A binary lensing event toward the LMC: Observations and dark matter implications

D. P. Bennett; C. Alcock; R. A. Allsman; D. Alves; T. S. Axelrod; A. Becker; K. H. Cook; K. C. Freeman; K. Griest; J. Guern; M. J. Lehner; S. L. Marshall; D. Minniti; B. A. Peterson; M. R. Pratt; P. J. Quinn; S. H. Rhie; A. W. Rodgers; C. W. Stubbs; W. Sutherland; D. Welch

doi:10.1016/S0920-5632(96)00497-5

A binary lensing event toward the LMC: Observations and dark matter implications

D. P. Bennett, C. Alcock, R. A. Allsman, D. Alves, T. S. Axelrod, A. Becker, K. H. Cook, K. C. Freeman, K. Griest, J. Guern, M. J. Lehner, S. L. Marshall, D. Minniti, B. A. Peterson, M. R. Pratt, P. J. Quinn, S. H. Rhie, A. W. Rodgers, C. W. Stubbs, W. SutherlandD. Welch

Exact Sciences School

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Abstract

The MACHO collaboration has recently analyzed 2.1 years of photometric data for about 8.5 million stars in the Large Magellanic Cloud (LMC). This analysis has revealed 8 candidate microlensing events and a total microlensing optical depth of τ _meas = 2.9 ^+1.4_-0.9 × 10^-7. This significantly exceeds the number of events (1.1) and the microlensing optical depth predicted from known stellar populations: τ_back = 5.4 × 10^-8, but it is consistent with models in which about half of the standard dark halo mass is composed of Machos of mass ∼ 0.5M⊙. One of these 8 events appears to be a binary lensing event with a caustic crossing that is partially resolved, and the measured caustic crossing time allows us to estimate the distance to the lenses. Under the assumption that the source star is a single star and not a short period binary, we show that the lensing objects are very likely to reside in the LMC. However, if we assume that the optical depth for LMC-LMC lensing is large enough to account for our entire lensing signal, then the binary event does not appear to be consistent with lensing of a single LMC source star by a binary residing in the LMC. Thus, while the binary lens may indeed reside in the LMC, there is no indication that most of the lenses reside in the LMC.

Original language	English
Pages (from-to)	152-156
Number of pages	5
Journal	Nuclear Physics B - Proceedings Supplements
Volume	51
Issue number	2
DOIs	https://doi.org/10.1016/S0920-5632(96)00497-5
Publication status	Published - Nov 1996

ASJC Scopus subject areas

Atomic and Molecular Physics, and Optics
Nuclear and High Energy Physics

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Bennett, D. P., Alcock, C., Allsman, R. A., Alves, D., Axelrod, T. S., Becker, A., Cook, K. H., Freeman, K. C., Griest, K., Guern, J., Lehner, M. J., Marshall, S. L., Minniti, D., Peterson, B. A., Pratt, M. R., Quinn, P. J., Rhie, S. H., Rodgers, A. W., Stubbs, C. W., ... Welch, D. (1996). A binary lensing event toward the LMC: Observations and dark matter implications. Nuclear Physics B - Proceedings Supplements, 51(2), 152-156. https://doi.org/10.1016/S0920-5632(96)00497-5

@article{e5e814d72b7f4e90a8d07139ae2458c4,

title = "A binary lensing event toward the LMC: Observations and dark matter implications",

abstract = "The MACHO collaboration has recently analyzed 2.1 years of photometric data for about 8.5 million stars in the Large Magellanic Cloud (LMC). This analysis has revealed 8 candidate microlensing events and a total microlensing optical depth of τ meas = 2.9 +1.4-0.9 × 10-7. This significantly exceeds the number of events (1.1) and the microlensing optical depth predicted from known stellar populations: τback = 5.4 × 10-8, but it is consistent with models in which about half of the standard dark halo mass is composed of Machos of mass ∼ 0.5M⊙. One of these 8 events appears to be a binary lensing event with a caustic crossing that is partially resolved, and the measured caustic crossing time allows us to estimate the distance to the lenses. Under the assumption that the source star is a single star and not a short period binary, we show that the lensing objects are very likely to reside in the LMC. However, if we assume that the optical depth for LMC-LMC lensing is large enough to account for our entire lensing signal, then the binary event does not appear to be consistent with lensing of a single LMC source star by a binary residing in the LMC. Thus, while the binary lens may indeed reside in the LMC, there is no indication that most of the lenses reside in the LMC.",

author = "Bennett, {D. P.} and C. Alcock and Allsman, {R. A.} and D. Alves and Axelrod, {T. S.} and A. Becker and Cook, {K. H.} and Freeman, {K. C.} and K. Griest and J. Guern and Lehner, {M. J.} and Marshall, {S. L.} and D. Minniti and Peterson, {B. A.} and Pratt, {M. R.} and Quinn, {P. J.} and Rhie, {S. H.} and Rodgers, {A. W.} and Stubbs, {C. W.} and W. Sutherland and D. Welch",

