### Abstract

Continued photometric monitoring of the gravitational lens system 0957+561 A, B in the g and r bands with the Apache Point Observatory (APO) 3.5 m telescope during 1996 shows a sharp g-band event in the trailing (B) image light curve at the precise time predicted in an earlier paper. The prediction was based on the observation of the event during 1995 in the leading (A) image and on a differential time delay of 415 days. This success confirms the so-called short delay, and the absence of any such feature at a delay near 540 days rejects the "long delay" for this system, thus resolving a long-standing controversy. A series of statistical analyses of our light-curve data yield a best-fit delay of 417 ± 3 days (95% confidence interval) and demonstrate that this result is quite robust against variations in the analysis technique, data subsamples, and assumed parametric relationship of the two light curves. Recent improvements in the modeling of the lens system (consisting of a galaxy plus a galaxy cluster) allow us to derive a value of the global value (at z = 0.36) of Hubble's constant H_{0} using Refsdal's method, a simple and direct (single-step) distance determination based on experimentally verified and securely understood physics and geometry. The result is H_{0} = 64 ± 13 km s^{-1} Mpc^{-1} (for Ω = 1), where this 95% confidence interval is dominantly due to remaining lens model uncertainties. However, it is reassuring that available observations of the lensing mass distribution overconstrain the model and thus provide an internal consistency check on its validity. We argue that this determination of the extragalactic distance scale (10% accurate at 1 σ) is now of comparable quality, in terms of both statistical and systematic uncertainties, to those based on more conventional techniques. Finally, we briefly discuss the prospects for improved H_{0} determinations using gravitational lenses, and some other possible implications and uses of the 0957 + 561 A, B light curves.

Original language | English (US) |
---|---|

Pages (from-to) | 75-82 |

Number of pages | 8 |

Journal | Astrophysical Journal |

Volume | 482 |

Issue number | 1 PART I |

DOIs | |

State | Published - 1997 |

Externally published | Yes |

### Fingerprint

### Keywords

- Distance scale
- Gravitational lensing

### ASJC Scopus subject areas

- Space and Planetary Science

### Cite this

*Astrophysical Journal*,

*482*(1 PART I), 75-82. https://doi.org/10.1086/304147

**A robust determination of the time delay in 0957+561A, B and a measurement of the global value of Hubble's constant.** / Kundić, Tomislav; Turner, Edwin L.; Colley, Wesley N.; Gott, J. Richard; Rhoads, James E.; Wang, Yun; Bergeron, Louis E.; Gloria, Karen A.; Long, Daniel C.; Malhotra, Sangeeta; Wambsganss, Joachim.

Research output: Contribution to journal › Article

*Astrophysical Journal*, vol. 482, no. 1 PART I, pp. 75-82. https://doi.org/10.1086/304147

}

TY - JOUR

T1 - A robust determination of the time delay in 0957+561A, B and a measurement of the global value of Hubble's constant

AU - Kundić, Tomislav

AU - Turner, Edwin L.

AU - Colley, Wesley N.

AU - Gott, J. Richard

AU - Rhoads, James E.

AU - Wang, Yun

AU - Bergeron, Louis E.

AU - Gloria, Karen A.

AU - Long, Daniel C.

AU - Malhotra, Sangeeta

AU - Wambsganss, Joachim

PY - 1997

Y1 - 1997

N2 - Continued photometric monitoring of the gravitational lens system 0957+561 A, B in the g and r bands with the Apache Point Observatory (APO) 3.5 m telescope during 1996 shows a sharp g-band event in the trailing (B) image light curve at the precise time predicted in an earlier paper. The prediction was based on the observation of the event during 1995 in the leading (A) image and on a differential time delay of 415 days. This success confirms the so-called short delay, and the absence of any such feature at a delay near 540 days rejects the "long delay" for this system, thus resolving a long-standing controversy. A series of statistical analyses of our light-curve data yield a best-fit delay of 417 ± 3 days (95% confidence interval) and demonstrate that this result is quite robust against variations in the analysis technique, data subsamples, and assumed parametric relationship of the two light curves. Recent improvements in the modeling of the lens system (consisting of a galaxy plus a galaxy cluster) allow us to derive a value of the global value (at z = 0.36) of Hubble's constant H0 using Refsdal's method, a simple and direct (single-step) distance determination based on experimentally verified and securely understood physics and geometry. The result is H0 = 64 ± 13 km s-1 Mpc-1 (for Ω = 1), where this 95% confidence interval is dominantly due to remaining lens model uncertainties. However, it is reassuring that available observations of the lensing mass distribution overconstrain the model and thus provide an internal consistency check on its validity. We argue that this determination of the extragalactic distance scale (10% accurate at 1 σ) is now of comparable quality, in terms of both statistical and systematic uncertainties, to those based on more conventional techniques. Finally, we briefly discuss the prospects for improved H0 determinations using gravitational lenses, and some other possible implications and uses of the 0957 + 561 A, B light curves.

AB - Continued photometric monitoring of the gravitational lens system 0957+561 A, B in the g and r bands with the Apache Point Observatory (APO) 3.5 m telescope during 1996 shows a sharp g-band event in the trailing (B) image light curve at the precise time predicted in an earlier paper. The prediction was based on the observation of the event during 1995 in the leading (A) image and on a differential time delay of 415 days. This success confirms the so-called short delay, and the absence of any such feature at a delay near 540 days rejects the "long delay" for this system, thus resolving a long-standing controversy. A series of statistical analyses of our light-curve data yield a best-fit delay of 417 ± 3 days (95% confidence interval) and demonstrate that this result is quite robust against variations in the analysis technique, data subsamples, and assumed parametric relationship of the two light curves. Recent improvements in the modeling of the lens system (consisting of a galaxy plus a galaxy cluster) allow us to derive a value of the global value (at z = 0.36) of Hubble's constant H0 using Refsdal's method, a simple and direct (single-step) distance determination based on experimentally verified and securely understood physics and geometry. The result is H0 = 64 ± 13 km s-1 Mpc-1 (for Ω = 1), where this 95% confidence interval is dominantly due to remaining lens model uncertainties. However, it is reassuring that available observations of the lensing mass distribution overconstrain the model and thus provide an internal consistency check on its validity. We argue that this determination of the extragalactic distance scale (10% accurate at 1 σ) is now of comparable quality, in terms of both statistical and systematic uncertainties, to those based on more conventional techniques. Finally, we briefly discuss the prospects for improved H0 determinations using gravitational lenses, and some other possible implications and uses of the 0957 + 561 A, B light curves.

KW - Distance scale

KW - Gravitational lensing

UR - http://www.scopus.com/inward/record.url?scp=0040033559&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0040033559&partnerID=8YFLogxK

U2 - 10.1086/304147

DO - 10.1086/304147

M3 - Article

VL - 482

SP - 75

EP - 82

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1 PART I

ER -