A transient, flat spectrum radio pulsar near the Galactic Centre

Dexter, Jason; Degenaar, N.; Kerr, M.; Deller, Adam T.; Deneva, J. S.; Lazarus, P.; Krämer, M.; Champion, D. J.; Karuppusamy, R.

doi:10.1093/mnras/stx583

Cited by 9 publications

(6 citation statements)

References 54 publications

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“…We observed the 3 other sufficiently bright known GC pulsars. The flat spectrum, young pulsar J1746-2850 was not observed, since it has not been detected in recent observations (Ng et al 2015;Schnitzeler et al 2016) and may be a magnetar-like object whose radio emission has since shut off (Dexter et al 2017).…”

Section: Sample Selectionmentioning

confidence: 93%

Locating the intense interstellar scattering towards the inner Galaxy

Dexter

Deller

Bower³

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We use VLBA+VLA observations to measure the sizes of the scatter-broadened images of 6 of the most heavily scattered known pulsars: 3 within the Galactic Centre (GC) and 3 elsewhere in the inner Galactic plane (∆l < 20 • ). By combining the measured sizes with temporal pulse broadening data from the literature and using the thin-screen approximation, we locate the scattering medium along the line of sight to these 6 pulsars. At least two scattering screens are needed to explain the observations of the GC sample. We show that the screen inferred by previous observations of SGR J1745−2900 and Sgr A*, which must be located far from the GC, falls off in strength on scales 0.2 degree. A second scattering component closer to (∆ < 2 kpc) or even (tentatively) within (∆ < 700 pc) the GC produces most or all of the temporal broadening observed in the other GC pulsars. Outside the GC, the scattering locations for all three pulsars are ≃ 2 kpc from Earth, consistent with the distance of the Carina-Sagittarius or Scutum spiral arm. For each object the 3D scattering origin coincides with a known HII region (and in one case also a supernova remnant), suggesting that such objects preferentially cause the intense interstellar scattering seen towards the Galactic plane. We show that the HII regions should contribute 25% of the total dispersion measure (DM) towards these pulsars, and calculate reduced DM distances. Those distances for other pulsars lying behind HII regions may be similarly overestimated.

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Section: Sample Selectionmentioning

confidence: 93%

Locating the intense interstellar scattering towards the inner Galaxy

Dexter

Deller

Bower³

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…14 qF256 (WN8-9ha), -274 (WN8-9ha) and -406 (O7-8 Ia + ) and LHO01 (O7-8 Ia + /WNLha) and -54 (O7-8 Ia + ) within the Quintuplet and Wd1-5 (WN10-11h/B0.5 Ia + ), -13 (B0.5 Ia + ), -27 (O7-8 Ia + ), -30a (O4-5 Ia + ), -44 (WN9h), and W1049 (B1-2Ia + ). A187, page 13 of 19 transient magnetar -is located in close proximity to the Quintuplet (∼5 pc; Deneva et al 2009;Dexter et al 2017) although, given the population of isolated massive stars in the central molecular zone, an unambiguous physical association has yet to be proven. Finally, in terms of stellar content -and hence agethe host cluster of SGR 1806−20 appears to be directly comparable to the Quintuplet (Figer et al 2005;Bibby et al 2008).…”

Section: Comparison To Other Young Massive Clustersmentioning

confidence: 99%

A VLT/FLAMES survey for massive binaries in Westerlund 1

Clark

Ritchie

Negueruela

2020

A&A

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Context. The formation, properties, and evolution of massive stars remain subject to considerable theoretical and observational uncertainty. This impacts on fields as diverse as galactic feedback, the production of cosmic rays, and the nature of the progenitors of both electromagnetic and gravitational wave transients. Aims. The young massive clusters many such stars reside within provide a unique laboratory for addressing these issues. In this work we provide a comprehensive stellar census of Westerlund 1 in order to to underpin such efforts. Methods. We employed optical spectroscopy of a large sample of early-type stars to determine cluster membership for photometrically-identified candidates, characterise their spectral type, and identify new candidate spectroscopic binaries. Results. Sixty nine new members of Westerlund 1 are identified via I-band spectroscopy. Together with previous observations, they illustrate a smooth and continuous morphological sequence from late-O giant through to OB supergiant. Subsequently, the progression bifurcates, with one branch yielding mid-B to late-F hypergiants, and cool supergiants, and the other massive blue stragglers prior to a diverse population of H-depleted WRs. We identify a substantial population of O-type stars with very broad Paschen series lines, a morphology that is directly comparable to known binaries in the cluster. In a few cases additional low-resolution R-band spectroscopy is available, revealing double-lined He I profiles and confirming binarity for these objects; suggesting a correspondingly high binary fraction amongst relatively unevolved cluster members. Conclusions. Our current census remains incomplete, but indicates that Westerlund 1 contains at least 166 stars with initial masses estimated to lie between ∼25 M⊙ and ∼50 M⊙, with more massive stars already lost to supernova. Our data is consistent with the cluster being co-eval, although binary interaction is clearly required to yield the observed stellar population, which is characterised by a uniquely rich cohort of hypergiants ranging from spectral type O to F, with both mass-stripped primaries and rejuvenated secondaries or merger products present. Future observations of Wd1 and similar stellar aggregates hold out the prospect of characterising both single- and binary- evolutionary channels for massive stars and determining their relative contributions. This in turn will permit the physical properties of such objects at the point of core-collapse to be predicted, which is of direct relevance for understanding the formation of relativistic remnants such as the magnetars associated with Wd1 and other young massive clusters.

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“…Following the indications of (Dexter et al 2017) for a Galactic Center region of ∼ 50 pc radius, the value of τ scat is taken to be the same as the one observed for the magnetar SGR J1745+29 (Spitler et al 2014): The smearing effect due to the dispersive nature of the ISM follows the law:…”

Section: Observability Of Pulsarsmentioning

confidence: 99%

Probing the formation history of the nuclear star cluster at the Galactic Centre with millisecond pulsars

Abbate

Mastrobuono-Battisti

Colpi

et al. 2017

Monthly Notices of the Royal Astronomical Society

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The origin of the Nuclear Star Cluster in the centre of our Galaxy is still unknown. One possibility is that it formed after the disruption of stellar clusters that spiralled into the Galactic Centre due to dynamical friction. We trace the formation of the Nuclear Star Cluster around the central black hole, using state-of-the-art N-body simulations, and follow the dynamics of the neutron stars born in the clusters. We then estimate the number of Millisecond Pulsars (MSPs) that are released in the Nuclear Star Cluster during its formation. The assembly and tidal dismemberment of globular clusters lead to a population of MSPs distributed over a radius of about 20 pc, with a peak near 3 pc. No clustering is found on the sub-parsec scale. We simulate the detectability of this population with future radio telescopes like the MeerKAT radio telescope and SKA1, and find that about of order ten MSPs can be observed over this large volume, with a paucity of MSPs within the central parsec. This helps discriminating this scenario from the in-situ formation model for the Nuclear Star Cluster that would predict an over abundance of MSPs closer to the black hole. We then discuss the potential contribution of our MSP population to the gamma-ray excess at the Galactic Centre.

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A transient, flat spectrum radio pulsar near the Galactic Centre

Cited by 9 publications

References 54 publications

Locating the intense interstellar scattering towards the inner Galaxy

Locating the intense interstellar scattering towards the inner Galaxy

A VLT/FLAMES survey for massive binaries in Westerlund 1

Probing the formation history of the nuclear star cluster at the Galactic Centre with millisecond pulsars

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