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Subject = Pulsars;
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Displaying Results 1 - 15 of 15 on page 1 of 1
Marked
Mark
A search for optical bursts from the rotating radio transient j1819−1458 with ultracam - ii. simultaneous ultracam-lovell telescope observations
(2018)
Dhillon, V. S.; Keane, E. F.; Marsh, T. R.; Stappers, B. W.; Copperwheat, C. M.; Hickma...
A search for optical bursts from the rotating radio transient j1819−1458 with ultracam - ii. simultaneous ultracam-lovell telescope observations
(2018)
Dhillon, V. S.; Keane, E. F.; Marsh, T. R.; Stappers, B. W.; Copperwheat, C. M.; Hickman, R. D. G.; Jordan, C. A.; Kerry, P.; Kramer, M.; Littlefair, S. P.; Lyne, A. G.; Mignani, R. P.; Shearer, A.
Abstract:
The rotating radio transient (RRAT) J1819-1458 exhibits similar to 3ms bursts in the radio every similar to 3 min, implying that it is visible for only similar to 1 s per day. Assuming that the optical light behaves in a similar manner, long exposures of the field would be relatively insensitive due to the accumulation of sky photons. A much better way of detecting optical emission from J1819-1458 would then be to observe with a high-speed optical camera simultaneously with radio observations, and co-add only those optical frames coincident with the dispersion-corrected radio bursts. We present the results of such a search, using simultaneous ULTRACAM and Lovell Telescope observations. We find no evidence for optical bursts in J1819-1458 at magnitudes brighter than i' = 19.3 (5 sigma limit). This is nearly 3 mag fainter than the previous burst limit, which had no simultaneous radio observations.
http://hdl.handle.net/10379/11180
Marked
Mark
A search for the optical counterpart of PSR B1951+32 in the supernova remnant CTB 80
(1998)
O'Sullivan, Créidhe; Shearer, A.; Colhoun, M.; Golden, A.; Redfern, M.; Butler, R....
A search for the optical counterpart of PSR B1951+32 in the supernova remnant CTB 80
(1998)
O'Sullivan, Créidhe; Shearer, A.; Colhoun, M.; Golden, A.; Redfern, M.; Butler, R.; Beskin, G.M.; Niezvestny, S.I.; Neustroev, V.V.; Plokhotnichenko, V.L.; Danks, A.
Abstract:
Using time-resolved two-dimensional aperture photometry we have put upper limits on the pulsed emission from two proposed optical counterparts for PSR B1951+32. Our pulsed upper limits of mv,pulsed > 23.3, mb,pulsed > 24.4, for the first candidate and mv,pulsed > 23.6, mb,pulsed > 24.3 for the second, make it unlikely that either of these is, in fact, the pulsar. We discuss three further candidates, but also reject these on the basis of timing results. A search of a 5.""5 × 5.""5 area centred close to these stars failed to find any significant pulsations at the reported pulsar period.
http://mural.maynoothuniversity.ie/7101/
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Circular polarization of synchrotron radiation in high magnetic fields
(2016)
de Burca, Diarmaid; Shearer, Andrew
Circular polarization of synchrotron radiation in high magnetic fields
(2016)
de Burca, Diarmaid; Shearer, Andrew
Abstract:
The general model for incoherent synchrotron radiation has long been known, with the first theory being published by Westfold in 1959 and continued by Westfold and Legg in 1968. When this model was first developed, it was applied to radiation from Jupiter, with a magnetic field of approximate to 1G. Pulsars have a magnetic field of approximate to 10(12) G. The Westfold and Legg model predict a circular polarization which is proportional to the square root of the magnetic field, and consequently predicts greater than 100 per cent circular polarization at high magnetic fields. Here a new model is derived based upon a more detailed analysis of the pitch angle distribution. This model is concerned with the frequency range f(B0)/gamma
DdeB acknowledges the National University of Galway, Ireland’s College of Science PhD scholarship which funded this work.
http://hdl.handle.net/10379/5648
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Development of a high time resolution optical polarimeter for astronomy
(2019)
O'Connor, Eoin
Development of a high time resolution optical polarimeter for astronomy
(2019)
O'Connor, Eoin
Abstract:
This work started in September, 2014 and initially started as an investigation of the characterisation issues associated with using Electron Multiplying Charge- Coupled Devices (EMCCDs) in a two beam polarimeter. It was necessary to undertake a work placement with Andor Technology Ltd. (Belfast) in 2015 to carry out testing and characterisation of CMOS and CCD sensors and to investigate how they could be integrated as imaging sensors with the GASP instrument. EMCCDs were selected due to their low noise performance under low light level conditions and the GASP instrument has been used over the duration of this work on three different telescopes, namely: the William Herschel Telescope in La Palma in December 2015, the Observatoire de Haute-Provence (OHP) 1.93m telescope in September 2017 and the La Silla Observatory 3.6m Telescope in February 2018. The main initial design and fabrication work on the retarding beamsplitting (RBS) prism was undertaken previously in NUI Galway. The work ...
http://hdl.handle.net/10379/14897
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Long-term photometric variations in the candidate white-dwarf pulsar AR Scorpii from K2 , CRTS, and ASAS-SN observations
(2017)
Littlefield, Colin; Garnavich, Peter M.; Kennedy, Mark R.; Callanan, Paul J.; Shappee, ...
