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`. Short-Term Variability in Quasar Magnitude. Brian T. Fleming 1 , Julia Kennefick 2 , S. Bursick 2. 1 Illinois Institute of Technology, Chicago, IL USA. 2 University of Arkansas, Fayetteville, AR USA. Understanding Quazi-Stellar Objects (QSO’s). Quasars Selected for Variability Study.

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Short term variability in quasar magnitude


Short-Term Variability in Quasar Magnitude

Brian T. Fleming1,Julia Kennefick2, S. Bursick2

1Illinois Institute of Technology, Chicago, IL USA

2University of Arkansas, Fayetteville, AR USA

Understanding Quazi-Stellar Objects (QSO’s)

Quasars Selected for Variability Study

Purpose of Study

  • First observed in 50’s as radio sources without a corresponding visible source.

    • 1960 - 3C 48 tied to faint blue star-like object – Spectrum contained anomalous emission lines. Classified as “unknown”

    • 1963 – 3C 273 determined to have a redshift of z=0.1592

      • Traveling away from Earth at 44,000 km/sec

      • Nearly 2 billion light years away (Using Hubble’s Law: )

    • Dubbed Quazi-Stellar Objects because they looked like stars

  • Today it is known that quasars are galaxies with super-massive black holes – differentiated from the term “QSO”

    • Only about 10% are radio sources (“Radio Loud Quasars”)

    • Excited matter accelerated in the accretion disk of the black hole give off staggering amounts of energy (~1.8 x 1046 ergs/s for 3C 273 ≈ 4.7 trillion suns)

    • Most distant and luminous objects known

  • Five known Quasars were selected using the NASA Extragalactic Database (NED) for this study

    • Three areas of sky were observed using the NFO Webscope with two of those areas containing two separate quasars resolvable by the telescope

    • In order to help find the quasar in each image, the quasar’s relationship to neighboring objects was established. In figures 3-5 below the quasar is marked by the purple circle.

  • Observe five (5) quasars for 45 days

    • Can the QUEST quasar variation be detected

    • Look for variation in the other quasars

  • Challenges

    • Short time interval

    • Faint magnitudes push limits of the NFO webscope

  • Will help set standard for quasar variability astronomy limits

Fig. 7 – A Quasar. The outer edge of the accretion disk is barely visible partially eclipsing the luminous region6


Take Images as often as possible over study time period (45 days)

Sequential Logic

Fig. 3

HS 1603+3820

High magnitude and redshift

Magnitude: 15.9

Redshift: 2.51

Monitor change in nearby stable stars to remove interference

Quasar Detection and Identification

Fig. 4

VCV J162021.8+173623

Magnitude: 16.4

Redshift: z = 0.55510

VCV J162011.3+172428

Magnitude: 15.5

Redshift: z = 0.11244

  • Quasars usually appear as stars in optical wavelengths

    • Too distant to resolve as galaxies with most telescopes

    • Differentiated from stars using spectroscopy – most common method of detection

The NFO Webscope

Subtract average stellar variation from quasar variation

Record day to day quasar magnitude variation

  • Robotic Telescope

  • 24 Inch diameter

  • Capable of resolving objects with m≤18 with stacked images

Quasar Variability Observed

Fig. 5

Previously studied for variability.

QUEST J150724.0-020212.1

Magnitude: 14.5

Redshift: 1.090

QUEST J150706.7-020728.9

Magnitude: 17.3

Redshift: 1.920

Fig 8 – Red Filter

VCV J162011.3+172428

No appreciable variation. Slight downward trend within error range. 13 days observed.

  • Stars fall in highly populated color region (fig.1 – left4) due to stellar cores being primarily dominant fusion cycles

  • Quasars (and other anomalous objects) will usually outside the populous region

Fig 9 – Red Filter

VCV J162021.8+173623

No appreciable variation. Slight upward trend within error range. 13 days observed.

Quasar Variability

  • Type of matter in the accretion disk is not constant with time

    • Galaxies, while primarily Hydrogen, are not uniform

    • Supernova remnants will be rich in heavy elements

  • Amount of matter is also not constant

    • Larger and older galaxies tend to have pockets of heavier concentration of matter due to gravity

    • Spiral galaxies have spaces between the arms

  • Over time, these fluctuations will cause noticeable variation in the wavelength (and magnitude) of light emitted

  • Spectra of the Anomalous Objects that reveal strong emission lines for Hydrogen (primary element in a galaxy) identify objects as quasars (fig.2 – right5)

Fig 10 – Red Filter

HS 1603+3820

No appreciable variation.

9 days observed

The QUEST Quasar Variability Survey 6

  • QUEST survey concluded that with a 80% confidence level, about 75% of quasars that they surveyed will show variability over a 26 month period6

    • 50% will show at least 0.15 mag variation over 2 years

    • Nearly all will vary by at least 0.05 mag over 15 years

  • The QUEST survey was the first survey to use variation as a means of quasar discovery as opposed to the standard multi-color analysis method

Fig. 6

A plot of magnitude versus time for the QUEST J140621.6-012121.2 quasar.6

Primary References

3Quasar Astronomy Daniel W. Weedman, Cambridge University Press, 1986

4University of Tokyo, “Multicolor Survey for High Redshift Quasars”,

S. Oyabu, 1998

5The Astrophysical Journal, “2DF QSO Redshift Survey”, S.M Croom, 1998

6The Astrophysical Journal, “New Quasars Detected Via Variability in the QUEST1 Survey”, A.W Rengstorf, May 2004