Search

We present observations of the most radio-luminous broad absorption-line (BAL) quasar known, 1624+3758, at redshift . The quasar has several unusual properties. (1) The Fe ii UV191 1787-Å emission line is very prominent. (2) The BAL trough (BALnicity index 2990 km s−1) is detached by 21 000 km s−1 and extends to velocity . There are additional intrinsic absorbers at −1900 and −2800 km s−1. (3) The radio rotation measure of the quasar, 18 350 rad m−2, is the second highest known. The radio luminosity is and the radio loudness is . The radio source is compact and the radio spectrum is GHz-peaked, consistent with it being relatively young. The width of the C iv emission line, in conjunction with the total optical luminosity, implies a black hole mass . The high Eddington ratio and the radio-loudness place this quasar in one corner of Boroson's two-component scheme for the classification of active galactic nuclei, implying a very high accretion rate, and this may account for some of the unusual observed properties. The absorber is a possible Lyman-limit system, with , and a covering factor of 0.7. A complex mini-BAL absorber at to −3400 km s−1 is detected in each of C iv, N v and O vi. The blue and red components of the C iv doublet happen to be unblended, allowing both the covering factor and optical depth to be determined as a function of velocity. Variation of the covering factor with velocity dominates the form of the mini-BAL, with the absorption being saturated over most of the velocity range. The velocity dependence of the covering factor and the large velocity width imply that the mini-BAL is intrinsic to the quasar. There is some evidence of line-locking between velocity components in the C iv mini-BAL, suggesting that radiation pressure plays a role in accelerating the outflow. [ABSTRACT FROM AUTHOR]

We obtain a sample of 87 radio-loud quasi-stellar objects (QSOs) in the redshift range 3.6 ≤ z ≤ 4.4 by cross-correlating sources in the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) radio survey (S1.4 GHz > 1 mJy) with star-like objects having r < 20.2 in Sloan Digital Sky Survey (SDSS) Data Release 7. Of these 87 QSOs, 80 are spectroscopically classified in previous work (mainly SDSS), and form the training set for a search for additional such sources. We apply our selection to 2916 FIRST-DR7 pairs and find 15 likely candidates. Seven of these are confirmed as high-redshift quasars, bringing the total to 87. The candidates were selected using a neural-network, which yields 97 per cent completeness (fraction of actual high-z QSOs selected as such) and an efficiency (fraction of candidates which are high-z QSOs) in the range of 47-60 per cent. We use this sample to estimate the binned optical luminosity function (LF) of radio-loud QSOs at z ~ 4, and also the LF of the total QSO population and its comoving density. Our results suggest that the radio-loud fraction at high z is similar to that at low z and that other authors may be underestimating the fraction at high z. Finally, we determine the slope of the optical LF and obtain results consistent with previous studies of radio-loud QSOs and of the whole population of QSOs. The evolution of the LF with redshift was for many years interpreted as a flattening of the bright-end slope, but has recently been re-interpreted as strong evolution of the break luminosity for high-z QSOs, and our results, for the radio-loud population, are consistent with this. [ABSTRACT FROM AUTHOR]

We report a transit timing study of the transiting exoplanetary system HD 189733. In total, we observed 10 transits in 2006 and 2008 with the 2.6-m Nordic Optical Telescope, and two transits in 2007 with the 4.2-m William Herschel Telescope. We used Markov Chain Monte Carlo simulations to derive the system parameters and their uncertainties, and our results are in a good agreement with previously published values. We performed two independent analyses of transit timing residuals to place upper mass limits on putative perturbing planets. The results show no evidence for the presence of planets down to 1 Earth mass near the 1:2 and 2:1 resonance orbits, and planets down to 2.2 Earth masses near the 3:5 and 5:3 resonance orbits with HD 189733b. These are the strongest limits to date on the presence of other planets in this system. [ABSTRACT FROM AUTHOR]

