Cameron, D. T., McHardy, Ian M., Dwelly, T., Breedt, E., Uttley, P., Lira, Paulina and Arévalo, P.. (2012) Correlated X-ray/ultraviolet/optical variability in the very low mass AGN NGC 4395. Monthly Notices of the Royal Astronomical Society, Vol.422 (No.1). pp. 902-912. ISSN 0035-8711

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Abstract

We report the results of a 1-yr Swift X-ray/ultraviolet (UV)/optical programme monitoring the dwarf Seyfert nucleus in NGC4395 in 2008-2009. The UV/optical flux from the nucleus was found to vary dramatically over the monitoring period, with a similar pattern of variation in each of the observed UV/optical bands (spanning 1900-5500 Å). In particular, the luminosity of NGC4395 in the 1900 Å band changed by more than a factor of 8 over the monitoring period. The fractional variability was smaller in the UV/optical bands than that seen in the X-rays, with the X-ray/optical ratio increasing with increasing flux. Pseudo-instantaneous flux measurements in the X-ray and each UV/optical band were well correlated, with cross-correlation coefficients of ≥0.7, significant at 99.9per cent confidence. Archival Swift observations from 2006 sample the intra-day X-ray/optical variability on NGC4395. These archival data show a very strong correlation between the X-ray and b bands, with a cross-correlation coefficient of 0.84 (significant at >99per cent confidence). The peak in the cross-correlation function is marginally resolved and asymmetric, suggesting that X-rays lead the b band, but by ≤1h. In response to recent (2011 August) very high X-ray flux levels from NGC4395 we triggered Swift target of opportunity observations, which sample the intra-hour X-ray/UV variability. These observations indicate, albeit with large uncertainties, a lag of the 1900 Å band behind the X-ray flux of ∼400s. The tight correlation between the X-ray and UV/optical lightcurves, together with the constraints we place on the lag time-scale, is consistent with the UV/optical variability of NGC4395 being primarily due to reprocessing of X-ray photons by the accretion disc.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science > Physics
Library of Congress Subject Headings (LCSH):	Active galactic nuclei
Journal or Publication Title:	Monthly Notices of the Royal Astronomical Society
Publisher:	Wiley-Blackwell Publishing, Inc
ISSN:	0035-8711
Date:	2012
Volume:	Vol.422
Number:	No.1
Page Range:	pp. 902-912
Identification Number:	10.1111/j.1365-2966.2012.20677.x
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Funder:	University of Southampton. School of Physics and Astronomy, Science and Technology Facilities Council (Great Britain) (STFC), Fondo Nacional de Desarrollo Científico y Tecnológico (Chile) (FONDECYT)
Grant number:	1110049 (FONDECYT)
References:	Abazajian K. N. et al., 2009, ApJS, 182, 543 Ar´evalo P., Uttley P., Kaspi S., Breedt E., Lira P., McHardy I. M., 2008, MNRAS, 389, 1479 Ar´evalo P., Uttley P., Lira P., Breedt E., McHardy I. M., Churazov E., 2009, MNRAS, 397, 2004 Breedt E. et al., 2009, MNRAS, 394, 427 Breedt E. et al., 2010, MNRAS, 403, 605 Breeveld A. A. et al., 2010, MNRAS, 406, 1687 Burrows D. N. et al., 2005, Space Sci. Rev., 120, 165 Cackett E. M., Horne K., Winkler H., 2007, MNRAS, 380, 669 Collier S. J. et al., 1998, ApJ, 500, 162 Czerny B., 2006, in Gaskell C. M.,McHardy I. M., Peterson B.M., Sergeev S. G., eds, ASP Conf. Ser. Vol. 360, AGN Variability from X-Rays to Radio Waves. Astron. Soc. Pac., San Francisco, p. 265 Desroches L.-B. et al., 2006, ApJ, 650, 88 Edelson R. A., Krolik J. H., 1988, ApJ, 333, 646 Fabian A. C. et al., 2012, MNRAS, 419, 116 Filippenko A. V., Ho L. C., 2003, ApJ, 588, L13 Filippenko A. V., Sargent W. L. W., 1989, ApJ, 342, L11 Gehrels N. et al., 2004, ApJ, 611, 1005 Gierli´nski M., Done C., Page K., 2009, MNRAS, 392, 1106 Janiuk A., Czerny B., 2011, MNRAS, 414, 2186 Kaaret P., Feng H., 2009, ApJ, 702, 1679 Krolik J. H., Horne K., Kallman T. R., Malkan M. A., Edelson R. A., Kriss G. A., 1991, ApJ, 371, 541 Lira P., Lawrence A., O’Brien P., Johnson R. A., Terlevich R., Bannister N., 1999, MNRAS, 305, 109 Lira P., Ar´evalo P., Uttley P., McHardy I., Breedt E., 2011, MNRAS, 415, 1290 Minezaki T. et al., 2006, ApJ, 643, L5 O’Neill P. M. et al., 2006, ApJ, 645, 160 Peng C. Y., Ho L. C., Impey C. D., Rix H.-W., 2002, AJ, 124, 266 Peng C. Y., Ho L. C., Impey C. D., Rix H.-W., 2010, AJ, 139, 2097 Peterson B. M. et al., 2005, ApJ, 632, 799 Peterson B. M. et al., 2006, ApJ, 641, 638 Poole T. S. et al., 2008, MNRAS, 383, 627 Roming P. W. A. et al., 2005, Space Sci. Rev., 120, 95 Roming P. W. A. et al., 2009, ApJ, 690, 163 Rowan-Robinson M. et al., 2008, MNRAS, 386, 697 Schlegel D. J., Finkbeiner D. P., Davis M., 1998, ApJ, 500, 525 Sergeev S. G., Doroshenko V. T., Golubinskiy Y. V., Merkulova N. I., Sergeeva E. A., 2005, ApJ, 622, 129 Shakura N. I., Sunyaev R. A., 1973, A&A, 24, 337 Thim F., Hoessel J. G., Saha A., Claver J., Dolphin A., Tammann G. A., 2004, AJ, 127, 2322 Timmer J., Koenig M., 1995, A&A, 300, 707 Uttley P., McHardy I. M., 2001, MNRAS, 323, L26 Vaughan S., Iwasawa K., Fabian A. C., Hayashida K., 2005, MNRAS, 356, 524 Wanders I. et al., 1997, ApJ, 113, 69
URI:	http://wrap.warwick.ac.uk/id/eprint/44402

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