17473456
Is the Broad-Line Region Clumped or Smooth? Constraints from the Hα Profile in NGC 4395, the Least Luminous Seyfert 1 Galaxy
The origin and configuration of the gas that emits broad lines in Type I active galactic nuclei is not established yet. The lack of small-scale structure in the broad emission-line profiles is consistent with either a smooth gas flow or a clumped flow with many small clouds. An attractive possibility for the origin of many small clouds is the atmospheres of bloated stars, an origin that also provides a natural mechanism for the cloud confinement. Earlier studies of the broad-line profiles have already put strong lower limits on the minimum number of such stars, but these limits are sensitive to the assumed width of the lines produced by each cloud. Here we revisit this problem using high-resolution Keck spectra of the H? line in NGC?4395, which has the smallest known broad-line region (~1014?cm). Only a handful of the required bloated stars (each having r* ? 1014?cm) could fit into the broad-line region of NGC?4395, yet the observed smoothness of the H? line implies a lower limit of ~104-105 on the number of discrete clouds. This conclusively rules out the bloated-stars scenario, regardless of any plausible line-broadening mechanisms. The upper limit on the size of the clouds is ~1012?cm, which is comparable to the size implied by photoionization models. This strongly suggests that gas in the broad-line region is structured as a smooth rather than a clumped flow, most likely in a rotationally dominated thick disklike configuration. However, it remains to be clarified why such a smooth, gravity-dominated flow generates double-peaked emission lines only in a small fraction of active galactic nuclei.
14709478
The lick AGN monitoring project: photometric light curves and optical variability characteristics
The Lick AGN Monitoring Project targeted 13 nearby Seyfert 1 galaxies with the intent of measuring the masses of their central black holes using reverberation mapping. The sample includes 12 galaxies selected to have black holes with masses roughly in the range 106-107 M ☉, as well as the well-studied active galactic nucleus (AGN) NGC 5548. In conjunction with a spectroscopic monitoring campaign, we obtained broadband B and V images on most nights from 2008 February through 2008 May. The imaging observations were carried out by four telescopes: the 0.76 m Katzman Automatic Imaging Telescope, the 2 m Multicolor Active Galactic Nuclei Monitoring telescope, the Palomar 60 inch (1.5 m) telescope, and the 0.80 m Tenagra II telescope. Having well-sampled light curves over the course of a few months is useful for obtaining the broad-line reverberation lag and black hole mass, and also allows us to examine the characteristics of the continuum variability. In this paper, we discuss the observational methods and the photometric measurements, and present the AGN continuum light curves. We measure various variability characteristics of each of the light curves. We do not detect any evidence for a time lag between the B- and V-band variations, and we do not find significant color variations for the AGNs in our sample.
118631879
Supernovae in Low-Redshift Galaxy Clusters: Observations by the Wise Observatory Optical Transient Search (WOOTS)
We describe the Wise Observatory Optical Transient Search (WOOTS), a survey for supernovae (SNe) and other variable and transient objects in the fields of redshift 0.06-0.2 Abell galaxy clusters. We present the survey design and data analysis procedures, and our object detection and follow-up strategies. We have obtained follow-up spectroscopy for all viable SN candidates and present the resulting SN sample here. Out of the 12 SNe we have discovered, 7 are associated with our target clusters while 5 are foreground or background field events. All but 1 of the SNe (a foreground field event) are Type Ia SNe. Our noncluster SN sample is uniquely complete, since all SN candidates have been either spectroscopically confirmed or ruled out. This allows us to estimate that the sample of field (noncluster) SNe, found in flux-limited surveys similar to WOOTS, would be dominated (~80%) by SNe Ia. Our spectroscopic follow-up observations also elucidate the difficulty in distinguishing active galactic nuclei from SNe. In separate papers we use the WOOTS sample to derive the SN rate in clusters for this redshift range and to measure the fraction of intergalactic cluster SNe. We also briefly report here on some quasars and asteroids discovered by WOOTS.
