Astronomical data analysis software and systems

Measuring Reddening with SDSS Stellar Spectra

In the Spring of 2011 we carried out a 2.5 month reverberation mapping campaign using the 3 m Shane telescope at Lick Observatory, monitoring 15 low-redshift Seyfert 1 galaxies. This paper describes the observations, reductions and measurements, and data products from the spectroscopic campaign. The reduced spectra were fitted with a multicomponent model in order to isolate the contributions of various continuum and emission-line components. We present light curves of broad emission lines and the active galactic nucleus (AGN) continuum, and measurements of the broad Hβ line widths in mean and rms spectra. For the most highly variable AGNs we also measured broad Hβ line widths and velocity centroids from the nightly spectra. In four AGNs exhibiting the highest variability amplitudes, we detect anticorrelations between broad Hβ width and luminosity, demonstrating that the broad-line region “breathes” on short timescales of days to weeks in response to continuum variations. We also find that broad Hβ velocity centroids can undergo substantial changes in response to continuum variations; in NGC 4593, the broad Hβ velocity shifted by ∼250 km s −1 over a 1 month period. This reverberation-induced velocity shift effect is likely to contribute a significant source of confusion noise to binary black hole searches that use multi-epoch quasar spectroscopy to detect binary orbital motion. We also present results from simulations that examine biases that can occur in measurement of broad-line widths from rms spectra due to the contributions of continuum variations and photon-counting noise.

The Lick AGN Monitoring Project 2011: Spectroscopic Campaign and Emission-Line Light Curves ; Astrophysical Journal Supplement Series

Love Love Love

ABSTRA C T We show how wavelength-dependent time delays between continuum flux variations of active galactic nuclei (AGNs) can be used to test the standard black hole-accretion disc paradigm, by measuring the temperature structure TORU of the gaseous material surrounding the purported black hole. Reprocessing of high-energy radiation in a steady-state blackbody accretion disc with T ~ R ˇ3=4 incurs a wavelength-dependent light travel time delay t ~ l 4=3 . The Interna- tional AGN Watch multiwavelength monitoring campaign on NGC 7469 showed optical continuum variations lagging behind those in the UV by about 1 d at 4800 Aand about 2 d at 7500 A ˚ . These UV/optical continuum lags imply a radial temperature structure T ~ R ˇ3=4 , consistent with the classical accretion disc model, and hence strongly support the existence of a disc in this system. We assume that the observed time delays are indeed caused by a classical accretion disc structure, and derive a redshift-independent luminosity distance to NGC 7469. The luminosity distance allows us to estimate a Hubble constant of H0Ocos i=0:7U 1=2 a 42 6 9 km s ˇ1 Mpc ˇ1 . The interpretation of the observed time delays and spectral energy distribution in the context of an accretion disc structure requires further validation. At the same time, efforts to minimize the systematic uncertainties in our method to derive a more accurate measurement of H0, e.g. by obtaining an independent accurate determination of the disc inclination i or statistical average of a moderate sample of active galaxies, are required. However, this remains a promising new method of determining redshift-independent distances to AGNs.

Measuring the Hubble constant from reverberating accretion discs in active galaxies

Accretion onto black holes is key to their growth over cosmic time1, especially during the active galactic nuclei phase when the inflowing material forms a radiatively efficient accretion disk2. To probe the disk, indirect imaging methods such as reverberation mapping3–6 and microlensing7,8 are required. Recent findings suggest that the disk may be larger than theoretical predictions by a factor of a few4,6,9, thus casting doubt on our understanding of accretion in the general astrophysical context. Whether new physics is implied10–12 or poorly understood biases are in effect5,6,13,14 is a longstanding question. Here, we report new reverberation data based on a unique narrowband-imaging design15, and argue that time delays between adjacent optical bands are primarily associated with the reprocessing of light by a farther away under-appreciated non-disk component. This component is associated with high-density photoionized material that is uplifted from the outer accretion disk, probably by radiation-pressure force on dust, and thus may represent the long-sought origin of the broad-line region16. Our findings suggest that the optical phenomenology of some active galactic nuclei may be substantially affected by non-disk continuum emission with implications for measuring the fundamental properties of black holes and their active environs over cosmic time. New variability data of the accretion disk in active galactic nuclei argue for the existence of a farther away under-appreciated non-disk component associated with high-density photoionized material that is uplifted from the outer accretion disk.

