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12 results on '"Kennedy, M.R."'

1. Mass estimates from optical modelling of the new TRAPUM redback PSR J1910−5320

Author

Dodge, O.G., Breton, R.P., Clark, C.J., Burgay, M., Strader, J., Au, K.-Y., Barr, E.D., Buchner, S., Dhillon, V.S., Ferrara, E.C., Freire, P.C.C., Griessmeier, J.-M., Kennedy, M.R., Kramer, M., Li, K.-L., Padmanabh, P.V., Phosrisom, A., Stappers, B.W., Swihart, S.J., Thongmeearkom, T., Dodge, O.G., Breton, R.P., Clark, C.J., Burgay, M., Strader, J., Au, K.-Y., Barr, E.D., Buchner, S., Dhillon, V.S., Ferrara, E.C., Freire, P.C.C., Griessmeier, J.-M., Kennedy, M.R., Kramer, M., Li, K.-L., Padmanabh, P.V., Phosrisom, A., Stappers, B.W., Swihart, S.J., and Thongmeearkom, T.

Abstract

Spider pulsars continue to provide promising candidates for neutron star mass measurements. Here we present the discovery of PSR J1910−5320, a new millisecond pulsar discovered in a MeerKAT observation of an unidentified Fermi-LAT gamma-ray source. This pulsar is coincident with a recently identified candidate redback binary, independently discovered through its periodic optical flux and radial velocity. New multicolour optical light curves obtained with ULTRACAM/New Technology Telescope in combination with MeerKAT timing and updated SOAR/Goodman spectroscopic radial velocity measurements allow a mass constraint for PSR J1910−5320. ICARUS optical light curve modelling, with streamlined radial velocity fitting, constrains the orbital inclination and companion velocity, unlocking the binary mass function given the precise radio ephemeris. Our modelling aims to unite the photometric and spectroscopic measurements available by fitting each simultaneously to the same underlying physical model, ensuring self-consistency. This targets centre-of-light radial velocity corrections necessitated by the irradiation endemic to spider systems. Depending on the gravity darkening prescription used, we find a moderate neutron star mass of either 1.6 ± 0.2 or 1.4 ± 0.2 M⊙. The companion mass of either 0.45 ± 0.04 or M⊙ also further confirms PSR J1910−5320 as an irradiated redback spider pulsar.

Published
2024

2. Neutron star mass estimates from gamma-ray eclipses in spider millisecond pulsar binaries

Author

Clark, C.J., Kerr, M., Barr, E.D., Bhattacharyya, B., Breton, R.P., Bruel, P., Camilo, F., Chen, W., Cognard, I., Cromartie, H.T., Deneva, J., Dhillon, V.S., Guillemot, L., Kennedy, M.R., Kramer, M., Lyne, A.G., Sánchez, D. Mata, Nieder, L., Phillips, C., Ransom, S.M., Ray, P.S., Roberts, M.S.E., Roy, J., Smith, D.A., Spiewak, R., Stappers, B.W., Tabassum, S., Theureau, G., Voisin, G., Clark, C.J., Kerr, M., Barr, E.D., Bhattacharyya, B., Breton, R.P., Bruel, P., Camilo, F., Chen, W., Cognard, I., Cromartie, H.T., Deneva, J., Dhillon, V.S., Guillemot, L., Kennedy, M.R., Kramer, M., Lyne, A.G., Sánchez, D. Mata, Nieder, L., Phillips, C., Ransom, S.M., Ray, P.S., Roberts, M.S.E., Roy, J., Smith, D.A., Spiewak, R., Stappers, B.W., Tabassum, S., Theureau, G., and Voisin, G.

Abstract

Reliable neutron star mass measurements are key to determining the equation of state of cold nuclear matter, but such measurements are rare. Black widows and redbacks are compact binaries consisting of millisecond pulsars and semi-degenerate companion stars. Spectroscopy of the optically bright companions can determine their radial velocities, providing inclination-dependent pulsar mass estimates. Although inclinations can be inferred from subtle features in optical light curves, such estimates may be systematically biased due to incomplete heating models and poorly understood variability. Using data from the Fermi Large Area Telescope, we have searched for gamma-ray eclipses from 49 spider systems, discovering significant eclipses in 7 systems, including the prototypical black widow PSR B1957+20. Gamma-ray eclipses require direct occultation of the pulsar by the companion, and so the detection, or significant exclusion, of a gamma-ray eclipse strictly limits the binary inclination angle, providing new robust, model-independent pulsar mass constraints. For PSR B1957+20, the eclipse implies a much lighter pulsar (1.81 ± 0.07 solar masses) than inferred from optical light curve modelling.

