arXiv subjects

Alexei V. Filippenko

Publications and source records attributed to Alexei V. Filippenko.

At least 487 records · Page 27Linked to original sources

arXiv2007

Constraints on Circumstellar Material Around the Type Ia Supernova 2007af

Patat et al. recently inferred the existence of circumstellar material around a normal Type Ia supernova (SN) for the first time, finding time-variable Na I D absorption lines in the spectrum of SN 2006X. We present high-resolution spectroscopy of the bright SN Ia 2007af at three epochs and search for variability in any of the Na D absorption components. Over the time range from 4 days before to 24 days after maximum light, we find that the host-galaxy Na D lines appear to be of interstellar rather than circumstellar origin and do not vary down to the level of 18 mA (column density of 2 x 10^11 cm^-2). We limit any circumstellar absorption lines to be weaker than ~10 mA (6 x 10^10 cm^-2). For the case of material distributed in spherically symmetric shells of radius ~10^16 cm surrounding the progenitor system, we place an upper limit on the shell mass of ~(3 x 10^-8)/X Msun, where X is the Na ionization fraction. We also show that SN 2007af is a photometrically and spectroscopically normal SN Ia. Assuming that the variable Na D lines in SN 2006X came from circumstellar matter, we therefore conclude that either there is a preferred geometry for the detection of variable absorption components in Type Ia supernovae, or SN 2007af and SN 2006X had different types of progenitor systems.

astro-ph↗

arXiv2007

Supernovae in the Subaru Deep Field: An Initial Sample, and Type Ia Rate, out to Redshift 1.6

Large samples of high-redshift supernovae (SNe) are potentially powerful probes of cosmic star formation, metal enrichment, and SN physics. We present initial results from a new deep SN survey, based on re-imaging in the R, i', z' bands, of the 0.25 deg2 Subaru Deep Field (SDF), with the 8.2-m Subaru telescope and Suprime-Cam. In a single new epoch consisting of two nights of observations, we have discovered 33 candidate SNe, down to a z'-band magnitude of 26.3 (AB). We have measured the photometric redshifts of the SN host galaxies, obtained Keck spectroscopic redshifts for 17 of the host galaxies, and classified the SNe using the Bayesian photometric algorithm of Poznanski et al. (2007) that relies on template matching. After correcting for biases in the classification, 55% of our sample consists of Type Ia supernovae and 45% of core-collapse SNe. The redshift distribution of the SNe Ia reaches z ~ 1.6, with a median of z ~ 1.2. The core-collapse SNe reach z ~ 1.0, with a median of z ~ 0.5. Our SN sample is comparable to the Hubble Space Telescope/GOODS sample both in size and redshift range. The redshift distributions of the SNe in the SDF and in GOODS are consistent, but there is a trend (which requires confirmation using a larger sample) for more high-z SNe Ia in the SDF. This trend is also apparent when comparing the SN Ia rates we derive to those based on GOODS data. Our results suggest a fairly constant rate at high redshift that could be tracking the star-formation rate. Additional epochs on this field, already being obtained, will enlarge our SN sample to the hundreds, and determine whether or not there is a decline in the SN Ia rate at z >~ 1.

astro-ph↗

arXiv2007

SN 2006gy: Discovery of the most luminous supernova ever recorded, powered by the death of an extremely massive star like Eta Carinae

(abridged) We report our discovery and observations of the peculiar Type IIn supernova SN2006gy in NGC1260, revealing that it reached a peak magnitude of -22, making it the most luminous supernova ever recorded. It is not yet clear what powers the total radiated energy of 1e51 erg, but we argue that any mechanism -- thermal emission, circumstellar interaction, or 56Ni decay -- requires a very massive progenitor star. The circumstellar interaction hypothesis would require truly exceptional conditions around the star probably experienced an LBV eruption like the 19th century eruption of eta Carinae. Alternatively, radioactive decay of 56Ni may be a less objectionable hypothesis. That power source would imply a large Ni mass of 22 Msun, requiring that SN2006gy was a pair-instability supernova where the star's core was obliterated. SN2006gy is the first supernova for which we have good reason to suspect a pair-instability explosion. Based on a number of lines of evidence, we rule out the hypothesis that SN 2006gy was a ``Type IIa'' event. Instead, we propose that the progenitor may have been a very massive evolved object like eta Carinae that, contrary to expectations, failed to completely shed its massive hydrogen envelope before it died. Our interpretation of SN2006gy implies that the most massive stars can explode earlier than expected, during the LBV phase, preventing them from ever becoming Wolf-Rayet stars. SN2006gy also suggests that the most massive stars can create brilliant supernovae instead of dying ignominious deaths through direct collapse to a black hole.

