Optical Spectroscopy of Bright Fermi LAT Blazars Shaw, Michael S; Romani, Roger W; Healey, Stephen E ...
Astrophysical journal/The Astrophysical journal,
10/2009, Letnik:
704, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We report on Hobby-Eberly Telescope and Palomar 5 m spectroscopy of recently identified Delta *g-ray blazars in the Fermi LAT Bright Source List. These data provide identifications for 10 newly ...discovered Delta *g-ray flat spectrum radio quasars and six new BL Lacertae (BL Lac) objects plus improved spectroscopy for six additional BL Lac objects. We substantially improve the identification completeness of the bright LAT blazars and give new redshifts and z constraints, new estimates of the black hole masses, and new measurements of the optical spectral energy distribution.
Abstract
We present deep CCS and HC
7
N observations of the L1495-B218 filaments in the Taurus molecular cloud obtained using the
K
-band focal plane array on the 100 m Green Bank Telescope. We ...observed the L1495-B218 filaments in CCS
J
N
= 2
1
–1
0
and HC
7
N
J
= 21−20 with a spectral resolution of 0.038 km s
−1
and an angular resolution of 31″. We observed strong CCS emission in both evolved and young regions and weak emission in two evolved regions. HC
7
N emission is observed only in L1495A-N and L1521D. We find that CCS and HC
7
N intensity peaks do not coincide with NH
3
or dust continuum intensity peaks. We also find that the fractional abundance of CCS does not show a clear correlation with the dynamical evolutionary stage of dense cores. Our findings and chemical modeling indicate that the fractional abundances of CCS and HC
7
N are sensitive to the initial gas-phase C/O ratio, and they are good tracers of young condensed gas only when the initial C/O is close to solar value. Kinematic analysis using multiple lines, including NH
3
, HC
7
N, CCS, CO, HCN, and HCO
+
, suggests that there may be three different star formation modes in the L1495-B218 filaments. At the hub of the filaments, L1495A/B7N has formed a stellar cluster with large-scale inward flows (fast mode), whereas L1521D, a core embedded in a filament, is slowly contracting because of its self-gravity (slow mode). There is also one isolated core that appears to be marginally stable and may undergo quasi-static evolution (isolated mode).
The Cosmic Background Imager 2 Taylor, Angela C.; Jones, Michael E.; Allison, James R. ...
Monthly Notices of the Royal Astronomical Society,
12/2011, Letnik:
418, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We describe an upgrade to the Cosmic Background Imager instrument to increase its surface brightness sensitivity at small angular scales. The upgrade consisted of replacing the 13 0.9-m antennas with ...1.4-m antennas incorporating a novel combination of design features, which provided excellent sidelobe and spillover performance for low manufacturing cost. Off-the-shelf spun primaries were used, and the secondary mirrors were oversized and shaped relative to a standard Cassegrain in order to provide an optimum compromise between aperture efficiency and low spillover lobes. Low-order distortions in the primary mirrors were compensated for by custom machining of the secondary mirrors. The secondaries were supported on a transparent dielectric foam cone to minimize scattering. The antennas were tested in the complete instrument, and the beam shape and spillover noise contributions were as expected. We demonstrate the performance of the telescope and the intercalibration with the previous system using observations of the Sunyaev-Zel'dovich effect in the cluster Abell 1689. The enhanced instrument has been used to study the cosmic microwave background, the Sunyaev-Zel'dovich effect and diffuse Galactic emission.
Filling in the Gaps in the 4.85 GHz Sky Healey, Stephen E; Fuhrmann, Lars; Taylor, Gregory B ...
The Astronomical journal,
10/2009, Letnik:
138, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We describe a 4.85 GHz survey of bright, flat-spectrum radio sources conducted with the Effelsberg 100 m telescope in an attempt to improve the completeness of existing surveys, such as CRATES. We ...report the results of these observations and of follow-up 8.4 GHz observations with the VLA of a subset of the sample. We comment on the connection to the Wilkinson Microwave Anisotropy Probe point source catalog and on the survey's effectiveness at supplementing the CRATES sky coverage.
In September 2012, the high-synchrotron-peaked (HSP) blazar Markarian 421 underwent a rapid wideband radio flare, reaching nearly twice the brightest level observed in the centimeter band in over ...three decades of monitoring. In response to this event we carried out a five epoch centimeter- to millimeter-band multifrequency Very Long Baseline Array (VLBA) campaign to investigate the aftermath of this emission event. Rapid radio variations are unprecedented in this object and are surprising in an HSP BL Lac object. In this flare, the 15 GHz flux density increased with an exponential doubling time of about 9 days, then faded to its prior level at a similar rate. This is comparable with the fastest large-amplitude centimeter-band radio variability observed in any blazar. Similar flux density increases were detected up to millimeter bands. This radio flare followed about two months after a similarly unprecedented GeV gamma-ray flare (reaching a dailyE > 100 MeV flux of (1.2 + or - 0.7) x 10 super(-6) ph cm super(-2) s super(-1)) reported by the Fermi Large Area Telescope (LAT) collaboration, with a simultaneous tentative TeV detection by ARGO-YBJ. A cross-correlation analysis of long-term 15 GHz and LAT gamma-ray light curves finds a statistically significant correlation with the radio lagging ~40 days behind, suggesting that the gamma-ray emission originates upstream of the radio emission. Preliminary results from our VLBA observations show brightening in the unresolved core region and no evidence for apparent superluminal motions or substantial flux variations downstream.
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