1. Photometric Reverberation Mapping of NGC 4395 The Restless Nature of AGNs 22 May, 2013 Stephen Rafter – The Technion, Haifa Israel

2. Collaborators Haim Edri – Masters Student - the Technion Doron Chelouche – Tel Aviv University/Univ. of Haifa Shai Kaspi – Tel Aviv University/the Technion Ehud Behar – the Technion

3. Broad Band Photometric RM Use broad band filters to detect time lags between continuum and emission lines when their signal is mixed in a given band NGC 4395 & SDSS filters

4. The Photometric RM Method We follow the method developed by Chelouche & Daniel (2012) as follows: (1) F X (t) = f X c (t) Take 2 filters, one which covers a ‘continuum only’ region, and a second which covers a region with lines and continuum such that we can define light curves for filters X and Y such that (2) F Y (t) = f Y c (t) + f Y l (t)

5. The Photometric RM Method The CCF between the lines and continuum is given by: (3) CCF lc (τ) = f Y l (t + τ) * f Y c (t) Since the continuum is the dominant variable source contributing to the band (> 80%) we assume: (5) f Y c (t) ≈ F X (t) (4) CCF lc (τ) = [F Y (t + τ) - f Y c (t + τ)] * f Y c (t) (6) CCF lc (τ) = [F Y (t + τ) - F X (t + τ)] * F X (t) (7) CCF lc (τ) = CCF XY (τ) - ACF X (τ)

6. Simulations Generate a ‘continuum’ light curve (LC) Shift by hand in time (τ) and scale down amplitude of variability to simulate line response to continuum variations Add the line and continuum LCs F X (t) F Y (t)

7. Simulations Compute the CCF and ACF and look for a peak in the difference. We recover the input time lag of ~4 hours Units in the lower panel have no ‘physical’ significance

8. Simulations Flux randomization (FR) within measured error bars in a Monte Carlo simulation (also random subsets, RSS) Final measurement is τ = 3.8 +1.5 hours -1.1

9. Why NGC 4395? Lowest luminosity of any confirmed AGN: L bol = 7 x 10 39 erg s -1 Nearby, so it’s bright and well studied D L ≈ 5 Mpc g` ≈ 14.5 mag Low luminosity implies R BLR on the order of a few hours HST C IV RM gives R BLR ≈ 1 hour (Peterson et al. 2005)

10. Photometric Observations and LCs 9 nights using the Wise Observatory's 1 meter telescope SDSS g', r' and i' broad band filters, 5 minute exposure

11. NGC 4395 – g` & r` Bands The g` band is ‘continuum’ τ = 3.68 +0.70 hours -0.84

12. NGC 4395 – i` & r` Bands The i` band is continuum τ = 3.46 +1.59 hours -0.36

13. NGC 4395 Velocity Hβ is fit atypically here with 3 components: Narrow ~ 65 km/s (modeled using [OIII] lines) Intermediate ~ 250 km/s (put in by hand) Broad ~ 1500 km/s (free parameter) Hi-Res Keck Spectrum 2011 from Ari Laor

14. Mass Estimation To calculate the mass we take: ΔV = 1500 ± 500 km/s τ = 3.6 ± 0.8 hours f = 0.75 (isotropic circular velocity field) M BH = 1.464 x 10 5 (R BLR /days) (ΔV/1000 km s -1 ) 2 M BH = 4.9 ± 2.6 x 10 4 M  Based on this study NGC 4395 is about here

15. Comparing to Previous Work

16. The Next Step: The Multivariate Correlation Function An extension of the CCF-ACF method outlined in Chelouche & Zucker (2013, accepted by ApJ.) Adds an extra parameter, α, which is the fractional line contribution to the total flux in the band where: α = 1 is a pure line emission light curve α = 0 is a pure continuum light curve Alleviates the need for spectral decomposition to obtain a pure continuum light curve, which can be subjective due to broad line wings and line blends in spectroscopic RM.

17. SDSS NLS1 Candidate “SL01” & The Multivariate Correlation Function

18. MCF Time Lag for Hα Maximum at τ = 18 +3 days and α = 0.12 -7 Warmer colors represent a higher correlation coefficient

19. Comparison of Methods ICCF and ZDCF determined spectroscopically

20. Comparing RM Methods Broad Band Photometric Reverberation SpectroscopyPhotometry Resolved linesBroad band filters Accurately measure flux in the lines and continuum Continuum and emission lines are mixed Observationally time consuming but more accurate Relatively quick but less accurate Only about 50 objects have been mapped Possible to use current and future large area surveys to estimate the masses of numerous AGNs (LSST will monitor ~ 10 7 AGNs)

21. Conclusions We use broad band filters and the CCF – ACF difference method to estimate R BLR for NGC 4395 (see Edri et al. 2012 for formal results) We introduce the MCF method which adds an addition parameter to characterize the contribution of variable line emission to a broad band light curves The MCF method can be applied to moderate/low resolution spectra to determine time lags as well as broad band light curves These methods can be applied to large area time series surveys like LSST to estimate R BLR for a very large number of AGN Still a lot of work to do and there will be more results to follow…