10 results on '"Evangelia Tremou"'
Search Results
2. The MAVERIC Survey: Radio Catalogs and Source Counts from Deep Very Large Array Imaging of 25 Galactic Globular Clusters
- Author
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Laura Shishkovsky, Jay Strader, Laura Chomiuk, Evangelia Tremou, Vlad Tudor, James C. A. Miller-Jones, Arash Bahramian, Craig O. Heinke, Thomas J. Maccarone, and Gregory R. Sivakoff
- Published
- 2020
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3. X-Ray and Radio Observations of Central Black Holes in Nearby Low-mass Early-type Galaxies: Preliminary Evidence for Low Eddington Fractions
- Author
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Ryan Urquhart, Lauren I. McDermott, Jay Strader, Anil C. Seth, Laura Chomiuk, Nadine Neumayer, Dieu D. Nguyen, and Evangelia Tremou
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Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics - Astrophysics of Galaxies - Abstract
We present new radio and X-ray observations of two nearby ($< 4$ Mpc) low-mass early-type galaxies with dynamically-confirmed central black holes: NGC 5102 and NGC 205. NGC 5102 shows a weak nuclear X-ray source and has no core radio emission. However, for the first time we demonstrate that it shows luminous extended radio continuum emission in low-resolution, low-frequency ($< 3$ GHz) data, consistent with jet lobes on scales $\gtrsim 100$ pc formed from past accretion and jet activity. By contrast, in new, extremely deep, strictly-simultaneous Very Large Array and Chandra observations, no radio or X-ray emission is detected from the black hole in NGC 205. We consider these measurements and upper limits in the context of the few other low-mass early-type galaxies with dynamically-confirmed black holes, and show that the mean ratio of bolometric to Eddington luminosity in this sample is only $\textrm{log} \, (L_{\rm bol}/L_{\rm Edd}) = -6.57\pm0.50$. These Eddington ratios are lower than typical in a comparison sample of more massive early-type galaxies, though this conclusion is quite tentative due to our small sample of low-mass galaxies and potential biases in the comparison sample. This preliminary result is in mild tension with previous work using less sensitive observations of more distant galaxies, which predict higher X-ray luminosities than we observe for low-mass galaxies. If it is confirmed that central black holes in low-mass galaxies typically have low Eddington ratios, this presents a challenge to measuring the occupation fraction of central black holes with standard optical emission line, X-ray, or radio surveys., 13 pages, 4 figures, 3 tables. Accepted for publication in ApJ
- Published
- 2022
4. 1RXH J082623.6–505741: A New Long-period Cataclysmic Variable with an Evolved Donor and a Low Mass-transfer Rate
- Author
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Kirill V. Sokolovsky, Jay Strader, Samuel J. Swihart, Elias Aydi, Arash Bahramian, Laura Chomiuk, Craig O. Heinke, Allison K. Hughes, Kwan-Lok Li, Raimundo Lopes de Oliveira, James C. A. Miller-Jones, Koji Mukai, David J. Sand, Laura Shishkovsky, Evangelia Tremou, and Karina Voggel
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High Energy Astrophysical Phenomena (astro-ph.HE) ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics - High Energy Astrophysical Phenomena ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
We report the discovery of 1RXH J082623.6-505741, a 10.4 hr orbital period compact binary. Modeling extensive optical photometry and spectroscopy reveals a $\sim 0.4 M_{\odot}$ K-type secondary transferring mass through a low-state accretion disk to a non-magnetic $\sim 0.8 M_{\odot}$ white dwarf. The secondary is overluminous for its mass and dominates the optical spectra at all epochs, and must be evolved to fill its Roche Lobe at this orbital period. The X-ray luminosity $L_X \sim 1$-$2 \times 10^{32}$ erg s$^{-1}$ derived from both new XMM-Newton and archival observations, although high compared to most CVs, still only requires a modest accretion rate onto the white dwarf of $\dot{M} \sim 3 \times 10^{-11}$ to $3 \times 10^{-10} M_{\odot}$ yr$^{-1}$, lower than expected for a cataclysmic variable with an evolved secondary. No dwarf nova outbursts have yet been observed from the system, consistent with the low derived mass transfer rate. Several other cataclysmic variables with similar orbital periods also show unexpectedly low mass transfer rates, even though selection effects disfavor the discovery of binaries with these properties. This suggests the abundance and evolutionary state of long-period, low mass transfer rate cataclysmic variables is worthy of additional attention., Comment: 21 pages, 8 figures, 1 table, accepted to ApJ
