Faint Arc Research Articles

Euclid preparation

Forthcoming imaging surveys will increase the number of known galaxy-scale strong lenses by several orders of magnitude. For this to happen, images of billions of galaxies will have to be inspected to identify potential candidates. In this context, deep-learning techniques are particularly suitable for finding patterns in large data sets, and convolutional neural networks (CNNs) in particular can efficiently process large volumes of images. We assess and compare the performance of three network architectures in the classification of strong-lensing systems on the basis of their morphological characteristics. In particular, we implemented a classical CNN architecture, an inception network, and a residual network. We trained and tested our networks on different subsamples of a data set of 40 000 mock images whose characteristics were similar to those expected in the wide survey planned with the ESA mission Euclid, gradually including larger fractions of faint lenses. We also evaluated the importance of adding information about the color difference between the lens and source galaxies by repeating the same training on single- and multiband images. Our models find samples of clear lenses with ≳90% precision and completeness. Nevertheless, when lenses with fainter arcs are included in the training set, the performance of the three models deteriorates with accuracy values of ~0.87 to ~0.75, depending on the model. Specifically, the classical CNN and the inception network perform similarly in most of our tests, while the residual network generally produces worse results. Our analysis focuses on the application of CNNs to high-resolution space-like images, such as those that the Euclid telescope will deliver. Moreover, we investigated the optimal training strategy for this specific survey to fully exploit the scientific potential of the upcoming observations. We suggest that training the networks separately on lenses with different morphology might be needed to identify the faint arcs. We also tested the relevance of the color information for the detection of these systems, and we find that it does not yield a significant improvement. The accuracy ranges from ~0.89 to ~0.78 for the different models. The reason might be that the resolution of the Euclid telescope in the infrared bands is lower than that of the images in the visual band.

A VLA monitoring study of JVAS B1422+231: investigation of time delays and detection of extrinsic variability

ABSTRACTWe present an analysis of two seasons of archival, multifrequency VLA monitoring of the quad lens system JVAS B1422+231, the 15-GHz data of which have previously been published. The 8.4- and 15-GHz variability curves show significant variability, especially in polarization, but lack features on short time-scales that would be necessary for an accurate measurement of the very short predicted time delays ($\lesssim$1 d) between the three bright images. Time delays can only realistically be measured to the very faint image D and for the first time we detect its long-term variability and determine its polarization properties. However, image-dependent (extrinsic) variability (including variations on time-scales of hours) is present in multiple images and the magnitude of this is largest in image D at 15 GHz (±10 per cent). As the variations appear to increase in amplitude with frequency, we suggest that the most likely cause is microlensing by compact objects in the lensing galaxy. Combining the monitoring data allows us to detect a faint arc of emission lying between images B and C and the jets responsible for this are imaged using archival VLBA data. Finally, we have also measured the rotation measure of the three bright images and detected the polarization properties of image D.

A Morphological Study of Two Young Multipolar Planetary Nebulae

We carry out an optical morphological and infrared spectral study for two young planetary nebulae (PNs) Hen 2-158 and Pe 1-1 to understand their complex shapes and dust properties. Hubble Space Telescope optical images reveal that these nebulae have several bipolar-lobed structures and a faint arc with a clear boundary is located at the northwestern side of Pe 1-1. The presence of this arc-shaped structure suggests that the object interacts with its nearby interstellar medium. Spitzer IRS spectroscopic observations of these young nebulae clearly show prominent unidentified infrared emission features and a weak silicate band in Pe 1-1, indicating that Hen 2-158 is a carbon-rich nebula and Pe 1-1 has a mixed chemistry dust environment. Furthermore, we construct two three-dimensional models for these PNs to realize their intrinsic structures. The simulated models of the nebulae suggest that multipolar nebulae may be more numerous than we thought. Our analyses of spectral energy distributions for Hen 2-158 and Pe 1-1 show that they have low luminosities and low stellar effective temperatures, suggesting that these nebulae are young PNs. A possible correlation between typical multipolar young PNs and nested nebulae is also discussed.

Multi‐Wavelength Imaging Observations of STEVE at Athabasca, Canada

AbstractWe present the first multi‐wavelength imaging observations of strong thermal emission velocity enhancement (STEVE) using an all‐sky imager at Athabasca (magnetic latitude = 61.5°N), Canada. This study is based on three STEVE events which were accompanied by picket fence structures in the green‐line. Although the STEVE arc was dominant in 630 and 557.7‐nm, weak emissions were also found in other wavelengths including OI at 844.6, Hβ, Na, and the nominal background filter at 572.5‐nm. As observed at 630 and 557.7‐nm, the STEVE arc started as a faint arc close to the auroral oval and moved equatorward. The 557.7‐nm arc exhibited picket fence structure at later times after it moved equatorward. The picket fence was sometimes found to persist even after the 630‐nm arc had disappeared. During a particular event, the STEVE arcs in both the 630 and 557.7‐nm were found to carry a ribbon‐like motion moving along the arc. We have found that STEVE arcs are embedded in a region of weak diffuse auroral emissions. The STEVE arcs have sharp boundaries and these boundaries are different in red‐ and green‐line. The sharp decrease in the intensity at the immediate poleward edge of the STEVE arc appears as a “dark‐band” in the green‐line images. Based on the horizontal component of the geomagnetic field at Fort Smith (magnetic latitude 67.28°N), we find that the STEVE arc detachment, its equatorward motion, and its brightness coincided with changes in the magnetic activity during the recovery phase of a substorm.