astro-ph↗

arXiv2007

SubmilliJansky Transients in Archival Radio Observations

[ABRIDGED] We report the results of a 944-epoch survey for transient sources with archival data from the Very Large Array spanning 22 years with a typical epoch separation of 7 days. Observations were obtained at 5 or 8.4 GHz for a single field of view with a full-width at half-maximum of 8.6' and 5.1', respectively, and achieved a typical point-source detection threshold at the beam center of ~300 microJy per epoch. Ten transient sources were detected with a significance threshold such that only one false positive would be expected. Of these transients, eight were detected in only a single epoch. Two transients were too faint to be detected in individual epochs but were detected in two-month averages. None of the ten transients was detected in longer-term averages or associated with persistent emission in the deep image produced from the combination of all epochs. The cumulative rate for the short timescale radio transients above 370 microJy at 5 and 8.4 GHz is 0.07 < R < 40 deg^-2 yr^-1, where the uncertainty is due to the unknown duration of the transients, 20 min < t_char < 7 days. A two-epoch survey for transients will detect 1.5 +/- 0.4 transient per square degrees above a flux density of 370 microJy. Two transients are associated with galaxies at z=0.040 and z=0.249. These may be similar to the peculiar Type Ib/c radio supernova SN 1998bw associated with GRB 980428. Six transients have no counterparts in the optical or infrared (R=27, Ks=18). The hosts and progenitors of these transients are unknown.

astro-ph↗

arXiv2007

Keck and ESO-VLT View of the Symmetry of the Ejecta of the XRF/SN 2006aj

Nebular-phase spectra of SN 2006aj, which was discovered in coincidence with X-ray flash 060218, were obtained with Keck in 2006 July and the Very Large Telescope in 2006 September. At the latter epoch spectropolarimetry was also attempted, yielding an upper limit of ~ 2% for the polarization. The spectra show strong emission lines of [OI] and MgI], as expected from a Type Ic supernova, but weak CaII lines. The [FeII] lines that were strong in the spectra of SN 1998bw are much weaker in SN 2006aj, consistent with the lower luminosity of this SN. The outer velocity of the line-emitting ejecta is ~ 8000 km/s in July and ~ 7400 km/s in September, consistent with the relatively low kinetic energy of expansion of SN 2006aj. All emission lines have similar width, and the profiles are symmetric, indicating that no major asymmetries are present in the ejecta at the velocities sampled by the nebular lines (v < 8000 km/s), except perhaps in the innermost part. The spectra were modelled with a non-LTE code. The mass of 56Ni required to power the emission spectrum is ~ 0.20 Msun, in excellent agreement with the results of early light curve modelling. The oxygen mass is ~ 1.5 Msun, again much less than in SN 1998bw but larger by ~ 0.7 Msun than the value derived from the early-time modelling. The total ejected mass is ~ 2 Msun below 8000 km/s. This confirms that SN 2006aj was only slightly more massive and energetic than the prototypical Type Ic SN 1994I, but also indicates the presence of a dense inner core, containing ~ 1 Msun of mostly oxygen and carbon. The presence of such a core is inferred for all broad-lined SNe Ic. This core may have the form of an equatorial oxygen-dominated region, but it is too deep to affect the early light curve and too small to affect the late polarization spectrum.

astro-ph↗

arXiv2007

On the Progenitors of Two Type II-P Supernovae in the Virgo Cluster

Direct identification of the progenitors of supernovae (SNe) is rare because of the required spatial resolution and depth of the archival data prior to the SN explosions. Here we report on the identification of the progenitors of two nearby SNe in the Virgo cluster: SN 2006my in NGC 4651 and SN 2006ov in M61. We obtained high-quality ground-based images of SN 2006my with the Canada-France-Hawaii Telescope, and are able to locate the site of the SN on pre-SN {\it Hubble Space Telescope} ({\it HST}) Wide Field Planetary Camera 2 images to a high precision (1$σ$ uncertainty of $\pm0\farcs$05). We pinpoint the site of SN 2006ov to within 0$\farcs$02 from {\it HST} Advanced Camera for Surveys images of the SN. We detected a red supergiant progenitor for each SN within the error circles, with an inferred zero-age main-sequence mass ($M_{\rm ZAMS}$) of $10^{+5}_{-3}$ $M_\odot$ and $15^{+5}_{-3}$ $M_\odot$ for the progenitors of SNe 2006my and 2006ov, respectively. The mass estimates for the progenitors of both SNe confirm a suggested trend that the most common Type II-plateau SNe originate from low-mass supergiants with $M_{\rm ZAMS} \approx 8$--20 $M_\odot$.

