Gaia17biu/SN 2017egm in NGC 3191: The Closest Hydrogen-poor Superluminous Supernova to Date Is in a “Normal,” Massive, Metal-rich Spiral Galaxy

Bose, Subhash,Dong, Subo,Pastorello, A.,Filippenko, Alexei V.,Kochanek, C. S.,Mauerhan, Jon,Romero-Cañ,izales, C.,Brink, Thomas G.,Chen, Ping,Prieto, J. L.,Post, R.,Ashall, Christopher,Grupe, Di American Astronomical Society 2018 The Astrophysical journal Vol.853 No.1

<P>Hydrogen-poor superluminous supernovae (SLSNe-I) have been predominantly found in low-metallicity, star-forming dwarf galaxies. Here we identify Gaia17biu/SN 2017egm as an SLSN-I occurring in a 'normal' spiral galaxy (NGC 3191) in terms of stellar mass (several times 10(10) M-circle dot) and metallicity (roughly solar). At redshift z = 0.031, Gaia17biu is also the lowest-redshift SLSN-I to date, and the absence of a larger population of SLSNe-I in dwarf galaxies of similar redshift suggests that metallicity is likely less important to the production of SLSNe-I than previously believed. With the smallest distance and highest apparent brightness for an SLSN-I, we are able to study Gaia17biu in unprecedented detail. Its pre-peak near-ultraviolet to optical color is similar to that of Gaia16apd and among the bluest observed for an SLSN-I, while its peak luminosity (M-g = -21 mag) is substantially lower than that of Gaia16apd. Thanks to the high signal-to-noise ratios of our spectra, we identify several new spectroscopic features that may help to probe the properties of these enigmatic explosions. We detect polarization at the similar to 0.5% level that is not strongly dependent on wavelength, suggesting a modest, global departure from spherical symmetry. In addition, we put the tightest upper limit yet on the radio luminosity of an SLSN-I with < 5.4 x 10(26) erg s(-1) Hz(-1) at 10 GHz, which is almost a factor of 40 better than previous upper limits and one of the few measured at an early stage in the evolution of an SLSN-I. This limit largely rules out an association of this SLSN-I with known populations of gamma-ray-burst-like central engines.</P>

Shock Acceleration Model for the Toothbrush Radio Relic

Kang, Hyesung,Ryu, Dongsu,Jones, T. W. American Astronomical Society 2017 The Astrophysical journal Vol.840 No.1

<P>Although many of the observed properties of giant radio relics detected in the outskirts of galaxy clusters can be explained by relativistic electrons accelerated at merger-driven shocks, significant puzzles remain. In the case of the so-called Toothbrush relic, the shock Mach number estimated from X-ray observations (M-X approximate to 1.2-1.5) is substantially weaker than that inferred from the radio spectral index (M-rad approximate to 2.8). Toward understanding such a discrepancy, we here consider the following diffusive shock acceleration (DSA) models: (1) weak-shock models with Ms. 2 and a preexisting population of cosmic-ray electrons (CRe) with a flat energy spectrum, and (2) strong-shock models with M-s approximate to 3 and either shock-generated suprathermal electrons or preexisting fossil CRe. We calculate the synchrotron emission from the accelerated CRe, following the time evolution of the electron DSA, and the subsequent radiative cooling and postshock turbulent acceleration (TA). We find that both models could reproduce reasonably well the observed integrated radio spectrum of the Toothbrush relic, but the observed broad transverse profile requires the stochastic acceleration by downstream turbulence, which we label 'turbulent acceleration' or TA to distinguish it from DSA. Moreover, to account for the almost uniform radio spectral index profile along the length of the relic, the weak-shock models require a preshock region over 400. kpc with a uniform population of preexisting CRe with a high cutoff energy (greater than or similar to 40 GeV). Due to the short cooling time, it is challenging to explain the origin of such energetic electrons. Therefore, we suggest the strong-shock models with low-energy seed CRe (less than or similar to 150 MeV) are preferred for the radio observations of this relic.</P>

Ionized Gas Outflows in Infrared-bright Dust-obscured Galaxies Selected with<i>WISE</i>and SDSS