SHARP - I. A high-resolution multiband view of the infrared Einstein ring of JVAS B1938+666

We present new mass models for the gravitational lens system B1938+666, using multi-wavelength data acquired from Keck adaptive optics (AO) and Hubble Space Telescope (HST) observations. These models are the first results from the Strong-lensing at High Angular Resolution Program (SHARP), a project designed to study known quadruple-image and Einstein ring lenses using high-resolution imaging, in order to probe their mass distributions in unprecedented detail. Here, we specifically highlight differences between AO- and HST-derived lens models, finding that -- at least when the lens and source galaxies are both bright and red, and the system has a high degree of circular symmetry -- AO-derived models place significantly tighter constraints on model parameters. Using this improved precision, we infer important physical properties about the B1938+666 system, including the mass density slope of the lensing galaxy (gamma = 2.045), the projected dark matter mass fraction within the Einstein radius (M_dark/M_lens = 0.55), and the total magnification factor of the source galaxy (~ 13). Additionally, we measure an upper-limit constraint on luminous substructure (M_V > 16.2), based on the non-detection of bright satellite galaxies in all data sets. Finally, we utilize the improved image resolution of the AO data to reveal the presence of faint arcs outside of the primary Einstein ring. The positions and orientations of these arcs raise the intriguing possibility that B1938+666 has a second source galaxy, located at a more distant redshift. However, future work is needed to verify this hypothesis.

SNR 0104-72.3: A REMNANT OF A TYPE Ia SUPERNOVA IN A STAR-FORMING REGION?

We report our 110 ks Chandra observations of the supernova remnant (SNR) 0104-72.3 in the Small Magellanic Cloud (SMC). The X-ray morphology shows two prominent lobes along the northwest-southeast direction and a soft faint arc in the east. Previous low resolution X-ray images attributed the unresolved emission from the southeastern lobe to a Be/X-ray star. Our high resolution Chandra data clearly shows that this emission is diffuse, shock-heated plasma, with negligible X-ray emission from the Be star. The eastern arc is positionally coincident with a filament seen in optical and infrared observations. Its X-ray spectrum is well fit by plasma of normal SMC abundances, suggesting that it is from shocked ambient gas. The X-ray spectra of the lobes show overabundant Fe, which is interpreted as emission from the reverse-shocked Fe-rich ejecta. The overall spectral characteristics of the lobes and the arc are similar to those of Type Ia SNRs, and we propose that SNR 0104-72.3 is the first case for a robust candidate Type Ia SNR in the SMC. On the other hand, the remnant appears to be interacting with dense clouds toward the east and to be associated with a nearby star-forming region. These features are unusual for a standard Type Ia SNR. Our results suggest an intriguing possibility that the progenitor of SNR 0104-72.3 might have been a white dwarf of a relatively young population.

Rare display of eight concentric halos in Tampere, Finland, on 5 June 2008

On 5 June 2008 there was a rare display of eight concentric halos in Tampere, Finland. I present a preliminary analysis of this display. A brief comparison with earlier major odd-radius displays is made. Short faint arcs intersecting the Sun and their resemblance to the theoretical odd-radius helic arcs are discussed. A stacked image consisting of 72 individual frames of the display is presented. A single frame is provided for comparison, and the visual observation is described in some detail. Postprocessing techniques for halo photographs are discussed. A stacked simulation and the relevant crystal populations are presented.

Two Pulsar Wind Nebulae:Chandra/XMM‐NewtonImaging of GeV J1417−6100

We report on Chandra ACIS and XMM-Newton MOS/pn imaging observations of two pulsar wind nebulae (K3/PSR J1420-6048 and G313.3+0.1, the Rabbit) associated with the Galactic unidentified γ-ray source GeV J1417-6100. With excellent ACIS imaging the very energetic pulsar PSR J1420-6048 is separated from its surrounding nebula. This nebula has surprisingly little compact structure, although a faint arc is seen near the pulsar. Similarly, two point sources are resolved in the Rabbit Nebula. The large XMM-Newton collecting area provides useful spectral constraints on the Rabbit and the associated point sources. Based on spectra and X-ray morphology, we identify one point source as a plausible pulsar counterpart. Large backgrounds and low source counts limited pulse search sensitivities, but we report pulse upper limits and a candidate 108 ms period for the Rabbit Pulsar based on the XMM-Newton data and an ACIS CC observation. Comparison of the X-ray images with high-resolution ATCA radio maps shows that the nonthermal X-ray emission corresponds well with the radio structure.