Published
2023

4. Multi-colour optical light curves of the companion star to the millisecond pulsar PSR J2051−0827

Author

Dhillon, V.S., Kennedy, M.R., Breton, R.P., Clark, C.J., Sánchez, D.M., Voisin, G., Breedt, E., Brown, A.J., Dyer, M.J., Green, M.J., Kerry, P., Littlefair, S.P., Marsh, T.R., Parsons, S.G., Pelisoli, I., Sahman, D.I., Wild, J.F., van Kerkwijk, M.H., and Stappers, B.W.

Abstract

We present simultaneous, multi-colour optical light curves of the companion star to the black-widow pulsar PSR J2051−0827, obtained approximately 10 years apart using ULTRACAM and HiPERCAM, respectively. The ULTRACAM light curves confirm the previously reported asymmetry in which the leading hemisphere of the companion star appears to be brighter than the trailing hemisphere. The HiPERCAM light curves, however, do not show this asymmetry, demonstrating that whatever mechanism is responsible for it varies on timescales of a decade or less. We fit the symmetrical HiPERCAM light curves with a direct-heating model to derive the system parameters, finding an orbital inclination of 55.9+4.8−4.1 degrees, in good agreement with radio-eclipse constraints. We find that approximately half of the pulsar’s spin-down energy is converted to optical luminosity, resulting in temperatures ranging from approximately 5150+190−190 K on the day side to 2750+130−150 K on the night side of the companion star. The companion star is close to filling its Roche lobe (⁠fRL=0.88+0.02−0.02⁠) and has a mass of 0.039+0.010−0.011 M⊙, giving a mean density of 20.24+0.59−0.44 g cm−3 and an apsidal motion constant in the range 0.0036 < k2 < 0.0047. The companion mass and mean density values are consistent with those of brown dwarfs, but the apsidal motion constant implies a significantly more centrally-condensed internal structure than is typical for such objects.

Published
2022

5. Evidence that short-period AM CVn systems are diverse in outburst behaviour

Author

Duffy, C., Ramsay, G., Steeghs, D., Dhillon, V., Kennedy, M.R., Mata Sánchez, D., Ackley, K., Dyer, M., Lyman, J., Ulaczyk, K., Galloway, D.K., O’Brien, P., Noysena, K., Nuttall, L., and Pollacco, D.

Abstract

We present results of our analysis of up to 15 yr of photometric data from eight AM CVn systems with orbital periods between 22.5 and 26.8 min. Our data have been collected from the GOTO, ZTF, Pan-STARRS, ASAS-SN, and Catalina all-sky surveys and amateur observations collated by the AAVSO. We find evidence that these interacting ultracompact binaries show a similar diversity of long-term optical properties as the hydrogen accreting dwarf novae. We found that AM CVn systems in the previously identified accretion disc instability region are not a homogenous group. Various members of the analysed sample exhibit behaviour reminiscent of Z Cam systems with long superoutbursts (SOs) and standstills, SU UMa systems with regular, shorter SOs, and nova-like systems that appear only in a high state. The addition of TESS full frame images of one of these systems, KL Dra, reveals the first evidence for normal outbursts appearing as a precursor to SOs in an AM CVn system. Our results will inform theoretical modelling of the outbursts of hydrogen deficient systems.

Published
2021

6. Optical, X-ray, and γ-ray observations of the candidate transitional millisecond pulsar 4FGL J0427.8-6704

Author

Kennedy, M.R., Breton, R.P., Clark, C.J., Dhillon, V.S., Kerr, M., Buckley, D.A.H., Potter, S.B., Mata Sánchez, D., Stringer, J.G., and Marsh, T.R.

Abstract

We present an optical, X-ray, and γ-ray study of 1SXPS J042749.2-670434, an eclipsing X-ray binary that has an associated γ-ray counterpart, 4FGL J0427.8-6704. This association has led to the source being classified as a transitional millisecond pulsar (tMSP) in an accreting state. We analyse 10.5 yr of Fermi LAT data and detect a γ-ray eclipse at the same phase as optical and X-ray eclipses at the >5 σ level, a significant improvement on the 2.8 σ level of the previous detection. The confirmation of this eclipse solidifies the association between the X-ray source and the γ-ray source, strengthening the tMSP classification. However, analysis of several optical data sets and an X-ray observation do not reveal a change in the source’s median brightness over long time-scales or a bi-modality on short time-scales. Instead, the light curve is dominated by flickering, which has a correlation time of 2.6 min alongside a potential quasi-periodic oscillation at ∼21 min. The mass of the primary and secondary stars is constrained to be M1=1.43+0.33−0.19 M⊙ and M2=0.3+0.17−0.12 M⊙ through modelling of the optical light curve. While this is still consistent with a white dwarf primary, we favour the tMSP in a low accretion state classification due to the significance of the γ-ray eclipse detection.

