETION ,SPECTRAL ENERGY-DISTRIBUTION ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,cosmology: observations ,RADIO-EMISSION ,X-RAY ,Spectral energy distribution ,galaxies: evolution - Abstract
We present new observations of the GOODS-N field obtained at 5.5 GHz with the Karl G. Jansky Very Large Array (VLA). The central region of the field was imaged to a median r.m.s. of 3 microJy/beam with a resolution of 0.5 arcsec. From a 14-arcmin diameter region we extracted a sample of 94 radio sources with signal-to-noise ratio greater than 5. Near-IR identifications are available for about 88 percent of the radio sources. We used different multi-band diagnostics to separate active galactic nuclei (AGN), both radiatively efficient and inefficient, from star-forming galaxies. From our analysis, we find that about 80 percent of our radio-selected sample is AGN-dominated, with the fraction raising to 92 percent when considering only the radio sources with redshift >1.5. This large fraction of AGN-dominated radio sources at very low flux densities (the median flux density at 5.5 GHz is 42 microJy), where star-forming galaxies are expected to dominate, is somewhat surprising and at odds with other results. Our interpretation is that both the frequency and angular resolution of our radio observations strongly select against radio sources whose brightness distribution is diffuse on scale of several kpc. Indeed, we find that the median angular sizes of the AGN-dominated sources is around 0.2-0.3 arcsec against 0.8 arcsec for star-forming galaxies. This highlights the key role that high frequency radio observations can play in pinpointing AGN-driven radio emission at microJy levels. This work is part of the eMERGE legacy project., 18 pages, 11 figures. Online material (table 1, table 4 and appendix) available in the source file. Accepted for publication in MNRAS
- Published
- 2017
22. The nearby universe
- Author
-
Robert Beswick, Jonathon Westcott, Megan Argo, and Miguel A. Pérez-Torres
- Subjects
Physics ,010308 nuclear & particles physics ,media_common.quotation_subject ,Big Rip ,Astronomy ,Astronomy and Astrophysics ,01 natural sciences ,Universe ,Geophysics ,Geochemistry and Petrology ,0103 physical sciences ,010303 astronomy & astrophysics ,media_common - Abstract
Megan Argo and colleagues discuss what can be determined from galactic observations and surveys using e-MERLIN.
- Published
- 2016
23. Star formation: The role of high resolution radio surveys
- Author
-
Robert Beswick, T. W. B. Muxlow, Megan Argo, Nicholas Wrigley, and Jack Radcliffe
- Subjects
Physics ,Star formation ,Astronomy ,High resolution ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
The role of star-formation is critical for galaxy evolution. It is a ubiquitous process in galaxies that is both influenced by, and drives their evolution. In this article we will review the current status of high resolution studies of star-formation processes within galaxies from the local to the distant Universe. In particular this review will focus on the state-of-the-art radio surveys that arenow underway which provide some of the highest angular resolution and unobscured views of star-formation in galaxies. These surveys significantly add to our understanding of the processes of star-formation and provide the first glimps of what will be achievable with the SKA in the coming decades
- Published
- 2016
24. Flux density variations of radio sources in M82 over the last three decades
- Author
-
M. A. Gendre, Danielle Fenech, Megan Argo, T. W. B. Muxlow, and Robert Beswick
- Subjects
Physics ,Interstellar medium ,Supernova ,Interferometry ,Space and Planetary Science ,Astronomy ,Flux ,Astronomy and Astrophysics ,Astrophysics ,Supernova remnant ,MERLIN ,Galaxy ,Term (time) - Abstract
This paper presents the results of the 2009-2010 monitoring sessions of the starburst galaxy M82, obtained with the Multi-Element Radio-Linked Interferometer Network (MERLIN) at 5GHz and e-MERLIN at 6GHz. Combining several 5GHz MERLIN epochs to form a map with 33.0 uJy/bm noise level, 52 discrete sources, mostly supernova remnants and HII regions, are identified. These include three objects which were not detected in the 2002 5GHz MERLIN monitoring session: supernova SN2008iz, the transient source 43.78+59.3, and a new supernova remnant shell. Flux density variations, in the long (1981 to 2010), medium (2002 to 2010) and short (2009 to 2010) term, are investigated. We find that flux densities of SNRs in M82 stay constant in most of the sample (~95%). In addition, aside from SN2008iz and the well-known variable source 41.95+57.5, two sources display short and medium term variations over the period 2009-2010. These sources being among the most compact SNR in M82, these flux density variations could be due to changes in the circumstellar and interstellar medium in which the shocks travel.