32188849
THE COLLIMATION AND ENERGETICS OF THE BRIGHTEST SWIFT GAMMA-RAY BURSTS
Long-duration gamma-ray bursts (GRBs) are widely believed to be highly collimated explosions (bipolar conical outflows with half-opening angle θ ≈ 1°-10°). As a result of this beaming factor, the true energy release from a GRB is usually several orders of magnitude smaller than the observed isotropic value. Measuring this opening angle, typically inferred from an achromatic steepening in the afterglow light curve (a "jet" break), has proven exceedingly difficult in the Swift era. Here, we undertake a study of five of the brightest (in terms of the isotropic prompt γ-ray energy release, E_(γ,iso)) GRBs in the Swift era to search for jet breaks and hence constrain the collimation-corrected energy release. We present multi-wavelength (radio through X-ray) observations of GRBs 050820A, 060418, and 080319B, and construct afterglow models to extract the opening angle and beaming-corrected energy release for all three events. Together with results from previous analyses of GRBs 050904 and 070125, we find evidence for an achromatic jet break in all five events, strongly supporting the canonical picture of GRBs as collimated explosions. The most natural explanation for the lack of observed jet breaks from most Swift GRBs is therefore selection effects. However, the opening angles for the events in our sample are larger than would be expected if all GRBs had a canonical energy release of ~10^(51) erg. The total energy release we measure for the "hyper-energetic" (E_(tot) ≳ 10^(52) erg) events in our sample is large enough to start challenging models with a magnetar as the compact central remnant.
50829074
The Luminous Infrared Host Galaxy of Short-duration GRB 100206A
The known host galaxies of short-hard gamma-ray bursts (GRBs) to date are characterized by low to moderate star formation rates (SFRs) and a broad range of stellar masses, in general agreement with models associating the phenomenon with an old progenitor, such as merging neutron stars. In this paper, we positionally associate the recent unambiguously short-hard Swift GRB 100206A with a disk galaxy at redshift z = 0.4068 that is rapidly forming stars at a rate of {approx}30 M {sub Sun} yr{sup -1}, almost an order of magnitude higher than any previously identified short-GRB host. The galaxy is very red (g - K = 4.3 AB mag), heavily obscured (A{sub V} Almost-Equal-To 2 mag), and has the highest metallicity of any GRB host to date (12 + log[O/H]{sub KD02} = 9.2): it is a classical luminous infrared galaxy (LIRG), with L {sub IR} Almost-Equal-To 4 Multiplication-Sign 10{sup 11} L {sub Sun }. While these properties could be interpreted to support an association of this GRB with recent star formation, modeling of the broadband spectral energy distribution also indicates that a substantial stellar mass of mostly older stars is also present. The specific SFR is modest (sSFR Almost-Equal-To 0.5 Gyr{sup -1}), themore » current SFR is not substantially elevated above its long-term average, and the host morphology shows no sign of recent merger activity. Our observations are therefore equally consistent with an older progenitor. Given the precedent established by previous short-GRB hosts and the significant fraction of the universe's stellar mass in LIRG-like systems at z {approx}> 0.3, an older progenitor represents the most likely origin of this event.« less
6886263
Submillijansky Transients in Archival Radio Observations
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 and achieved a typical point-source detection threshold at the beam center of 300 μJy 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 2 month averages. None of the 10 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 μJy at 5 and 8.4 GHz is 0.07 deg-2 yr -1 ≲ R ≲ 40 deg-2 yr-1, where the uncertainty is due to the unknown duration of the transients, 20 minutes < tchar < 7 days. A two-epoch survey for transients will detect 1.5 ± 0.4 transients per square degree above a flux density of 3 70 μJy. 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. We detect no counterparts for six transients in deep optical and infrared imaging. The hosts and progenitors of these transients are unknown. © 2007. The American Astronomical Society. All rights reserved.
16820646
Analytic representations based on SU(1,1) coherent states and their applications
We consider two analytic representations of the SU(1,1) Lie group: the representation in the unit disc based on the SU(1,1) Perelomov coherent states and the Barut - Girardello representation based on the eigenstates of the SU(1,1) lowering generator. We show that these representations are related through a Laplace transform. A `weak' resolution of the identity in terms of the Perelomov SU(1,1) coherent states is presented which is valid even when the Bargmann index k is smaller than . Various applications of these results in the context of the two-photon realization of SU(1,1) in quantum optics are also discussed.