We aim to obtain a complete sample of redshift radio quasi-stellar objects (QSOs) from the Faint Images of the Radio Sky at Twenty cm survey (FIRST) sources having star-like counterparts in the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) photometric survey . Our starting sample of 8665 FIRST–DR5 pairs includes 4250 objects with spectra in DR5, 52 of these being QSOs. We found that simple supervised neural networks, trained on the sources with DR5 spectra, and using optical photometry and radio data, are very effective for identifying high- z QSOs in a sample without spectra. For the sources with DR5 spectra the technique yields a completeness (fraction of actual high- z QSOs classified as such by the neural network) of 96 per cent, and an efficiency (fraction of objects selected by the neural network as high- z QSOs that actually are high- z QSOs) of 62 per cent. Applying the trained networks to the 4415 sources without DR5 spectra we found QSO candidates. We obtained spectra of 27 of them, and 17 are confirmed as high- z QSOs. Spectra of 13 additional candidates from the literature and from SDSS Data Release 6 (DR6) revealed seven more QSOs, giving an overall efficiency of 60 per cent (24/40). None of the non-candidates with spectra from NASA/IPAC Extragalactic Database (NED) or DR6 is a QSO, consistently with a high completeness. The initial sample of high- z QSOs is increased from 52 to 76 sources, i.e. by a factor of 1.46. From the new identifications and candidates we estimate an incompleteness of SDSS for the spectroscopic classification of FIRST QSOs of 15 per cent for . [ABSTRACT FROM AUTHOR]

Context. Broad absorption lines (BALs) are present in the spectra of ∼20% of quasars (QSOs); this indicates fast outflows (up to 0.2c) that intercept the observer's line of sight. These QSOs can be distinguished again into radio-loud (RL) BAL QSOs and radio-quiet (RQ) BAL QSOs. The first are very rare, even four times less common than RQ BAL QSOs. The reason for this is still unclear and leaves open questions about the nature of the BAL-producing outflows and their connection with the radio jet. Aims. We explored the spectroscopic characteristics of RL and RQ BAL QSOs with the aim to find a possible explanation for the rarity of RL BAL QSOs. Methods. We identified two samples of genuine BAL QSOs from SDSS optical spectra, one RL and one RQ, in a suitable redshift interval (2.5 < z < 3.5) that allowed us to observe the Mg ii and Hβ emission lines in the adjacent near-infrared (NIR) band. We collected NIR spectra of the two samples using the Telescopio Nazionale Galileo (TNG, Canary Islands). By using relations known in the literature, we estimated the black-hole mass, the broad-line region radius, and the Eddington ratio of our objects and compared the two samples. Results. We found no statistically significant differences from comparing the distributions of the cited physical quantities. This indicates that they have similar geometries, accretion rates, and central black-hole masses, regardless of whether the radio-emitting jet is present or not. Conclusions. These results show that the central engine of BAL QSOs has the same physical properties with and without a radio jet. The reasons for the rarity of RL BAL QSOs must reside in different environmental or evolutionary variables. [ABSTRACT FROM AUTHOR]

Context. The origin of broad-absorption-line quasi-stellar objects (BAL QSOs) remains unclear. Accounting for ∼20% of the QSO population, these objects have broad absorption lines in their optical spectra generated from outflows with velocities of up to 0.2 c. In this work, we present the results of a multi-frequency study of a well-defined radio-loud BAL QSO sample, and a comparison sample of radio-loud non-BAL QSOs, both selected from the Sloan Digital Sky Survey (SDSS). Aims. We aim to test which of the currently popular models of the BAL phenomenon - "orientation" or "evolutionary" - best accounts for the radio properties of BAL quasars. We also consider a third model in which BALs are produced by polar jets driven by radiation pressure. Methods. Observations from 1.4 to 43 GHz have been obtained with the VLA and Effelsberg telescopes, and data from 74 to 408 MHz have been compiled from the literature. The spectral indices give clues about the orientation, while the determination of the peak frequency can constrain the age, and test the evolutionary scenario, in which BAL QSOs are young QSOs. The fractional polarisation and the rotation measure in part reflect the local magnetic field strength and particle density. Results. The fractions of resolved sources in the BAL and non-BAL QSO samples are similar (16% versus (vs.) 12%). The resolved sources in the two samples have similar linear sizes (20 to 400 kpc) and morphologies. There is weak evidence that the fraction of variable sources amongst BAL QSOs is smaller. The fractions of candidate GHz-peaked sources are similar in the two samples (36 ± 12% vs. 23 ± 8%), suggesting that BAL QSOs are not generally younger than non-BAL QSOs. Both BAL and non-BAL QSOs have a wide range of spectral indices, including flat-spectrum and steep-spectrum sources, consistent with a broad range of orientations. There is weak evidence (91% confidence) that the spectral indices of the BAL QSOs are steeper than those of non-BAL QSOs, mildly favouring edge-on orientations. At a higher level of significance (≥=97%), the spectra of BAL QSOs are no flatter than those of non-BAL QSOs, which suggests that a polar orientation is not preferred. The distributions of fractional polarisation in the two samples have similar median values (1-3%). The distributions of rotation measure are also similar, the only outlier being the BAL QSO 1624+37, which has an extreme rest-frame rotation measure (from the literature) of -18 350 ± 570 rad m-2. [ABSTRACT FROM AUTHOR]