- Published
- 2016
25. A Hard X-ray Study of the Normal Star-Forming Galaxy M83 with NuSTAR
- Author
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Tonia M. Venters, Daniel Stern, S. E. Boggs, J. Tyler, Andy Ptak, Fiona A. Harrison, V. Replicon, William W. Zhang, Megan Argo, Bret D. Lehmer, C. Hailey, Mihoko Yukita, Daniel R. Wik, Vallia Antoniou, Roman Krivonos, Ann Hornschemeier, Finn Erland Christensen, Thomas J. Maccarone, Keith Bechtol, Kip D. Kuntz, William W. Craig, and Andreas Zezas
- Subjects
Active galactic nucleus ,010504 meteorology & atmospheric sciences ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,star formation [Galaxies] ,Luminosity ,0103 physical sciences ,010303 astronomy & astrophysics ,individual (M83) [Galaxies] ,Astrophysics::Galaxy Astrophysics ,0105 earth and related environmental sciences ,Luminosity function (astronomy) ,Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Astronomy and Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,galaxies [X-rays] ,Black hole ,Neutron star ,Stars ,starburst [Galaxies] ,Star cluster ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Astrophysics - High Energy Astrophysical Phenomena - Abstract
We present results from sensitive, multi-epoch NuSTAR observations of the late-type star-forming galaxy M83 (d=4.6 Mpc), which is the first investigation to spatially resolve the hard (E>10 keV) X-ray emission of this galaxy. The nuclear region and ~ 20 off-nuclear point sources, including a previously discovered ultraluminous X-ray (ULX) source, are detected in our NuSTAR observations. The X-ray hardnesses and luminosities of the majority of the point sources are consistent with hard X-ray sources resolved in the starburst galaxy NGC 253. We infer that the hard X-ray emission is most likely dominated by intermediate accretion state black hole binaries and neutron star low-mass X-ray binaries (Z-sources). We construct the X-ray binary luminosity function (XLF) in the NuSTAR band for an extragalactic environment for the first time. The M83 XLF has a steeper XLF than the X-ray binary XLF in NGC 253, consistent with previous measurements by Chandra at softer X-ray energies. The NuSTAR integrated galaxy spectrum of M83 drops quickly above 10 keV, which is also seen in the starburst galaxies NGC253, NGC 3310 and NGC 3256. The NuSTAR observations constrain any AGN to be either highly obscured or to have an extremely low luminosity of $_{\sim}^, Comment: Accepted for publication in ApJ (25 pages, 17 figures)
- Published
- 2016
- Full Text
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26. Wide-field Global VLBI and MERLIN combined monitoring of supernova remnants in M82
- Author
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A. Pedlar, Danielle Fenech, Megan Argo, T. W. B. Muxlow, and Robert Beswick
- Subjects
Physics ,Deceleration parameter ,Astrophysics::High Energy Astrophysical Phenomena ,Flux ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Galaxy ,Interferometry ,Supernova ,Space and Planetary Science ,Very-long-baseline interferometry ,Supernova remnant ,Astrophysics::Galaxy Astrophysics ,MERLIN - Abstract
From a combination of MERLIN (Multi-Element Radio-Linked Interferometer Network) and global VLBI (Very Long Baseline Interferometry) observations of the starburst galaxy M82, images of 36 discrete sources at resolutions ranging from ~3 to ~80 mas at 1.7 GHz are presented. Of these 36 sources, 32 are identified as supernova remnants, 2 are HII regions, and 3 remain unclassified. Sizes, flux densities and radio brightnesses are given for all of the detected sources. Additionally, global VLBI only data from this project are used to image four of the most compact radio sources. These data provide a fifth epoch of VLBI observations of these sources, covering a 19-yr time-line. In particular, the continued expansion of one of the youngest supernova remnants, 43.31+59.3 is discussed. The deceleration parameter is a power-law index used to represent the time evolution of the size of a supernova remnant. For the source 43.31+59.3, a lower limit to the deceleration parameter is calculated to be 0.53+/-0.06, based on a lower limit of the age of this source.
- Published
- 2010
27. High-velocity-resolution observations of OH main line masers in the M82 starburst
- Author
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T. W. B. Muxlow, A. Pedlar, D Fenech, Robert Beswick, and Megan Argo
- Subjects
Physics ,Cosmology and Nongalactic Astrophysics (astro-ph.CO) ,High velocity ,Resolution (electron density) ,FOS: Physical sciences ,Astronomy and Astrophysics ,Starburst region ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Laser ,Spectral line ,law.invention ,Space and Planetary Science ,law ,Astrophysics::Solar and Stellar Astrophysics ,Maser ,Astrophysics::Galaxy Astrophysics ,Astrophysics - Cosmology and Nongalactic Astrophysics ,Line (formation) - Abstract
Using the VLA, a series of high velocity resolution observations have been made of the M82 starburst at 1.6 GHz. These observations follow up on previous studies of the main line OH maser emission in the central kiloparsec of this starburst region, but with far greater velocity resolution, showing significant velocity structure in some of the maser spots for the first time. A total of thirteen masers were detected, including all but one of the previously known sources. While some of these masers are still unresolved in velocity, these new results clearly show velocity structure in spectra from several of the maser regions. Position-velocity plots show good agreement with the distribution of H{\sc i} including interesting velocity structure on the blueward feature in the west of the starburst which traces the velocity distribution seen in the ionised gas., Comment: MNRAS in press. 15 pages, 9 figures