Long-term photometric variations in the candidate white-dwarf pulsar AR Scorpii from K2 , CRTS, and ASAS-SN observations
(2017)
Littlefield, Colin; Garnavich, Peter M.; Kennedy, Mark R.; Callanan, Paul J.; Shappee, Benjamin; Holoien, Thomas
Abstract:
We analyze long-cadence Kepler K2 observations of AR Sco from 2014, along with survey photometry obtained between 2005 and 2016 by the Catalina Real-Time Sky Survey and the All-Sky Automated Survey for Supernovae. The K2 data show the orbital modulation to have been fairly stable during the 78 days of observations, but we detect aperiodic deviations from the average waveform with an amplitude of ~2% on a timescale of a few days. A comparison of the K2 data with the survey photometry reveals that the orbital waveform gradually changed between 2005 and 2010, with the orbital maximum shifting to earlier phases. We compare these photometric variations with proposed models of this unusual system.
http://hdl.handle.net/10468/5443
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Multi-wavelength and Polarisation Studies of Pulsars: the Crab, Vela, and PSR J0205+6449
(2014)
Moran, Paul
Multi-wavelength and Polarisation Studies of Pulsars: the Crab, Vela, and PSR J0205+6449
(2014)
Moran, Paul
Abstract:
This thesis outlines the findings of a multi-wavelength and polarimetric study of a number of rotation-powered pulsars. Polarisation studies of pulsars are just one example of obtaining insight into the geometry of their emission regions. Such measurements provide observational constraints on the various theoretical models of the pulsar emission mechanism. Hence, it is possible to limit these competing models and find the model that best matches observations. A comparison of the optical light curves to the radio, X-ray, and gamma-ray ones is also important to locate diff erent emission regions in the neutron star magnetosphere. The phase-averaged optical linear polarisation of the Crab nebula and pulsar was measured using observations from the HST/ACS. These findings were then compared to the results of hard-X-ray/soft-gamma -ray polarisation observations of the system using INTEGRAL/IBIS. In both cases it was found that the polarisation position angle (PA) of the pulsar is alig...
http://hdl.handle.net/10379/4789
Marked
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Multi-wavelength and polarisation studies of pulsars: the crab, vela, and PSR J0205+6449
(2015)
Moran, Paul
Multi-wavelength and polarisation studies of pulsars: the crab, vela, and PSR J0205+6449
(2015)
Moran, Paul
Abstract:
This thesis outlines the findings of a multi-wavelength and polarimetric study of a number of rotation-powered pulsars. Polarisation studies of pulsars are just one example of obtaining insight into the geometry of their emission regions. Such measurements provide observational constraints on the various theoretical models of the pulsar emission mechanism. Hence, it is possible to limit these competing models and find the model that best matches observations. A comparison of the optical light curves to the radio, X-ray, and gamma-ray ones is also important to locate diff erent emission regions in the neutron star magnetosphere. The phase-averaged optical linear polarisation of the Crab nebula and pulsar was measured using observations from the HST/ACS. These findings were then compared to the results of hard-X-ray/soft-gamma-ray polarisation observations of the system using INTEGRAL/IBIS. In both cases it was found that the polarisation position angle (PA) of the pulsar is align...
http://hdl.handle.net/10379/5029
Marked
Mark
Optical photometry and spectroscopy of the accretion-powered millisecond pulsar HETE J1900.1-2455
(2008)
Elebert, Patrick; Callanan, Paul J.; Filippenko, Alexei V.; Garnavich, Peter M.; Mackie...
Optical photometry and spectroscopy of the accretion-powered millisecond pulsar HETE J1900.1-2455
(2008)
Elebert, Patrick; Callanan, Paul J.; Filippenko, Alexei V.; Garnavich, Peter M.; Mackie, G.; Hill, J. M.; Burwitz, V.
