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Long-term pulse period evolution of the ultra-luminous X-ray pulsar NGC 7793 P13 (2021)
Journal Article
Fuerst, F., Walton, D., Heida, M., Bachetti, M., Pinto, C., Middleton, M., Brightman, M., Earnshaw, H., Barret, D., Fabian, A., Kretschmar, P., Pottschmidt, K., Ptak, A., Roberts, T., Stern, D., Webb, N., & Wilms, J. (2021). Long-term pulse period evolution of the ultra-luminous X-ray pulsar NGC 7793 P13. Astronomy & Astrophysics, 651, Article A75. https://doi.org/10.1051/0004-6361/202140625

Ultra-luminous X-ray pulsars (ULXPs) provide a unique opportunity to study persistent super-Eddington accretion. Here we present the results of a long-term monitoring campaign of ULXP NGC 7793 P13, focusing on the pulse period evolution and the deter... Read More about Long-term pulse period evolution of the ultra-luminous X-ray pulsar NGC 7793 P13.

XMM-Newton campaign on the ultraluminous X-ray source NGC 247 ULX-1: outflows (2021)
Journal Article
Pinto, C., Soria, R., Walton, D., D'Ai, A., Pintore, F., Kosec, P., Alston, W., Fuerst, F., Middleton, M., Roberts, T., Del Santo, M., Barret, D., Ambrosi, E., Robba, A., Earnshaw, H., & Fabian, A. (2021). XMM-Newton campaign on the ultraluminous X-ray source NGC 247 ULX-1: outflows. Monthly Notices of the Royal Astronomical Society, 505(4), 5058-5074. https://doi.org/10.1093/mnras/stab1648

Most ultraluminous X-ray sources (ULXs) are believed to be powered by super-Eddington accreting neutron stars and, perhaps, black holes. Above the Eddington rate the disc is expected to thicken and to launch powerful winds through radiation pressure.... Read More about XMM-Newton campaign on the ultraluminous X-ray source NGC 247 ULX-1: outflows.

Quasi-periodic dipping in the ultraluminous X-ray source, NGC 247 ULX-1 (2021)
Journal Article
Alston, W., Pinto, C., Barret, D., D'Ai, A., Del Santo, M., Earnshaw, H., Fabian, A., Fuerst, F., Kara, E., Kosec, P., Middleton, M., Parker, M., Pintore, F., Robba, A., Roberts, T., Sathyaprakash, R., Walton, D., & Ambrosi, E. (2021). Quasi-periodic dipping in the ultraluminous X-ray source, NGC 247 ULX-1. Monthly Notices of the Royal Astronomical Society, 505(3), 3722-3729. https://doi.org/10.1093/mnras/stab1473

Most ultraluminous X-ray sources (ULXs) are believed to be stellar mass black holes or neutron stars accreting beyond the Eddington limit. Determining the nature of the compact object and the accretion mode from broad-band spectroscopy is currently a... Read More about Quasi-periodic dipping in the ultraluminous X-ray source, NGC 247 ULX-1.

A new transient ultraluminous X-ray source in NGC 7090 (2020)
Journal Article
Walton, D., Heida, M., Bachetti, M., Fürst, F., Brightman, M., Earnshaw, H., Evans, P., Fabian, A., Grefenstette, B., Harrison, F., Israel, G., Lansbury, G., Middleton, M., Pike, S., Rana, V., Roberts, T., Rodriguez Castillo, G., Salvaterra, R., Song, X., & Stern, D. (2021). A new transient ultraluminous X-ray source in NGC 7090. Monthly Notices of the Royal Astronomical Society, 501(1), 1002-1012. https://doi.org/10.1093/mnras/staa3666

We report on the discovery of a new, transient ultraluminous X-ray source (ULX) in the galaxy NGC 7090. This new ULX, which we refer to as NGC 7090 ULX3, was discovered via monitoring with Swift during 2019–2020, and to date has exhibited a peak lumi... Read More about A new transient ultraluminous X-ray source in NGC 7090.

NIR Counterparts to ULXs (III): Completing the photometric survey and selected spectroscopic results* (2020)
Journal Article
López, K., Heida, M., Jonker, P., Torres, M., Roberts, T., Walton, D., Moon, D.-S., & Harrison, F. (2020). NIR Counterparts to ULXs (III): Completing the photometric survey and selected spectroscopic results*. Monthly Notices of the Royal Astronomical Society, 497(1), 917-932. https://doi.org/10.1093/mnras/staa1920

We present results from the remaining sources in our search for near-infrared (NIR) candidate counterparts to ultraluminous X-ray sources (ULXs) within ≃ 10 Mpc. We observed 23 ULXs in 15 galaxies and detected NIR candidate counterparts to six of the... Read More about NIR Counterparts to ULXs (III): Completing the photometric survey and selected spectroscopic results*.