- Published
- 2010
28. Things that go bump in the night: the curious case of NGC660
- Author
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Ilse van Bemmel, Megan Argo, S. Connolly, and Robert Beswick
- Published
- 2015
29. The e-MERLIN Data Reduction Pipeline
- Author
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Megan Argo and STFC
- Subjects
Computer science ,Physics ,astrophysics ,radio astronomy ,interferometry ,FOS: Physical sciences ,Library and Information Sciences ,Software ,e-MERLIN ,data reduction ,radio interferometry ,calibration ,Calibration ,Instrumentation and Methods for Astrophysics (astro-ph.IM) ,computer.programming_language ,lcsh:Computer software ,business.industry ,Plain text ,computer.file_format ,Modular design ,Python (programming language) ,Astronomical image processing ,lcsh:QA76.75-76.765 ,Astrophysics - Instrumentation and Methods for Astrophysics ,business ,Raw data ,computer ,Computer hardware ,astro-ph.IM ,Information Systems ,Data reduction - Abstract
Written in Python and utilising ParselTongue to interface with the Astronomical Image Processing System (AIPS), the e-MERLIN data reduction pipeline is intended to automate the procedures required in processing and calibrating radio astronomy data from the e-MERLIN correlator. Driven by a plain text file of input parameters, the pipeline is modular and can be run in stages by the user, depending on requirements. The software includes options to load raw data, average in time and/or frequency, flag known sources of interference, flag more comprehensively with SERPent, carry out some or all of the calibration procedures including self-calibration), and image in either normal or wide-field mode. It also optionally produces a number of useful diagnostic plots at various stages so that the quality of the data can be assessed. The software is available for download from the e-MERLIN website or via Github., Comment: 6 pages, 1 figure. Code DOI: 10.5281/zenodo.10163 [ascl:1407.017]
- Published
- 2015
30. SKA studies of nearby galaxies: star-formation, accretion processes and molecular gas across all environments
- Author
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Megan Argo, Susanne Aalto, T. W. B. Muxlow, Elias Brinks, Eric J. Murphy, A. Rushton, Miguel A. Pérez-Torres, Eva Schinnerer, Clive Dickinson, D Fenech, Michael W. Peel, John Conway, Anita M. S. Richards, A. Alberdi, I. van Bemmel, Robert Beswick, Malcolm Gray, and H. R. Kloeckner
- Subjects
Physics ,Cosmology and Nongalactic Astrophysics (astro-ph.CO) ,Molecular line ,Star formation ,Astrophysics::High Energy Astrophysical Phenomena ,Astrophysics::Instrumentation and Methods for Astrophysics ,Astronomy ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Accretion (astrophysics) ,Astrophysics of Galaxies (astro-ph.GA) ,Surface brightness ,Astrophysics::Galaxy Astrophysics ,Astrophysics - Cosmology and Nongalactic Astrophysics - Abstract
The SKA will be a transformational instrument in the study of our local Universe. In particular, by virtue of its high sensitivity (both to point sources and diffuse low surface brightness emission), angular resolution and the frequency ranges covered, the SKA will undertake a very wide range of astrophysical research in the field of nearby galaxies. By surveying vast numbers of nearby galaxies of all types with $\mu$Jy sensitivity and sub-arcsecond angular resolutions at radio wavelengths, the SKA will provide the cornerstone of our understanding of star-formation and accretion activity in the local Universe. In this chapter we outline the key continuum and molecular line science areas where the SKA, both during phase-1 and when it becomes the full SKA, will have a significant scientific impact., Comment: 23 pages, 4 figures, to appear as part of 'Continuum Science' in Proceedings 'Advancing Astrophysics with the Square Kilometre Array' PoS(AASKA14)070
- Published
- 2014
31. CLASS B0445+123: a new two-image gravitational lens system
- Author
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John McKean, Roger Blandford, Megan Argo, Iwa Browne, Christopher D. Fassnacht, David Rusin, Steven T. Myers, T. J. Pearson, A. G. de Bruyn, Peter N. Wilkinson, D. R. Marlow, A. C. S. Readhead, Kyu-Hyun Chae, Léon V. E. Koopmans, M. A. Norbury, P. M. Phillips, T. York, Neal Jackson, A. D. Biggs, Astronomy, and Kapteyn Astronomical Institute
- Subjects
Physics ,Spectral index ,COSMIC cancer database ,Component (thermodynamics) ,Astrophysics::High Energy Astrophysical Phenomena ,Astrophysics (astro-ph) ,gravitational lensing ,Astrophysics::Instrumentation and Methods for Astrophysics ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,galaxies : individual : B0445+123 ,law.invention ,Lens (optics) ,Gravitational lens ,Space and Planetary Science ,law ,Feature (computer vision) ,Magnitude (astronomy) ,Astrophysics::Galaxy Astrophysics ,MERLIN - Abstract
A new two-image gravitational lens system has been discovered as a result of the Cosmic Lens All-Sky Survey (CLASS). Radio observations with the VLA, MERLIN and the VLBA at increasingly higher resolutions all show two components with a flux density ratio of ~7:1 and a separation of 1.34". Both components are compact and have the same spectral index. Followup observations made with the VLA at 8.4 GHz show evidence of a feature to the south-east of the brighter component and a corresponding extension of the weaker component to the north-west. Optical observations with the WHT show ~1.7" extended emission aligned in approximately the same direction as the separation between the radio components with an R-band magnitude of 21.8 +/- 0.4., 6 pages, 5 figures, accepted by MNRAS