note = "Funding Information: under contract W-7405.ENG. Work performed by the CfPA personnel is supported by the NSF through AST 9120005. The work at MSSSO is supported by the Aus-tralian Dept. of Industry, Science, and Technology., K.G. acknowledges support from DOE 031, Sloan, and Cotrell awards. C.S. acknowledges the support of the Packard and Funding Information: *Work performed at LLNL is supported by the DOE",

year = "1996",

month = nov,

doi = "10.1016/S0920-5632(96)00497-5",

language = "English",

volume = "51",

pages = "152--156",

journal = "Nuclear and Particle Physics Proceedings",

issn = "2405-6014",

publisher = "Elsevier",

number = "2",

}

Bennett, DP, Alcock, C, Allsman, RA, Alves, D, Axelrod, TS, Becker, A, Cook, KH, Freeman, KC, Griest, K, Guern, J, Lehner, MJ, Marshall, SL, Minniti, D, Peterson, BA, Pratt, MR, Quinn, PJ, Rhie, SH, Rodgers, AW, Stubbs, CW, Sutherland, W & Welch, D 1996, 'A binary lensing event toward the LMC: Observations and dark matter implications', Nuclear Physics B - Proceedings Supplements, vol. 51, no. 2, pp. 152-156. https://doi.org/10.1016/S0920-5632(96)00497-5

TY - JOUR

T1 - A binary lensing event toward the LMC

T2 - Observations and dark matter implications

AU - Bennett, D. P.

AU - Alcock, C.

AU - Allsman, R. A.

AU - Alves, D.

AU - Axelrod, T. S.

AU - Becker, A.

AU - Cook, K. H.

AU - Freeman, K. C.

AU - Griest, K.

AU - Guern, J.

AU - Lehner, M. J.

AU - Marshall, S. L.

AU - Minniti, D.

AU - Peterson, B. A.

AU - Pratt, M. R.

AU - Quinn, P. J.

AU - Rhie, S. H.

AU - Rodgers, A. W.

AU - Stubbs, C. W.

AU - Sutherland, W.

AU - Welch, D.

N1 - Funding Information: under contract W-7405.ENG. Work performed by the CfPA personnel is supported by the NSF through AST 9120005. The work at MSSSO is supported by the Aus-tralian Dept. of Industry, Science, and Technology., K.G. acknowledges support from DOE 031, Sloan, and Cotrell awards. C.S. acknowledges the support of the Packard and Funding Information: *Work performed at LLNL is supported by the DOE

PY - 1996/11

Y1 - 1996/11

N2 - The MACHO collaboration has recently analyzed 2.1 years of photometric data for about 8.5 million stars in the Large Magellanic Cloud (LMC). This analysis has revealed 8 candidate microlensing events and a total microlensing optical depth of τ meas = 2.9 +1.4-0.9 × 10-7. This significantly exceeds the number of events (1.1) and the microlensing optical depth predicted from known stellar populations: τback = 5.4 × 10-8, but it is consistent with models in which about half of the standard dark halo mass is composed of Machos of mass ∼ 0.5M⊙. One of these 8 events appears to be a binary lensing event with a caustic crossing that is partially resolved, and the measured caustic crossing time allows us to estimate the distance to the lenses. Under the assumption that the source star is a single star and not a short period binary, we show that the lensing objects are very likely to reside in the LMC. However, if we assume that the optical depth for LMC-LMC lensing is large enough to account for our entire lensing signal, then the binary event does not appear to be consistent with lensing of a single LMC source star by a binary residing in the LMC. Thus, while the binary lens may indeed reside in the LMC, there is no indication that most of the lenses reside in the LMC.

AB - The MACHO collaboration has recently analyzed 2.1 years of photometric data for about 8.5 million stars in the Large Magellanic Cloud (LMC). This analysis has revealed 8 candidate microlensing events and a total microlensing optical depth of τ meas = 2.9 +1.4-0.9 × 10-7. This significantly exceeds the number of events (1.1) and the microlensing optical depth predicted from known stellar populations: τback = 5.4 × 10-8, but it is consistent with models in which about half of the standard dark halo mass is composed of Machos of mass ∼ 0.5M⊙. One of these 8 events appears to be a binary lensing event with a caustic crossing that is partially resolved, and the measured caustic crossing time allows us to estimate the distance to the lenses. Under the assumption that the source star is a single star and not a short period binary, we show that the lensing objects are very likely to reside in the LMC. However, if we assume that the optical depth for LMC-LMC lensing is large enough to account for our entire lensing signal, then the binary event does not appear to be consistent with lensing of a single LMC source star by a binary residing in the LMC. Thus, while the binary lens may indeed reside in the LMC, there is no indication that most of the lenses reside in the LMC.

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U2 - 10.1016/S0920-5632(96)00497-5

DO - 10.1016/S0920-5632(96)00497-5

M3 - Article

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VL - 51

SP - 152

EP - 156

JO - Nuclear and Particle Physics Proceedings

JF - Nuclear and Particle Physics Proceedings

SN - 2405-6014

IS - 2

ER -

A binary lensing event toward the LMC: Observations and dark matter implications

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