Toba, Yoshiki,Bae, Hyun-Jin,Nagao, Tohru,Woo, Jong-Hak,Wang, Wei-Hao,Wagner, Alexander Y.,Sun, Ai-Lei,Chang, Yu-Yen American Astronomical Society 2017 The Astrophysical journal Vol.850 No.2

<P>We present the ionized gas properties of infrared (IR)-bright dust-obscured galaxies (DOGs) that show an extreme optical/IR color, (i - [22])(AB) > 7.0, selected with the Sloan Digital Sky Survey (SDSS) and Wide-field Infrared Survey Explorer (WISE). For 36 IR-bright DOGs that show [O III]lambda 5007 emission in the SDSS spectra, we performed a detailed spectral analysis to investigate their ionized gas properties. In particular, we measured the velocity offset (the velocity with respect to the systemic velocity measured from the stellar absorption lines) and the velocity dispersion of the [O III] line. We found that the derived velocity offset and dispersion of most IR-bright DOGs are larger than those of Seyfert 2 galaxies (Sy2s) at z < 0.3, meaning that the IR-bright DOGs show relatively strong outflows compared to Sy2s. This can be explained by the difference in IR luminosity contributed from active galactic nuclei, LIR (AGN), because we found that (i) L(IR ()AGN) correlates with the velocity offset and dispersion of [O III] and (ii) our IR-bright DOG sample has larger L-IR (AGN) than Sy2s. Nevertheless, the fact that about 75% IR-bright DOGs have a large (> 300 km s(-1)) velocity dispersion, which is a larger fraction compared to other AGN populations, suggests that IR-bright DOGs are good laboratories to investigate AGN feedback. The velocity offset and dispersion of [O III] and [Ne III]lambda 3869 are larger than those of [O II]lambda 3727, which indicates that the highly ionized gas tends to show stronger outflows.</P>

Calibration and Limitations of the Mg ii Line-based Black Hole Masses

Woo, Jong-Hak,Le, Huynh Anh N.,Karouzos, Marios,Park, Dawoo,Park, Daeseong,Malkan, Matthew A.,Treu, Tommaso,Bennert, Vardha N. American Astronomical Society 2018 The Astrophysical journal Vol.859 No.2

<P>We present single-epoch black hole mass (M-BH) calibrations based on the rest-frame ultraviolet (UV) and optical measurements of Mg II 2798 angstrom and H beta 4861 angstrom lines and the active galactic nucleus (AGN) continuum, using a sample of 52 moderate-luminosity AGNs at z similar to 0.4 and z similar to 0.6 with high-quality Keck spectra. We combine this sample with a large number of luminous AGNs from the Sloan Digital Sky Survey to increase the dynamic range for a better comparison of UV and optical velocity and luminosity measurements. With respect to the reference M-BH based on the line dispersion of H beta and continuum luminosity at 5100 angstrom, we calibrate the UV and optical mass estimators by determining the best-fit values of the coefficients in the mass equation. By investigating whether the UV estimators show a systematic trend with Eddington ratio, FWHM of H beta, Fe II strength, or UV/optical slope, we find no significant bias except for the slope. By fitting the systematic difference of Mg II-based and H beta-based masses with the L-3000/L-5100 ratio, we provide a correction term as a function of the spectral index as Delta C = 0.24 (1 + alpha(lambda)) + 0.17, which can be added to the Mg II-based mass estimators if the spectral slope can be well determined. The derived UV mass estimators typically show >similar to 0.2 dex intrinsic scatter with respect to the H beta-based MBH, suggesting that the UV-based mass has an additional uncertainty of similar to 0.2 dex, even if high-quality rest-frame UV spectra are available.</P>

OGLE-2017-BLG-0329L: A Microlensing Binary Characterized with Dramatically Enhanced Precision Using Data from Space-based Observations

Han, C.,Novati, S. Calchi,Udalski, A.,Lee, C.-U.,Gould, A.,Bozza, V.,Mró,z, P.,Pietrukowicz, P.,Skowron, J.,Szymań,ski, M. K.,Poleski, R.,Soszyń,ski, I.,Kozłowski, S.,Ulaczyk, K.,Pawla American Astronomical Society 2018 The Astrophysical journal Vol.859 No.2

