47 research outputs found
Hyper-Accreting Black Holes and Gamma-Ray Bursts
A variety of current models for gamma-ray bursts (GRBs) suggest a common
engine - a black hole of several solar masses accreting matter from a disk at a
rate 0.01 to 10 solar masses per second. Using a numerical model for
relativistic disk accretion, we have studied steady-state accretion at these
high rates. Inside a radius ~ 10**8 cm, for accretion rates greater than about
0.01 solar masses per second, a global state of balanced power comes to exist
between neutrino losses, chiefly pair capture on nucleons, and dissipation.
Energy emitted in neutrinos is less, and in the case of low accretion rates,
very much less, than the maximum efficiency factor for black hole accretion
(0.057 for no rotation; 0.42 for extreme Kerr rotation) times Mdot c**2. The
efficiency for producing a pair fireball along the rotational axis by neutrino
annihilation is calculated and found to be highly variable and very sensitive
to the accretion rate. For some of the higher accretion rates studied, it can
be several per cent or more; for accretion rates less than 0.05 solar masses
per second, it is essentially zero. The efficiency of the Blandford-Znajek
mechanism in extracting rotational energy from the black hole is also
estimated. In light of these results, the viability of various gamma-ray burst
models is discussed and the sensitivity of the results to disk viscosity, black
hole rotation rate, and black hole mass explored. A diverse range of GRB
energies seems unavoidable and neutrino annihilation in hyper-accreting black
hole systems can explain bursts up to 10**52 erg. Larger energies may be
inferred for beaming systems.Comment: 46 pages, includes 9 figures, LaTeX (uses aaspp4.sty), accepted by
The Astrophysical Journal. Additional solutions in Tables and Figs. 4 and 5,
minor revisions to text, references adde
The Extreme Hosts of Extreme Supernovae
We use GALEX ultraviolet (UV) and optical integrated photometry of the hosts
of seventeen luminous supernovae (LSNe, having peak M_V < -21) and compare them
to a sample of 26,000 galaxies from a cross-match between the SDSS DR4 spectral
catalog and GALEX interim release 1.1. We place the LSNe hosts on the galaxy
NUV-r versus M_r color magnitude diagram (CMD) with the larger sample to
illustrate how extreme they are. The LSN hosts appear to favor low-density
regions of the galaxy CMD falling on the blue edge of the blue cloud toward the
low luminosity end. From the UV-optical photometry, we estimate the star
formation history of the LSN hosts. The hosts have moderately low star
formation rates (SFRs) and low stellar masses (M_*) resulting in high specific
star formation rates (sSFR). Compared with the larger sample, the LSN hosts
occupy low-density regions of a diagram plotting sSFR versus M_* in the area
having higher sSFR and lower M_*. This preference for low M_*, high sSFR hosts
implies the LSNe are produced by an effect having to do with their local
environment. The correlation of mass with metallicity suggests that perhaps
wind-driven mass loss is the factor that prevents LSNe from arising in
higher-mass, higher-metallicity hosts. The massive progenitors of the LSNe
(>100 M_sun), by appearing in low-SFR hosts, are potential tests for theories
of the initial mass function that limit the maximum mass of a star based on the
SFR.Comment: 8 pages, 3 figures, 2 tables, accepted to ApJ, amended references and
updated SN designation
Episodic mass loss in binary evolution to the Wolf-Rayet phase: Keck and HST proper motions of RY Scuti's nebula
Binary mass transfer via Roche-lobe overflow (RLOF) is a key channel for
producing stripped-envelope Wolf-Rayet (WR) stars and may be critical to
account for SN Ib/c progenitors. RY Scuti is an extremely rare example of a
massive binary star caught in this brief but important phase. Its toroidal
nebula indicates equatorial mass loss during RLOF, while the mass-gaining star
is apparently embedded in an opaque accretion disk. RY Scuti's toroidal nebula
has two components: an inner ionised double-ring system, and an outer dust
torus that is twice the size of the ionised rings. We present two epochs of
Lband Keck NGS-AO images of the dust torus, plus three epochs of HST images of
the ionised gas rings. Proper motions show that the inner ionised rings and the
outer dust torus came from two separate ejection events roughly 130 and 250 yr
ago. This suggests that RLOF in massive contact binaries can be accompanied by
eruptive and episodic burst of mass loss, reminiscent of LBVs. We speculate
that the repeating outbursts may arise in the mass gainer from instabilities
associated with a high accretion rate. If discrete mass-loss episodes in other
RLOF binaries are accompanied by luminous outbursts, they might contribute to
the population of extragalactic optical transients. When RLOF ends for RY
Scuti, the overluminous mass gainer, currently surrounded by an accretion disk,
will probably become a B[e] supergiant and may outshine the hotter mass-donor
star that should die as a Type Ib/c supernova.Comment: 15 pages, 7 figures, submitted to MNRA