Direct evidence of non-disk optical continuum emission around an active black hole

A class of methods for measuring time delays between astronomical time series is introduced in the context of quasar reverberation mapping, which is based on measures of randomness or complexity of the data. Several distinct statistical estimators are considered that do not rely on polynomial interpolations of the light curves nor on their stochastic modeling, and do not require binning in correlation space. Methods based on von Neumann's mean-square successive-difference estimator are found to be superior to those using other estimators. An optimized von Neumann scheme is formulated, which better handles sparsely sampled data and outperforms current implementations of discrete correlation function methods. This scheme is applied to existing reverberation data of varying quality, and consistency with previously reported time delays is found. In particular, the size-luminosity relation of the broad-line region in quasars is recovered with a scatter comparable to that obtained by other works, yet with fewer assumptions made concerning the process underlying the variability. The proposed method for time-lag determination is particularly relevant for irregularly sampled time series, and in cases where the process underlying the variability cannot be adequately modeled.

Methods of Reverberation Mapping. I. Time-lag Determination by Measures of Randomness

At the Universitaetssternwarte Bochum near Cerro Armazones we have monitored the Seyfert-1 galaxy 3C 120 between September 2014 and March 2015 in BVRI and a narrow band filter covering the redshifted H alpha line; in addition we obtained a single con-temporary spectrum with FAST at Mt. Hopkins. Compared to earlier epochs 3C 120 is about a factor of three brighter, allowing us to study the shape of the broad line region (BLR) and the dust torus in a high luminosity phase. The analysis of the light curves yields that the dust echo is rather sharp and symmetric in contrast to the more complex broad H alpha BLR echo. We investigate how far this supports an optically thick bowl-shaped BLR and dust torus geometry as proposed by Kawaguchi & Mori (2010) and Goad et al. (2012). The comparison with several parameterizations of these models supports the following geometry: the BLR clouds lie inside the bowl closely above the bowl rim, up to a half covering angle 0 deg < theta < 40 deg (measured against the equatorial plane). Then the BLR is spread over many isodelay surfaces, yielding a smeared and structured echo as observed. Furthermore, if the BLR clouds shield the bottom of the bowl rim against radiation from the nucleus, the hot dust emission comes essentially from the top edge of the bowl (40 deg < theta < 45 deg). Then, for small inclinations as for 3C120, the top dust edge forms a ring which largely coincides with a narrow range of isodelay surfaces, yielding the observed sharp dust echo. The scale height of the BLR increases with radial distance from the black hole. This leads to luminosity dependent foreshortening effects of the lag. We discuss implications and possible corrections of the foreshortening for the black hole mass determination and consequences for the lag (size) - luminosity relationships and the difference to interferometric torus sizes.

/pdf/simultaneous-h-alpha-and-dust-reverberation-mapping-of-3c120-4hern96i19.pdf

Simultaneous H alpha and dust reverberation mapping of 3C120: Testing the bowl-shaped torus geometry

Simultaneous Hα and dust reverberation mapping of 3C 120: Testing the bowl-shaped torus geometry

New $B$- and $V$-band monitoring in 2014 $-$ 2015 reveals that the Seyfert 1 Galaxy, 3C120, has brightened by a magnitude of $1.4$, compared to our campaign that took place in 2009 $-$ 2010. This allowed us to check for the debated luminosity and time-dependent color variations claimed for SDSS quasars. For our 3C120 data, we find that the $B/V$ flux ratio of the variable component in the bright epoch is indistinguishable from the faint one. We do not find any color variability on different timescales ranging from about $1$ to $1800$ days. We suggest that the luminosity and time-dependent color variability is an artifact caused by analyzing the data in magnitudes instead of fluxes. The flux variation gradients of both epochs yield consistent estimates of the host galaxy contribution to our 7.5" aperture. These results confirm that the optical flux variation gradient method works well for Seyfert galaxies.

/pdf/the-stability-of-the-optical-flux-variation-gradient-for-1fv4jyg601.pdf

Francisco Pozo Nuñez

Papers

Direct evidence of non-disk optical continuum emission around an active black hole

Methods of Reverberation Mapping. I. Time-lag Determination by Measures of Randomness

Simultaneous H alpha and dust reverberation mapping of 3C120: Testing the bowl-shaped torus geometry

Simultaneous Hα and dust reverberation mapping of 3C 120: Testing the bowl-shaped torus geometry

The stability of the optical flux variation gradient for 3C120