- Published
- 2003
32. A Focused, Hard X-ray Look at Arp 299 with NuSTAR
- Author
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Finn Erland Christensen, William W. Craig, C. J. Hailey, Ann Hornschemeier, Andy Ptak, Daniel R. Wik, M. Tatum, Roman Krivonos, Fiona A. Harrison, Thomas J. Maccarone, Steven E. Boggs, William W. Zhang, Keith Bechtol, Mihoko Yukita, Lucía Ballo, Andreas Zezas, Tonia M. Venters, Bret D. Lehmer, R. Della Ceca, Daniel Stern, Megan Argo, and Vallia Antoniou
- Subjects
Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,active [Galaxies] ,individual (Arp 299) [Galaxies] ,X-ray ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Spectral line ,Luminosity ,galaxies [X-rays] ,starburst [Galaxies] ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Astrophysics - High Energy Astrophysical Phenomena - Abstract
We report on simultaneous observations of the local starburst system Arp 299 with NuSTAR and Chandra, which provides the first resolved images of this galaxy up to energies of ~ 45 keV. Fitting the 3-40 keV spectrum reveals a column density of $N_{\rm H}$ ~ 4 x10^{24} cm^{-2}, characteristic of a Compton-thick AGN, and a 10-30 keV luminosity of 1.2x 10^{43} ergs s^{-1}. The hard X-rays detected by NuSTAR above 10 keV are centered on the western nucleus, Arp 299-B, which previous X-ray observations have shown to be the primary source of neutral Fe-K emission. Other X-ray sources, including Arp 299-A, the eastern nucleus which is also thought to harbor an AGN, as well as X-ray binaries, contribute $\lesssim 10%$ to the 10-20 keV emission from the Arp 299 system. The lack of significant emission above 10 keV other than that attributed to Arp 299-B suggests that: a) any AGN in Arp 299-A must be heavily obscured ($N_{\rm H}$ > 10^{24} cm^{-2}) or have a much lower luminosity than Arp 299-B and b) the extranuclear X-ray binaries have spectra that cut-off above ~10 keV. Such soft spectra are characteristic of ultraluminous X-ray (ULX) sources observed to date by NuSTAR., 9 pages; accepted for publication in Astrophysical Journal
- Published
- 2014
- Full Text
- View/download PDF
33. Spatially resolving a starburst galaxy at hard X-ray energies: NuSTAR, CHANDRA, AND VLBA observations of NGC 253
- Author
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B. Lehmer, Megan Argo, William W. Craig, Vallia Antoniou, D. Stern, Daniel R. Wik, Roman Krivonos, Andreas Zezas, C. J. Hailey, Finn Erland Christensen, Fiona A. Harrison, Steven E. Boggs, W. W. Zhang, Tonia M. Venters, M. Yukita, Keith Bechtol, Thomas J. Maccarone, Andy Ptak, and Ann Hornschemeier
- Subjects
Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Astrophysics::High Energy Astrophysical Phenomena ,Galactic Center ,Local Group ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Redshift ,Galaxy ,Star cluster ,Pulsar ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Astrophysics - High Energy Astrophysical Phenomena ,Very Long Baseline Array ,Astrophysics::Galaxy Astrophysics ,Fermi Gamma-ray Space Telescope - Abstract
Prior to the launch of NuSTAR, it was not feasible to spatially resolve the hard (E > 10 keV) emission from galaxies beyond the Local Group. The combined NuSTAR dataset, comprised of three ~165 ks observations, allows spatial characterization of the hard X-ray emission in the galaxy NGC 253 for the first time. As a follow up to our initial study of its nuclear region, we present the first results concerning the full galaxy from simultaneous NuSTAR, Chandra, and VLBA monitoring of the local starburst galaxy NGC 253. Above ~10 keV, nearly all the emission is concentrated within 100" of the galactic center, produced almost exclusively by three nuclear sources, an off-nuclear ultraluminous X-ray source (ULX), and a pulsar candidate that we identify for the first time in these observations. We detect 21 distinct sources in energy bands up to 25 keV, mostly consisting of intermediate state black hole X-ray binaries. The global X-ray emission of the galaxy - dominated by the off-nuclear ULX and nuclear sources, which are also likely ULXs - falls steeply (photon index >~ 3) above 10 keV, consistent with other NuSTAR-observed ULXs, and no significant excess above the background is detected at E > 40 keV. We report upper limits on diffuse inverse Compton emission for a range of spatial models. For the most extended morphologies considered, these hard X-ray constraints disfavor a dominant inverse Compton component to explain the ��-ray emission detected with Fermi and H.E.S.S. If NGC 253 is typical of starburst galaxies at higher redshift, their contribution to the E > 10 keV cosmic X-ray background is < 1%., 20 pages, 14 figures, accepted for publication in ApJ
- Published
- 2014
34. Peering into the heart of the M82 starburst
- Author
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Megan Argo, Robert Beswick, Danielle Fenech, and T. W. B. Muxlow
- Subjects
Physics ,Space and Planetary Science ,Peering ,Astronomy ,Astronomy and Astrophysics ,Astrophysics - Abstract
We present multi-epoch millarcsecond resolution images of the most compact supernova remnants in the nearby starburst galaxy M82, spanning 25 years of evolution. In particular, we will briefly discuss the new transient source first detected in 2009 as well as the unusual object 41.95+57.5 and its potential as a GRB afterglow.