- Published
- 2022
5. 2FGL J0846.0+2820: A New Neutron Star Binary with a Giant Secondary and Variable gamma-Ray Emission
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Tyrel J. Johnson, Laura Chomiuk, Søren S. Larsen, Asher Wasserman, David J. Sand, Daniel E. Reichart, G. V. Simonian, Jean P. Brodie, J. B. Haislip, Samuel J. Swihart, Evangelia Tremou, Jay Strader, C. C. Cheung, and Laura Shishkovsky
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Physics ,010308 nuclear & particles physics ,Astronomy ,Astrophysics::High Energy Astrophysical Phenomena ,Binary number ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Neutron star ,Variable (computer science) ,Space and Planetary Science ,0103 physical sciences ,ComputingMethodologies_DOCUMENTANDTEXTPROCESSING ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Astrophysics - High Energy Astrophysical Phenomena ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
We present optical photometric and spectroscopic observations of the likely stellar counterpart to the unassociated \emph{Fermi}-Large Area Telescope (LAT) $\gamma$-ray source 2FGL J0846.0+2820, selected for study based on positional coincidences of optical variables with unassociated LAT sources. Using optical spectroscopy from the SOAR telescope, we have identified a late-G giant in an eccentric ($e$ = 0.06) 8.133 day orbit with an invisible primary. Modeling the spectroscopy and photometry together lead us to infer a heavy neutron star primary of $\sim 2 M_{\odot}$ and a partially stripped giant secondary of $\sim 0.8 M_{\odot}$. H$\alpha$ emission is observed in some of the spectra, perhaps consistent with the presence of a faint accretion disk. We find the $\gamma$-ray flux of 2FGL J0846.0+2820 dropped substantially in mid-2009, accompanied by an increased variation in the optical brightness, and since then it has not been detected by \emph{Fermi}. The long period and giant secondary are reminiscent of the $\gamma$-ray bright binary 1FGL J1417.7--4407, which hosts a millisecond pulsar apparently in the final stages of the pulsar recycling process. The discovery of 2FGL J0846.0+2820 suggests the identification of a new subclass of millisecond pulsar binaries that are the likely progenitors of typical field millisecond pulsars., Comment: 12 pages, 8 figures, 3 tables. Accepted for publication in ApJ
- Published
- 2017
6. The MAVERIC Survey: Radio Catalogs and Source Counts from Deep Very Large Array Imaging of 25 Galactic Globular Clusters
- Author
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Jay Strader, Gregory R. Sivakoff, Vlad Tudor, Laura Shishkovsky, Thomas J. Maccarone, Laura Chomiuk, Craig O. Heinke, Arash Bahramian, James Miller-Jones, Evangelia Tremou, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)
- Subjects
High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,Very large array ,Astrophysics::High Energy Astrophysical Phenomena ,X-ray binary ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,01 natural sciences ,010305 fluids & plasmas ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Globular cluster ,0103 physical sciences ,Source counts ,Astrophysics - High Energy Astrophysical Phenomena ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics - Abstract
The MAVERIC survey is the first deep radio continuum imaging survey of Milky Way globular clusters, with a central goal of finding and classifying accreting compact binaries, including stellar-mass black holes. Here we present radio source catalogs for 25 clusters with ultra-deep Karl G. Jansky Very Large Array observations. The median observing time was 10 hr per cluster, resulting in typical rms sensitivities of 2.3 and 2.1 uJy per beam at central frequencies of 5.0 and 7.2 GHz, respectively. We detect nearly 1300 sources in our survey at 5 sigma, and while many of these are likely to be background sources, we also find strong evidence for an excess of radio sources in some clusters. The radio spectral index distribution of sources in the cluster cores differs from the background, and shows a bimodal distribution. We tentatively classify the steep-spectrum sources (those much brighter at 5.0 GHz) as millisecond pulsars and the flat-spectrum sources as compact or other kinds of binaries. These provisional classifications will be solidified with the future addition of X-ray and optical data. The outer regions of our images represent a deep, relatively wide field (~ 0.4/sq. deg) and high resolution C band background survey, and we present source counts calculated for this area. We also release radio continuum images for these 25 clusters to the community., published in ApJ. table 3 available as an ancillary CSV file. pending final hosting by the NRAO archive, the FITS images may be found at: https://www.dropbox.com/sh/a7a9qsqrepq5fmb/AABTtfMkftMSTUEFjzw6NU6Xa