astro-ph↗

arXiv2007

SN 2006jc: A Wolf-Rayet Star Exploding in a Dense He-Rich Circumstellar Medium

We present optical photometry and spectra of the peculiar Type Ib supernova (SN) 2006jc. Strong and relatively narrow He I emission lines indicate the progenitor star exploded inside a dense circumstellar medium (CSM) rich in He. An exceptionally blue apparent continuum persists from our first spectrum obtained 15 days after discovery through our last spectrum ~1 month later. Based on the presence of isolated Fe II emission lines, we interpret the blue "continuum" as blended, perhaps fluorescent, Fe emission. One or two of the reddest He I line profiles in our spectra are double peaked, suggesting that the CSM has an aspherical geometry. The He I lines that are superposed on the blue continuum show P-Cygni profiles, while the redder He I lines do not, implying that the blue continuum also originates from an asymmetric mass distribution. The He-rich CSM, aspherical geometry, and line velocities indicate that the progenitor star was a WNE Wolf-Rayet (WR) star. A recent (2 years before the SN), coincident, luminous outburst similar to those seen in luminous blue variables (LBVs) is the leading candidate for the dense CSM. Such an eruption associated with a WR star has not been seen before, indicating that the progenitor star may have recently transitioned from the LBV phase. We also present unpublished spectral and photometric data on SN 2002ao which, along with SN 1999cq, is very similar to SN 2006jc. We propose that these three objects may represent a new and distinct class of SNe arising from WR progenitors surrounded by a dense CSM.

astro-ph↗

arXiv2007

Supernovae in Low-Redshift Galaxy Clusters: the Type-Ia Supernova Rate

Supernova (SN) rates are a potentially powerful diagnostic of star formation history (SFH), metal enrichment, and SN physics, particularly in galaxy clusters with their deep, metal-retaining potentials, and simple SFH. However, a low-redshift cluster SN rate has never been published. We derive the SN rate in galaxy clusters at 0.06<z<0.19, based on type Ia supernovae (SNe Ia) that were discovered by the Wise Observatory Optical Transient Survey. As described in a separate paper, a sample of 140 rich Abell clusters was monitored, in which six cluster SNe Ia were found and confirmed spectroscopically. Here, we determine the SN detection efficiencies of the individual survey images, and combine the efficiencies with the known spectral properties of SNe Ia to calculate the effective visibility time of the survey. The cluster stellar luminosities are measured from the Sloan Digital Sky Survey (SDSS) database in the griz SDSS bands. Uncertainties are estimated using Monte-Carlo simulations in which all input parameters are allowed to vary over their known distributions. We derive SN rates normalized by stellar luminosity, in SNU units (SNe per century per 10^10 L_sun) in five photometric bandpasses, of 0.36+/-(0.22,0.14)+/-0.02 (B), 0.351+/-(0.210,0.139)+/-0.020 (g), 0.288+/-(0.172,0.114)+/-0.018 (r), 0.229+/-(0.137,0.091)+/-0.014 (i), 0.186+/-(0.111,0.074)+/-0.010 (z), where the quoted errors are statistical and systematic, respectively. The SN rate per stellar mass unit, derived using a color-luminosity-mass relation, is 0.098+/-(0.059,0.039)+/-0.009 SNe (century 10^10 M_sun)^-1. The low cluster SN rates we find are similar to, and consistent with, the SN Ia rate in local elliptical galaxies.

astro-ph↗

arXiv2007

Signatures of Delayed Detonation, Asymmetry, and Electron Capture in the Mid-Infrared Spectra of Supernovae 2003hv and 2005df