- Published
- 2015
35. NuSTAR and Chandra Insight into the Nature of the 3-40 keV Nuclear Emission in NGC 253
- Author
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Finn Erland Christensen, William W. Zhang, Andreas Zezas, Fiona A. Harrison, Vallia Antoniou, J. Leyder, Tonia M. Venters, Andy Ptak, Megan Argo, Thomas J. Maccarone, Daniel Stern, Bret D. Lehmer, Walter Craig, Ann Hornschemeier, Stephen E. Boggs, Daniel R. Wik, C. J. Hailey, Roman Krivonos, and Keith Bechtol
- Subjects
Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,X-ray astronomy ,Active galactic nucleus ,Cosmology and Nongalactic Astrophysics (astro-ph.CO) ,Point source ,Star formation ,Radio galaxy ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astronomy and Astrophysics ,Quasar ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Galaxy ,law.invention ,Telescope ,Space and Planetary Science ,law ,Astrophysics - High Energy Astrophysical Phenomena ,Astrophysics::Galaxy Astrophysics ,Astrophysics - Cosmology and Nongalactic Astrophysics - Abstract
We present results from three nearly simultaneous NuSTAR and Chandra monitoring observations between 2012 Sep 2 and 2012 Nov 16 of local star-forming galaxy NGC 253. The 3-40 keV NuSTAR intensity of the inner 20 arcsec (~400 pc) nuclear region varied by a factor of ~2 across the three monitoring observations. The Chandra data reveal that the nuclear region contains three bright X-ray sources, including a luminous (L2-10 keV ~ few x 10^39 erg/s) point source ~1 arcsec from the dynamical center of the galaxy (within the 3sigma positional uncertainty of the dynamical center); this source drives the overall variability of the nuclear region at energies >3 keV. We make use of the variability to measure the spectra of this single hard X-ray source when it was in bright states. The spectra are well described by an absorbed (NH ~ 1.6 x 10^23 cm^-2) broken power-law model with spectral slopes and break energies that are typical of ultraluminous X-ray sources (ULXs), but not AGN. A previous Chandra observation in 2003 showed a hard X-ray point source of similar luminosity to the 2012 source that was also near the dynamical center (~0.4 arcsec); however, this source was offset from the 2012 source position by ~1 arcsec. We show that the probability of the 2003 and 2012 hard X-ray sources being unrelated is >>99.99% based on the Chandra spatial localizations. Interestingly, the Chandra spectrum of the 2003 source (3-8 keV) is shallower in slope than that of the 2012 hard X-ray source. Its proximity to the dynamical center and harder Chandra spectrum indicate that the 2003 source is a better AGN candidate than any of the sources detected in our 2012 campaign; however, we were unable to rule out a ULX nature for this source. Future NuSTAR and Chandra monitoring would be well equipped to break the degeneracy between the AGN and ULX nature of the 2003 source, if again caught in a high state., Accepted for publication in ApJ (7 pages, 5 figures)
- Published
- 2013
36. Probing the nature of compact ultrasteep spectrum radio sources with the e-EVN and e-MERLIN
- Author
-
M. Mahmud, H. J. A. Röttgering, Z. Paragi, G. Miley, Megan Argo, and Hans-Rainer Klöckner
- Subjects
European VLBI Network ,Cosmology and Nongalactic Astrophysics (astro-ph.CO) ,Radio galaxy ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Radio spectrum ,X-shaped radio galaxy ,0103 physical sciences ,Very-long-baseline interferometry ,galaxies ,active radio-continuum ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Physics ,Spectral index ,010308 nuclear & particles physics ,Astrophysics::Instrumentation and Methods for Astrophysics ,Astronomy ,Astronomy and Astrophysics ,Small sample ,Galaxy ,Space and Planetary Science ,Astrophysics - Cosmology and Nongalactic Astrophysics - Abstract
We present first results from electronic Multi-Element Remotely Linked Interferometer Network (e-MERLIN) and electronic European VLBI Network (e-EVN) observations of a small sample of ultra-steep spectrum radio sources, defined as those sources with a spectral index alpha < -1.4 between 74 MHz and 325 MHz, which are unresolved on arcsecond scales. Such sources are currently poorly understood and a number of theories as to their origin have been proposed in the literature. The new observations described here have resulted in the first detection of two of these sources at milliarcsecond scales and show that a significant fraction of ultra-steep spectrum sources may have compact structures which can only be studied at the high resolution available with very long baseline interferometry (VLBI)., Five pages, two tables, one figure. Accepted to MNRAS Letters
- Published
- 2013
37. VLBI Monitoring of the most compact sources in M82
- Author
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Megan Argo, Danielle Fenech, T. W. B. Muxlow, Robert Beswick, and A. Pedlar
- Subjects
Very-long-baseline interferometry ,Astronomy ,Environmental science - Published
- 2011
38. Wide-fiIeld imaging of M31 - rst results
- Author
-
Megan Argo
- Published
- 2011
39. VLBI observations of SN2011dh: imaging of the youngest radio supernova
- Author
-
Chris Stockdale, K. W. Weiler, J. M. Marcaide, A. J. van der Horst, Ivan Marti-Vidal, Z. Paragi, Jun Yang, Eduardo Ros, J. C. Guirado, Megan Argo, Miguel A. Pérez-Torres, Antonio Alberdi, Valeriu Tudose, and M. A. Garrett
- Subjects
Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Cosmology and Nongalactic Astrophysics (astro-ph.CO) ,Epoch (reference date) ,Astrophysics::High Energy Astrophysical Phenomena ,Astrophysics::Instrumentation and Methods for Astrophysics ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Supernova ,Space and Planetary Science ,Very-long-baseline interferometry ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics - High Energy Astrophysical Phenomena ,Astrophysics::Galaxy Astrophysics ,Astrophysics - Cosmology and Nongalactic Astrophysics - Abstract
We report on the VLBI detection of supernova SN2011dh at 22GHz using a subset of the EVN array. The observations took place 14 days after the discovery of the supernova, thus resulting in a VLBI image of the youngest radio-loud supernova ever. We provide revised coordinates for the supernova with milli-arcsecond precision, linked to the ICRF. The recovered flux density is a factor 2 below the EVLA flux density reported by other authors at the same frequency and epoch of our observations. This discrepancy could be due to extended emission detected with the EVLA or to calibration problems in the VLBI and/or EVLA observations., Comment: Letter. Accepted in A&A
- Published
- 2011
- Full Text
- View/download PDF
40. Discovery of an unusual new radio source in the star-forming galaxy M82: Faint supernova, supermassive blackhole, or an extra-galactic microquasar?