Abstract:
We present phase resolved optical photometry and spectroscopy of the accreting millisecond pulsar HETE J1900.1-2455. Our R-band light curves exhibit a sinusoidal modulation, at close to the orbital period, which we initially attributed to X-ray heating of the irradiated face of the secondary star. However, further analysis reveals that the source of the modulation is more likely due to superhumps caused by a precessing accretion disc. Doppler tomography of a broad Ha emission line reveals an emission ring, consistent with that expected from an accretion disc. Using the velocity of the emission ring as an estimate for the projected outer disc velocity, we constrain the maximum projected velocity of the secondary to be 200 km s(-1), placing a lower limit of 0.05 M-circle dot on the secondary mass. For a 1.4 M-circle dot primary, this implies that the orbital inclination is low, less than or similar to 20 degrees. Utilizing the observed relationship between the secondary mass and the o...
http://hdl.handle.net/10468/4978
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Mark
Optical spectroscopy and photometry of SAX J1808.4-3658 in outburst
(2009)
Elebert, Patrick; Reynolds, M. T.; Callanan, Paul J.; Hurley, Daniel Jason; Ramsay, G.;...
Optical spectroscopy and photometry of SAX J1808.4-3658 in outburst
(2009)
Elebert, Patrick; Reynolds, M. T.; Callanan, Paul J.; Hurley, Daniel Jason; Ramsay, G.; Lewis, F.; Russell, D. M.; Nord, B.; Kane, S. R.; DePoy, D. L.; Hakala, P.
Abstract:
We present phase resolved optical spectroscopy and photometry of V4580 Sagittarii, the optical counterpart to the accretion powered millisecond pulsar SAX J1808.4-3658, obtained during the 2008 September/October outburst. Doppler tomography of the NIII lambda 4640.64 Bowen blend emission line reveals a focused spot of emission at a location consistent with the secondary star. The velocity of this emission occurs at 324 +/- 15 km s(-1); applying a 'K-correction', we find the velocity of the secondary star projected on to the line of sight to be 370 +/- 40 km s-1. Based on existing pulse timing measurements, this constrains the mass ratio of the system to be 0.044(-0.004)(+0.005), and the mass function for the pulsar to be 0.44(-0.13)(+0.16)M(circle dot). Combining this mass function with various inclination estimates from other authors, we find no evidence to suggest that the neutron star in SAX J1808.4-3658 is more massive than the canonical value of 1.4M(circle dot). Our ...
http://hdl.handle.net/10468/4971
Marked
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Polarisation of synchrotron radiation from isolated neutron stars
(2016)
de Burca, Diarmaid
Polarisation of synchrotron radiation from isolated neutron stars
(2016)
de Burca, Diarmaid
Abstract:
Pulsars are enigmatic neutron stars which have defied efforts to understand them for over 40 years. POREC (Pulsar Optical Reverse Engineering Code) was first written to constrain pulsar emission theories through constraining the emission location. POREC originally used the Westfold, Legg and Gleeson (WLG) model to calculate the incoher- ent optical emission that would be seen. In this work it is shown that the WLG model fails for optical (and higher) wavelengths in high magnetic fields (> 10^6 G). A new model for incoherent synchrotron radiation in high magnetic fields (the DS model) is proposed. While this does solve the original problems associated with the WLG model, the DS model has its own weaknesses. A full discussion of the derivation of the DS model and of the various weaknesses of the DS model will be covered. POREC is updated to the DS model. A new pitch angle distribution (PAD) for POREC is proposed, and the problems with this new PAD discussed. The new simulations are...
http://hdl.handle.net/10379/5622
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The light curve of the companion to PSR B1957+20
(2007)
Reynolds, Mark T.; Callanan, Paul J.; Fruchter, Andrew S.; Torres, M. A. P.; Beer, M. E...
The light curve of the companion to PSR B1957+20
(2007)
Reynolds, Mark T.; Callanan, Paul J.; Fruchter, Andrew S.; Torres, M. A. P.; Beer, M. E.; Gibbons, R. A.
Abstract:
We present a new analysis of the light curve for the secondary star in the eclipsing binary millisecond pulsar system PSR B1957+20. Combining previous data and new data points at minimum from the Hubble Space Telescope, we have 100 per cent coverage in the R-band. We also have a number of new K-s-band data points, which we use to constrain the infrared magnitude of the system. We model this with the eclipsing light-curve (ELC) code. From the modelling with the ELC code we obtain colour information about the secondary at minimum light in BVRI and K. For our best-fitting model we are able to constrain the system inclination to 65 degrees +/- 2 degrees for pulsar masses ranging from 1.3 to 1.9 M-circle dot. The pulsar mass is unconstrained. We also find that the secondary star is not filling its Roche lobe. The temperature of the unirradiated side of the companion is in agreement with previous estimates and we find that the observed temperature gradient across the secondary star is phy...
http://hdl.handle.net/10468/4980
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The mass of the neutron star in the binary millisecond pulsar PSR J1012+5307
(1998)
Callanan, Paul J.; Garnavich, Peter M.; Koester, D.
