Spectral variability of quasars in the sloan digital sky survey. I. Wavelength dependence

Brian C. Wilhite, Daniel E. Vanden Berk, Richard G. Kron, Donald P. Schneider, Nicholas Pereyra, Robert J. Brunner, Gordon T. Richards, Jonathan V. Brinkmann

Research output: Contribution to journalArticle

91 Citations (Scopus)

Abstract

SDSS repeat spectroscopic observations have resulted in multiepoch spectroscopy for ∼2500 quasars observed more than 50 days apart. From this sample, calibrating against stars observed simultaneously, we identify 315 quasars that have varied significantly between observations (with respect to assumed nonvariable stars observed concurrently). These variable quasars range in redshift from 0.5 to 4.72. This is the first large quasar sample studied spectroscopically for variability and represents a potentially useful sample for future high-redshift reverberation mapping studies. This also marks the first time the precise wavelength dependence of quasar variability has been determined, allowing both the continuum and emission-line variability to be studied. We create an ensemble difference spectrum (bright phase minus faint phase) covering rest-frame wavelengths from 1000 to 6000 Å. This average difference spectrum is bluer than the average single-epoch quasar spectrum; a power-law fit to the difference spectrum yields a spectral index αλ = -2.00, compared to an index of α λ = -1.35 for the single-epoch spectrum. This confirms that quasar continua are bluer when brighter. The difference spectrum also exhibits very weak or absent emission-line features; the strongest emission lines vary only 30% as much as the continuum. This small emission-line variability with respect to the continuum is consistent with the intrinsic Baldwin effect. Due to the lack of variability of the lines, measured photometric color is not always bluer in brighter phases but depends on redshift and the filters used. Lastly, the difference spectrum is bluer than the ensemble quasar spectrum only for λrest < 2500 Å, indicating that the variability cannot result from a simple scaling of the average quasar spectrum.

Original languageEnglish (US)
Pages (from-to)638-648
Number of pages11
JournalAstrophysical Journal
Volume633
Issue number2 I
DOIs
StatePublished - Nov 10 2005

Fingerprint

quasars
wavelength
wavelengths
continuums
time measurement
stars
reverberation
calibrating
power law
coverings
spectroscopy
filter
color
filters
scaling

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Wilhite, B. C., Vanden Berk, D. E., Kron, R. G., Schneider, D. P., Pereyra, N., Brunner, R. J., ... Brinkmann, J. V. (2005). Spectral variability of quasars in the sloan digital sky survey. I. Wavelength dependence. Astrophysical Journal, 633(2 I), 638-648. https://doi.org/10.1086/430821
Wilhite, Brian C. ; Vanden Berk, Daniel E. ; Kron, Richard G. ; Schneider, Donald P. ; Pereyra, Nicholas ; Brunner, Robert J. ; Richards, Gordon T. ; Brinkmann, Jonathan V. / Spectral variability of quasars in the sloan digital sky survey. I. Wavelength dependence. In: Astrophysical Journal. 2005 ; Vol. 633, No. 2 I. pp. 638-648.
@article{336315932f1f4cb98cbe70dc26b028cb,
title = "Spectral variability of quasars in the sloan digital sky survey. I. Wavelength dependence",
abstract = "SDSS repeat spectroscopic observations have resulted in multiepoch spectroscopy for ∼2500 quasars observed more than 50 days apart. From this sample, calibrating against stars observed simultaneously, we identify 315 quasars that have varied significantly between observations (with respect to assumed nonvariable stars observed concurrently). These variable quasars range in redshift from 0.5 to 4.72. This is the first large quasar sample studied spectroscopically for variability and represents a potentially useful sample for future high-redshift reverberation mapping studies. This also marks the first time the precise wavelength dependence of quasar variability has been determined, allowing both the continuum and emission-line variability to be studied. We create an ensemble difference spectrum (bright phase minus faint phase) covering rest-frame wavelengths from 1000 to 6000 {\AA}. This average difference spectrum is bluer than the average single-epoch quasar spectrum; a power-law fit to the difference spectrum yields a spectral index αλ = -2.00, compared to an index of α λ = -1.35 for the single-epoch spectrum. This confirms that quasar continua are bluer when brighter. The difference spectrum also exhibits very weak or absent emission-line features; the strongest emission lines vary only 30{\%} as much as the continuum. This small emission-line variability with respect to the continuum is consistent with the intrinsic Baldwin effect. Due to the lack of variability of the lines, measured photometric color is not always bluer in brighter phases but depends on redshift and the filters used. Lastly, the difference spectrum is bluer than the ensemble quasar spectrum only for λrest < 2500 {\AA}, indicating that the variability cannot result from a simple scaling of the average quasar spectrum.",
author = "Wilhite, {Brian C.} and {Vanden Berk}, {Daniel E.} and Kron, {Richard G.} and Schneider, {Donald P.} and Nicholas Pereyra and Brunner, {Robert J.} and Richards, {Gordon T.} and Brinkmann, {Jonathan V.}",
year = "2005",
month = "11",
day = "10",
doi = "10.1086/430821",
language = "English (US)",
volume = "633",
pages = "638--648",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2 I",