- Author
-
Andreas Zezas, A. Pedlar, Martin Ward, Andreas Brunthaler, Danielle Fenech, Simon Garrington, T. W. B. Muxlow, Robert Beswick, J. van Eymeren, and Megan Argo
- Subjects
Physics ,Cosmology and Nongalactic Astrophysics (astro-ph.CO) ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Star (graph theory) ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Supernova ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,MERLIN ,Astrophysics::Galaxy Astrophysics ,Astrophysics - Cosmology and Nongalactic Astrophysics - Abstract
A faint new radio source has been detected in the nuclear region of the starburst galaxy M82 using MERLIN radio observations designed to monitor the flux density evolution of the recent bright supernova SN2008iz. This new source was initially identified in observations made between 1-5th May 2009 but had not been present in observations made one week earlier, or in any previous observations of M82. In this paper we report the discovery of this new source and monitoring of its evolution over its first 9 months of existence. The true nature of this new source remains unclear, and we discuss whether this source may be an unusual and faint supernova, a supermassive blackhole associated with the nucleus of M82, or intriguingly the first detection of radio emission from an extragalactic microquasar., 6 pages, 3 figures (2 colour), MNRAS letters accepted
- Published
- 2010
41. OH masers in nearby galaxies
- Author
-
D Fenech, Megan Argo, Robert Beswick, A. Pedlar, and T. W. B. Muxlow
- Subjects
law ,Astrophysics ,Maser ,Galaxy ,law.invention - Published
- 2010
42. A mildly relativistic radio jet from the otherwise normal Type Ic Supernova 2007gr
- Author
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Zsolt Paragi, S. Bourke, M. A. Garrett, Jonathan Granot, H. J. van Langevelde, Michael Bietenholz, G. B. Taylor, Y. Pidopryhora, Arpad Szomoru, Megan Argo, A. J. van der Horst, B. Paczyński, Chryssa Kouveliotou, and Enrico Ramirez-Ruiz
- Subjects
Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Jet (fluid) ,Multidisciplinary ,Astrophysics::High Energy Astrophysical Phenomena ,Astronomy ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Type II supernova ,Supernova ,Astrophysical jet ,Speed of light ,Astrophysics::Solar and Stellar Astrophysics ,Ejecta ,Gamma-ray burst ,Astrophysics - High Energy Astrophysical Phenomena ,Relativistic speed ,Astrophysics::Galaxy Astrophysics - Abstract
The class of type Ic supernovae have drawn increasing attention since 1998 owing to their sparse association (only four so far) with long duration gamma-ray bursts. Although both phenomena originate from the core collapse of a massive star, supernovae emit mostly at optical wavelengths, whereas GRBs emit mostly in soft gamma-rays or hard X-rays. Though the GRB central engine generates ultra-relativistic jets, which beam the early emission into a narrow cone, no relativistic outflows have hitherto been found in type Ib/c supernovae explosions, despite theoretical expectations and searches. Here we report radio (interferometric) observations that reveal a mildly relativistic expansion in a nearby type Ic supernova, SN 2007gr. Using two observational epochs 60 days apart, we detect expansion of the source and establish a conservative lower limit for the average apparent expansion velocity of 0.6c. Independently, a second mildly relativistic supernova has been reported. Contrary to the radio data, optical observations of SN 2007gr indicate a typical type Ic supernova with ejecta velocities ~6000 km/s, much lower than in GRB-associated supernovae. We conclude that in SN 2007gr a small fraction of the ejecta produced a low-energy mildly relativistic bipolar radio jet, while the bulk of the ejecta were slower and, as shown by optical spectro-polarimetry, mildly aspherical., Comment: Nature, 10 pages (including supplementary material), 2 figures
- Published
- 2010
- Full Text
- View/download PDF
43. 23 GHz VLBI Observations of SN 2008ax
- Author
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Eduardo Ros, Stefan Immler, Robert Beswick, Ivan Marti-Vidal, A. Pedlar, J. M. Marcaide, S. D. Van Dyk, Miguel A. Pérez-Torres, Megan Argo, K. W. Weiler, Chris Stockdale, Richard A. Sramek, J. C. Guirado, T. W. B. Muxlow, Irwin I. Shapiro, Nino Panagia, and A. Alberdi
- Subjects
Physics ,Image (category theory) ,Flux ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Standard deviation ,Supernova ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Very-long-baseline interferometry ,Ejecta ,Very Long Baseline Array ,Noise (radio) - Abstract