We present new spectroscopic and photometric data of the Type Ibn supernovae 2006jc, 2000er and 2002ao. We discuss the general properties of this recently proposed supernova family, which also includes SN 1999cq. The early-time monitoring of SN 2000er traces the evolution of this class of objects during the first few days after the shock breakout. An overall similarity in the photometric and spectroscopic evolution is found among the members of this group, which would be unexpected if the energy in these core-collapse events was dominated by the interaction between supernova ejecta and circumstellar medium. Type Ibn supernovae appear to be rather normal Type Ib/c supernova explosions which occur within a He-rich circumstellar environment. SNe Ibn are therefore likely produced by the explosion of Wolf–Rayet progenitors still embedded in the He-rich material lost by the star in recent mass-loss episodes, which resemble known luminous blue variable eruptions. The evolved Wolf–Rayet star could either result from the evolution of a very massive star or be the more evolved member of a massive binary system. We also suggest that there are a number of arguments in favour of a Type Ibn classification for the historical SN 1885A (S-Andromedae), previously considered as an anomalous Type Ia event with some resemblance to SN 1991bg. [ABSTRACT FROM AUTHOR]

We present multifrequency observations of a sample of 15 radio-emitting broad absorption-line quasars (BAL QSOs), covering a spectral range between 74 MHz and 43 GHz. They mostly display convex radio spectra which typically peak at about 1–5 GHz (in the observer's rest frame), flatten at MHz frequencies, probably due to synchrotron self-absorption, and become steeper at high frequencies, i.e. ν≳ 20 GHz. Very Large Array (VLA) 22-GHz maps (HPBW ∼80 mas) show unresolved or very compact sources, with linear projected sizes of ≤1 kpc. About two-thirds of the sample looks unpolarized or weakly polarized at 8.4 GHz, frequency in which reasonable upper limits could be obtained for polarized intensity. Statistical comparisons have been made between the spectral index distributions of samples of BAL and non-BAL QSOs, both in the observed and in the rest frame, finding steeper spectra among non-BAL QSOs. However, constraining this comparison to compact sources results in no significant differences between both distributions. This comparison is consistent with BAL QSOs not being oriented along a particular line of sight. In addition, our analysis of the spectral shape, variability and polarization properties shows that radio BAL QSOs share several properties common to young radio sources like compact steep spectrum or gigahertz peaked spectrum sources. [ABSTRACT FROM AUTHOR]