Discovery of a 2.8 s Pulsar in a 2 Day Orbit High-mass X-Ray Binary Powering the Ultraluminous X-Ray Source ULX-7 in M51 (2020)
Journal Article
Rodríguez Castillo, G., Israel, G., Belfiore, A., Bernardini, F., Esposito, P., Pintore, F., De Luca, A., Papitto, A., Stella, L., Tiengo, A., Zampieri, L., Bachetti, M., Brightman, M., Casella, P., D’Agostino, D., Dall’Osso, S., Earnshaw, H., Fürst, F., Haberl, F., Harrison, F., …Wolter, A. (2020). Discovery of a 2.8 s Pulsar in a 2 Day Orbit High-mass X-Ray Binary Powering the Ultraluminous X-Ray Source ULX-7 in M51. Astrophysical Journal, 895(1), Article 60. https://doi.org/10.3847/1538-4357/ab8a44

We discovered 2.8 s pulsations in the X-ray emission of the ultraluminous X-ray source (ULX) M51 ULX-7 within the UNSEeN project, which was designed to hunt for new pulsating ULXs (PULXs) with XMM-Newton. The pulse shape is sinusoidal, and large vari... Read More about Discovery of a 2.8 s Pulsar in a 2 Day Orbit High-mass X-Ray Binary Powering the Ultraluminous X-Ray Source ULX-7 in M51.

The unusual broad-band X-ray spectral variability of NGC 1313 X-1 seen with XMM–Newton, Chandra, and NuSTAR (2020)
Journal Article
Walton, D., Pinto, C., Nowak, M., Bachetti, M., Sathyaprakash, R., Kara, E., Roberts, T., Soria, R., Brightman, M., Canizares, C., Earnshaw, H., Fürst, F., Heida, M., Middleton, M., Stern, D., Tao, L., Webb, N., Alston, W., Barret, D., Fabian, A., …Kosec, P. (2020). The unusual broad-band X-ray spectral variability of NGC 1313 X-1 seen with XMM–Newton, Chandra, and NuSTAR. Monthly Notices of the Royal Astronomical Society, 494(4), 6012-6029. https://doi.org/10.1093/mnras/staa1129

We present results from the major coordinated X-ray observing programme on the ULX NGC 1313 X-1 performed in 2017, combining XMM–Newton, Chandra, and NuSTAR, focusing on the evolution of the broad-band (∼0.3–30.0 keV) continuum emission. Clear and un... Read More about The unusual broad-band X-ray spectral variability of NGC 1313 X-1 seen with XMM–Newton, Chandra, and NuSTAR.

XMM–Newton campaign on ultraluminous X-ray source NGC 1313 X-1: wind versus state variability (2020)
Journal Article
Pinto, C., Walton, D., Kara, E., Parker, M., Soria, R., Kosec, P., Middleton, M., Alston, W., Fabian, A., Guainazzi, M., Roberts, T., Fuerst, F., Earnshaw, H., Sathyaprakash, R., & Barret, D. (2020). XMM–Newton campaign on ultraluminous X-ray source NGC 1313 X-1: wind versus state variability. Monthly Notices of the Royal Astronomical Society, 492(4), 4646-4665. https://doi.org/10.1093/mnras/staa118

Most ultraluminous X-ray sources (ULXs) are thought to be powered by neutron stars and black holes accreting beyond the Eddington limit. If the compact object is a black hole or a neutron star with a magnetic field ≲1012 G, the accretion disc is expe... Read More about XMM–Newton campaign on ultraluminous X-ray source NGC 1313 X-1: wind versus state variability.

The (re)appearance of NGC 925 ULX-3, a new transient ULX (2020)
Journal Article
Earnshaw, H. P., Heida, M., Brightman, M., Fürst, F., Harrison, F. A., Jaodand, A., Middleton, M. J., Roberts, T. P., Sathyaprakash, R., Stern, D., & Walton, D. J. (2020). The (re)appearance of NGC 925 ULX-3, a new transient ULX. Astrophysical Journal, 891(2), Article 153. https://doi.org/10.3847/1538-4357/ab77b8

We report the discovery of a third ULX in NGC 925 (ULX-3), detected in 2017 November by Chandra at a luminosity of L X = (7.8 ± 0.8) × 1039 erg s−1. Examination of archival data for NGC 925 reveals that ULX-3 was detected by Swift at a similarly high... Read More about The (re)appearance of NGC 925 ULX-3, a new transient ULX.

