Travis A. Rector

The Properties of the Radio-Selected 1 Jy Sample of BL Lacertae Objects*

We present new optical and near-IR spectroscopy, as well as new high dynamic range, arcsecond-resolution VLA radio maps, of BL Lacertae objects from the complete radio-selected 1 jansky (1 Jy) sample (RBLs) for which such data were not previously available. Redshift information is now available for all but six of the 37 BL Lac objects in the 1 Jy sample. Of the 31 with redshift information, four redshifts are only minimum values based on absorption lines, and four other objects have uncertain redshifts based on the detection of only a single emission line. Unlike BL Lac objects from the complete X-ray–selected Einstein Medium Sensitivity Survey (EMSS) sample (XBLs), most RBLs possess weak but moderately luminous emission lines. The emission-line luminosities of RBLs are several orders of magnitude lower than flat-spectrum radio quasars (FSRQs); however, there is significant overlap in the luminosity distributions of the two classes. All but one object in the 1 Jy sample has now been observed with the VLA, and extended flux was detected for all but three of the observed objects. Whereas nearly all XBLs have extended power levels consistent with FR 1s, more than half of the RBLs have extended radio power levels too luminous to be beamed FR 1 radio galaxies. In fact, we find evidence for and examples of three distinct mechanisms for creating the BL Lac phenomenon in the 1 Jy sample: beamed FR 1s, beamed FR 2s, and possibly a few gravitationally lensed quasars. The V/Vmax value determined for the 1 Jy sample is 0.614 ± 0.047, which is markedly different from the negative evolution seen in the EMSS and other XBL samples. A correlation between logarithmic X-ray–to–radio flux ratio and V/Vmax value is observed across the EMSS and 1 Jy samples from negative evolution in the more extreme XBLs to positive evolution in the more extreme RBLs. There is evidence that the selection criteria chosen by Stickel et al. eliminates some BL Lac objects from the 1 Jy sample, although how many is unknown. In addition, several objects currently in the sample have exhibited strong emission lines in one or more epochs, suggesting that they should be reclassified as FSRQs. However, these selection effects cannot account for the observed discrepancy in XBL and RBL properties. From these observational properties, we conclude that RBLs and XBLs cannot be related by viewing angle alone, and that RBLs are more closely related to FSRQs.

The Properties of the X-Ray-selected EMSS Sample of BL Lacertae Objects

We present updated and complete radio, optical, and X-ray data for BL Lac objects in the Einstein Medium Sensitivity Survey (EMSS). The complete M91 sample first presented in Morris et al. is updated to include 26 BL Lac objects in total, and we define a new, virtually complete sample consisting of 41 EMSS BL Lac objects (the D40 sample). New high signal-to-noise ratio, arcsecond-resolution VLA observations are also presented for 11 EMSS BL Lac objects, completing VLA observations of the M91 sample. The addition of four new objects, as well as updated X-ray flux and redshift information, has increased the Ve/Va value for the M91 sample to 0.399 ± 0.057 and Ve/Va = 0.427 ± 0.045 for the newly defined D40 sample. In conjunction with other studies of X-ray–selected BL Lac (XBL) samples, these results solidify negative evolution for XBLs, especially for more extreme high-energy–peaked BL Lac objects, for which we find Ve/Va = 0.271 ± 0.077. The observed Ve/Va, spectral, and radio properties of XBLs are completely consistent with being the beamed population of low-luminosity, FR-1 radio galaxies. However, our VLA observations do confirm that XBLs are too core dominated to be consistent with a beamed population of FR-1s seen at intermediate angles, as suggested by the unified model, if XBLs have moderate outflow velocities (γ ~ 5).

Intrinsic curvature in the X-ray spectra of BL lacertae objects

We report results from XMM-Newton observations of 13 X-ray bright BL Lacertae objects, selected from the Einstein Slew Survey sample (SSS). The survey was designed to look for evidence of departures of the X-ray spectra from a simple power-law shape (i.e., curvature and/or line features) and to find objects worthy of deeper study. Our data are generally well fit by power-law models, with three cases having hard (? < 2; dN/dE E-?) spectra that indicate synchrotron peaks at E 5 keV. Previous data had suggested a presence of absorption features in the X-ray spectra of some BL Lac objects. In contrast, none of these spectra show convincing examples of line features in either absorption or emission, suggesting that such features are rare among BL Lac objects, or, more likely, are artifacts caused by instrumental effects. We find significant evidence for intrinsic curvature [steepening by d?/d(log E) = 0.4 ? 0.15] in 14 of the 17 X-ray spectra. This cannot be explained satisfactorily via excess absorption, since the curvature is essentially constant from 0.5-6 keV, an observation that is inconsistent with the modest amounts of absorption that would be required. We use the XMM-Newton Optical Monitor data with concurrent radio monitoring to derive broadband spectral energy distributions and peak frequency estimates. From these, we examine models of synchrotron emission and model the spectral curvature we see as the result of episodic particle acceleration.

