Observing Summary 2004

90 Pages·2013·4.63 MB·English

Observing Nummary
2001,

Scientific Highlights ■SI
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Detection of HCN in a z=2.3 Galaxy - Hydrogen cyanide (HCN) emission has been detected in the z=2.2857 source IRAS
F10214+4724 using the GBT. This is only the second detection of HCN in a high redshift galaxy. HCN is a signpost of star
formation, and F10214 clearly contains a starburst that contributes, together with its embedded quasar, to its overall infrared
luminosity. The peak emission of the detected spectral line is about 0.45 mjy with a noise level of -0.090 mjy. A new
technique for removing spectral baselines in the search for weak, broad emission lines was utilized for this project.
New Interstellar Molecules detected with the GBT - The GBT has been used to detect two new interstellar molecules,
propenal (CH2CHCHO) and propanal (CH3CH2CHO). These are the first new molecules detected with the GBT. These
molecules were detected in the star-forming region Sagittarius B2 (N). The GBT was also used to observe the previously
reported molecule propynal (HC2CHO). These molecules differ only in the number of hydrogen atoms present. The
presence of these three molecular species in Sgr B2 (N) suggests that simple hydrogen addition on interstellar grains may
account for their formation. The Sgr B2 (N) cloud appears to have ample energy sources to allow such grain reactions to
proceed. This result suggests that successive hydrogen addition may be an important formation pathway for complex,
interstellar molecules.
Neutral Hydrogen Emission of the Spitzer Extragalactic First-Look Survey Field - The GBT has been used to image the
21 cm Galactic HI emission over a 3° x 3° square centered on the Spitzer Extragalactic First-Look Survey field. The effective
angular resolution was 9.8' and the velocity resolution was 0.62 km s1. The Galactic HI in this region was found to have a
very interesting structure. There is a high-velocity cloud, several intermediate-velocity clouds, and narrow-line low velocity
filaments. The HI emission shows a strong and detailed correlation with dust. Except for the high-velocity cloud, all features
in the Nm map have counterparts in an E(B - V) map derived from infrared data. Relatively high E(B - V)/Nm ratios in some
directions suggest the presence of molecular gas. The best diagnostic of such regions was found to be peak HI line brightness
temperature, not the total NHI: directions where Tb > 12 K have E(B - V)/NHI significantly above the average value. The data
corrected for stray radiation have been released via the web.
Scientific Highlights
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NVSS Provides Support for Dark Energy Model - The "dark energy" presumably responsible for the acceleration of the
expansion of the Universe also is believed to affect the evolution of fluctuations in the density of matter. Researchers using
the NRAO VLA Sky Survey data, along with all-sky X-ray maps, have found a correlation between large-scale structure in the
Universe and fluctuations in the Cosmic Microwave Background as mapped with the WMAP satellite. This correlation is
consistent with the predictions of the dark-energy model, and thus provides an important independent confirmation of that
model.
VLA Helps Confirm New Class of Gamma Ray Burst - Multiple flux measurements and radio light curves made with the
VLA were an essential element leading to the conclusion that Gamma Ray Burst (GRB) 031203 was an intrinsically sub-
energetic event compared to "classic" GRBs. Multi-wavelength studies of the afterglow suggest that GRB 031203 is an analog
to GRB 980425, which was associated with supernova 1998bw. This discovery implies the existence of a new class of low-
energy GRBs, most of which remain below current detection limits.
Multiple Pulsar Detections in the Globular Cluster Terzan 5 - A single six-hour observation in July 2004 using the GBT at
2 GHz resulted in the discovery of 14 new pulsars in the rich globular cluster Terzan 5. Follow-up observations in October
resulted in the discovery of at least three additional pulsars. Terzan 5, which is located near the Galactic Center, has long been
suspected of harboring many millisecond pulsars (MSPs) because of its large predicted stellar interaction rate and the steep-
spectrum radio emission observed in its core. However, earlier pulsar searches using the Parkes radio telescope only
uncovered three pulsars. These new GBT discoveries confirm that Terzan 5 is one of the largest producers of MSPs among
the Galactic globular clusters and imply that the 20+ known pulsars are but the tip of the iceberg. At least nine of the new
pulsars are members of binaries. Among these new pulsars there are also two or more eclipsing systems, the third- and
fourth-fastest known rotators, a rare long-orbital-period binary, and two highly eccentric systems. Timing of the eccentric
binaries over the next year will provide their total masses and may (after several years) allow separation of the pulsar and
companion masses. Timing observations of the ensemble of pulsars will probe stellar and binary evolutionary scenarios, the
mass-to-light ratio of the cluster core (and provide evidence for or against a black hole residing there), and other aspects of
globular-cluster dynamics.
Scientific Highlights
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VLA Shows Young Galaxy with Black Hole, Almost No Stellar Bulge - VLA observations of 1148+5351, the most distant
quasar yet found, at z=6.4, show that the mass of molecular gas plus the mass of the presumed supermassive black hole at the
