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 »
- Authors:
-
- Univ. of California, Berkeley, CA (United States). Department of Astronomy; Univ. of California, Los Angeles, CA (United States). Department of Physics & Astronomy
- Stanford Univ., CA (United States). Dept. of Physics
- Univ. of California, Berkeley, CA (United States). Department of Astronomy
- NASA/Goddard Space Flight Center, Greenbelt, MD (United States)
- Univ. Bordeaux, CENBG (France); CNRS, IN2P3, CENBG (France)
- Publication Date:
- 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
Citation Formats
Cohen, Daniel P., Romani, Roger W., Filippenko, Alexei V., Cenko, S. Bradley, Lott, Benoit, Zheng, WeiKang, and Li, Weidong. TEMPORAL CORRELATIONS BETWEEN OPTICAL AND GAMMA-RAY ACTIVITY IN BLAZARS. United States: N. p., 2014.
Web. doi:10.1088/0004-637X/797/2/137.
Cohen, Daniel P., Romani, Roger W., Filippenko, Alexei V., Cenko, S. Bradley, Lott, Benoit, Zheng, WeiKang, & Li, Weidong. TEMPORAL CORRELATIONS BETWEEN OPTICAL AND GAMMA-RAY ACTIVITY IN BLAZARS. United States. https://doi.org/10.1088/0004-637X/797/2/137
Cohen, Daniel P., Romani, Roger W., Filippenko, Alexei V., Cenko, S. Bradley, Lott, Benoit, Zheng, WeiKang, and Li, Weidong. Mon .
"TEMPORAL CORRELATIONS BETWEEN OPTICAL AND GAMMA-RAY ACTIVITY IN BLAZARS". United States. https://doi.org/10.1088/0004-637X/797/2/137. https://www.osti.gov/servlets/purl/1356349.
@article{osti_1356349,
title = {TEMPORAL CORRELATIONS BETWEEN OPTICAL AND GAMMA-RAY ACTIVITY IN BLAZARS},
author = {Cohen, Daniel P. and Romani, Roger W. and Filippenko, Alexei V. and Cenko, S. Bradley and Lott, Benoit and Zheng, WeiKang and Li, Weidong},
abstractNote = {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 0 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.},
doi = {10.1088/0004-637X/797/2/137},
journal = {The Astrophysical Journal (Online)},
number = 2,
volume = 797,
place = {United States},
year = {Mon Dec 08 00:00:00 EST 2014},
month = {Mon Dec 08 00:00:00 EST 2014}
}
Web of Science
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