The Ultraluminous X-ray sources population of the galaxy NGC 7456 (2020)
Journal Article
Pintore, F., Marelli, M., Salvaterra, R., Israel, G., Rodríguez Castillo, G., Esposito, P., Belfiore, A., De Luca, A., Wolter, A., Mereghetti, S., Stella, L., Rigoselli, M., Earnshaw, H., Pinto, C., Roberts, T., Walton, D., Bernardini, F., Haberl, F., Salvaggio, C., Tiengo, A., …Middleton, M. (2020). The Ultraluminous X-ray sources population of the galaxy NGC 7456. Astrophysical Journal, 890(2), Article 166. https://doi.org/10.3847/1538-4357/ab6ffd

Ultraluminous X-ray sources (ULXs) are a class of accreting compact objects with X-ray luminosities above 1039 erg s−1. The ULX population counts several hundred objects but only a fraction are well studied. Here we present a detailed analysis of all... Read More about The Ultraluminous X-ray sources population of the galaxy NGC 7456.

Thermal stability of winds driven by radiation pressure in super-Eddington accretion discs (2019)
Journal Article
Pinto, C., Mehdipour, M., Walton, D., Middleton, M., Roberts, T., Fabian, A., Guainazzi, M., Soria, R., Kosec, P., & Ness, J. .-U. (2020). Thermal stability of winds driven by radiation pressure in super-Eddington accretion discs. Monthly Notices of the Royal Astronomical Society, 491(4), 5702-5716. https://doi.org/10.1093/mnras/stz3392

Ultraluminous X-ray sources (ULXs) are mainly powered by accretion in neutron stars or stellar-mass black holes. Accreting at rates exceeding the Eddington limit by factors of a few up to hundreds, radiation pressure is expected to inflate the accret... Read More about Thermal stability of winds driven by radiation pressure in super-Eddington accretion discs.

Discovery of a soft X-ray lag in the Ultraluminous X-ray Source NGC 1313 X-1 (2019)
Journal Article
Kara, E., Pinto, C., Walton, D., Alston, W., Bachetti, M., Barret, D., Brightman, M., Canizares, C., Earnshaw, H., Fabian, A., Furst, F., Kosec, P., Middleton, M., Roberts, T., Soria, R., Tao, L., & Webb, N. (2020). Discovery of a soft X-ray lag in the Ultraluminous X-ray Source NGC 1313 X-1. Monthly Notices of the Royal Astronomical Society, 491(4), 5172-5178. https://doi.org/10.1093/mnras/stz3318

Ultraluminous X-ray Sources (ULXs) provide a unique opportunities to probe the geometry and energetics of super-Eddington accretion. The radiative processes involved in super-Eddington accretion are not well understood, and so studying correlated var... Read More about Discovery of a soft X-ray lag in the Ultraluminous X-ray Source NGC 1313 X-1.

The Hunt for Pulsating Ultraluminous X-ray Sources (2019)
Journal Article
Song, X., Walton, D., Lansbury, G., Evans, P., Fabian, A., Earnshaw, H., & Roberts, T. (2020). The Hunt for Pulsating Ultraluminous X-ray Sources. Monthly Notices of the Royal Astronomical Society, 491(1), 1260-1277. https://doi.org/10.1093/mnras/stz3036

Motivated by the recent discoveries that six Ultraluminous X-ray Sources (ULXs) are powered by highly super-Eddington X-ray pulsars, we searched for additional pulsating ULX (PULX) candidates by identifying sources that exhibit long-term flux variabi... Read More about The Hunt for Pulsating Ultraluminous X-ray Sources.

Discovery and analysis of a ULX nebula in NGC 3521★ (2019)
Journal Article
López, K., Jonker, P., Heida, M., Torres, M., Roberts, T., Walton, D., Moon, D.-S., & Harrison, F. (2019). Discovery and analysis of a ULX nebula in NGC 3521★. Monthly Notices of the Royal Astronomical Society, 489(1), 1249-1264. https://doi.org/10.1093/mnras/stz2127

We present Very Large Telescope/X-shooter and Chandra X-ray observatory/ACIS observations of the ULX [SST2011] J110545.62+000016.2 in the galaxy NGC 3521. The source identified as a candidate near-infrared counterpart to the ULX in our previous study... Read More about Discovery and analysis of a ULX nebula in NGC 3521★.