- Published
- 2020
7. Improved Dynamical Constraints on the Masses of the Central Black Holes in Nearby Low-mass Early-type Galactic Nuclei and the First Black Hole Determination for NGC 205
- Author
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Renuka Pechetti, Nikolay Kacharov, Anil C. Seth, Phuong M. Nguyen, Karina T. Voggel, Evangelia Tremou, Nadine Neumayer, Mark den Brok, Arash Bahramian, Fabio Pacucci, Kouichiro Nakanishi, Michele Cappellari, Jay Strader, Laura Chomiuk, Dieu D. Nguyen, Cuc K. Ly, Satoru Iguchi, Takafumi Tsukui, Christopher P. Ahn, and Antoine Dumont
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Physics ,Solar mass ,010504 meteorology & atmospheric sciences ,Star formation ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Galactic nuclei ,Astrophysics - Astrophysics of Galaxies ,01 natural sciences ,Galaxy ,Early type ,Black hole ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Low Mass ,Spectroscopy ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,0105 earth and related environmental sciences - Abstract
We improve the dynamical black hole (BH) mass estimates in three nearby low-mass early-type galaxies--NGC 205, NGC 5102, and NGC 5206. We use new \hst/STIS spectroscopy to fit the star formation histories of the nuclei in these galaxies, and use these measurements to create local color--mass-to-light ratio (\ml) relations. We then create new mass models from \hst~imaging and combined with adaptive optics kinematics, we use Jeans dynamical models to constrain their BH masses. The masses of the central BHs in NGC 5102 and NGC 5206 are both below one million solar masses and are consistent with our previous estimates, $9.12_{-1.53}^{+1.84}\times10^5$\Msun~and $6.31_{-2.74}^{+1.06}\times10^5$\Msun~(3$\sigma$ errors), respectively. However, for NGC 205, the improved models suggest the presence of a BH for the first time, with a best-fit mass of $6.8_{-6.7}^{+95.6}\times10^3$\Msun~(3$\sigma$ errors). This is the least massive central BH mass in a galaxy detected using any method. We discuss the possible systematic errors of this measurement in detail. Using this BH mass, the existing upper limits of both X-ray, and radio emissions in the nucleus of NGC 205 suggest an accretion rate $\lesssim$$10^{-5}$ of the Eddington rate. We also discuss the color--\mleff~relations in our nuclei and find that the slopes of these vary significantly between nuclei. Nuclei with significant young stellar populations have steeper color--\mleff~relations than some previously published galaxy color--\mleff~relations., Comment: 31 pages, 19 figures, 6 tables, Accepted to ApJ
- Published
- 2019
8. Optical Spectroscopy and Demographics of Redback Millisecond Pulsar Binaries
- Author
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Jerome A. Orosz, Christopher T. Britt, Arash Bahramian, Jay Strader, R. Salinas, Samuel J. Swihart, Evangelia Tremou, Mark B. Peacock, C. C. Cheung, Kristen C. Dage, Roberto Mignani, Laura Shishkovsky, Laura Chomiuk, K. L. Li, Jules P. Halpern, 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), Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), and 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)
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010504 meteorology & atmospheric sciences ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Context (language use) ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,gamma rays: stars ,01 natural sciences ,Luminosity ,stars: neutron ,X-rays: binaries ,Pulsar ,Millisecond pulsar ,pulsars: general ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Spectroscopy ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics ,0105 earth and related environmental sciences ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,Sigma ,Astronomy and Astrophysics ,Radial velocity ,Neutron star ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Astrophysics::Earth and Planetary Astrophysics ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] ,Astrophysics - High Energy Astrophysical Phenomena ,binaries: spectroscopic - Abstract
