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Short-Term Variability in Quasar MagnitudeShort-Term Variability in Quasar Magnitude Brian T. FlemingBrian T. Fleming11,, Julia KennefickJulia Kennefick22, S. Bursick, S. Bursick22

11Illinois Institute of Technology, Chicago, IL USAIllinois Institute of Technology, Chicago, IL USA

Sequential Logic

22University of Arkansas, Fayetteville, AR USAUniversity of Arkansas, Fayetteville, AR USA

Understanding Quazi-Stellar Objects (QSO’s)•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

Quasar Detection and Identification

The NFO Webscope

•Robotic Telescope

•24 Inch diameter

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

•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

•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

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

The QUEST Quasar Variability Survey 6

Quasars Selected for Variability Study•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.

Fig. 3 HS 1603+3820

High magnitude and redshiftMagnitude: 15.9Redshift: 2.51

Fig. 4 VCV

J162021.8+173623Magnitude: 16.4

Redshift: z = 0.55510VCV

J162011.3+172428Magnitude: 15.5

Redshift: z = 0.11244 Fig. 5Previously studied for variability.

QUEST J150724.0-020212.1

Magnitude: 14.5Redshift: 1.090

QUEST J150706.7-020728.9

Magnitude: 17.3Redshift: 1.920

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

Purpose of Study

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

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

Monitor change in nearby stable stars to remove interference

Subtract average stellar variation from

quasar variation

Record day to day quasar magnitude

variation

•Observe five (5) Observe five (5) quasars for 45 daysquasars for 45 days

•Can the QUEST Can the QUEST quasar variation be quasar variation be detecteddetected• Look for variation Look for variation in the other quasarsin the other quasars

•ChallengesChallenges•Short time interval Short time interval •Faint magnitudes Faint magnitudes push limits of the push limits of the NFO webscopeNFO webscope

•Will help set standard Will help set standard for quasar variability for quasar variability astronomy limitsastronomy limits

Quasar Variability Observed

Primary References3Quasar Astronomy Daniel W. Weedman, Cambridge University Press, 19864University of Tokyo, “Multicolor Survey for High Redshift Quasars”,

S. Oyabu, 19985The 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

•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

VCV J162021.8+173623

16.98

17

17.02

17.04

17.06

17.08

17.1

17.12

17.14

17.16

3-Jun 5-Jun 7-Jun 9-Jun 11-Jun 13-Jun 15-Jun 17-Jun 19-Jun 21-Jun

Date of Observation

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HS 1603+3820

16.2

16.22

16.24

16.26

16.28

16.3

16.32

16.34

16.36

16.38

9-J un 10-J un 11-J un 12-J un 13-J un 14-J un 15-J un 16-J un 17-J un 18-J un 19-J un 20-J un

Date of Observation

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Fig 8 – Red FilterVCV

J162011.3+172428No appreciable variation.

Slight downward trend within error range. 13 days

observed.Fig 9 – Red Filter

VCV J162021.8+173623

No appreciable variation. Slight upward trend within

error range. 13 days observed.

Fig 10 – Red FilterHS 1603+3820

No appreciable variation. 9 days observed

VCV J162011.3+172428

15.42

15.44

15.46

15.48

15.5

15.52

15.54

15.56

15.58

15.6

3-Jun 5-Jun 7-Jun 9-Jun 11-Jun 13-Jun 15-Jun 17-Jun 19-Jun 21-Jun

Date of Observation

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Ma

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