A SEARCH FOR LOW-LUMINOSITY BL LACERTAE OBJECTS

Many properties of BL Lacs have become explicable in terms of the relativistic beaming hypothesis, whereby BL Lacs are FR 1 radio galaxies viewed nearly along the jet axis. However, a possible problem with this model is that a transition population between beamed BL Lacs and unbeamed FR 1 galaxies has not been detected. A transition population of low-luminosity BL Lacs was predicted to exist in abundance in X-ray-selected samples such as the Einstein Extended Medium Sensitivity Survey (EMSS) by Browne & Marcha. However, these BL Lacs may have been misidentified as clusters of galaxies. We have conducted a search for such objects in the EMSS with the ROSAT High-Resolution Imager (HRI); here we present ROSAT HRI images, optical spectra, and VLA radio maps for a small number of BL Lacs that were previously misidentified in the EMSS catalog as clusters of galaxies. While these objects are slightly lower in luminosity than other EMSS BL Lacs, their properties are too similar to the other BL Lacs in the EMSS sample to bridge the gap between BL Lacs and FR 1 radio galaxies. Also, the number of new BL Lacs found is too low to alter significantly the X-ray luminosity function or V/Vmax value for the X-ray-selected EMSS BL Lac sample. Thus, these observations do not explain fully the V/Vmax discrepancy between the X-ray- and radio-selected BL Lac samples.

OUTGASSING BEHAVIOR OF C/2012 S1 (ISON) FROM 2011 SEPTEMBER TO 2013 JUNE

We report photometric observations for comet C/2012 S1 (ISON) obtained during the time period immediately after discovery (r = 6.28xa0AU) until it moved into solar conjunction in mid-2013 June using the UH2.2xa0m, and Gemini North 8xa0m telescopes on Mauna Kea, the Lowell 1.8xa0m in Flagstaff, the Calar Alto 1.2xa0m telescope in Spain, the VYSOS-5 telescopes on Mauna Loa Hawaii and data from the CARA network. Additional pre-discovery data from the Pan STARRS1 survey extends the light curve back to 2011 September 30 (r = 9.4xa0AU). The images showed a similar tail morphology due to small micron sized particles throughout 2013. Observations at submillimeter wavelengths using the James Clerk Maxwell Telescope on 15 nights between 2013 March 9 (r = 4.52xa0AU) and June 16 (r = 3.35xa0AU) were used to search for CO and HCN rotation lines. No gas was detected, with upper limits for CO ranging between 3.5-4.5 × 1027xa0moleculesxa0s–1. Combined with published water production rate estimates we have generated ice sublimation models consistent with the photometric light curve. The inbound light curve is likely controlled by sublimation of CO2. At these distances water is not a strong contributor to the outgassing. We also infer that there was a long slow outburst of activity beginning in late 2011 peaking in mid-2013 January (r ~ 5xa0AU) at which point the activity decreased again through 2013 June. We suggest that this outburst was driven by CO injecting large water ice grains into the coma. Observations as the comet came out of solar conjunction seem to confirm our models.

IMAGE-PROCESSING TECHNIQUES FOR THE CREATION OF PRESENTATION-QUALITY ASTRONOMICAL IMAGES

The quality of modern astronomical data and the agility of current image-processing software enable the visualization of data in a way that exceeds the traditional definition of an astronomical image. Two developments in particular have led to a fundamental change in how astronomical images can be assembled. First, the availability of high-quality multiwavelength and narrowband data allow for images that do not correspond to the wavelength sensitivity of the human eye, thereby introducing ambiguity in the usage and interpretation of color. Second, many image-processing software packages now use a layering metaphor that allows for any number of astronomical data sets to be combined into a color image. With this technique, images with as many as eight data sets have been produced. Each data set is intensity-scaled and colorized independently, creating an immense parameter space that can be used to assemble the image. Since such images are intended for data visualization, scaling and color schemes must be chosen that best illustrate the science. A practical guide is presented on how to use the layering metaphor to generate publication-ready astronomical images from as many data sets as desired. A methodology is also given on how to use intensity scaling, color, and composition to create contrasts in an image that highlight the scientific detail. Examples of image creation are discussed.