The mass of the neutron star in the binary millisecond pulsar PSR J1012+5307
(1998)
Callanan, Paul J.; Garnavich, Peter M.; Koester, D.
Abstract:
We have measured the radial velocity variation of the white dwarf secondary in the binary system containing the millisecond pulsar PSR J1012 + 5307. Combined with the orbital parameters of the radio pulsar, we infer a mass ratio q (=M-1/M-2) = 10.5 +/- 0.5 OUT optical spectroscopy has also allowed us to determine the mass of the white dwarf companion by fitting the spectrum to a grid of DA model atmospheres: we estimate M-2 = 0.16 +/- 0.02 M., and hence the mass of the neutron star is 1.64 +/- 0.22 M., where the error is dominated by that of M-2. The orbital inclination is 52 +/- 4 deg. For an initial neutron star mass of similar to 1.4 M., only a few tenths of a solar mass at most has been successfully accreted over the lifetime of the progenitor low-mass X-ray binary. If the initial mass of the secondary was similar to 1 M., our result suggests that the mass transfer may have been non-conservative.
http://hdl.handle.net/10468/4992
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The optical development and calibration of the Galway Astronomical Stokes Polarimeter (GASP) as a multi-detector system for the polarimetric observations of variable optical sources
(2014)
Kyne, Gillian
The optical development and calibration of the Galway Astronomical Stokes Polarimeter (GASP) as a multi-detector system for the polarimetric observations of variable optical sources
(2014)
Kyne, Gillian
Abstract:
Polarised light from astronomical targets can yield a wealth of information about their source radiation mechanisms, and about the geometry of the scattered light regions. To date, stellar observations have focused, for the most part, on the linearly polarised component of the optical emission. Observations have been restricted due to inadequate instrumentation, and particularly the need for suitable observing conditions and the availability of luminous targets. The motivation in developing the Galway Astronomical Stokes Polarimeter (GASP) makes possible the ability to observe beyond these sources. GASP is based upon division of amplitude polarimeter (DOAP) (Compain and Drevillon, 1998), which measures the four components of the Stokes vector (I, Q, U and V) simultaneously. This work establishes a suitable optical design that develops GASP as an imaging polarimeter, enabling an acceptable FOV and pixelscale for a 5-m class telescope. It also focuses on two important aspects of using...
http://hdl.handle.net/10379/4572
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Veritas: the very energetic radiation imaging telescope array system
(2018)
Weekes, T.C; Badran, H; Biller, S.D; Bond, I; Bradbury, S; Buckley, J; Carter-Lewis, D;...
Veritas: the very energetic radiation imaging telescope array system
(2018)
Weekes, T.C; Badran, H; Biller, S.D; Bond, I; Bradbury, S; Buckley, J; Carter-Lewis, D; Catanese, M; Criswell, S; Cui, W; Dowkontt, P; Duke, C; Fegan, D.J; Finley, J; Fortson, L; Gaidos, J; Gillanders, G.H; Grindlay, J; Hall, T.A; Harris, K
http://hdl.handle.net/10379/9978
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VLT polarimetry observations of the middle-aged pulsar PSR B0656+14
(2016)
Moran, Paul; Shearer, Andrew
VLT polarimetry observations of the middle-aged pulsar PSR B0656+14
(2016)
Moran, Paul; Shearer, Andrew
Abstract:
Context. Optical polarisation measurements are key tests for different models of the pulsar magnetosphere. Furthermore, comparing the relative orientation of the phase-averaged linear polarisation direction and the pulsar proper motion vector may unveil a peculiar alignment, clearly seen in the Crab pulsar.Aims. Our goal is to obtain the first measurement of the phase-averaged optical linear polarisation of the fifth brightest optical pulsar, PSR B0656+14, which also has a precisely measured proper motion, and to verify a possible alignment between the polarisation direction and the proper motion vector.Methods. We carried out observations with the Very Large Telescope (VLT) to measure the phase-averaged optical polarisation degree (PD) and position angle (PA) of PSR B0656+14.Results. We measured a PD of 11.9% +/- 5.5% and a PA of 125.8 degrees +/- 13.2 degrees, measured east of north. Albeit of marginal significance, this is the first measurement of the phase-averaged optical PD fo...
http://hdl.handle.net/10379/5649
Displaying Results 1 - 15 of 15 on page 1 of 1
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Maynooth University (1)
NUI Galway (9)
University College Cork (5)
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Peer-reviewed (8)
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