Published
2020

7. Einstein@Home discovery of the gamma-ray millisecond pulsar PSR J2039-5617 confirms its predicted redback nature

Author

Clark, C.J., Nieder, L., Voisin, G., Allen, B., Aulbert, C., Behnke, O., Breton, R.P., Choquet, C., Corongiu, A., Dhillon, V.S., Eggenstein, H.B., Fehrmann, H., Guillemot, L., Harding, A.K., Kennedy, M.R., Machenschalk, B., Marsh, T.R., Sánchez, D.M., Mignani, R.P., Stringer, J., Wadiasingh, Z., Wu, J., Clark, C.J., Nieder, L., Voisin, G., Allen, B., Aulbert, C., Behnke, O., Breton, R.P., Choquet, C., Corongiu, A., Dhillon, V.S., Eggenstein, H.B., Fehrmann, H., Guillemot, L., Harding, A.K., Kennedy, M.R., Machenschalk, B., Marsh, T.R., Sánchez, D.M., Mignani, R.P., Stringer, J., Wadiasingh, Z., and Wu, J.

Abstract

The Fermi Large Area Telescope gamma-ray source 3FGL J2039.6-5618 contains a periodic optical and X-ray source that was predicted to be a 'redback' millisecond pulsar (MSP) binary system. However, the conclusive identification required the detection of pulsations from the putative MSP. To better constrain the orbital parameters for a directed search for gamma-ray pulsations, we obtained new optical light curves in 2017 and 2018, which revealed long-term variability from the companion star. The resulting orbital parameter constraints were used to perform a targeted gamma-ray pulsation search using the Einstein@Home-distributed volunteer computing system. This search discovered pulsations with a period of 2.65 ms, confirming the source as a binary MSP now known as PSR J2039-5617. Optical light-curve modelling is complicated, and likely biased, by asymmetric heating on the companion star and long-term variability, but we find an inclination i ≳ 60°, for a low pulsar mass between 1.1 M⊙ < Mpsr < 1.6 M⊙, and a companion mass of 0.15-0.22 M⊙z, confirming the redback classification. Timing the gamma-ray pulsations also revealed significant variability in the orbital period, which we find to be consistent with quadrupole moment variations in the companion star, suggestive of convective activity. We also find that the pulsed flux is modulated at the orbital period, potentially due to inverse Compton scattering between high-energy leptons in the pulsar wind and the companion star's optical photon field.

Published
2020

8. Searching for electromagnetic counterparts to gravitational-wave merger events with the prototype Gravitational-Wave Optical Transient Observer (GOTO-4)

Author

Gompertz, B.P., Cutter, R., Steeghs, D., Galloway, D.K., Lyman, J., Ulaczyk, K., Dyer, M.J., Ackley, K., Dhillon, V.S., O’Brien, P.T., Ramsay, G., Poshyachinda, S., Kotak, R., Nuttall, L., Breton, R.P., Pallé, E., Pollacco, D., Thrane, E., Aukkaravittayapun, S., Awiphan, S., Brown, M.J.I., Burhanudin, U., Chote, P., Chrimes, A.A., Daw, E., Duffy, C., Eyles-Ferris, R.A.J., Heikkilä, T., Irawati, P., Kennedy, M.R., Killestein, T., Levan, A.J., Littlefair, S., Makrygianni, L., Marsh, T., Mata Sánchez, D., Mattila, S., Maund, J., McCormac, J., Mkrtichian, D., Mong, Y.-L., Mullaney, J., Müller, B., Obradovic, A., Rol, E., Sawangwit, U., Stanway, E.R., Starling, R.L.C., Strøm, P.A., Tooke, S., West, R., Wiersema, K., Gompertz, B.P., Cutter, R., Steeghs, D., Galloway, D.K., Lyman, J., Ulaczyk, K., Dyer, M.J., Ackley, K., Dhillon, V.S., O’Brien, P.T., Ramsay, G., Poshyachinda, S., Kotak, R., Nuttall, L., Breton, R.P., Pallé, E., Pollacco, D., Thrane, E., Aukkaravittayapun, S., Awiphan, S., Brown, M.J.I., Burhanudin, U., Chote, P., Chrimes, A.A., Daw, E., Duffy, C., Eyles-Ferris, R.A.J., Heikkilä, T., Irawati, P., Kennedy, M.R., Killestein, T., Levan, A.J., Littlefair, S., Makrygianni, L., Marsh, T., Mata Sánchez, D., Mattila, S., Maund, J., McCormac, J., Mkrtichian, D., Mong, Y.-L., Mullaney, J., Müller, B., Obradovic, A., Rol, E., Sawangwit, U., Stanway, E.R., Starling, R.L.C., Strøm, P.A., Tooke, S., West, R., and Wiersema, K.

Abstract

Contains fulltext : 221952.pdf (publisher's version ) (Open Access)

Published
2020

9. The dry continent

Author

Kennedy, M.R.

Subjects
Rain and rainfall -- Australia, Droughts -- Australia, Arid regions -- Natural history, Australia -- Natural history
Published
1983

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