Modelling element abundances in semi-analytic models of galaxy formation
We update the treatment of chemical evolution in the Munich semi-analytic model, L-GALAXIES. Our new implementation includes delayed enrichment from stellar winds, supernovae type II (SNe-II) and supernovae type Ia (SNe-Ia), as well as metallicity-dependent yields and a reformulation of the associated supernova feedback. Two different sets of SN-II yields and three different SN-Ia delay-time distributions (DTDs) are considered, and eleven heavy elements (including O, Mg and Fe) are self-consistently tracked. We compare the results of this new implementation with data on a) local, star-forming galaxies, b) Milky Way disc G dwarfs, and c) local, elliptical galaxies. We find that the z=0 gas-phase mass-metallicity relation is very well reproduced for all forms of DTD considered, as is the [Fe/H] distribution in the Milky Way disc. The [O/Fe] distribution in the Milky Way disc is best reproduced when using a DTD with less than or equal to 50 per cent of SNe-Ia exploding within ~400 Myrs. Positive slopes in the mass-[alpha/Fe] relations of local ellipticals are also obtained when using a DTD with such a minor `prompt' component. Alternatively, metal-rich winds that drive light alpha elements directly out into the circumgalactic medium also produce positive slopes for all forms of DTD and SN-II yields considered. Overall, we find that the best model for matching the wide range of observational data considered here should include a power-law SN-Ia DTD, SN-II yields that take account of prior mass loss through stellar winds, and some direct ejection of light alpha elements out of galaxies
Spectra of Hydrogen-poor Superluminous Supernovae from the Palomar Transient Factory
Most Type I superluminous supernovae (SLSNe-I) reported to date have been identified by their high peak luminosities and spectra lacking obvious signs of hydrogen. We demonstrate that these events can be distinguished from normal-luminosity SNe (including Type Ic events) solely from their spectra over a wide range of light-curve phases. We use this distinction to select 19 SLSNe-I and four possible SLSNe-I from the Palomar Transient Factory archive (including seven previously published objects). We present 127 new spectra of these objects and combine these with 39 previously published spectra, and we use these to discuss the average spectral properties of SLSNe-I at different spectral phases. We find that Mn II most probably contributes to the ultraviolet spectral features after maximum light, and we give a detailed study of the O II features that often characterize the early-time optical spectra of SLSNe-I. We discuss the velocity distribution of O II, finding that for some SLSNe-I this can be confined to a narrow range compared to relatively large systematic velocity shifts. Mg II and Fe II favor higher velocities than O II and C II, and we briefly discuss how this may constrain power-source models. We tentatively group objects by how well they match either SN 2011ke or PTF12dam and discuss the possibility that physically distinct events may have been previously grouped together under the SLSN-I label
A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007
We present the results of the first search for gravitational wave bursts
associated with high energy neutrinos. Together, these messengers could reveal
new, hidden sources that are not observed by conventional photon astronomy,
particularly at high energy. Our search uses neutrinos detected by the
underwater neutrino telescope ANTARES in its 5 line configuration during the
period January - September 2007, which coincided with the fifth and first
science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed
for candidate gravitational-wave signals coincident in time and direction with
the neutrino events. No significant coincident events were observed. We place
limits on the density of joint high energy neutrino - gravitational wave
emission events in the local universe, and compare them with densities of
merger and core-collapse events.Comment: 19 pages, 8 figures, science summary page at
http://www.ligo.org/science/Publication-S5LV_ANTARES/index.php. Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p120000
ASASSN-15lh: a superluminous ultraviolet rebrightening observed by Swift and Hubble
We present and discuss ultraviolet and optical photometry from the Ultraviolet/Optical Telescope
and X-ray limits from the X-Ray Telescope on Swift and imaging polarimetry and ultraviolet/optical
spectroscopy with the Hubble Space Telescope of ASASSN-15lh. It has been classified as a hydrogenpoor
superluminous supernova (SLSN I) more luminous than any other supernova observed. ASASSN-
15lh is not detected in the X-rays in individual or coadded observations. From the polarimetry we
determine that the explosion was only mildly asymmetric. We find the flux of ASASSN-15lh to
increase strongly into the ultraviolet, with a ultraviolet luminosity a hundred times greater than the
hydrogen-rich, ultraviolet-bright SLSN II SN 2008es. We find objects as bright as ASASSN-15lh are
