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Title: Time correlation between the radio and gamma-ray activity in blazars and the production site of the gamma-ray emission

In order to determine the location of the gamma-ray emission site in blazars, we investigate the time-domain relationship between their radio and gamma-ray emission. Light-curves for the brightest detected blazars from the first 3 years of the mission of the Fermi Gamma-ray Space Telescope are cross-correlated with 4 years of 15GHz observations from the OVRO 40-m monitoring program. The large sample and long light-curve duration enable us to carry out a statistically robust analysis of the significance of the cross-correlations, which is investigated using Monte Carlo simulations including the uneven sampling and noise properties of the light-curves. Modeling the light-curves as red noise processes with power-law power spectral densities, we find that only one of 41 sources with high quality data in both bands shows correlations with significance larger than 3σ (AO0235+164), with only two more larger than even 2.25σ (PKS 1502+106 and B2 2308+34). Additionally, we find correlated variability in Mrk 421 when including a strong flare that occurred in July-September 2012. These results demonstrate very clearly the difficulty of measuring statistically robust multiwavelength correlations and the care needed when comparing light-curves even when many years of data are used. This should be a caution. In all four sourcesmore » the radio variations lag the gamma-ray variations, suggesting that the gamma-ray emission originates upstream of the radio emission. Continuous simultaneous monitoring over a longer time period is required to obtain high significance levels in cross-correlations between gamma-ray and radio variability in most blazars.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [4] ;  [5] ;  [4] ;  [4] ;  [6] ;  [6] ;  [7] ;  [8] ;  [9] ;  [6]
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States); National Radio Astronomy Observatory (NRAO), Socorro, NM
  2. California Inst. of Technology (CalTech), Pasadena, CA (United States); Aalto Univ., Kylmala (Finland). Metsahovi Radio Observatory
  3. Purdue Univ., West Lafayette, IN (United States)
  4. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  5. California Inst. of Technology (CalTech), Pasadena, CA (United States); Univ. of Concepcion (Chile)
  6. Max Planck Inst. for Radioastronomy, Bonn (Germany)
  7. Univ. of Manchester (United Kingdom)
  8. Max Planck Inst. for Radioastronomy, Bonn (Germany); California Inst. of Technology (CalTech), Pasadena, CA (United States); Univ. of Crete (Greece)
  9. SLAC National Accelerator Lab., Menlo Park, CA (United States)
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Volume: 445; Journal Issue: 1; Journal ID: ISSN 0035-8711
Publisher:
Royal Astronomical Society
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS
OSTI Identifier:
1356451

Max-Moerbeck, W., Hovatta, T., Richards, J. L., King, O. G., Pearson, T. J., Readhead, A. C. S., Reeves, R., Shepherd, M. C., Stevenson, M. A., Angelakis, E., Fuhrmann, L., Grainge, K. J. B., Pavlidou, V., Romani, R. W., and Zensus, J. A.. Time correlation between the radio and gamma-ray activity in blazars and the production site of the gamma-ray emission. United States: N. p., Web. doi:10.1093/mnras/stu1749.
Max-Moerbeck, W., Hovatta, T., Richards, J. L., King, O. G., Pearson, T. J., Readhead, A. C. S., Reeves, R., Shepherd, M. C., Stevenson, M. A., Angelakis, E., Fuhrmann, L., Grainge, K. J. B., Pavlidou, V., Romani, R. W., & Zensus, J. A.. Time correlation between the radio and gamma-ray activity in blazars and the production site of the gamma-ray emission. United States. doi:10.1093/mnras/stu1749.
Max-Moerbeck, W., Hovatta, T., Richards, J. L., King, O. G., Pearson, T. J., Readhead, A. C. S., Reeves, R., Shepherd, M. C., Stevenson, M. A., Angelakis, E., Fuhrmann, L., Grainge, K. J. B., Pavlidou, V., Romani, R. W., and Zensus, J. A.. 2014. "Time correlation between the radio and gamma-ray activity in blazars and the production site of the gamma-ray emission". United States. doi:10.1093/mnras/stu1749. https://www.osti.gov/servlets/purl/1356451.
@article{osti_1356451,
title = {Time correlation between the radio and gamma-ray activity in blazars and the production site of the gamma-ray emission},
author = {Max-Moerbeck, W. and Hovatta, T. and Richards, J. L. and King, O. G. and Pearson, T. J. and Readhead, A. C. S. and Reeves, R. and Shepherd, M. C. and Stevenson, M. A. and Angelakis, E. and Fuhrmann, L. and Grainge, K. J. B. and Pavlidou, V. and Romani, R. W. and Zensus, J. A.},
abstractNote = {In order to determine the location of the gamma-ray emission site in blazars, we investigate the time-domain relationship between their radio and gamma-ray emission. Light-curves for the brightest detected blazars from the first 3 years of the mission of the Fermi Gamma-ray Space Telescope are cross-correlated with 4 years of 15GHz observations from the OVRO 40-m monitoring program. The large sample and long light-curve duration enable us to carry out a statistically robust analysis of the significance of the cross-correlations, which is investigated using Monte Carlo simulations including the uneven sampling and noise properties of the light-curves. Modeling the light-curves as red noise processes with power-law power spectral densities, we find that only one of 41 sources with high quality data in both bands shows correlations with significance larger than 3σ (AO0235+164), with only two more larger than even 2.25σ (PKS 1502+106 and B2 2308+34). Additionally, we find correlated variability in Mrk 421 when including a strong flare that occurred in July-September 2012. These results demonstrate very clearly the difficulty of measuring statistically robust multiwavelength correlations and the care needed when comparing light-curves even when many years of data are used. This should be a caution. In all four sources the radio variations lag the gamma-ray variations, suggesting that the gamma-ray emission originates upstream of the radio emission. Continuous simultaneous monitoring over a longer time period is required to obtain high significance levels in cross-correlations between gamma-ray and radio variability in most blazars.},
doi = {10.1093/mnras/stu1749},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 1,
volume = 445,
place = {United States},
year = {2014},
month = {9}
}