Images of the site of the Type Ic supernova (SN) 2002ap taken before explosion were analysed previously by Smartt et al. We have uncovered new unpublished, archival pre-explosion images from the Canada–France–Hawaii Telescope (CFHT) that are vastly superior in depth and image quality. In this paper we present a further search for the progenitor star of this unusual Type Ic SN. Aligning high-resolution Hubble Space Telescope observations of the SN itself with the archival CFHT images allowed us to pinpoint the location of the progenitor site on the ground-based observations. We find that a source visible in the B- and R-band pre-explosion images close to the position of the SN is (1) not coincident with the SN position within the uncertainties of our relative astrometry and (2) is still visible ∼4.7-yr post-explosion in late-time observations taken with the William Herschel Telescope. We therefore conclude that it is not the progenitor of SN 2002ap. We derived absolute limiting magnitudes for the progenitor of and . These are the deepest limits yet placed on a Type Ic SN progenitor. We rule out all massive stars with initial masses greater than (the lower mass limit for stars to undergo core collapse) that have not evolved to become Wolf–Rayet stars. This is consistent with the prediction that Type Ic SNe should result from the explosions of Wolf–Rayet stars. Comparing our luminosity limits with stellar models of single stars at appropriate metallicity and with standard mass-loss rates, we find no model that produces a Wolf–Rayet star of low enough mass and luminosity to be classed as a viable progenitor. Models with twice the standard mass-loss rates provide possible single star progenitors but all are initially more massive than . We conclude that any single star progenitor must have experienced at least twice the standard mass-loss rates, been initially more massive than and exploded as a Wolf–Rayet star of final mass . Alternatively a progenitor star of lower initial mass may have evolved in an interacting binary system. Mazzali et al. propose such a binary scenario for the progenitor of SN 2002ap in which a star of initial mass is stripped by its binary companion, becoming a Wolf–Rayet star prior to explosion. We constrain any possible binary companion to a main-sequence star of , a neutron star or a black hole. By combining the pre-explosion limits with the ejecta mass estimates and constraints from X-ray and radio observations we conclude that any binary interaction most likely occurred as Case B mass transfer, either with or without a subsequent common-envelope evolution phase. [ABSTRACT FROM AUTHOR]

We selected from the VLA FIRST survey a sample of 94 objects with star-like counterparts in the Sloan Digital Sky Survey (SDSS), and with APM POSS-I colour , i.e. consistent with their being high-redshift quasars. 78 of the 94 candidates can be classified spectroscopically on the basis of either published data (mainly SDSS) or the observations presented here. The fractions of QSOs (51 out of 78) and redshift QSOs (23 out of 78, 29 per cent) are comparable to those found in other photometric searches for high-redshift QSOs. We confirm that selecting colour ensures inclusion of all QSOs with . The fraction of QSOs with broad absorption lines (BALs) is 27 ± 10 per cent (7/26) and the estimated BAL fraction for radio-loud QSOs is at least as high as for optically selected QSOs (∼13 per cent). Both the high BAL fraction and the high fraction of low-ionization BALs among BALs (four to five out of seven) in our sample, compared to previous work, are likely due to the red colour selection . The space density of radio-loud QSOs in the range with and is . Adopting a radio-loud fraction of 13.4 ± 3 per cent, this corresponds to , in substantial agreement with the cumulative luminosity function of SDSS QSOs in Fan et al. We note the unusual flat-spectrum radio-luminous QSO FIRST 1413+4505 , which shows strong associated Lyα absorption (rest-frame equivalent width ∼40 Å) and an extreme observed luminosity, . [ABSTRACT FROM AUTHOR]

We present a monitoring study of SN 2004A and probable discovery of a progenitor star in pre-explosion Hubble Space Telescope ( HST) images. The photometric and spectroscopic monitoring of SN 2004A show that it was a normal Type II-P which was discovered in NGC 6207 about two weeks after explosion. We compare SN 2004A to the similar Type II-P SN 1999em and estimate an explosion epoch of 2004 January 6. We also calculate three new distances to NGC 6207 of and . The former was calculated using the Standard Candle Method (SCM) for SNe II-P, and the latter two from the brightest supergiants method (BSM). We combine these three distances with existing kinematic distances, to derive a mean value of . Using this distance, we estimate that the ejected nickel mass in the explosion is . The progenitor of SN 2004A is identified in pre-explosion WFPC2 F814W images with a magnitude of , but is below the detection limit of the F606W images. We show that this was likely a red supergiant (RSG) with a mass of . The object is detected at 4.7σ above the background noise. Even if this detection is spurious, the 5σ upper limit would give a robust upper mass limit of for a RSG progenitor. These initial masses are very similar to those of two previously identified RSG progenitors of the Type II-P SNe and . [ABSTRACT FROM AUTHOR]