X-Ray Spectral Variability of PKS 2005–489 During the Spectacular 1998 November Flare

We report on monitoring of the BL Lac object PKS 2005-489 by the Rossi X-Ray Timing Explorer (RXTE) in 1998 October-December. During these months, the source underwent a spectacular flare; at its peak on November 10, its 2-10 keV flux was 3.33 × 10-10 ergs cm-2 s-1, over 30 times brighter than in quiescence. During the rising phase, the X-ray spectrum of PKS 2005-489 hardened considerably, reaching α = 1.32 (Fν ∝ ν-α) near maximum. During the declining phase, the X-ray spectrum steepened rapidly, reaching α = 1.82, then became somewhat harder toward the end of December (α ~ 1.6). While such behavior has been seen before, the simplicity, magnitude, and duration of this flare allowed us to study it in great detail. We argue that this flare was caused by either the injection of particles into the jet or in situ particle acceleration and that the spectral steepening which followed the flare maximum was the result of synchrotron cooling. Contrary to other recently observed blazar flares (e.g., Mrk 501, 3C 279, PKS 2155-304), our results do not imply a major shift in the location of the synchrotron peak during this flare.

“Dark Matter” in Accretion Disks

Using Spitzer Space Telescope photometric observations of the eclipsing, interacting binary WZ Sge, we have discovered that the accretion disk is far more complex than previously believed. Our 4.5 and 8 µm time series observations reveal that the well-known gaseous accretion disk is surrounded by an asymmetric disk of dusty material with a radius approximately 15 times larger than the gaseous disk. This dust ring contains only a small amount of mass and is completely invisible at optical and near-IR wavelengths, hence consisting of dark matter. We have produced a model dust ring using 1 µm spherical particles with a density of 3 g cm^(-3) and with a temperature profile ranging from 700 to 1500 K. Our discovery about the accretion disk structure and the presence of a larger, outer dust ring have great relevance for accretion disks in general, including those in other interacting binary systems, pre-main-sequence stars, and active galaxies.

RECURRENT NOVAE IN M31

The reported positions of 964 suspected nova eruptions in M31 recorded through the end of calendar year 2013 have been compared in order to identify recurrent nova candidates. To pass the initial screen and qualify as a recurrent nova candidate two or more eruptions were required to be coincident within 0.1, although this criterion was relaxed to 0.15 for novae discovered on early photographic patrols. A total of 118 eruptions from 51 potential recurrent nova systems satisfied the screening criterion. To determine what fraction of these novae are indeed recurrent the original plates and published images of the relevant eruptions have been carefully compared. This procedure has resulted in the elimination of 27 of the 51 progenitor candidates (61 eruptions) from further consideration as recurrent novae, with another 8 systems (17 eruptions) deemed unlikely to be recurrent. Of the remaining 16 systems, 12 candidates (32 eruptions) were judged to be recurrent novae, with an additional 4 systems (8 eruptions) being possibly recurrent. It is estimated that ~4% of the nova eruptions seen in M31 over the past century are associated with recurrent novae. A Monte Carlo analysis shows that the discovery efficiency for recurrent novae may be as low as 10% that for novae in general, suggesting that as many as one in three nova eruptions observed in M31 arise from progenitor systems having recurrence times <~100 yr. For plausible system parameters, it appears unlikely that recurrent novae can provide a significant channel for the production of Type Ia supernovae.

The discovery of a disk-jet system directly exposed to strong ultraviolet fields in the Rosette Nebula

We report on the discovery of an optical jet with a striking morphology in the Rosette Nebula. It could be the most extreme case known of an accretion disk and jet system directly exposed to strong ionization fields that impose strong effects on disk evolution. Unlike typical optical flows, this jet system is found to have a high excitation nature mainly due to disruptive interaction with the violent environment. As a result, the extension of the highly collimated jet and possible former episodes of the degenerated counterjet all show bow-shocked structures. Our results provide implications on how incipience of massive stars in giant molecular clouds prevents further generations of low-mass star formation, and possibly also how isolated substellar/planetary-mass objects in regions of massive star formation are formed.