After the Fall: The Dust and Gas in E+A Post-starburst Galaxies

Smercina, A.,Smith, J. D. T.,Dale, D. A.,French, K. D.,Croxall, K. V.,Zhukovska, S.,Togi, A.,Bell, E. F.,Crocker, A. F.,Draine, B. T.,Jarrett, T. H.,Tremonti, C.,Yang, Yujin,Zabludoff, A. I. American Astronomical Society 2018 The Astrophysical journal Vol.855 No.1

<P>The traditional picture of post-starburst galaxies as dust-and gas-poor merger remnants, rapidly transitioning to quiescence, has been recently challenged. Unexpected detections of a significant interstellar medium (ISM) in many post-starburst galaxies raise important questions. Are they truly quiescent, and if so, what mechanisms inhibit further star formation? What processes dominate their ISM energetics? We present an infrared spectroscopic and photometric survey of 33 E+A post-starbursts selected by the Sloan Digital Sky Survey, aimed at resolving these questions. We find compact, warm dust reservoirs with high PAH abundances and total gas and dust masses significantly higher than expected from stellar recycling alone. Both polycyclic aromatic hydrocarbon (PAH)/total infrared (TIR) and dust-to-burst stellar mass ratios are seen to decrease with post-burst age, indicative of the accumulating effects of dust destruction and an incipient transition to hot, early-type ISM properties. Their infrared spectral properties are unique, with dominant PAH emission, very weak nebular lines, unusually strong H-2. rotational emission, and deep [C II] deficits. There is substantial scatter among star formation rate (SFR) indicators, and both PAH and TIR luminosities provide overestimates. Even as potential upper limits, all tracers show that the SFR has typically experienced a decline of more than two orders of magnitude since the starburst and that the SFR is considerably lower than expected given both their stellar masses and molecular gas densities. These results paint a coherent picture of systems in which star formation was, indeed, rapidly truncated, but in which the ISM was not completely expelled, and is instead supported against collapse by latent or continued injection of turbulent or mechanical heating. The resulting aging burst populations provide a 'high-soft' radiation field that seemingly dominates the E+A galaxies' unusual ISM energetics.</P>

Fan Loops Observed by<i>IRIS</i>, EIS, and AIA

Ghosh, Avyarthana,Tripathi, Durgesh,Gupta, G. R.,Polito, Vanessa,Mason, Helen E.,Solanki, Sami K. American Astronomical Society 2017 The Astrophysical journal Vol.835 No.2

<P>A comprehensive study of the physical parameters of active region fan loops is presented using the observations recorded with the Interface Region Imaging Spectrometer (IRIS), the EUV Imaging Spectrometer (EIS) on board Hinode, and the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). The fan loops emerging from non-flaring AR. 11899 (near the disk center) on 2013 November 19 are clearly discernible in AIA 171 angstrom images and in those obtained in Fe VIII and Si VII images using EIS. Our measurements of electron densities reveal that the footpoints of these loops are at an approximately constant pressure with electron densities of log N-e = 10.1cm(-3) at log [T/K]=5.15 (O IV), and log N-e = 8.9 cm(-3) at log[T/K]=6.15 (Si X). The electron temperature diagnosed across the fan loops by means of EM-Loci suggest that two temperature components exist at log[T/K]=4.95 and 5.95 at the footpoints. These components are picked up by IRIS lines and EIS lines, respectively. At higher heights, the loops are nearly isothermal at log[T/K]=5.95, which remained constant along the loop. The measurement of the Doppler shift using IRIS lines suggests that the plasma at the footpoints of these loops is predominantly redshifted by 2-3 km s(-1) in C II, 10-15 km s(-1) in Si IV, and 15-20 km s(-1) in O IV, reflecting the increase in the speed of downflows with increasing temperature from log[T/K]=4.40 to 5.15. These observations can be explained by low-frequency nanoflares or impulsive heating, and provide further important constraints on the modeling of the dynamics of fan loops.</P>

