The 8th annual computational and systems neuroscience (Cosyne) meeting

peer reviewe

Weak and Strong Lensing Statistics

After a brief introduction to gravitational lensing theory, a rough overview of the types of gravitational lensing statistics that have been performed so far will be given. I shall then concentrate on recent results of galaxy-galaxy lensing, which indicate that galactic halos extend much further than can be probed via rotation of stars and gas.Comment: 10 pages, 2 figures, talk given at the ISSI-Workshop "Matter in the Universe", 19-23 March 2001 Bern (Switzerland

The Rise and Peak of the Luminous Type IIn SN 2017hcc/ATLAS17lsn from ASAS-SN and Swift UVOT Data

We present observations of the rise and peak of the Type IIn supernova SN 2017hcc/ATLAS17lsn obtained by the All-Sky Automated Survey for Supernovae (ASAS-SN) and Swift UVOT. The light curve of SN 2017hcc/ATLAS17lsn peaks at $V\simeq 13.7$ mag, which from the estimated redshift of the host galaxy ($z=0.0168$, $D\simeq 73$ Mpc) implies an absolute peak magnitude $M_{V,peak} \simeq -20.7$ mag. The near-UV to optical spectral energy distribution of SN 2017hcc/ATLAS17lsn from Swift UVOT is consistent with a hot, but cooling blackbody with $\rm T_{bb}\simeq 16500$ K on Oct. 28.4 and $\rm T_{bb} \simeq 11700$ K on Nov. 19.6. The estimated peak bolometric luminosity $L_{bol, peak}\simeq 1.3\times 10^{44}$ erg s$^{-1}$ makes SN2017hcc/ATLAS17lsn one of the most luminous Type IIn supernovae studied to date. From the bolometric light curve we constrain the risetime to be $\sim 27$ days and the total radiated energy of the event to date is $4\times 10^{50}$ erg

The Hubble Constant

I review the current state of determinations of the Hubble constant, which gives the length scale of the Universe by relating the expansion velocity of objects to their distance. There are two broad categories of measurements. The first uses individual astrophysical objects which have some property that allows their intrinsic luminosity or size to be determined, or allows the determination of their distance by geometric means. The second category comprises the use of all-sky cosmic microwave background, or correlations between large samples of galaxies, to determine information about the geometry of the Universe and hence the Hubble constant, typically in a combination with other cosmological parameters. Many, but not all, object-based measurements give $H_0$ values of around 72-74km/s/Mpc , with typical errors of 2-3km/s/Mpc. This is in mild discrepancy with CMB-based measurements, in particular those from the Planck satellite, which give values of 67-68km/s/Mpc and typical errors of 1-2km/s/Mpc. The size of the remaining systematics indicate that accuracy rather than precision is the remaining problem in a good determination of the Hubble constant. Whether a discrepancy exists, and whether new physics is needed to resolve it, depends on details of the systematics of the object-based methods, and also on the assumptions about other cosmological parameters and which datasets are combined in the case of the all-sky methods.Comment: Extensively revised and updated since the 2007 version: accepted by Living Reviews in Relativity as a major (2014) update of LRR 10, 4, 200

ASASSN-18di: discovery of a ΔV∼10ΔV \sim 10 flare on a mid-M dwarf

We report and characterize a white-light superflare on a previously undiscovered M dwarf detected by the ASAS-SN survey. Employing various color-magnitude and color-spectral type relationships, we estimate several stellar parameters, including the quiescent V-band magnitude, from which we derive a flare amplitude of $\Delta V \sim 10$. We determine an r-band absolute magnitude of $M_{r} = 11.4$, consistent with a mid-M dwarf, and an approximate distance to the source of $2.2$ kpc. Using classical-flare models, we infer a flare energy of $E_{V} \simeq (4.1\pm 2.2)\times 10^{36}$ ergs, making this one of the strongest flares documented on an M dwarf

