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ObtervinfSummanj National Radio 2000 atLsgf Astronomy Observatory A facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. NATIONAL RADIO ASTRONOMY OBSERVATORY Observing Summary 2000 Statistics April 2001 Scientific Highlights ■El 0b$ervin?Jummanj2ooo i Very Large Array (VLA) studies have revealed a paradox about pulsar ages. A multi-epoch study of pulsar B1757-24 and its associated radio supernova remnant G5.4-1.2 indicates that the pulsar may be much older than indicated by the "characteristic age" based on its spin-down rate. The pulsar has a calculated characteristic age of 16,000 years, but based on a VLA proper-motion study using 1993 and 1999 images, the pulsar appears to have taken about 39,000 years to move from the center of the supernova remnant to its present position. The result calls into question the determination of pulsar ages, with wide-ranging implications for the understanding of neutron stars, pulsars, and even particle physics. • Powerful radio bursts from a brown dwarf have been discovered at the VLA by members of a student science project. Brown dwarfs, discovered only five years ago, are cool, dim objects with masses between that of Jupiter and the sun (about 8 percent of the solar mass). As such, their cores never become hot enough to ignite the fusion process that powers ordinary stars, so they are expected gradually to cool and fade after they form. Not only were the radio bursts from the brown dwarf much stronger than those from Jupiter, but follow-up observations showed that the object's magnetic field was surprisingly weak, since flares are normally powered by the energy in magnetic fields. These observations promise new understanding of the difference between true stars and brown dwarfs. For instance, the cooler cores of brown dwarfs might create less turbulence inside the dwarfs, and consequently weaker magnetic fields, but possibly with conformations that make them more likely to reconnect and produce flares. • The first discovery of a simple sugar molecule in space was made by the 12 Meter Telescope. The sugar molecule glycolaldehyde was detected in a giant cloud of gas and dust near the Galactic Center where new stars are forming. This makes it likely that the chemical precursors to life are formed in such clouds long before planets develop around stars. Glycolaldehyde is an 8-atom molecule with the structure HO-CH2-CHO, which can combine with other molecules to form the more complex sugars Ribose and Glucose. Ribose is a building block of nucleic acids such as RNA and DNA, which carry the genetic code of living organisms. Glucose is the sugar found in fruits. Glycolaldehyde contains exactly the same atoms, though in a different molecular structure, as methyl formate and acetic acid, both of which were detected previously in space. All three of these isomers are believed to catalyze on interstellar grains. • Very Long Baseline Array (VLBA) observations of the Galactic black hole binary GRS 1915+105 have revealed the smallest synchrotron jet yet known. This compact jet, about 10 AU in length at the microquasar's core, is the first of its size imaged in any black hole binary. It is present continuously, reestablishing itself within eight hours of major radio outbursts. It increases in intensity about 30 minutes after dips in the core X-ray emission occur, suggesting that it is powered by injections of plasma from the accretion disk. The VLBA observations also show, at larger scales (~ 500 AU), superluminal motions of ejecta from outbursts associated with abrupt changes in the X-ray emission. The VLBA observations of this microquasar take advantage of its status as a unique laboratory for the study of both the plateau and flare states seen separately in other black hole binaries. Scientific Highlights Observinfiummariizooo 2 • As one of its last research projects, the 140 Foot Telescope has discovered an interstellar cloud of unprecedented size and mass which consists almost entirely of atomic hydrogen. Hydrogen in interstellar clouds quickly converts to molecular form in the presence of dust grains, so the question of how large an atomic cloud can be is important to understand basic interstellar physics. The present cloud, at longitude 28 degrees 5 in the plane, has an extent of 150 pc and a mass of 10 M0. Its core is cold and is seen in self-absorption, while the outer regions are warmer and are seen in emission. OH is seen in the core, signaling the onset of a small amount of molecular hydrogen there. It appears that the cloud is just now entering a spiral shock and has been caught in the transition between atomic and molecular