Two fast X-ray transients in archival Chandra data

We present the discovery of two new X-ray transients in archival Chandra data. The first transient, XRT 110103, occurred in January 2011 and shows a sharp rise of at least three orders of magnitude in count rate in less than 10 s, a flat peak for about 20 s and decays by two orders of magnitude in the next 60 s. We find no optical or infrared counterpart to this event in preexisting survey data or in an observation taken by the SIRIUS instrument at the Infrared Survey Facility 2.1 yr after the transient, providing limiting magnitudes of J>18.1, H>17.6 and Ks>16.3. This event shows similarities to the transient previously reported in Jonker et al. which was interpreted as the possible tidal disruption of a white dwarf by an intermediate mass black hole. We discuss the possibility that these transients originate from the same type of event. If we assume these events are related a rough estimate of the rates gives 1.4*10^5 per year over the whole sky with a peak 0.3-7 keV X-ray flux greater than 2*10^-10 erg cm^-2 s^-1 . The second transient, XRT 120830, occurred in August 2012 and shows a rise of at least three orders of magnitude in count rate and a subsequent decay of around one order of magnitude all within 10 s, followed by a slower quasi-exponential decay over the remaining 30 ks of the observation. We detect a likely infrared counterpart with magnitudes J=16.70+/-0.06, H=15.92+/-0.04 and Ks=15.37+/-0.06 which shows an average proper motion of 74+/-19 milliarcsec per year compared to archival 2MASS observations. The JHKs magnitudes, proper motion and X-ray flux of XRT 120830 are consistent with a bright flare from a nearby late M or early L dwarf.Comment: Accepted for publication in MNRAS, 6 pages, 5 figure

Laboratory Measurements Of White Dwarf Photospheric Spectral Lines: H Beta

We spectroscopically measure multiple hydrogen Balmer line profiles from laboratory plasmas to investigate the theoretical line profiles used in white dwarf (WD) atmosphere models. X-ray radiation produced at the Z Pulsed Power Facility at Sandia National Laboratories initiates plasma formation in a hydrogen-filled gas cell, replicating WD photospheric conditions. Here we present time-resolved measurements of H beta and fit this line using different theoretical line profiles to diagnose electron density, n(e), and n = 2 level population, n2. Aided by synthetic tests, we characterize the validity of our diagnostic method for this experimental platform. During a single experiment, we infer a continuous range of electron densities increasing from n(e) similar to 4 to similar to 30 x 10(16) cm(-3) throughout a 120-ns evolution of our plasma. Also, we observe n(2) to be initially elevated with respect to local thermodynamic equilibrium (LTE); it then equilibrates within similar to 55 ns to become consistent with LTE. This supports our electrontemperature determination of T-e similar to 1.3 eV (similar to 15,000 K) after this time. At n(e) greater than or similar to 10(17) cm(-3), we find that computer-simulation-based line-profile calculations provide better fits (lower reduced chi(2)) than the line profiles currently used in the WD astronomy community. The inferred conditions, however, are in good quantitative agreement. This work establishes an experimental foundation for the future investigation of relative shapes and strengths between different hydrogen Balmer lines.Laboratory Directed Research and Development programUnited States Department of Energy DE-AC04-94AL85000, DE-SC0010623National Science Foundation DGE-1110007Astronom

Chemo-Sensitive Running Droplet

Chemical control of the spontaneous motion of a reactive oil droplet moving on a glass substrate under an aqueous phase is reported. Experimental results show that the self-motion of an oil droplet is confined on an acid-treated glass surface. The transient behavior of oil-droplet motion is also observed with a high-speed video camera. A mathematical model that incorporates the effect of the glass surface charge is built based on the experimental observation of oil-droplet motion. A numerical simulation of this mathematical model reproduced the essential features concerning confinement within a certain chemical territory of oil-droplet motion, and also its transient behavior. Our results may shed light on physical aspects of reactive spreading and a chemotaxis in living things.Comment: 17 pages, 10 figure

The expanding bipolar shell of the helium nova V445 Puppis

From multi-epoch adaptive optics imaging and integral field unit spectroscopy, we report the discovery of an expanding and narrowly confined bipolar shell surrounding the helium nova V445 Puppis (Nova Puppis 2000). An equatorial dust disc obscures the nova remnant, and the outflow is characterized by a large polar outflow velocity of 6720 +/- 650 km s(-1) and knots moving at even larger velocities of 8450 +/- 570 km s(-1). We derive an expansion parallax distance of 8.2 +/- 0.5 kpc and deduce a pre-outburst luminosity of the underlying binary of log L/L-circle dot = 4.34 +/- 0.36. The derived luminosity suggests that V445 Puppis probably contains a massive white dwarf accreting at high rate from a helium star companion making it part of a population of binary stars that potentially lead to supernova Ia explosions due to accumulation of helium-rich material on the surface of a massive white dwarf

Tomography of full sawtooth crashes on the Tokamak Fusion Test Reactor

Full sawtooth crashes in high temperature plasmas have been investigated on the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Fusion 33, 1509 (1991)]. A strong asymmetry in the direction of major radius, a feature of the ballooning mode, and a remaining m=1 region after the crash have been observed with electron cyclotron emission image reconstructions. The TFTR data is not consistent with two-dimensional (2-D) models; it rather suggests a three-dimensional (3-D) localized reconnection arising on the bad curvature side. This process explains the phenomenon of fast heat transfer which keeps the condition q0<1

Tomography of (2, 1) and (3, 2) magnetic island structures on Tokamak Fusion Test Reactor

High-resolution electron cyclotron emission (ECE) image reconstruction has been used to observe (m,n)=(2,1) and (3, 2) island structures on Tokamak Fusion Test Reactor [Plasma Phys. Controlled. Fusion 33, 1509 (1991)], where m and n are the poloidal and the toroidal mode number, respectively. The observed island structure is compared with other diagnostics, such as soft x-ray tomography and magnetic measurements. A cold elliptic island is observed after lithium pellet injection. Evidence for the enhancement of the heat transfer due to the island is observed. A relaxation phenomenon due to the m=2 mode is newly observed in Ohmic plasmas

The redshift and afterglow of the extremely energetic gamma-ray burst GRB 080916C

The detection of GeV photons from gamma-ray bursts (GRBs) has important consequences for the interpretation and modelling of these most-energetic cosmological explosions. The full exploitation of the high-energy measurements relies, however, on the accurate knowledge of the distance to the events. Here we report on the discovery of the afterglow and subsequent redshift determination of GRB 080916C, the first GRB detected by the Fermi Gamma-Ray Space Telescope with high significance detection of photons at >0.1 GeV. Observations were done with 7-channel imager GROND at the 2.2m MPI/ESO telescope, the SIRIUS instrument at the Nagoya-SAAO 1.4m telescope in South Africa, and the GMOS instrument at Gemini-S. The afterglow photometric redshift of z=4.35+-0.15, based on simultaneous 7-filter observations with the Gamma-Ray Optical and Near-infrared Detector (GROND), places GRB 080916C among the top 5% most distant GRBs, and makes it the most energetic GRB known to date. The detection of GeV photons from such a distant event is rather surprising. The observed gamma-ray variability in the prompt emission together with the redshift suggests a lower limit for the Lorentz factor of the ultra-relativistic ejecta of Gamma > 1090. This value rivals any previous measurements of Gamma in GRBs and strengthens the extreme nature of GRB 080916C.Comment: 6 pages, 5 figures; subm. to A&