easily detectable beyond redshifts of âŒ4 with the single-visit depths planned for the Large Synoptic
Survey Telescope. Deep near-infrared surveys could detect such objects past a redshift of âŒ20 enabling
a probe of the earliest star formation. A late rebrightening â most prominent at shorter wavelengths
â is seen about two months after the peak brightness, which is itself as bright as a superluminous
supernova. The ultraviolet spectra during the rebrightening are dominated by the continuum without
the broad absorption or emission lines seen in SLSNe or tidal disruption events and the early optical
spectra of ASASSN-15lh. Our spectra show no strong hydrogen emission, showing only Lyα absorption
near the redshift previously found by optical absorption lines of the presumed host. The properties
of ASASSN-15lh are extreme when compared to either SLSNe or tidal disruption events
Uncertainty sources for measurable ocean carbonate chemistry variables
21 pages, 3 figures, 2 tables, supporting information https://doi.org/10.1002/lno.12477.-- Data availability statement: The GLODAPv2.2022 data product is freely available at the project website https://glodap.info/. The metadata data product is released as a supplementary .xlsx and .csv file with this submissionThe ocean carbonate system is critical to monitor because it plays a major role in regulating Earth's climate and marine ecosystems. It is monitored using a variety of measurements, and it is commonly understood that all components of seawater carbonate chemistry can be calculated when at least two carbonate system variables are measured. However, several recent studies have highlighted systematic discrepancies between calculated and directly measured carbonate chemistry variables and these discrepancies have large implications for efforts to measure and quantify the changing ocean carbon cycle. Given this, the Ocean Carbonate System Intercomparison Forum (OCSIF) was formed as a working group through the Ocean Carbon and Biogeochemistry program to coordinate and recommend research to quantify and/or reduce uncertainties and disagreements in measurable seawater carbonate system measurements and calculations, identify unknown or overlooked sources of these uncertainties, and provide recommendations for making progress on community efforts despite these uncertainties. With this paper we aim to (1) summarize recent progress toward quantifying and reducing carbonate system uncertainties; (2) advocate for research to further reduce and better quantify carbonate system measurement uncertainties; (3) present a small amount of new data, metadata, and analysis related to uncertainties in carbonate system measurements; and (4) restate and explain the rationales behind several OCSIF recommendations. We focus on open ocean carbonate chemistry, and caution that the considerations we discuss become further complicated in coastal, estuarine, and sedimentary environmentsThe Ocean Carbonate System Intercomparison Forum (OCSIF, https://www.us-ocb.org/ocean-carbonate-system-intercomparison-forum/) is a working group of subject matter experts that was established in 2019 with support from the Ocean Carbon and Biogeochemistry (OCB, us-ocb.org) Project Office, which receives funding from the National Science Foundation (NSF OCE-1850983) and the National Aeronautics and Space Administration (NASA NNX17AB17G). [...] B.R.C. thanks the Global Ocean Monitoring and Observing program of NOAA for funding the Carbon Data Management and Synthesis Program (Fund Ref. 100007298, program officer: Kathy Tedesco) and thereby supporting his involvement in OCSIF activities, as well as the funding the NA21OAR4310251 award (program officer: Virginia Selz), which supported the development and update of Supplementary Data S1. J.D.S. thanks the Global Ocean Monitoring and Observing program of NOAA (Award NA21OAR4310251), NOAA PMEL, and the University of Washington CICOES. R.J.W. acknowledges the National Science Foundation Division of Ocean Sciences (Oceans and Atmosphere [CSIRO] Canberra, Australia) and the MIT mTerra Catalyst fund. K.M.S. thanks the William and Elsie Knight Endowed Fellowship Fund for Marine Science (University of South Florida College of Marine Science), NOAA AOML, and the University of Miami CIMAS. K.L.F. thanks the St. Petersburg Downtown Partnership Fellowship in Coastal Science (University of South Florida College of Marine Science). M.I.G.-I. acknowledges the âSevero Ochoa Centre of Excellenceâ accreditation (CEX2019-000928-S). A.J.F. was supported by NOAA PMEL. M.Ă. thanks the IEO internal project RADPROF. W.-J.C., R.A.E., and X.L. thank NOAA's Ocean Acidification Program via award: NA17OAR0170332. W.-J.C. also thanks NSF for support (EPSCoR-1757353 and OCE-2123768UW). [...] This research was carried out in part under the auspices of the Cooperative Institute for Climate, Ocean, and Ecosystem Studies (CICOES) and the Cooperative Institute for Marine and Atmospheric Studies (CIMAS), cooperative agreements NA20OAR4320271 and NA20OAR4320472, respectivelyPeer reviewe