phases. The peculiar nature of the OH excitation, also seen in other parts of the Milky Way, suggests that there may be about 100 other objects like this one, which could be detected if observed in HI at sufficiently high angular resolution, such as available with the Green Bank Telescope. • The closest known black hole to Earth has been discovered with the VLA. Rapid response to reports of an optical and X-ray outburst from the variable V4641 Sgr showed relativistic expansion of radio jets. A presumed black hole binary system, V4641 Sgr showed the most dramatic X-ray intensity changes ever seen from such a system. The first VLA observations, made within 24 hours of the X-ray outburst, indicated that the jets had expanded sufficiently to show structure. The object's behavior makes it part of a new subclass of X-ray novae, and at a distance of 1600 light years, the black hole in this system is the closest to Earth yet discovered. • The gas flow in the central regions of the barred galaxy NGC 1097 has been revealed by the VLA. Sensitive polarization observations have shown that shocked gas in the galaxy is diverted by nearly 90 degrees to flow directly down the bar toward the nucleus. The polarization shows the magnetic field orientation, which is a tracer of the gas velocity. The results are in general agreement with computer simulations, but show that the shock front where the diversion occurs is closer to the center of the bar, not at its edge as the simulations suggest. In addition, the observed magnetic field near the center of the galaxy indicates that magnetic stress may serve as the mechanism for feeding the central black hole with the amount of material required to account for the observed activity. • VLBA "Movie" Shows "Missing Link" Gas Cloud Near AGN Jet. A 16-month series of VLBA images of the jet of 3C120 shows the jet colliding with a gas cloud. The cloud is intermediate in distance from the AGN core between the close, broad-line clouds and the farther narrow-line clouds. The collision caused "flickering" in the radio emission at a specific location in the jet, leading to the conclusion that the jet changed direction. Further studies of the newly-discovered cloud could yield dynamical information important to understanding the regions near galactic supermassive black holes. Observing Hours im> 0bservin;iumman)2ooo 40 30 o est. o 2 20 est. X 10 0 1988 89 90 91 92 93 94 95 96 97 98 99 2000 01 02 03 Calendar Year 140 Foot GBT £2] 12 Meter Egg VLA Q VLBA Figure 1. This figure shows the hours for observing on each telescope during the last decade. It includes astronomical observing, testing, and calibration. The 12 Meter Telescope closed in July of 2000, and the GBT is expected to begin operations in the spring of 2001. Distribution of Scheduled Observing Time Observinfiummanjzooo h 12 Meter VLA VLBA o o o m® 2 v, v, v. '/, ^ MMM vmYAYAV. ™ iiMiiiiiMm 1991 92 93 94 95 96 97 98 99 00 1991 92 93 94 95 96 97 98 99 00 1993 94 95 96 97 98 99 00 Calendar Year Calendar Year Calendar Year NRAO Staff * '/// Visitors** ^gg^Testing and Calibration Includes NRAO 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. 12 Meter Radio Telescope Summary rttfc Observing iummari) 2000 100 - - * ^ d 4 1 f A / / /* jr JL A w, A Si- 80 / i \ i I \ n T f - 60 \ h A J \ A f 1 A f \ A r ■\ A 7 \ A f \ ft r ^ h J ^ L- - - ft £ 40 t T \ V 7 _v V V 20 i V v !» 1 VI J L i V V 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 Calendar Year Observing Installation, Maintenance, and Calibration Equipment Failure, Weather, and Interference Figure3. This summary for each quarter of the calendar year shows the percentage of the total time in the year (5112 hours) that the telescope was scheduled for observing; for routine calibration, maintenance, and installation of new experiments; and the percentage of time lost due to equipment failure, bad weather, and radio interference. The telescope was closed in July 2000. Very Large Array Telescope Summary IRSD Observing (ummari) 2000 6 100 __ - - 80 k* -> ^ »■*■» ^ mt "" ^ ^ -s \* "^ 00 " S^ ^ - ' ^ V ^ ^ •* ^ ^ "^ ^ c 60 - I 40 - ^ _ ~. ..^ ^ - - ^ ^ „- m s^ 20 »*», m »^ "^« .- .*. ■ «■ 1 .. i tmt. 0 •~ ,— i^' »^ j^ ii»« 1^^ ^^ ... - . m . „ •» ■ •« m* ■ ™ mm i ■ Ml ■ Ml ■ ^1 ... mm* ■^^i ... imm* -x' m Calendar Year Observing Testing, Maintenance and Calibration Downtime Figure 4. This summary for each quarter of the calendar year shows the percentage of the total time in the year (8760 hours) that the telescope was scheduled for observing; for routine system testing, maintenance, and calibration; and the percentage of time lost due to hardware or software failure, power failure, or bad weather.