}

Wilhite, BC, Vanden Berk, DE, Kron, RG, Schneider, DP, Pereyra, N, Brunner, RJ, Richards, GT & Brinkmann, JV 2005, 'Spectral variability of quasars in the sloan digital sky survey. I. Wavelength dependence', Astrophysical Journal, vol. 633, no. 2 I, pp. 638-648. https://doi.org/10.1086/430821

Spectral variability of quasars in the sloan digital sky survey. I. Wavelength dependence. / Wilhite, Brian C.; Vanden Berk, Daniel E.; Kron, Richard G.; Schneider, Donald P.; Pereyra, Nicholas; Brunner, Robert J.; Richards, Gordon T.; Brinkmann, Jonathan V.

In: Astrophysical Journal, Vol. 633, No. 2 I, 10.11.2005, p. 638-648.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Spectral variability of quasars in the sloan digital sky survey. I. Wavelength dependence

AU - Wilhite, Brian C.

AU - Vanden Berk, Daniel E.

AU - Kron, Richard G.

AU - Schneider, Donald P.

AU - Pereyra, Nicholas

AU - Brunner, Robert J.

AU - Richards, Gordon T.

AU - Brinkmann, Jonathan V.

PY - 2005/11/10

Y1 - 2005/11/10

N2 - SDSS repeat spectroscopic observations have resulted in multiepoch spectroscopy for ∼2500 quasars observed more than 50 days apart. From this sample, calibrating against stars observed simultaneously, we identify 315 quasars that have varied significantly between observations (with respect to assumed nonvariable stars observed concurrently). These variable quasars range in redshift from 0.5 to 4.72. This is the first large quasar sample studied spectroscopically for variability and represents a potentially useful sample for future high-redshift reverberation mapping studies. This also marks the first time the precise wavelength dependence of quasar variability has been determined, allowing both the continuum and emission-line variability to be studied. We create an ensemble difference spectrum (bright phase minus faint phase) covering rest-frame wavelengths from 1000 to 6000 Å. This average difference spectrum is bluer than the average single-epoch quasar spectrum; a power-law fit to the difference spectrum yields a spectral index αλ = -2.00, compared to an index of α λ = -1.35 for the single-epoch spectrum. This confirms that quasar continua are bluer when brighter. The difference spectrum also exhibits very weak or absent emission-line features; the strongest emission lines vary only 30% as much as the continuum. This small emission-line variability with respect to the continuum is consistent with the intrinsic Baldwin effect. Due to the lack of variability of the lines, measured photometric color is not always bluer in brighter phases but depends on redshift and the filters used. Lastly, the difference spectrum is bluer than the ensemble quasar spectrum only for λrest < 2500 Å, indicating that the variability cannot result from a simple scaling of the average quasar spectrum.

AB - SDSS repeat spectroscopic observations have resulted in multiepoch spectroscopy for ∼2500 quasars observed more than 50 days apart. From this sample, calibrating against stars observed simultaneously, we identify 315 quasars that have varied significantly between observations (with respect to assumed nonvariable stars observed concurrently). These variable quasars range in redshift from 0.5 to 4.72. This is the first large quasar sample studied spectroscopically for variability and represents a potentially useful sample for future high-redshift reverberation mapping studies. This also marks the first time the precise wavelength dependence of quasar variability has been determined, allowing both the continuum and emission-line variability to be studied. We create an ensemble difference spectrum (bright phase minus faint phase) covering rest-frame wavelengths from 1000 to 6000 Å. This average difference spectrum is bluer than the average single-epoch quasar spectrum; a power-law fit to the difference spectrum yields a spectral index αλ = -2.00, compared to an index of α λ = -1.35 for the single-epoch spectrum. This confirms that quasar continua are bluer when brighter. The difference spectrum also exhibits very weak or absent emission-line features; the strongest emission lines vary only 30% as much as the continuum. This small emission-line variability with respect to the continuum is consistent with the intrinsic Baldwin effect. Due to the lack of variability of the lines, measured photometric color is not always bluer in brighter phases but depends on redshift and the filters used. Lastly, the difference spectrum is bluer than the ensemble quasar spectrum only for λrest < 2500 Å, indicating that the variability cannot result from a simple scaling of the average quasar spectrum.

UR - http://www.scopus.com/inward/record.url?scp=28044437795&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=28044437795&partnerID=8YFLogxK

U2 - 10.1086/430821

DO - 10.1086/430821

M3 - Article

AN - SCOPUS:28044437795

VL - 633

SP - 638

EP - 648

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2 I

ER -