ASASSN-14ae: a tidal disruption event at 200 Mpc

ASASSN-14ae is a candidate tidal disruption event (TDE) found at the centre of SDSS J110840.11+340552.2 (d ≃ 200 Mpc) by the All-Sky Automated Survey for Supernovae (ASAS-SN). We present ground-based and Swift follow-up photometric and spectroscopic observations of the source, finding that the transient had a peak luminosity of L ≃ 8 × 1043 erg s−1 and a total integrated energy of E ≃ 1.7 × 1050 erg radiated over the ∼5 months of observations presented. The blackbody temperature of the transient remains roughly constant at T ∼ 20 000 K while the luminosity declines by nearly 1.5 orders of magnitude during this time, a drop that is most consistent with an exponential, L ∝ e-t/t 0 with t0 ≃ 39 d. The source has broad Balmer lines in emission at all epochs as well as a broad He ii feature emerging in later epochs. We compare the colour and spectral evolution to both supernovae and normal AGN to show that ASASSN-14ae does not resemble either type of object and conclude that a TDE is the most likely explanation for our observations. At z = 0.0436, ASASSN-14ae is the lowest-redshift TDE candidate discovered at optical/UV wavelengths to date, and we estimate that ASAS-SN may discover 0.1–3 of these events every year in the future

Interacting Supernovae: Types IIn and Ibn

Supernovae (SNe) that show evidence of strong shock interaction between their ejecta and pre-existing, slower circumstellar material (CSM) constitute an interesting, diverse, and still poorly understood category of explosive transients. The chief reason that they are extremely interesting is because they tell us that in a subset of stellar deaths, the progenitor star may become wildly unstable in the years, decades, or centuries before explosion. This is something that has not been included in standard stellar evolution models, but may significantly change the end product and yield of that evolution, and complicates our attempts to map SNe to their progenitors. Another reason they are interesting is because CSM interaction is an efficient engine for making bright transients, allowing super-luminous transients to arise from normal SN explosion energies, and allowing transients of normal SN luminosities to arise from sub-energetic explosions or low radioactivity yield. CSM interaction shrouds the fast ejecta in bright shock emission, obscuring our normal view of the underlying explosion, and the radiation hydrodynamics of the interaction is challenging to model. The CSM interaction may also be highly non-spherical, perhaps linked to binary interaction in the progenitor system. In some cases, these complications make it difficult to definitively tell the difference between a core-collapse or thermonuclear explosion, or to discern between a non-terminal eruption, failed SN, or weak SN. Efforts to uncover the physical parameters of individual events and connections to possible progenitor stars make this a rapidly evolving topic that continues to challenge paradigms of stellar evolution.Comment: Final draft of a chapter in the "SN Handbook". Accepted. 25 pages, 3 fig

ASASSN-15oi: A Rapidly Evolving, Luminous Tidal Disruption Event at 216 Mpc

We present ground-based and Swift photometric and spectroscopic observations of the tidal disruption event (TDE) ASASSN-15oi, discovered at the center of 2MASX J20390918-3045201 ($d\simeq216$ Mpc) by the All-Sky Automated Survey for SuperNovae (ASAS-SN). The source peaked at a bolometric luminosity of $L\simeq1.9\times10^{44}$ ergs s$^{-1}$ and radiated a total energy of $E\simeq5.0\times10^{50}$ ergs over the $\sim3.5$ months of observations. The early optical/UV emission of the source can be fit by a blackbody with temperature increasing from $T\sim2\times10^4$ K to $T\sim6\times10^4$ K while the luminosity declines from $L\simeq1.9\times10^{44}$ ergs s$^{-1}$ to $L\simeq2.8\times10^{43}$ ergs s$^{-1}$, requiring the photosphere to be shrinking rapidly. The optical/UV luminosity decline is broadly consistent with an exponential decline, $L\propto e^{-t/t_0}$, with $t_0\simeq35$ days. ASASSN-15oi also exhibits roughly constant soft X-ray emission that is significantly weaker than the optical/UV emission. Spectra of the source show broad helium emission lines and strong blue continuum emission in early epochs, although these features fade rapidly and are not present $\sim3$ months after discovery. The early spectroscopic features and color evolution of ASASSN-15oi are consistent with a TDE, but the rapid spectral evolution is unique among optically-selected TDEs

