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Gaia Data Release 2 distances and peculiar velocities for Galactic black hole transients

Gaia Data Release 2 distances and peculiar velocities for Galactic black hole transients
Gaia Data Release 2 distances and peculiar velocities for Galactic black hole transients
We report on a first census of Galactic black hole X-ray binary (BHXRB) properties with the second data release (DR2) of Gaia, focusing on dynamically confirmed and strong candidate BH transients. Gaia DR2 provides five-parameter astrometric solutions including position, parallax and proper motion for 11 out of a sample of 24 systems. Distance estimates are tested with parallax inversion as well as Bayesian inference. We derive an empirically motivated characteristic scalelength of L = 2.17 ± 0.12 kpc for this BHXRB population to infer distances based upon an exponentially decreasing space density prior. Geometric DR2 parallaxes provide new, independent distance estimates, but the faintness of this population in quiescence results in relatively large fractional distance uncertainties. Despite this, DR2 estimates generally agree with the distances found in the literature. The most discrepant case is BW Cir, for which detailed studies of the donor star have suggested a distant location at ≳25 kpc. The large parallax and relatively high proper motion measured by DR2 instead indicate significantly smaller distances, suggesting that the source might be amongst the nearest of XRBs. However, both larger and smaller distances create problems for the interpretation of the source, and follow-up data are required to resolve its true nature. DR2 also provides a first distance estimate to one source, MAXI J1820+070, and novel proper motion estimates for seven sources. Peculiar velocities relative to Galactic rotation exceed ≈ 50 km s-1 for the bulk of the sample, with a median system kinetic energy of peculiar motion of ˜ 5 × 1047 erg. BW Cir could be a new high-velocity BHXRB if its astrometry is confirmed. A putative anticorrelation between peculiar velocity and BH mass is found, as expected in mass-dependent BH kick formation channels, but this trend remains weak in the DR2 data.
accretion, accretion discs, parallaxes, proper motions, stars: black holes, stars: distances
0035-8711
2642-2655
Gandhi, Poshak
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9
Rao, Anjali
3a3aa402-cf58-4724-9e63-fe9fdc6f39a6
Johnson, Michael A. C.
33a0d8cb-491b-4b3f-b193-540a331ac705
Paice, John A.
0ccafe5a-82d8-40bf-8b73-f71a841ac550
Maccarone, Thomas J.
c2f1d87b-e2ef-4e33-b09f-a2861d917ea8
Gandhi, Poshak
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9
Rao, Anjali
3a3aa402-cf58-4724-9e63-fe9fdc6f39a6
Johnson, Michael A. C.
33a0d8cb-491b-4b3f-b193-540a331ac705
Paice, John A.
0ccafe5a-82d8-40bf-8b73-f71a841ac550
Maccarone, Thomas J.
c2f1d87b-e2ef-4e33-b09f-a2861d917ea8

Gandhi, Poshak, Rao, Anjali, Johnson, Michael A. C., Paice, John A. and Maccarone, Thomas J. (2019) Gaia Data Release 2 distances and peculiar velocities for Galactic black hole transients. Monthly Notices of the Royal Astronomical Society, 485 (2), 2642-2655. (doi:10.1093/mnras/stz438).

Record type: Article

Abstract

We report on a first census of Galactic black hole X-ray binary (BHXRB) properties with the second data release (DR2) of Gaia, focusing on dynamically confirmed and strong candidate BH transients. Gaia DR2 provides five-parameter astrometric solutions including position, parallax and proper motion for 11 out of a sample of 24 systems. Distance estimates are tested with parallax inversion as well as Bayesian inference. We derive an empirically motivated characteristic scalelength of L = 2.17 ± 0.12 kpc for this BHXRB population to infer distances based upon an exponentially decreasing space density prior. Geometric DR2 parallaxes provide new, independent distance estimates, but the faintness of this population in quiescence results in relatively large fractional distance uncertainties. Despite this, DR2 estimates generally agree with the distances found in the literature. The most discrepant case is BW Cir, for which detailed studies of the donor star have suggested a distant location at ≳25 kpc. The large parallax and relatively high proper motion measured by DR2 instead indicate significantly smaller distances, suggesting that the source might be amongst the nearest of XRBs. However, both larger and smaller distances create problems for the interpretation of the source, and follow-up data are required to resolve its true nature. DR2 also provides a first distance estimate to one source, MAXI J1820+070, and novel proper motion estimates for seven sources. Peculiar velocities relative to Galactic rotation exceed ≈ 50 km s-1 for the bulk of the sample, with a median system kinetic energy of peculiar motion of ˜ 5 × 1047 erg. BW Cir could be a new high-velocity BHXRB if its astrometry is confirmed. A putative anticorrelation between peculiar velocity and BH mass is found, as expected in mass-dependent BH kick formation channels, but this trend remains weak in the DR2 data.

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Accepted/In Press date: 4 February 2019
e-pub ahead of print date: 14 March 2019
Published date: May 2019
Keywords: accretion, accretion discs, parallaxes, proper motions, stars: black holes, stars: distances

Identifiers

Local EPrints ID: 430017
URI: https://eprints.soton.ac.uk/id/eprint/430017
ISSN: 0035-8711
PURE UUID: 2054fb94-354d-4799-a814-8b2b23ddbf6c
ORCID for Poshak Gandhi: ORCID iD orcid.org/0000-0003-3105-2615
ORCID for Michael A. C. Johnson: ORCID iD orcid.org/0000-0002-5566-6147

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Date deposited: 10 Apr 2019 16:30
Last modified: 16 Aug 2019 00:30

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Contributors

Author: Poshak Gandhi ORCID iD
Author: Anjali Rao
Author: Michael A. C. Johnson ORCID iD
Author: John A. Paice
Author: Thomas J. Maccarone

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