Photometric and spectroscopic observations of the faint Supernovae (SNe) 2002kg and 2003gm, and their precursors, in NGC 2403 and NGC 5334, respectively, are presented. The properties of these SNe are discussed in the context of previously proposed scenarios for faint SNe: low-mass progenitors producing underenergetic SNe; SNe with ejecta constrained by a circumstellar medium; and outbursts of massive Luminous Blue Variables (LBVs). The last scenario has been referred to as ‘Type V SNe’, ‘SN impostors’ or ‘fake SNe’. The faint SN 2002kg reached a maximum brightness of , much fainter than normal Type II SNe. The precursor of SN 2002kg is confirmed to be, as shown in previous work, the LBV NGC 2403-V37. Late-time photometry of SN 2002kg shows it to be only 0.6 mag fainter at 500 d than at the epoch of discovery. Two spectra of SN 2002kg, with an approximately 1-yr interval between observations, show only minor differences. Strong Fe ii lines are observed in the spectra of SN 2002kg, similar to both the LBV NGC 2363-V1 and the Type IIn SN 1995G. The spectrum of SN 2002kg does show strong resolved [N ii] at λλ6549,6583 Å. The identified progenitor of SN 2003gm is a bright yellow star, consistent with a F5-G2 supergiant, similar to the identified progenitor of SN 2004et. SN 2003gm, at the epoch of discovery, was of similar brightness to the possible fake SN 1997bs and the Type IIP SNe 1999br and 2005cs. Photometrically SN 2003gm shows the same decrease in brightness, over the same time period as SN 1997bs. The light curve and the spectral properties of SN 2003gm are also consistent with some intrinsically faint and low-velocity Type II SNe. The early-time spectra of SN 2003gm are dominated by Balmer emission lines, which at the observed resolution, appear similar to SN 2000ch. On the basis of the post-discovery photometric and spectroscopic observations presented here, we suggest that SN 2003gm is a similar event to SN 1997bs, although the SN/LBV nature of both of these objects is debated. At 226 d post-discovery the spectrum of SN 2003gm is strongle contaminated by H ii region emission lines, and it cannot be confirmed that the precursor star has disappeared. The presence of strong [N ii] lines, near Hα, is suggested as a possible means of identifying objects such as SN 2002kg/NGC 2403-V37 as being LBVs – although not as a general classification criterion of all LBVs masquerading as SNe. [ABSTRACT FROM AUTHOR]

We present photometric and spectroscopic data of the Type II-P supernova (SN II-P) 2003gd, which was discovered in M74 close to the end of its plateau phase. SN 2003gd is the first Type II supernova (SN) to have a directly confirmed red supergiant (RSG) progenitor. We compare SN 2003gd to SN 1999em, a similar SN II-P, and estimate an explosion date of 2003 March 18. We determine a reddening towards the SN of, using three different methods. We also calculate three new distances to M74 ofand. The former was estimated using the standard candle method (SCM), for Type II supernovae (SNe II), and the latter two using the brightest supergiants method (BSM). When combined with existing kinematic and BSM distance estimates, we derive a mean value of. SN 2003gd was found to have a lower tail luminosity compared with other normal Type II-P supernovae (SNe II-P) bringing into question the nature of this SN. We present a discussion concluding that this is a normal SN II-P, which is consistent with the observed progenitor mass of. [ABSTRACT FROM AUTHOR]

We present first-season infrared (IR) and optical photometry and spectroscopy of the Type Ia Supernova 1998bu in M96. We also report optical polarimetry of this event. SN 1998bu is one of the closest type Ia supernovae of modern times, and the distance of its host galaxy is well determined. We find that SN 1998bu is both photometrically and spectroscopically normal. However, the extinction to this event is unusually high, with We find that SN 1998bu peaked at an intrinsic Adopting a distance modulus of 30.25 (Tanvir et al.) and using Phillips et al.'s relations for the Hubble constant, we obtain Combination of our IR photometry with those of Jha et al. provides one of the most complete early-phase IR light curves for a SN Ia published so far. In particular, SN 1998bu is the first normal SN Ia for which good pre-t[sub Bmax] IR coverage has been obtained. It reveals that the J, H and K light curves peak about 5 days earlier than the flux in the B-band curve. [ABSTRACT FROM AUTHOR]

A correction to the article "Faint supernovae and supernova impostors: case studies of SN 2002kg/NGC 2403-V37 and SN 2003gm," by J. R. Maund, S. J. Smartt, R.-P. Kudritzki, A. Pastorello, G. Nelemans, F. Bresolin, F. Patat, G. F. Gilmore and C. R. Benn that was published in the previous issue is presented.