Observing Summary 2006 Statistics
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OBSERVING SUMMARY 2006 NATIONAL RADIO ASTRONOMY OBSGRVATORY NATIONAL RADIO ASTRONOMY OBSERVATORY Observing Summary 2006 Statistics Cover Image: The long tidal tail of Hydrogen gas shown in this image was shaken loose by the dance ofM51, the Whirlpool galaxy, with its companion NGC 5195. Investigators: A.H. Rots, J.M. van der Hulst, P.E. Seiden, R.C. Kennicutt, P.C. Crane, A. Bosma, L. Athanassoula, & D.M. Elmegreen. Image composition by Juan Uson. Scientific Highlights two Observing Summary 2006 VIA Reveals "Smoking Gun" Supporting One Formation Model for Multiple-Star Systems - The VLA imaged L1551 IRS5, in the Taurus star- forming region about 450 light years from Earth. A 1998 VLA study with 13 of the 27 antennas had revealed two young stars, accompanied by dust disks, orbiting each other within L1551IRS5. Imaging at 43 GHz, using the now fully outfitted VLA together with the fiber optic link to the Pie Town VLBA antenna, showed that the two primary protostellar disks are aligned with each other with the larger surrounding disk in which the stars are embedded, and with the orbital motion of the binary star system. This provides strong support for the theoretical model in which the two protostars and their surrounding dusty disks fragment from a larger parent disk, rather than being formed independently and then captured into a bound orbit. GBT Discovers New Organic Molecules in Space - Ever more complex organic molecules continue to be discovered in interstellar space, yielding increased insight into the process which produces pre-biotic molecules and chemistry under extreme conditions. The molecule acetamide, the largest interstellar molecule with a peptide bond, was discovered using GBT observations over a wide frequency range - 9 to 47 GHz. Its presence in interstellar clouds suggests that it will be present when comets form in pre-planetary systems, although this molecule has not yet been reported in comets. The first negatively charged molecule in space CeH- was also discovered this year with the GBT. While about 130 neutral and 14 positively charged molecules are known to exist in interstellar space, this is the first negative molecule, or anion, to be found. Its size is larger than most neutral and all positively-charged molecules known in space which may increase its stability in the harsh cosmic environment. The chemical process which forms CeH- may be ubiquitous, suggesting that other molecular anions are also present. VLBA Reveals Closest Pair of Supermassive Black Holes - Multi-frequency observations of the radio galaxy 0402+379 with the VLBA revealed two compact, variable, flat-spectrum active nuclei within this elliptical galaxy at redshift z = 0.055. The two nuclei represent the closest pair of supermassive black holes yet found, separated by only 7.3 pc, more than two orders of magnitude closer than any previously discovered pair. With a combined mass of 1.5 x 108 solar masses, this pair, were they to collide, would produce strong gravitational radiation. It is estimated that they will collide in no less than about 1018 years, if the orbit decays only due to emission of gravitational radiation. GBT Observations of a Remarkable Anomalous X-ray Pulsar - Anomalous X-ray pulsars are neutron stars with X-ray luminosities exceeding the energy available from braking of the star's rotation, likely generated by decay of extremely strong magnetic fields. They normally show no radio emission. Three years ago the anomalous X-ray pulsar XTE J1810-197 increased its X-ray luminosity by a factor of 100 and, a year later, was detected as a radio source at the VLA. It has recently been detected as a radio pulsar at Parkes and its properties measured at a number of frequencies with the GBT. It is a remarkable object, with relatively strong pulses visible up to 42 GHz; its radio spectrum is quite flat over a range of 100 in frequency, and above 20 GHz it is brighter than every other known neutron star. Observations of single pulses with the GBT at 42 GHz show a complex pulse structure with features as narrow as 0.2 milliseconds. The radio emission mechanism is unknown. Scientific Highlights two Observing Summary 2006 VLBA Imaging and Polarimetry Survey Completed - The VLBA Imaging and Polarimetry Survey, a 5 GHz imaging survey of more than 1100 flat- spectrum extragalactic radio sources, was observed in 2006; during the 4th quarter, the general results of this survey were accepted for publication. Automatic data reduction and classification algorithms enabled routine imaging and analysis of these 1100 images so that the survey could be published within months of the completion of the observations. A primary goal of the survey was to generate baseline images with milli- arcsec resolution of the target active galactic nuclei, most of which are expected to be detected as gamma-ray sources by the Gamma-ray Large Area Space Telescope after its launch in late 2007. In addition, approximately 20 