We report on phase-referenced 23 GHz Very-Long-Baseline-Interferometry (VLBI) observations of the type IIb supernova SN 2008ax, made with the Very Long Baseline Array (VLBA) on 2 April 2008 (33 days after explosion). These observations resulted in a marginal detection of the supernova. The total flux density recovered from our VLBI image is 0.8$\pm$0.3 mJy (one standard deviation). As it appears, the structure may be interpreted as either a core-jet or a double source. However, the supernova structure could be somewhat confused with a possible close by noise peak. In such a case, the recovered flux density would decrease to 0.48$\pm$0.12 mJy, compatible with the flux densities measured with the VLA at epochs close in time to our VLBI observations. The lowest average expansion velocities derived from our observations are $(1.90 \pm 0.30) \times 10^5$ km s$^{-1}$ (case of a double source) and $(5.2 \pm 1.3) \times 10^4$ km s$^{-1}$ (taking the weaker source component as a spurious, close by, noise peak, which is the more likely interpretation). These velocities are 7.3 and 2 times higher, respectively, than the maximum ejecta velocity inferred from optical-line observations., 4 pages, 3 figures. Accepted in A&A on 24/03/2009
- Published
- 2009
44. Radio searches for supernovae in nearby starburst galaxies
- Author
-
Megan Argo
- Subjects
Physics ,Supernova ,Planet ,Dark energy ,Astronomy ,Astrophysics ,Galaxy ,MERLIN - Abstract
Jodrell Bank ObservatoryE-mail: mkargo@manchester.ac.ukOver the last four years, we have been using both MERLIN and the VLA to regularly observea sample of nearby starburst galaxies, looking for new radio supernovae in order to investigatetheir starformationrates, and monitoring the ux es of known compact objects within each galaxy.In the course of this project we have observed many supernovae, discovering two, placing up-per limits on the early radio emission for several, and producing two of the most detailed radiolight curves for type II supernovae. Here we briey outline some of the recent results, includingMERLIN single-baseline observations carried out over September and October 2007.From Planets to Dark Energy: the Modern Radio UniverseOctober 1-5 2007The University of Manchester, UK
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- 2008
45. Deep MERLIN 5GHz Radio Imaging of Supernova Remnants in the M82 Starburst
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A. Pedlar, Megan Argo, T. W. B. Muxlow, D Fenech, and Robert Beswick
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Physics ,Astrophysics::High Energy Astrophysical Phenomena ,Astrophysics (astro-ph) ,Shell (structure) ,Flux ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Rms noise ,Galaxy ,Supernova ,Interferometry ,Space and Planetary Science ,Radio imaging ,MERLIN ,Astrophysics::Galaxy Astrophysics - Abstract
The results of an extremely deep, 8-day long observation of the central kpc of the nearby starburst galaxy M82 using MERLIN (Multi-Element Radio Linked Interferometer Network) at 5 GHz are presented. The 17E-06 Jy/beam, rms noise level in the naturally weighted image make it the most sensitive high resolution radio image of M82 made to date. Over 50 discrete sources are detected, the majority of which are supernova remnants, but with 13 identified as HII regions. Sizes, flux densities and radio brightnesses are given for all of the detected sources, which are all well resolved with a majority showing shell or partial shell structures. Those sources within the sample which are supernova remnants have diameters ranging from 0.3 to 6.7 pc, with a mean size of 2.9 pc. From a comparison with previous MERLIN 5 GHz observations made in July 1992, which gives a 9.75 year timeline, it has been possible to measure the expansion velocities of ten of the more compact sources, eight of which have not been measured before. These derived expansion velocities range between 2200 and 10500 km/s., Comment: 34 pages, 10 figures. Accepted by MNRAS
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- 2008
- Full Text
- View/download PDF
46. Transfer of a 1486.3 MHz frequency standard over installed fibre links for local oscillator distribution with a stability of 1 picosecond
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Roshene McCool, Michael L. Bentley, Ralph Spencer, Simon Garrington, and Megan Argo
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Physics ,Optical fiber ,business.industry ,Local oscillator ,Frequency standard ,Stability (probability) ,law.invention ,Optics ,law ,Transfer (computing) ,Picosecond ,Fiber laser ,business ,Radio astronomy - Abstract
Details of a local oscillator distribution system over 110 km of installed fibre with an r.m.s. stability of, 1 ps in 1 second, 2 ps in 1 minute and 4 ps in 10 minutes.