core of the AGN account for nearly the total mass of the system. This leaves little mass available for a central galactic bulge,
and much less mass than standard black hole-bulge relationships predict for such a bulge. This single example from the early
Universe of a young galaxy with a supermassive black hole but no significant bulge may serve as an important clue to the
long-standing question of whether the black hole or the bulge formed first, or coevally as some current popular models
suggest.
Cores of Extragalactic Radio Sources Shown to Contain Microarcsecond Structures - Morphologies of compact extragalactic
radio sources imaged with the VLBA have been compared to their scintillation properties. The short time-scale scintillation
of compact sources is thought to be caused by the interstellar medium in our own galaxy, and reveals the presence of radio-
emitting structures that are only a few micro-arcseconds in size. Statistical studies show that the VLBA images of scintillating
radio sources are significantly more core-dominated than images of a comparison sample of non-scintillating sources. This
demonstrates conclusively that the micro-arcsecond component is directly associated with the core of the radio source, and
hence with the actual nucleus of the host galaxy. At the typical large distances of the radio sources, this radio component is
no more than a few thousand astronomical units in size, probably only a few hundred times the gravitational radii of the
central massive black holes.
Cold Sugar Molecules near the Galactic Center - Investigators have used the GBT to detect a very cold interstellar cloud
containing the simple sugar molecule glycolaldehyde (CH20HCHO) in the Sgr B2 region. Four high signal-to-noise
transitions were detected between 13 and 22 GHz. The data included both emission and absorption features. An analysis of
the data indicated that the cloud is at a temperature of only ~8 K. These data, together with other information on the region,
suggest that the sugar molecules were formed on the surface of grains, then released into the gas phase through disruption of
the grain mantles by passing shock waves. The observed molecules now exist in the cold post-shock region. The GBT proved
very powerful in these observations owing to its frequency agility, wide spectral bandwidths, and small beam which coupled
very efficiently to background continuum sources allowing the detection of the absorption lines.
Scientific Highlights
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Moving Microquasar Linked to Natal Star Cluster - Using data from numerous observations with the VLBA and other
telescopes, researchers have measured the proper motion of a microquasar and concluded that it was propelled out of a
nearby star cluster by an asymmetric supernova explosion about a million years ago. The microquasar LSI +61 303 is moving
away from a star cluster named IC 1805 at more than 25 kilometers per second, and the companion to the compact object in
the microquasar shares the spectral characteristics of the cluster population. This is the first time that a binary pair has been
traced to a specific natal star cluster. The microquasar, containing a compact object of about 2 solar masses and a companion
of 14 solar masses, is about 130 light-years distant from the cluster.
Global VLBI Reveals Youngest Stellar Corpse - Ongoing studies of Supernova 1986J in NGC 891 have discovered a bright,
compact radio component at the center of the expanding shell. This bright component has only recently become visible. New
observations made using the VLBA, the GBT, the VLA and the EVN, indicate that the central component has an inverted
radio spectrum different from the shell. The new component likely is either the result of accretion onto a black hole or a
pulsar wind nebula. This result provides evidence for the first association of a compact object with a modem, observed
supernova and makes the black hole or neutron star by far the youngest known.
Observing Hours
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1990 91 92 93 94 95 96 97 98 99 2000 01 02 03 04 05 06
Calendar Year
240 Foot GBT □ 12 Meter VLA H VLBA
Figure 1. This figure shows the hours for observing on each telescope during the last 14 years. It includes astronomical
observing, testing, calibration, and commissioning.
Distribution of Scheduled Observing Time
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Calendar Year Calendar Year Calendar Year
NRAO Staff Visitors Testing and Calibration
Includes Research Associates Includes Students
Figure 2. These graphs show the number of hours scheduled for testing and calibration, and for observing
by the NRAO staff and by visitors on each telescope system.
Green Bank Telescope Summary
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Observing Testing, Maintenance & Calibration Lost Time
Figure 3. This summary for each quarter of the calendar year shows the percentage of the total time in the year that the telescope was
scheduled for observing; for commissioning, maintenance, and calibration; and the percentage of astronomical observing time lost
due to equipment failure, bad weather, and radio interference.
Very Large Array Telescope Summary
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Calendar Year
Observing Testing, Maintenance & Calibration Lost Time
Figure 4. This summary for each quarter of the calendar year shows the percentage of the total time in the year that
the telescope was scheduled for observing; for routine system testing, maintenance, and calibration; and the
percentage of astronomical observing time lost due to equipment failure, bad weather, and radio interference.