12-16 September 2016
CERN
Europe/Zurich timezone
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Multi-frequency, broad-band variability study of BL Lac OJ 287

12 Sep 2016, 17:30
15m
500/1-001 - Main Auditorium (CERN)

500/1-001 - Main Auditorium

CERN

400
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Oral Contributions Gamma-ray astrophysics Gamma-ray astrophysics

Speaker

Arti Goyal (AO-JU)

Description

The main results from our analysis are :
(1) nature of processes generating
flux variability at optical/radio frequencies is different from
those at GeV freqeuncies ($\beta \sim $ 2 and 1, respectively); this could
imply, that $\gamma-$ray variability, unlike the Synchrotron (radio-to-optical) one,
is generated by superposition of two stochastic processes with different
relaxation timescales, (2) the main driver behind the optical variability
is same on years, months, days, and hours timescales ($\beta \sim 2$), which argues
against the scenario where different drivers behind the long-term flux
changes and intra-night flux changes are considered, such as internal shocks
due to the jet bulk velocity fluctuation (long-term flux changes) versus small-scale magnetic
reconnection events taking place at the jet base (intra-night flux
changes). Implications of these results
are discussed in the context of blazar emission models.

Summary

The power spectral densities (PSDs) of blazar light curves,
$P(f) = A f^{-\beta}$, where A is the normalization and $\beta$ is the slope,
indicate that the variability is generated by the underlying {\it stochastic}
processes (i.e., $\beta \simeq 1-3$, characteristic of flicker/red noise).
Study of power-law slopes, normalization or characteristic
timescales (if any), in the PSD is important for constraining
the physics of emission and energy dissipation processes in the blazar jets.
We present the results of PSD analysis of the BL Lac object OJ 287
at GeV ({\it Fermi}-LAT), optical (R-band)
and radio (GHz band from UMRAO and OVRO programmes),
covering few decades to sub-hours timescales.
The novelty of this study is that at optical frequency,
by combining long-term (historical optical light curve starting from 1986),
Kepler 2 mission data and densely sampled intra-night
lightcurves, the PSD characterisitics are investigated for temporal frequencies
ranging over 7 orders of magnitude.

Primary author

Arti Goyal (AO-JU)

Presentation Materials