Title: TEMPORAL CORRELATIONS BETWEEN OPTICAL AND GAMMA-RAY ACTIVITY IN BLAZARS

Abstract

For this research, we have been using the 0.76 m Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory to optically monitor a sample of 157 blazars that are bright in gamma-rays being detected with high significance (≥10σ) in one year by the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. We attempt to observe each source on a three-day cadence with KAIT, subject to weather and seasonal visibility. The gamma-ray coverage is essentially continuous. KAIT observations extend over much of the five-year Fermi mission for several objects, and most have >100 optical measurements spanning the last three years. These blazars (flat-spectrum radio quasars and BL Lac objects) exhibit a wide range of flaring behavior. Using the discrete correlation function (DCF), here we search for temporal relationships between optical and gamma-ray light curves in the 40 brightest sources in hopes of placing constraints on blazar acceleration and emission zones. We find strong optical-gamma-ray correlation in many of these sources at time delays of ~1 to ~10 days, ranging between –40 and +30 days. A stacked average DCF of the 40 sources verifies this correlation trend, with a peak above 99% significance indicating a characteristic time delay consistent with 0more » days. These findings strongly support the widely accepted leptonic models of blazar emission. However, we also find examples of apparently uncorrelated flares (optical flares with no gamma-ray counterpart and gamma-ray flares with no optical counterpart) that challenge simple, one-zone models of blazar emission. Moreover, we find that flat-spectrum radio quasars tend to have gamma-rays leading the optical, while intermediate- and high-synchrotron peak blazars with the most significant peaks have smaller lags/leads. In conclusion, it is clear that long-term monitoring at high cadence is necessary to reveal the underlying physical correlation.« less

Authors:

Cohen, Daniel P.  ^[1];

• Search DOE PAGES for author "Cohen, Daniel P."
• Search DOE PAGES for ORCID "0000-0002-5221-2342"

Romani, Roger W.  ^[2];

• Search DOE PAGES for author "Romani, Roger W."
• Search DOE PAGES for ORCID "0000-0001-6711-3286"

Filippenko, Alexei V.  ^[3];

• Search DOE PAGES for author "Filippenko, Alexei V."
• Search DOE PAGES for ORCID "0000-0003-3460-0103"

Cenko, S. Bradley ^[4]; Lott, Benoit ^[5]; Zheng, WeiKang ^[3]; Li, Weidong ^[3]

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+ Show Author Affiliations

1. Univ. of California, Berkeley, CA (United States). Department of Astronomy; Univ. of California, Los Angeles, CA (United States). Department of Physics & Astronomy
2. Stanford Univ., CA (United States). Dept. of Physics
3. Univ. of California, Berkeley, CA (United States). Department of Astronomy
4. NASA/Goddard Space Flight Center, Greenbelt, MD (United States)
5. Univ. Bordeaux, CENBG (France); CNRS, IN2P3, CENBG (France)

Publication Date:

Mon Dec 08 00:00:00 EST 2014

Research Org.:

SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)

Sponsoring Org.:

USDOE

Contributing Org.:

Fermi-LAT Collaboration

OSTI Identifier:

1356349

Grant/Contract Number:  

AC02-76SF00515

Resource Type:

Accepted Manuscript

Journal Name:

The Astrophysical Journal (Online)

Additional Journal Information:

Journal Name: The Astrophysical Journal (Online); Journal Volume: 797; Journal Issue: 2; Journal ID: ISSN 1538-4357

Publisher:

Institute of Physics (IOP)

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; active galactic nuclei: blazars; galaxies: jets; quasars: general