Search Publications
Detection of Intra-day Variability Timescales of Four High-energy Peaked Blazars with XMM-Newton
Gupta, Alok C.; Wiita, Paul J.; Gaur, Haritma +1 more
We selected a sample of 24 XMM-Newton light curves (LCs) of four high energy peaked blazars, PKS 0548 - 322, ON 231, 1ES 1426+428, and PKS 2155 - 304. These data comprise continuous LCs of 7.67-18.97 hr in length. We searched for possible quasi-periodic oscillations (QPOs) and intra-day variability (IDV) timescales in the LCs of these blazars. We …
Weak Line Quasars at High Redshift: Extremely High Accretion Rates or Anemic Broad-line Regions?
Brandt, W. N.; Strauss, Michael A.; Anderson, Scott F. +9 more
We present Gemini-North K-band spectra of two representative members of the class of high-redshift quasars with exceptionally weak rest-frame ultraviolet emission lines (WLQs), SDSS J114153.34+021924.3 at z = 3.55 and SDSS J123743.08+630144.9 at z = 3.49. In both sources, we detect an unusually weak broad Hβ line and place tight upper limits on th…
Productivity of Solar Flares and Magnetic Helicity Injection in Active Regions
Wang, Haimin; Chae, Jongchul; Park, Sung-hong
The main objective of this study is to better understand how magnetic helicity injection in an active region (AR) is related to the occurrence and intensity of solar flares. We therefore investigate the magnetic helicity injection rate and unsigned magnetic flux, as a reference. In total, 378 ARs are analyzed using SOHO/MDI magnetograms. The 24 hr…
Meridional Circulation During the Extended Solar Minimum: Another Component of the Torsional Oscillation?
Howe, R.; Komm, R.; Hill, F. +1 more
We show here a component of the meridional circulation developing at medium-high latitudes (40°-50°) before the new solar cycle starts. Like the torsional oscillation of the zonal flows, this extra circulation seems to precede the onset of magnetic activity at the solar surface and moves slowly toward lower latitudes. However, the behavior of this…
Origin of Coronal Shock Waves Associated with Slow Coronal Mass Ejections
Zhukov, A. N.; Magdalenić, J.; Vršnak, B. +2 more
We present a multiwavelength study of five coronal mass ejection/flare events (CME/flare) and associated coronal shock waves manifested as type II radio bursts. The study is focused on the events in which the flare energy release, and not the associated CME, is the most probable source of the shock wave. Therefore, we selected events associated wi…
Finding the Instability Strip for Accreting Pulsating White Dwarfs From Hubble Space Telescope and Optical Observations
Holtzman, Jon; Szkody, Paula; Howell, Steve B. +9 more
Time-resolved low resolution Hubble Space Telescope ultraviolet spectra together with ground-based optical photometry and spectra are used to constrain the temperatures and pulsation properties of six cataclysmic variables containing pulsating white dwarfs (WDs). Combining our temperature determinations for the five pulsating WDs that are several …
Two Magnetar Candidates in HESS Supernova Remnants
Gotthelf, E. V.; Halpern, J. P.
We identify two candidate magnetars in archival X-ray observations of HESS-detected shell-type supernova remnants (SNRs). X-ray point sources in CTB 37B coincident with HESS J1713 - 381 and in G353.6 - 0.7 coincident with HESS J1731 - 347 both have anomalous X-ray pulsar (AXP) like spectra, much softer than those of ordinary, rotation-powered puls…
The Debris Disk of Vega: A Steady-state Collisional Cascade, Naturally
Krivov, A. V.; Löhne, T.; Müller, S.
The archetypical debris disk around Vega has been observed intensively over the past 25 years. It has been argued that the resulting photometric data and images may be in contradiction with a standard, steady-state collisional scenario of the disk evolution. In particular, the emission in the mid-infrared (mid-IR) appears to be in excess of what i…
Revealing Type Ia Supernova Physics with Cosmic Rates and Nuclear Gamma Rays
Beacom, John F.; Horiuchi, Shunsaku
Type Ia supernovae (SNe Ia) remain mysterious despite their central importance in cosmology and their rapidly increasing discovery rate. The progenitors of SNe Ia can be probed by the delay time between progenitor birth and explosion as SNe Ia. The explosions and progenitors of SNe Ia can be probed by MeV nuclear gamma rays emitted in the decays o…
The ACS LCID Project. II. Faint Variable Stars in the Isolated Dwarf Irregular Galaxy IC 1613
Skillman, Evan D.; Monelli, Matteo; Stetson, Peter B. +6 more
We present the results of a new search for variable stars in the Local Group (LG) isolated dwarf galaxy IC 1613, based on 24 orbits of F475W and F814W photometry from the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope. We detected 259 candidate variables in this field, of which only 13 (all of them bright Cepheids) were prev…