Giant emission features at large distances from PNe: A preliminary investigation

“Senile” PNe are very old nebulae of extremely low surface brightness and large linear size; they offer e.g. the possibility of probing the conditions of the ISM also non-locally. We give three examples of huge nebulae in a preliminary inquire.NGC 3242: An ESO Schmidt plate obtained in April 1996 shows the ‘wrapped’ morphology of the faint arc discovered by Deeming (1966, Astrophys. J. 146, 287) 11′ south-west of this PN. Probably this arc is part of a giant halo of very low surface brightness around NGC 3242, but up to now the detection of the halo is questionable. A spectrum of the filament obtained at Las Campanas shows [O iii]/Hα ∼ 5 compared with a value of ∼ 3 in the nebula (Perinotto et al. 1994, Astron. Astrophys. Supp., 107, 481). This high ratio is larger than that expected for the excitation class of NGC 3242, even larger than the maximum allowed for a photo-ionized nebula of more or less normal chemical abundance. Thus, due to the spectral characteristic and to the filamentary structure of the arc we suspect that shocks appear to play a role.

Polarization and visual intensity of the inner light echo around SN 1987A

The ESO Faint Object Spectrograph and Camera operating in the coronographic mode on the 3.6 m telescope was used with a broad-band V filter and four linear polarizers oriented at position angles 0 deg, 45 deg, 90 deg, and 135 deg to measure the total and polarized flux of radiation scattered from circumstellar material around SN 1987A. A faint arc of V band emission with a sharp inner and outer boundary centered on the supernova and of radius approximately equal to 8.3 arcsec and width approximately equal to 2.5 arcsec is clearly discernible above background, most prominently in the eastern quadrant between 45 deg and 135 deg position angle. Its azimuthally averaged surface brightness in this position angle range is 21.8 + or - 0.2 V mag/arcsec. In this region, the detected radiation is found to be partially linearly polarized with a degree of polarization 0.15 + or - 0.04 and an electric vector orientation of about 0 deg position angle. These results indicate that the reflecting material is confined to a thin sheet or shell of column density near 10 to the 18th to 10 to the 19th atoms/sq cm located at about 3-5 pc from the SN whichmore » may have arisen from a previous red giant phase of the SN progenitor. 16 refs.« less

Electric field configuration and plasma parameters in the vicinity of a faint auroral arc

To study auroral arc physics, coordinated rocket and EISCAT measurements were made across a faint arc. Observed plasma parameters and d.c. electric fields from both methods are discussed. The precipitation event was a moderate one and obviously a localized and temporary disturbance. The electric field configuration in the vicinity of the associated arc measured on board the rocket payload (apogee at 703 km) and deduced from EISCAT measurements of the plasma drift are discussed. The main features of the electric field in the arc region can be explained by polarization fields, but there is also some evidence of field-aligned electric fields.

Auroral kilometric radiation/aurora correlation

Auroral kilometric radiation (AKR) observations from the ISIS 1 topside sounder receiver were compared with visual auroral observations from the network of Alaskan all‐sky camera stations. The goal was to relate AKR source region encounters to specific auroral forms on the same magnetic field line. Thirty‐eight simultaneous data sets were identified and analyzed. In general, intense AKR was associated with bright auroral arcs, and conditions of weak or no AKR corresponded to times when either no aurora or only a faint arc or weak diffuse aurora was observed. Five cases, when both intense AKR and bright visual aurora were present, were analyzed in detail. Complete electron density Ne contours, from the satellite altitude down to the F region ionization peak, were obtained along N‐S traversals of the AKR source region. In addition, the ISIS 1 orbital tracks were projected down the magnetic field lines to the auroral altitude and compared to auroral features on a map derived from the all‐sky camera images. Density cavities (regions where Ne < 100 cm−3) were encountered on each of these passes. In one case the cavity extended in altitude down to just below 2000 km. The latitudinal extent of these cavities ranged from 3° to almost 30°. A variety of situations relating AKR to the visual aurora were identified, and both spatial (within about 100 km at the satellite altitude) and temporal (within about l min) correlations were identified. In addition to confirming that a density cavity is a necessary but not sufficient condition for the generation of AKR, the present results indicate that even the combination of a density cavity on an auroral‐arc field line is not always sufficient for AKR generation. Thus additional constraints must be satisfied in order to generate intense AKR from density cavities. These constraints most likely involve the characteristics of the energetic electron distribution function and possibly also latitudinal Ne gradients.