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- 2008
47. Supernova remnants in the central starburst region of M82
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Robert Beswick, W. M. Trotman, Megan Argo, A. Pedlar, T. W. B. Muxlow, and Danielle Fenech
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Physics ,Supernova ,European VLBI Network ,Epoch (reference date) ,Very-long-baseline interferometry ,Astronomy ,Starburst region ,Astrophysics ,MERLIN - Abstract
E-mail: dfenech@jb.man.ac.ukOn the 3rd March 2005, global Very Long Baseline Interferometry (VLBI) observations weremade of the central kiloparsec of M82 at 1.6GHz (18cm), with an angular resolution of 4mas.We present detailed images of four of the brightest, most compact supernova remnants as seen inthese observations. These data are the fth epoch of 1.6GHz VLBI observations of M82, the rstof which was made in December 1986, enabling study of these compact sources over a 19 yeartimescale. We will also discuss MERLIN 1.6GHz observations made simultaneously, which havebeen combined with the global VLBI data, to produce high delity images of a large number ofthe known supernova remnants and HII regions in M82.8th European VLBI Network SymposiumSeptember 26-29, 2006Torun,´ Poland
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- 2007
48. 8.4GHz VLBI observations of SN2004et in NGC6946
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Ivan Marti-Vidal, J. M. Marcaide, K. W. Weiler, L. M. Lara, J. C. Guirado, Eduardo Ros, Jozsef Vinko, Antonio Alberdi, Megan Argo, Miguel A. Pérez-Torres, Irwin I. Shapiro, A. Pedlar, Christopher Stockdale, Richard A. Sramek, Robert Beswick, and T. W. B. Muxlow
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media_common.quotation_subject ,FOS: Physical sciences ,Individual ,Astrophysics ,UNESCO::ASTRONOMÍA Y ASTROFÍSICA ,Asymmetry ,Luminosity ,law.invention ,law ,Very-long-baseline interferometry ,NGC 6946 ,media_common ,Physics ,Spiral galaxy ,Image (category theory) ,Astrophysics (astro-ph) ,Astronomy and Astrophysics ,Galaxies ,Stars ,ASTRONOMÍA Y ASTROFÍSICA::Cosmología y cosmogonia [UNESCO] ,Synchrotron ,Supernova ,Radio continuum ,Supernovae ,Space and Planetary Science ,Brightness temperature ,SN 2004et ,UNESCO::ASTRONOMÍA Y ASTROFÍSICA::Cosmología y cosmogonia ,ASTRONOMÍA Y ASTROFÍSICA [UNESCO] - Abstract
We report on 8.4GHz Very Long Baseline Interferometry (VLBI) observations of the type II-P supernova SN2004et in the spiral galaxy NGC 6946, made on 20 February 2005 (151 days after explosion). The Very Large Array (VLA) flux density was 1.23$\pm$0.07 mJy, corresponding to an isotropic luminosity at 8.4GHz of (4.45$\pm$0.3)$\times10^{25}$ erg s$^{-1}$ Hz$^{-1}$ and a brightness temperature of (1.3$\pm$0.3)$\times10^{8}$ K. We also provide an improved source position, accurate to about 0.5 mas in each coordinate. The VLBI image shows a clear asymmetry. From model fitting of the size of the radio emission, we estimate a minimum expansion velocity of 15,700$\pm$2,000 km s$^{-1}$. This velocity is more than twice the expected mean expansion velocity estimated from a synchrotron self-absorbed emission model, thus suggesting that synchrotron self-absorption is not relevant for this supernova. With the benefit of an optical spectrum obtained 12 days after explosion, we favor an emission model which consists of two hot spots on an underlying expanding shell of width comparable to that of SN 1993J., Accepted for publication in A&A (22/05/07)
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- 2007
49. OH main line masers in the M82 starburst
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Robert Beswick, T. W. B. Muxlow, Megan Argo, and A. Pedlar
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Very large array ,Physics ,Line-of-sight ,Astrophysics::High Energy Astrophysical Phenomena ,Astrophysics (astro-ph) ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Central region ,Galaxy ,law.invention ,Supernova ,Space and Planetary Science ,law ,Satellite line ,Maser ,Astrophysics::Galaxy Astrophysics - Abstract
A study of the distribution of OH gas in the central region of the nearby active starburst galaxy M82 has confirmed two previously known bright masers and revealed several new main line masers. Three of these are seen only at 1665 MHz, one is detected only at 1667 MHz, while the rest are detected in both lines. Observations covering both the 1665 and 1667 MHz lines, conducted with both the Very Large Array (VLA) and the Multi-Element Radio Linked Interferometer Network (MERLIN), have been used to accurately measure the positions and velocities of these features. This has allowed a comparison with catalogued continuum features in the starburst such as HII regions and supernova remnants, as well as known water and satellite line OH masers. Most of the main line masers appear to be associated with known HII regions although the two detected only at 1665 MHz are seen along the same line of sight as known supernova remnants., Comment: MNRAS accepted. 16 pages, 13 figures
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- 2007
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50. MERLIN monitoring of recent core-collapse supernovae
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Megan Argo, Beswick, R. J., Muxlow, T. W. B., Pedlar, A., Fenech, D., and Thrall, H.
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Astrophysics::High Energy Astrophysical Phenomena ,Astrophysics (astro-ph) ,FOS: Physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
The star formation rate (SFR) in starburst galaxies can be measured by many methods, one of which is through the supernova rate. Due to the heavy dust obscuration in these galaxies, searches for new supernovae in the optical or infra-red can easily miss events occurring in the central starburst regions. As part of a long term program to estimate the SFR in a sample of nearby starbursts we are using MERLIN and the VLA to regularly observe the galaxies for new radio supernovae. As part of this project, regular MERLIN observations have been made of two recent optically bright supernovae: 2004dj and 2004et. Both supernovae are of Type II and have been monitored frequently over periods of a few months, resulting in well sampled radio "light" curves for both objects., To appear in the proceedings of "Stellar End Products" conference held in Granada, Spain, 12-15 April 2005. Five pages, two figures. Corrected a couple of flux points
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- 2005
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