We present the first optical spectroscopy of five confirmed (or strong candidate) redback millisecond pulsar binaries, obtaining complete radial velocity curves for each companion star. The properties of these millisecond pulsar binaries with low-mass, hydrogen-rich companions are discussed in the context of the 14 confirmed and 10 candidate field redbacks. We find that the neutron stars in redbacks have a median mass of 1.78 +/- 0.09 M_sun with a dispersion of sigma = 0.21 +/- 0.09. Neutron stars with masses in excess of 2 M_sun are consistent with, but not firmly demanded by, current observations. Redback companions have median masses of 0.36 +/- 0.04 M_sun with a scatter of sigma = 0.15 +/- 0.04, and a tail possibly extending up to 0.7-0.9 M_sun. Candidate redbacks tend to have higher companion masses than confirmed redbacks, suggesting a possible selection bias against the detection of radio pulsations in these more massive candidate systems. The distribution of companion masses between redbacks and the less massive black widows continues to be strongly bimodal, which is an important constraint on evolutionary models for these systems. Among redbacks, the median efficiency of converting the pulsar spindown energy to gamma-ray luminosity is ~10%., Apj in press. Long/large tables 6 and 7 also included as ancillary machine-readable files; numbering different from published version for ease of use
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- 2019
9. The MAVERIC Survey: Still No Evidence for Accreting Intermediate-mass Black Holes in Globular Clusters
- Author
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Thomas J. Maccarone, Laura Chomiuk, Gregory R. Sivakoff, Evangelia Tremou, Vlad Tudor, Anil C. Seth, Laura Shishkovsky, Jay Strader, Craig O. Heinke, Eva Noyola, and James Miller-Jones
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High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,Very large array ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,Continuum (design consultancy) ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,01 natural sciences ,Accretion (astrophysics) ,law.invention ,Telescope ,Black hole ,Space and Planetary Science ,law ,Globular cluster ,0103 physical sciences ,Cluster (physics) ,Astrophysics - High Energy Astrophysical Phenomena ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
We present the results of an ultra-deep, comprehensive radio continuum survey for the accretion signatures of intermediate-mass black holes in globular clusters. The sample, imaged with the Karl G.~Jansky Very Large Array and the Australia Telescope Compact Array, comprises 50 Galactic globular clusters. No compelling evidence for an intermediate-mass black hole is found in any cluster in our sample. In order to achieve the highest sensitivity to low-level emission, we also present the results of an overall stack of our sample, as well as various subsamples, also finding non-detections. These results strengthen the idea that intermediate-mass black holes with masses $\gtrsim 1000 M_{\odot}$ are rare or absent in globular clusters., Comment: 27 pages, 7 figures, 2 tables. Accepted for publication in ApJ
- Published
- 2018
10. Ionized-gas Kinematics Along the Large-scale Radio Jets in Type-2 AGNs
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Huynh Anh N. Le, Taehyun Jung, Narae Hwang, Aeree Chung, Evangelia Tremou, Donghoon Son, Byeong-Gon Park, Marios Karouzos, and Jong-Hak Woo
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Physics ,Jet (fluid) ,Stellar kinematics ,Active galactic nucleus ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,Doubly ionized oxygen ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Radius ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,01 natural sciences ,Galaxy ,law.invention ,Telescope ,Space and Planetary Science ,law ,Astrophysics of Galaxies (astro-ph.GA) ,0103 physical sciences ,Emission spectrum ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
To investigate the connection between radio activity and AGN outflows, we present a study of ionized gas kinematics based on [O III] $\lambda$5007 emission line along the large-scale radio jet for six radio AGNs. These AGNs are selected based on the radio activity (i.e., $\mathrm{L_{1.4GHz}}$ $\geqslant$ 10$^{39.8}$ erg s$^{-1}$) as well as optical emission line properties as type 2 AGNs. Using the Red Channel Cross Dispersed Echellette Spectrograph at the Multiple Mirror Telescope, we investigate in detail the [O III] and stellar kinematics. We spatially resolve and probe the central AGN-photoionization sizes, which is important in understanding the structures and evolutions of galaxies. We find that the typical central AGN-photoionization radius of our targets are in range of 0.9$-$1.6 kpc, consistent with the size-luminosity relation of [O III] in the previous studies. We investigate the [O III] kinematics along the large-scale radio jets to test whether there is a link between gas outflows in the narrow-line region and extended radio jet emissions. Contrary to our expectation, we find no evidence that the gas outflows are directly connected to the large scale radio jets., Comment: 10 pages, 8 figures, accepted in ApJ
- Published
- 2017
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