candidate binary black holes were identified and will be followed up with the VLBA. GBT Discovers A Gigantic Eruption from the Inner Disk of the Milky Way - Winds and supemovae from clusters of massive stars can affect galaxies on global scales, altering the abundances and energetics of the interstellar medium. GBT observations of HI in the inner part of the Milky Way have discovered a coherent structure which seems to be a huge superbubble reaching higher than 3 kpc from the Galactic plane. It has been detected in both Ha and HI and mapped in detailed in HI. The total hydrogen mass within the outflow is « 106 solar masses and its energy content is of order 1053 ergs. At the top of the structure there is a peculiar cap consisting of more than 104 solar masses of hydrogen which appears to have a motion which lags behind Galactic rotation. This object offers a nearby perspective on the superbubble phenomenon. VLA Provides Evidence that X-Ray Flashes May Represent a New Class of Cosmic Explosions - An X-Ray Flash (XRF) detected by the Swift satellite on 18 February 2006 was subsequently studied with the VLA. The radio observations revealed that the ejecta from this blast are quasi- spherical, as opposed to the beamed ejecta common to Gamma-Ray Bursts (GRBs). This, along with data from other wavelengths, suggests that XRFs represent a type of burst roughly 100 times less energetic than GRBs but up to ten times more common. The observers speculate that a magnetar central engine may distinguish the subenergetic events from cosmological GRBs, which are thought to be powered by black holes. VLBA Reveals the Earliest Structure Resolved in a Nova Explosion - VLBA observations of the recurrent nova RS Ophiuchi following its 12 February 2006 outburst revealed the earliest spatially resolved structure in any nova (or indeed supernova) explosion. The observations clearly showed that, contrary to earlier assumptions of spherical explosion symmetry, the ejection is jet-like, collimated by the central binary whose orientation on the sky can be determined. The observers believe the lessons learned from this object can also be applied to supernova explosions. Teste of General Relativity from Timing the Double Pulsar - GBT observations of the remarkable pulsar-pulsar binary system J0737-3039 provide the most precise timing of its orbital parameters and consequent tests of general relativity. The double pulsar has much higher orbital velocities and accelerations than previously known pulsars in binary systems, and is unique because both neutron stars have detectable radio pulses. Observed pulse arrival times are modified by relativistic effects, which can have different form in different theories of gravity. A series of GBT observations each covering several orbits of the double pulsar have set the strictest limits to date on the accuracy of General Relatively in the strong-field limit, with agreement between measurements and the theory to within an uncertainty of 0.05%. ■si Scientific Highlights two Observing Summary 2006 VLBA Detects Magnetic Collimation of Jets from an Evolved Star - VLBA polarization measurements of the AGB star W43A, which is rapidly undergoing evolution into a planetary nebula, have produced the first direct evidence for magnetic collimation of an astrophysical jet. The VLBA observations measured the polarization of 22 GHz emission from water masers at opposing tips of the jets. The magnetic field direction was shown to be almost perfectly perpendicular to the jet, consistent with a toroidal magnetic field. The magnetic pressure in these regions is seen to dominate the gas pressure by a factor of 2-200. This result supports recent theoretical models that use magnetically collimated jets to explain the shape of asymmetric planetary nebulae. Giant, Ring-Like Structures Discovered Around Galaxy Cluster - Researchers using the VLA discovered giant, ring-like, radio-emitting structures around the galaxy cluster Abell 3376. The structures are believed to trace the elusive shock waves of cosmological large-scale matter flows. This discovery, combined with X-ray observations of the cluster, indicates the probable merger of a large group or small cluster with the main body, supporting the hierarchical-clustering model for the origin of large-scale structure. In addition, the large radio-emitting structures may be acceleration sites where magnetic shock could boost cosmic-ray particles to energies of 1018 to 1019 eV. GBT Detection of Molecular Gas at a Redshift of >3.9 - A significant fraction of high-z galaxies are undergoing starbursts at enormous rates, consistent with the formation of large elliptical galaxies. The molecular gas reservoir for such events can be studied in the ground-state transitions of CO, redshifted into the frequency range of the GBT. Several galaxies have now been detected at redshifts between 3.9 and 4.7 and indicate that very large masses of molecular gas seem concentrated in a compact nuclear region and not a luminous, extended, low surface brightness component.