We present the first mid-infrared (5.2-15.2 micron) spectra of Type Ia supernovae (SNe 2003hv and 2005df). The detection of Ni emission in SN 2005df 135 days after the explosion provides direct observational evidence of high-density nuclear burning forming a significant amount of stable Ni in a Type Ia supernova. The observed emission line profiles in the SN 2005df spectrum indicate a chemically stratified ejecta structure. The SN 2005df Ar lines also exhibit a two-pronged emission profile implying that the Ar emission deviates significantly from spherical symmetry. The spectrum of SN 2003hv also shows signs of asymmetry, exhibiting blueshifted [Co III] which matches the blueshift of [Fe II] lines in nearly coeval NIR spectra. Finally, local thermodynamic equilibrium abundance estimates for the yield of radioactive 56Ni give ~0.5 Msun, for SN 2003hv, but only ~0.13-0.22 Msun for the apparently subluminous SN 2005df, supporting the notion that the luminosity of SNe Ia is primarily a function of the radioactive 56Ni yield. The chemically stratified ejecta structure observed in SN 2005df matches the predictions of delayed-detonation (DD) models, but is entirely incompatible with current three-dimensional deflagration models. Furthermore the degree that this layering persists to the innermost regions of the supernova is difficult to explain even in a DD scenario, where the innermost ejecta are still the product of deflagration burning. Thus, while these results are roughly consistent with a delayed detonation, it is clear that a key piece of physics is still missing from our understanding of the earliest phases of SN Ia explosions.

astro-ph↗

arXiv2007

Direct Analysis of Spectra of the Unusual Type Ib Supernova 2005bf

Synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW are compared to spectra of the unusual Type Ib supernova 2005bf. We confirm the discovery by Folatelli et al. (2006) that very early spectra (about 30 days before maximum light) contain both photospheric-velocity (8000 km/s) features of He I, Ca II, and Fe II, and detached high-velocity (14,000 km/s) features of H-alpha, Ca II, and Fe II. An early spectrum of SN 2005bf is an almost perfect match to a near-maximum-light spectrum of the Type Ib SN 1999ex. Although these two spectra were at very different times with respect to maximum light (20 days before maximum for SN 2005bf and five days after for SN 1999ex), they were for similar times after explosion - about 20 days for SN 2005bf and 24 days for SN 1999ex. The almost perfect match clinches the previously suggested identification of H-alpha in SN 1999ex and supports the proposition that many if not all Type Ib supernovae eject a small amount of hydrogen. The earliest available spectrum of SN 2005bf resembles a near-maximum-light spectrum of the Type Ic SN 1994I. These two spectra also were at different times with respect to maximum light (32 days before maximum for SN 2005bf and four days before for SN 1994I) but at similar times after explosion - about eight days for SN 2005bf and 10 days for SN 1994I. The resemblance motivates us to consider a reinterpretation of the spectra of Type Ic supernovae, involving coexisting photospheric-velocity and high-velocity features. The implications of our results for the geometry of the SN 2005bf ejecta, which has been suggested to be grossly asymmetric, are briefly discussed.

astro-ph↗

arXiv2007

The Masses of Nuclear Black Holes in Luminous Elliptical Galaxies and Implications for the Space Density of the Most Massive Black Holes

Black hole masses predicted from the Mbh-sigma relationship conflict with those predicted from the Mbh-L relationship for the most luminous galaxies, such as brightest cluster galaxies (BCGs). This is because stellar velocity dispersion, sigma, increases only weakly with L for BCGs and other giant ellipticals. The Mbh-L relationship predicts that the most luminous BCGs may have Mbh approaching 10^{10}M_sol, while the M-sigma relationship always predicts Mbh<3X10^9M_sol. We argue that the Mbh-L relationship is a plausible or even preferred description for BCGs and other galaxies of similar luminosity. If cores in central stellar density are formed by binary BHs, then the inner-core cusp radius, r_gamma, may be an independent witness of Mbh. Using structural parameters derived from a large sample of early-type galaxies observed by HST, we argue that L is superior to sigma as an indicator of r_gamma in luminous galaxies. The observed r_gamma-Mbh relationship for 11 core galaxies with measured Mbh appears to be consistent with the Mbh-L relationship for BCGs. BCGs have large cores appropriate for their large luminosities that may be difficult to generate with the modest BH masses inferred from the Mbh-sigma relationship. Mbh~L may be expected to hold for BCGs, if they were formed in dissipationless mergers, which should preserve ratio of BH to stellar mass. This picture appears to be consistent with the slow increase in sigma with L and the more rapid increase in effective radii with L seen in BCGs. If BCGs have large BHs commensurate with their luminosities, then the local BH mass function for Mbh>3X10^9M_sol may be nearly an order of magnitude richer than that inferred from the Mbh-sigma relationship. The volume density of QSOs at earlier epochs may favor the predictions from the Mbh-L relationship.

