Preliminary galaxy extraction from DENIS images

The extragalactic applications of NIR surveys are summarized with a focus on the ability to map the interstellar extinction of our Galaxy. Very preliminary extraction of galaxies on a set of 180 consecutive images is presented, and the results illustrate some of the pitfalls in attempting an homogeneous extraction of galaxies from these wide-angle and shallow surveys.Comment: Invited talk at "The Impact of Large-Scale Near-IR Sky Surveys", meeting held in Tenerife, Spain, April 1996. 10 pages LaTeX with style file and 4 PS files include

Induction of tumours in intact and partially hepatectomized rats with ethyl methanesulphonate.

SINCE the suggestion was made that replicating liver cells may be especially sensitive to chemical carcinogens (Pound, 1968), much evidence has accumulated which supports this idea. As an instance of this, certain carcinogenic alkylating agents, dimethylnitrosamine (DMN) and nitrosomethylurea (NMU), which do not usually induce liver cancer by a single treatment, are hepatocarcinogens if given during the period of restorative hyper-plasia following partial hepatectomy (Craddock, 1971; Craddock and Frei, 1974). These results suggest that repli-cation of alkylated DNA is an initial event in carcinogenesis. Another methy-lating agent, methyl methanesulphonate (MMS), on the other hand, was not found to be a hepatocarcinogen, even when given after partial hepatectomy (Craddock, 1973a). Evidence suggests that this difference may be due to a difference in the nature of the reaction products formed in DNA. It appears likely that 06-alkylguanine rather than 7-alkylgua-nine is relevant in carcinogenesis (Love-less, 1969). DMN and NMU give rise to both these methylated bases, whereas no 06-methylguanine was detectable in rat liver after treatment with MMS (Craddock, 1973b). A small amount was measured after treatment of DNA with MMS in vitro (Lawley and Shah, 1972), and in mice treated with MMS in vivo (Frei and Lawley, 1976). In the case of ethy

Optical Observations of PSR J0205+6449

PSR J0205+6449 is a X-ray and radio pulsar in supernova remnant 3C 58. We report on observations of the central region of 3C 58 using the 4.2-m William Herschel Telescope with the intention of identifying the optical counterpart of PSR J0205+6449 and characterising its pulsar wind nebula. Around the pulsar position we identified extended emission with a magnitude of B = 23 \fm 97 \pm 0.10, V = 22 \fm 95 \pm 0.05 and R = 22 \fm 15 \pm 0.03 consistent with a pulsar wind nebula. From the R-band image we identified three knots with $m_R$ = 24 \fm 08 \pm 0.07 (o1), 24 \fm 15 \pm 0.07 (o2) and 24 \fm 24 \pm 0.08 (o3). We confirm the presence of an optical pulsar wind nebula around PSR J0205+6449 and give an upper limit of $m_R \approx$ 24 for the optical magnitude of the pulsar. Furthermore we make the tentative suggestion that our object o1, with an $m_R \approx$ 24.08 is the optical counterpart. If confirmed the pulsar would have an $L_R/L_x\approx 0.004$ and an optical efficiency of about 5% of the Crab pulsar. Such a low efficiency is more consistent with the characteristic age of the pulsar rather than that of SN 1181.Comment: The paper contains 3 figures and 3 tables, accepted for publication in MNRA

Finding the Electromagnetic Counterparts of Cosmological Standard Sirens

The gravitational waves (GW) emitted during the coalescence of supermassive black holes (SMBHs) in the mass range 10^4-10^7 M_sun will be detectable out to high redshifts with LISA. We calculate the size and orientation of the three-dimensional error ellipse in solid angle and redshift within which the LISA event could be localized using the GW signatures alone. We take into account uncertainties in LISA's measurements of the luminosity distance and direction to the source, in the background cosmology, in weak gravitational lensing magnification due to inhomogeneities along the line of sight, and potential source peculiar velocities. We find that weak lensing errors exceed other sources of uncertainties by nearly an order of magnitude. Under the plausible assumption that BH mergers are accompanied by gas accretion leading to Eddington-limited quasar activity, we then compute the number of quasars that would be found in a typical LISA error volume, as a function of BH mass and redshift. We find that low redshifts offer the best opportunities to identify quasar counterparts to cosmological standard sirens, and that the LISA error volume will typically contain a single near-Eddington quasar at z=1. This will allow a straightforward test of the hypothesis that BH mergers are accompanied by bright quasar activity and, if the hypothesis proves correct, will guarantee the identification of a unique quasar counterpart. This would yield unprecedented tests of the physics of SMBH accretion, and offer an alternative method to precisely constrain cosmological parameters [abridged].Comment: 11 pages, 4 figures, version accepted for publication in Ap