Onset of a Large Ejective Solar Eruption from a Typical Coronal-jet-base Field Configuration

Joshi, Navin Chandra,Sterling, Alphonse C.,Moore, Ronald L.,Magara, Tetsuya,Moon, Yong-Jae American Astronomical Society 2017 The Astrophysical journal Vol.845 No.1

<P>Utilizing multiwavelength observations and magnetic field data from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), SDO/Helioseismic and Magnetic Imager (HMI), the Geostationary Operational Environmental Satellite (GOES), and RHESSI, we investigate a large-scale ejective solar eruption of 2014 December 18 from active region NOAA 12241. This event produced a distinctive 'three-ribbon' flare, having two parallel ribbons corresponding to the ribbons of a standard two-ribbon flare, and a larger-scale third quasi-circular ribbon offset from the other two. There are two components to this eruptive event. First, a flux rope forms above a strong-field polarity inversion line and erupts and grows as the parallel ribbons turn on, grow, and spread apart from that polarity inversion line; this evolution is consistent with the mechanism of tether-cutting reconnection for eruptions. Second, the eruption of the arcade that has the erupting flux rope in its core undergoes magnetic reconnection at the null point of a fan dome that envelops the erupting arcade, resulting in formation of the quasi-circular ribbon; this is consistent with the breakout reconnection mechanism for eruptions. We find that the parallel ribbons begin well before (similar to 12 minutes) the onset of the circular ribbon, indicating that tether-cutting reconnection (or a non-ideal MHD instability) initiated this event, rather than breakout reconnection. The overall setup for this large-scale eruption (diameter of the circular ribbon similar to 10(5) km) is analogous to that of coronal jets (base size similar to 10(4) km), many of which, according to recent findings, result from eruptions of small-scale 'minifilaments.' Thus these findings confirm that eruptions of sheared-core magnetic arcades seated in fan-spine null-point magnetic topology happen on a wide range of size scales on the Sun.</P>

Exploring the Variability of the Flat-spectrum Radio Source 1633+382. II. Physical Properties

Algaba, Juan-Carlos,Lee, Sang-Sung,Rani, Bindu,Kim, Dae-Won,Kino, Motoki,Hodgson, Jeffrey,Zhao, Guang-Yao,Byun, Do-Young,Gurwell, Mark,Kang, Sin-Cheol,Kim, Jae-Young,Kim, Jeong-Sook,Kim, Soon-Wook,Par American Astronomical Society 2018 The Astrophysical journal Vol.859 No.2

<P>The flat-spectrum radio quasar 1633+382 (4C 38.41) showed a significant increase of its radio flux density during the period 2012 March-2015 August, which correlates with gamma-ray flaring activity. Multi-frequency simultaneous very long baseline interferometry (VLBI) observations were conducted as part of the interferometric monitoring of gamma-ray bright active galactic nuclei (iMOGABA) program and supplemented with additional radio monitoring observations with the OVRO 40. m telescope, the Boston University VLBI program, and the Submillimeter Array. The epochs of the maxima for the two largest gamma-ray flares coincide with the ejection of two respective new VLBI components. Analysis of the spectral energy distribution indicates a higher turnover frequency after the flaring events. The evolution of the flare in the turnover frequency-turnover flux density plane probes the adiabatic losses in agreement with the shock-in-jet model. The derived synchrotron self-absorption magnetic fields, of the order of 0.1. mG, do not seem to change dramatically during the flares, and are much weaker, by a factor 10(4), than the estimated equipartition magnetic fields, indicating that the source of the flare may be associated with a particle-dominated emitting region.</P>

The JCMT Transient Survey: Stochastic and Secular Variability of Protostars and Disks In the Submillimeter Region Observed over 18 Months

Johnstone, Doug,Herczeg, Gregory J.,Mairs, Steve,Hatchell, Jennifer,Bower, Geoffrey C.,Kirk, Helen,Lane, James,Bell, Graham S.,Graves, Sarah,Aikawa, Yuri,Chen, Huei-Ru Vivien,Chen, Wen-Ping,Kang, Miju American Astronomical Society 2018 The Astrophysical journal Vol.854 No.1