astro-ph↗

arXiv2006

New Hubble Space Telescope Discoveries of Type Ia Supernovae at z > 1: Narrowing Constraints on the Early Behavior of Dark Energy

We have discovered 21 new Type Ia supernovae (SNe Ia) with the Hubble Space Telescope (HST) and have used them to trace the history of cosmic expansion over the last 10 billion years. These objects, which include 13 spectroscopically confirmed SNe Ia at z > 1, were discovered during 14 epochs of reimaging of the GOODS fields North and South over two years with the Advanced Camera for Surveys on HST. Together with a recalibration of our previous HST-discovered SNe Ia, the full sample of 23 SNe Ia at z > 1 provides the highest-redshift sample known. Combined with previous SN Ia datasets, we measured H(z) at discrete, uncorrelated epochs, reducing the uncertainty of H(z>1) from 50% to under 20%, strengthening the evidence for a cosmic jerk--the transition from deceleration in the past to acceleration in the present. The unique leverage of the HST high-redshift SNe Ia provides the first meaningful constraint on the dark energy equation-of-state parameter at z >1. The result remains consistent with a cosmological constant (w(z)=-1), and rules out rapidly evolving dark energy (dw/dz >>1). The defining property of dark energy, its negative pressure, appears to be present at z>1, in the epoch preceding acceleration, with ~98% confidence in our primary fit. Moreover, the z>1 sample-averaged spectral energy distribution is consistent with that of the typical SN Ia over the last 10 Gyr, indicating that any spectral evolution of the properties of SNe Ia with redshift is still below our detection threshold.

astro-ph↗

arXiv2006

Keck Infrared Observations of GRO J0422+32 in Quiescence

We present Keck K-band photometry and low-resolution H & K-band spectroscopy of the X-ray nova GRO J0422+32 obtained while the system was in the quiescent state. No clear ellipsoidal modulation is present in the light curve, which is instead dominated by a strong flickering component. In the K-band we observe strong Br_gamma emission, with an equivalent width of 38 +/- 5 Angstroms. From this we conclude that the accretion disc is the most likely source of the observed photometric contamination, and that previous infrared-based attempts to constrain the mass of the putative black hole in this system are prone to considerable uncertainty. We finally proceed to show how it is possible to place meaningful constraints on some of the binary parameters of this system, even in the presence of a relatively high level of contamination from the disc.

astro-ph↗

arXiv2006

The Centers of Early-Type Galaxies with HST. VI. Bimodal Central Surface Brightness Profiles

We combine the results from several HST investigations of the central structure of early-type galaxies to generate a large sample of parameterized surface photometry. The studies included were those that used the "Nuker law" to characterize the inner light distributions of the galaxies. The sample comprises WFPC1 and WFPC2 V band observations published earlier by our group, R band WFPC2 photometry of Rest et al., NICMOS H band photometry by Ravindranath et al. and Quillen et al., and the BCG WFPC2 I band photometry of Laine et al. The distribution of the logarithmic slopes of the central profiles strongly affirms that the central structure of elliptical galaxies with Mv < -19 is bimodal, based on both parametric and non-parametric analysis. At the HST resolution limit, most galaxies are either power-law systems, which have steep cusps in surface brightness, or core systems, which have shallow cusps interior to a steeper envelope brightness distribution. A rapid transition between the two forms occurs over the luminosity range -22 < Mv < -20, with cores dominating at the highest luminosities, and power-laws at the lowest. There are a few "intermediate" systems that have both cusp slopes and total luminosities that fall within the core/power-law transition, but they are rare and do not fill in the overall bimodal distribution of cusp slopes. These results are inconsistent with the Ferrarese et al. Virgo Cluster Survey (VCS) analysis. However, using galaxies common to the VCS samples, we demonstrate that the VCS models of the cusps are either a poor match to the observations or consist of forms fitted to the galaxy envelopes and extrapolated inward to the HST resolution limit.

astro-ph↗

arXiv2006

Spitzer measurements of atomic and molecular abundances in the Type IIP SN 2005af