Supernova progenitors, their variability and the Type IIP Supernova ASASSN-16fq in M66

We identify a pre-explosion counterpart to the nearby Type IIP supernova ASASSN-16fq (SN 2016cok) in archival $\textit{Hubble Space Telescope}$ data. The source appears to be a blend of several stars that prevents obtaining accurate photometry. However, with reasonable assumptions about the stellar temperature and extinction, the progenitor almost certainly had an initial mass $M_*$ $\lesssim$ 17 M$_\odot$, and was most likely in the mass range of $M_*$ = 8–12 M$_\odot$. Observations once ASASSN-16fq has faded will have no difficulty accurately determining the properties of the progenitor. In 8 yr of Large Binocular Telescope (LBT) data, no significant progenitor variability is detected to rms limits of roughly 0.03 mag. Of the six nearby supernova (SN) with constraints on the low-level variability, SN 1987A, SN 1993J, SN 2008cn, SN 2011dh, SN 2013ej and ASASSN-16fq, only the slowly fading progenitor of SN 2011dh showed clear evidence of variability. Excluding SN 1987A, the 90 per cent confidence limit implied by these sources on the number of outbursts over the last decade before the SN that last longer than 0.1 yr (full width at half-maximum) and are brighter than $M_R$ < −8 mag is approximately $N_\text{out}$ $\lesssim$ 3. Our continuing LBT monitoring programme will steadily improve constraints on pre-SN progenitor variability at amplitudes far lower than achievable by SN surveys.CSK, KZS, JSB, SMA and TWSH are supported by NSF grants AST-1515876 and AST-1515927. BJS is supported by NASA through Hubble Fellowship grant HF-51348.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. TW-SH is supported by the DOE Computational Science Graduate Fellowship, grant number DE-FG02- 97ER25308. TS is partly supported by NSF grant PHY-1404311 to J. Beacom. This work was partly supported by the European Union FP7 programme through ERC grant number 320360. Support for JLP is provided in part by FONDECYT through the grant 1151445 and by the Ministry of Economy, Development, and Tourism’s Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS. SD is supported by the Strategic Priority Research Program ‘The Emergence of Cosmological Structures’ of the Chinese Academy of Sciences (Grant No. XDB09000000) and NSFC project 11573003. Some of the observations were carried out using the LBT at Mt Graham, AZ. The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are the University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max–Planck Society, the Astrophysical Institute Potsdam and Heidelberg University; the Ohio State University; and The Research Corporation, on behalf of the University of Notre Dame, University of Minnesota and University of Virginia. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA, and in part on observations made with the NASA/ESA HST obtained at the Space Telescope Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Some observations were obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA)

Probing the Universe with Weak Lensing

Gravitational lenses can provide crucial information on the geometry of the Universe, on the cosmological scenario of formation of its structures as well as on the history of its components with look-back time. In this review, I focus on the most recent results obtained during the last five years from the analysis of the weak lensing regime. The interest of weak lensing as a probe of dark matter and the for study of the coupling between light and mass on scales of clusters of galaxies, large scale structures and galaxies is discussed first. Then I present the impact of weak lensing for the study of distant galaxies and of the population of lensed sources as function of redshift. Finally, I discuss the potential interest of weak lensing to constrain the cosmological parameters, either from pure geometrical effects observed in peculiar lenses, or from the coupling of weak lensing with the CMB.Comment: To appear Annual Review of Astronomy and Astrophysiscs Vol. 37. Latex and psfig.sty. Version without figure, 54 pages, 73Kb. Complete version including 13 figures (60 pages) available on ftp.iap.fr anonymous account in /pub/from_users/mellier/AnnualReview ; file ARAAmellier.ps.gz 1.6 M