Observational limits on the X-ray emission from the bubble nebula surrounding Ho IX X-1 (2019)
Journal Article
Sathyaprakash, R., Roberts, T., & Siwek, M. (2019). Observational limits on the X-ray emission from the bubble nebula surrounding Ho IX X-1. Monthly Notices of the Royal Astronomical Society, 488(4), 4614-4622. https://doi.org/10.1093/mnras/stz2022

Optical and radio observations of shock-ionised bubble nebulae surrounding ultraluminous X-ray sources (ULXs) suggest that they are powered by jets or super-critical outflows presumably launched from the ULX accretion disc. Recent simulations of thes... Read More about Observational limits on the X-ray emission from the bubble nebula surrounding Ho IX X-1.

The Lense-Thirring timing-accretion plane for ULXs (2019)
Journal Article
Middleton, M., Fragile, P., Ingram, A., & Roberts, T. (2019). The Lense-Thirring timing-accretion plane for ULXs. Monthly Notices of the Royal Astronomical Society, 489(1), 282-296. https://doi.org/10.1093/mnras/stz2005

Identifying the compact object in ultraluminous X-ray sources (ULXs) has to-date required detection of pulsations or a cyclotron resonance scattering feature (CRSF), indicating a magnetised neutron star. However, pulsations are observed to be transie... Read More about The Lense-Thirring timing-accretion plane for ULXs.

The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2 (2019)
Journal Article
Sathyaprakash, R., Roberts, T., Walton, D., Fuerst, F., Bachetti, M., Pinto, C., Alston, W., Earnshaw, H., Fabian, A., Middleton, M., & Soria, R. (2019). The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2. Monthly Notices of the Royal Astronomical Society, 488(1), L35-L40. https://doi.org/10.1093/mnrasl/slz086

We report the detection of weak pulsations from the archetypal ultraluminous X-ray source (ULX) NGC 1313 X-2. Acceleration searches reveal sinusoidal pulsations in segments of two out of six new deep observations of this object, with a period of ∼1.5... Read More about The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2.

Discovery of a radio transient in M81 (2019)
Journal Article
Anderson, G., Miller-Jones, J., Middleton, M., Soria, R., Swartz, D., Urquhart, R., Hurley-Walker, N., Hancock, P., Fender, R., Gandhi, P., Markoff, S., & Roberts, T. (2019). Discovery of a radio transient in M81. Monthly Notices of the Royal Astronomical Society, 489(1), 1181-1196. https://doi.org/10.1093/mnras/stz1303

We report the discovery of a radio transient in the spiral galaxy M81. The transient was detected in early 2015 as part of a two year survey of M81 made up of 12 epochs using the Karl G. Jansky Very Large Array. While undetected on 2014 September 12,... Read More about Discovery of a radio transient in M81.

A new, clean catalogue of extragalactic non-nuclear X-ray sources in nearby galaxies (2018)
Journal Article
Earnshaw, H., Roberts, T., Middleton, M., Walton, D., & Mateos, S. (2019). A new, clean catalogue of extragalactic non-nuclear X-ray sources in nearby galaxies. Monthly Notices of the Royal Astronomical Society, 483(4), 5554-5573. https://doi.org/10.1093/mnras/sty3403

We have created a new, clean catalogue of extragalactic non-nuclear X-ray sources by correlating the 3XMM-DR4 data release of the XMM-Newton Serendipitous Source Catalogue with the Third Reference Catalogue of Bright Galaxies and the Catalogue of Nei... Read More about A new, clean catalogue of extragalactic non-nuclear X-ray sources in nearby galaxies.

A long hard-X-ray look at the dual active galactic nuclei of M51 with NuSTAR (2018)
Journal Article
Brightman, M., Baloković, M., Koss, M., Alexander, D., Annuar, A., Earnshaw, H., Gandhi, P., Harrison, F., Hornschemeier, A., Lehmer, B., Powell, M., Ptak, A., Rangelov, B., Roberts, T., Stern, D., Walton, D., & Zezas, A. (2018). A long hard-X-ray look at the dual active galactic nuclei of M51 with NuSTAR. Astrophysical Journal, 867(2), Article 110. https://doi.org/10.3847/1538-4357/aae1ae

We present a broadband X-ray spectral analysis of the M51 system, including the dual active galactic nuclei (AGN) and several off-nuclear point sources. Using a deep observation by NuSTAR, new high-resolution coverage of M51b by Chandra, and the late... Read More about A long hard-X-ray look at the dual active galactic nuclei of M51 with NuSTAR.