We present results based on Spitzer Space Telescope mid-infrared (3.6-30 micron) observations of the nearby IIP supernova 2005af. We report the first ever detection of the SiO molecule in a Type IIP supernova. Together with the detection of the CO fundamental, this is an exciting finding as it may signal the onset of dust condensation in the ejecta. From a wealth of fine-structure lines we provide abundance estimates for stable Ni, Ar, and Ne which, via spectral synthesis, may be used to constrain nucleosynthesis models.

astro-ph↗

arXiv2006

The Survey of Nearby Nuclei with STIS (SUNNS):Emission-Line Nuclei at Hubble Space Telescope Resolution

We present results from a program of optical spectroscopy for 23 nearby galaxy emission-line nuclei. This investigation takes advantage of the spatial resolution of the Hubble Space Telescope to study the structure and energetics of the central 10 - 20 pc, and the resulting data have value for quantifying central black hole masses, star formation histories, and nebular properties. This paper provides a description of the experimental design, and new findings from the study of emission lines. The sample targets span a range of nebular spectroscopic class, from HII to Seyfert nuclei. The line ratios indicative of nebular ionization show only modest variations over order-of-magnitude differences in radius, and demonstrate in a systematic way that geometrical dilution of the radiation field from a central source cannot be assumed as a primary driver of ionization structure. Comparisons between large- and small-aperture measurements for the HII/LINER transition objects provide a new test that challenges conventional wisdom concerning the composite nature of these systems. We also list a number of other quantitative results that are of interest for understanding galaxy nuclei, including (1) the spatial distribution/degree of concentration of H-alpha emission as a function of nebular type; (2) the radial variation in electron density as a function of nebular type; and (3) quantitative broad H-alpha estimates obtained at a second epoch for these low-luminosity nuclei. The resulting measurements provide a new basis for comparing the nuclei of other galaxies with that of the Milky Way. We find that the Galactic Center is representative across a wide span of properties as a low-luminosity emission-line nucleus.

astro-ph↗

arXiv2006

A neutron-star-driven X-ray flash associated with supernova SN 2006aj

Supernovae connected with long-duration gamma-ray bursts (GRBs) are hyper-energetic explosion resulting from the collapse of very massive stars (about 40Mo, where Mo is the mass of the Sun) stripped of their outher hydrogen and helium envelopes. A very massive progenitor, collapsing to a black hole, was thought to be a requirement for the launch of a GRB. Here we report the results of modelling the spectra and light curve of SN 2006aj, which demonstrate that the supernova had a much smaller explosion energy and ejected much less mass than the other GRB-sueprnovae, suggesting that it was produced by a star whose initial mass was only about 20Mo. A star of this mass is expected to form a neutron star rather than a black hole when its core collapses. The smaller explosion energy of SN 2006aj is matched by the weakness and softness of GRB 060218 (an X-ray flash), and the weakness of the radio flux of the supernova. Our results indicate that the supernova-GRB connection extends to a much broader range of stellar masses than previously thought, possibly involving different physical mechanisms: a `collapsar' for the more massive stars collapsing to a black hole, and magnetic activity of the nascent neutron star for the less massive stars.

astro-ph↗

arXiv2006

Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. III. Optical Variability and X-ray/UV/Optical Correlations

We present optical observations of the low-luminosity Seyfert 1 nucleus of NGC 4395, as part of a multiwavelength reverberation-mapping program. Observations were carried out over two nights in 2004 April at Lick, Wise, and Kitt Peak Observatories. We obtained V-band and B-band photometry, and spectra over the range 3500-6800 Angstroms. Simultaneous Hubble Space Telescope UV and Chandra X-ray observations are presented in companion papers. Even though NGC 4395 was in an extremely low state of activity, we detect significant continuum variability of 2-10%, increasing toward shorter wavelengths. The continuum light curves, both spectroscopic and photometric, are qualitatively similar to the simultaneous UV and X-ray light curves. Inter-band cross-correlations suggest that the optical continuum emission lags behind the UV continuum emission by 24 +7/-9 min, and that the optical continuum emission lags behind the X-ray continuum emission by 44 +/- 13 min, consistent with a reprocessing model for active galactic nucleus emission. There are also hints of Balmer emission lines lagging behind the optical continuum by an amount slightly larger than the emission-line lag detected in the UV. These results are all similar to those of other Seyfert 1 nuclei. The emission-line lag yields a mass measurement of the central black hole, which although not very significant, is consistent with the value derived from the simultaneous UV data.

astro-ph↗