Evidence for a shock wave in visible light and radio observations of the 1980 June 29 event

Shock waves, as evidenced by type II radio bursts, often accompany flares and coronal mass ejection transients. At present, the density enhancements observed by coronagraphs are believed by some to be ejected matter from the low corona, and by others to be the compressed material behind a shock front. If the former is correct, one would expect in some cases to see a density enhancement, associated with the compression region of the shock, some distance ahead of the transient ejecta. Such a density enhancement has not been previously reported. The coronal transient of 1980 June 29 (0233 UT) was observed with the High Altitude Observatory's Coronagraph/Polarimeter aboard SMM. This flare-associated coronal transient event was well observed with the Culgoora Radioheliograph, including a well-developed type II burst. Visible on the coronagraph images is a faint circular arc moving out well ahead of the transient loops. This arc is moving at more than 900 km s −1 while the transient itself is moving at a speed of about 600 km s −1. Both the arc and transient appear to have originated either prior to the X-ray flare or at some height above the flare at the time of the flare. The type II burst observed at Culgoora is associated with the transient loops, and no type II emission is identified with the faint arc. Due to its great speed, we interpret the faint arc as a manifestation of a shock wave, but also envision a separate shock wave associated with the transient loops as evidenced by the type II emission. Preliminary density measurements are consistent with this interpretation, and show the outer shock wave associated with the faint arc to have a Mach number M A ≤ 1.7. At present we have no convincing explanation for the lack of a type II burst in association with the arc. This work was supported in part by NASA through grants NSG-7287 and NAGW-91 to the University of Colorado, Boulder, and S-55989 to the High Altitude Observatory, National Center for Atmospheric Research. The National Center for Atmospheric Research, NCAR, is sponsored by the National Science Foundation.

Simultaneous observations of low-energy electron precipitation and optical auroral arcs in the evening sector by the DMSP 32 satellite

Results of the first detailed study of simultaneously low-energy electron precipitation and optical auroral observations during quiet geomagnetic conditions in the evening side of the auroral oval, observed by the DMSP 32 satellite, are reported. The precipitation characteristics are different for different types of quiet auroral arcs. (1) Inside a faint diffuse aurora, equatorward of the oval, the six-point differential energy spectrum is characterized by nearly constant differential fluxes from 0.2 to about 8 keV with a sharp cutoff above 8 keV: the precipitated energy flux is about 0.1 erg/cm/sup 2/ s sr between 0.2 and 20 keV. (2) A faint discrete arc is characterized by a spectral peak (about 10/sup 8/-10/sup 9/ el/cm/sup 2/ s sr keV) near 0.5 or 1.2 keV superposed on a soft spectrum and an energy flux of a fraction of 1 erg/cm/sup 2/ s sr. (3) Inside a bright discrete quiet arc a distinct spectral peak near 3.2 keV with fluxes between 10/sup 7/ and 10/sup 8/ el/cm/sup 2/ s sr keV on a hard spectrum is observed; the precipitated energy flux is a few ergs/cm/sup 2/ s sr. (AIP)

A metallographic study of the angra dos Reis (iron) meteorite

SummaryThe Angra dos Reis (iron) has been studied metallographically and an attempt has been made to discuss the circumstances under which the following elements of structure formed: clear etching and frosty etching kamacite, decorated Neumann lines, giant rhabdites, plate rbabdites, rhabdite clusters, microrhabdites, cohenite, and remelted troilite. The remelted troilite is taken to indicate a shock event. However, since there are no metallographically visible indications of shock in the kamacite and since the back reflection X-ray diffraction pattern shows only very faint Debye-Scherrer arcs superimposed on a pattern of sharp spots, it is concluded that the shock event took place at a temperature that allowed shock effects to anneal out of the kamacite almost completely. A submicroscopic precipitate in the metallic matrix is observable with the electron microscope and may represent the final precipitation of phosphide from shocked kamacite.

Isolation of Albumin from Human Serum by Means of Trichloroacetic Acid and Ethanol

Abstract A rapid method for nearly quantitative isolation of human serum albumin is described. The present technic (1) is a modification of the Schwert method (2). In the present method 4 ml. of serum is precipitated with trichloroacetic acid in a final concentration of 5% (w/v). The precipitate is washed with TCA, and after aqueous suspension, ethanol is added to a final concentration of 80%. The undissolved globulin is washed with ethanol and the solubilized albumin used for quantification, characterization, and isotope counting. Recovery of added human serum albumin was approximately 98%; recovery of added 131I albumin was 90%. Cellulose acetate electrophoresis showed a single band, and agar diffusion produced one precipitate line. Immunoelectrophoresis with anti-human serum revealed one or two very faint arcs in the α-, or α- and β-globulin regions, in addition to the major arc of albumin. The method has shown excellent reproducibility in replicate analyses of normal and pathologic serums.