30 research outputs found
Search for gamma ray lines from SS433
Data obtained with the Gamma Ray Spectrometer (0.3 to 9 MeV) aboard the Solar Maximum Mission satellite from 1980 to 1985 for evidence of the reported Doppler shifted lines from SS433 were examined. The data base covers a total of 468 days when SS433 was in the field of view and includes times of quiescent and flaring radio activity. In 9 day integrations of the SMM data no evidence is found for gamma ray line emission from SS433. The 99% confidence upper limits for 9 day integrations of the shifted 1.37 and 6.1 MeV lines are 0.0013 gamma/sq cm-s and 0.0007 gamma/sq cm-s, respectively. The 360 day time averaged upper limits are 0.0002 gamma/sq cm-s x 0.0001 gamma/sq cm-s for both lines
Sco X-1: The Evolution and Nature of the Twin Compact Radio Lobes
The radio components associated with the LMXB Sco X-1 have been monitored
with extensive VLBI imaging at 1.7 and 5.0 GHz over four years, including a
56-hour continuous VLBI observation in 1999 June. We often detected one strong
and one weak compact radio component, moving in opposite directions from the
radio core. We suggest that the moving components are radio lobes generated by
the disruption of energy flow in a twin-beam from the binary system. The
average lifetime of a lobe-pair, the space motion of the lobes and the measured
energy flow in the beam are discussed in arXiv:astro-ph/0104325. The lobe has a
flux density that is variable over a time-scale of one hour, a measured minimum
size of 1 mas (2.8 au), and is extended perpendicular to its motion. This short
electron radiative lifetime may be caused by synchrotron losses if the lobe
magnetic field is 300 G, or by adiabatic expansion of the electrons as soon as
they are produced at the working surface. The lobes also show periods of slow
expansion and a steepening radio spectrum, perhaps related to the
characteristics of the beam energy flow. The radio morphology for Sco X-1 is
more simple than for most other Galactic jet sources. The lobes of Sco X-1 are
similar to hot-spots found in many extragalactic double sources. Scaling the
phenomena observed in Sco X-1 to extragalactic sources implies hot-spot
variability time-scales of 10^4 yr and hot-spot lifetimes of 10^5 yr. The
recurrent formation of lobes in Sco X-1 probably does not occur for
extragalactic radio sources.Comment: 22 pages of text + 16 figures. ApJ, in pres
NASA's Evolution to K(sub a)- Band Space Communications for Near-Earth Spacecraft
Over the next several years, NASA plans to launch multiple earth-science missions which will send data from low-Earth orbits to ground stations at 1-3 Gbps, to achieve data throughputs of 5-40 terabits per day. These transmission rates exceed the capabilities of S-band and X-band frequency allocations used for science probe downlinks in the past. Accordingly, NASA is exploring enhancements to its space communication capabilities to provide the Agency's first Ka-band architecture solution for next generation missions in the near-earth regime. This paper describes the proposed Ka-band solution's drivers and concept, constraints and analyses which shaped that concept, and expansibility for future need
A One-sided, Highly Relativistic Jet from Cygnus X-3
Very Long Baseline Array images of the X-ray binary, Cygnus X-3, were
obtained 2, 4 and 7 days after the peak of a 10 Jy flare on 4 February 1997.
The first two images show a curved one-sided jet, the third a scatter-broadened
disc, presumably at the position of the core. The jet curvature changes from
the first to the second epoch, which strongly suggests a precessing jet. The
ratio of the flux density in the approaching to that in the (undetected)
receding jet is > 330; if this asymmetry is due to Doppler boosting, the
implied jet speed is > 0.81c. Precessing jet model fits, together with the
assumptions that the jet is intrinsically symmetric and was ejected during or
after the major flare, yield the following constraints: the jet inclination to
the line of sight must be < 14 degrees; the cone opening angle must be < 12
degrees; and the precession period must be > 60 days.Comment: 12 pages 7 figures, accepted by Ap
The Celestial Reference Frame at 24 and 43 GHz. II. Imaging
We have measured the sub-milli-arcsecond structure of 274 extragalactic
sources at 24 and 43 GHz in order to assess their astrometric suitability for
use in a high frequency celestial reference frame (CRF). Ten sessions of
observations with the Very Long Baseline Array have been conducted over the
course of 5 years, with a total of 1339 images produced for the 274
sources. There are several quantities that can be used to characterize the
impact of intrinsic source structure on astrometric observations including the
source flux density, the flux density variability, the source structure index,
the source compactness, and the compactness variability. A detailed analysis of
these imaging quantities shows that (1) our selection of compact sources from
8.4 GHz catalogs yielded sources with flux densities, averaged over the
sessions in which each source was observed, of about 1 Jy at both 24 and 43
GHz, (2) on average the source flux densities at 24 GHz varied by 20%-25%
relative to their mean values, with variations in the session-to-session flux
density scale being less than 10%, (3) sources were found to be more compact
with less intrinsic structure at higher frequencies, and (4) variations of the
core radio emission relative to the total flux density of the source are less
than 8% on average at 24 GHz. We conclude that the reduction in the effects due
to source structure gained by observing at higher frequencies will result in an
improved CRF and a pool of high-quality fiducial reference points for use in
spacecraft navigation over the next decade.Comment: 63 pages, 18 figures, 6 tables, accepted by the Astronomical Journa
A Potential Supernova Remnant/X-ray Binary Association in M31
The well-studied X-ray/Optical/Radio supernova remnant DDB 1-15 (CXOM31
J004327.8+411829; r3-63) in M31 has been investigated with archival XMM-Newton
and Chandra observations. The timing data from XMM-Newton reveals a power
density spectrum (PDS) characteristic of accreting compact objects in X-ray
binaries (XRBs). The PDS shows features typical of Roche lobe overflow
accretion, hinting that the XRB is low-mass. The Chandra observations resolve
the SNR into a shell and show a variable count rate at the 94% confidence level
in the northwest quadrant. Together, these XMM-Newton and Chandra data suggest
that there is an XRB in the SNR r3-63 and that the XRB is located in the
northwestern portion of the SNR. The currently-available X-ray and optical data
show no evidence that the XRB is high-mass. If the XRB is low-mass, r3-63 would
be the first SNR found to contain a low-mass X-ray binary.Comment: 30 pages, 3 tables, 11 figures, accepted for publication in Ap
The Nature of the Compact X-ray Source in Supernova Remnant RCW 103
The discovery of the 6.67 hr periodicity in the X-ray source 1E 161348-5055
associated with the supernova remnant RCW 103 has raised interesting
suggestions about the nature of the X-ray source. Here we argue that in either
accreting neutron star or magnetar model, a supernova fallback disk may be a
critical ingredient in theoretical interpretations of 1E 161348-5055. We
further emphasize the effect of fallback disks on the evolution of young
compact objects in various ways, and suggest that even SS 433 could also be
powered by fallback disk accretion process.Comment: 12 pages, 1 figure, accepted to ApJ
Three-dimensional hydrodynamical simulations of the large scale structure of W50-SS433
We present 3D hydrodynamical simulations of a precessing jet propagating inside a supernova remnant (SNR) shell, particularly applied to the W50-SS433 system in a search for the origin of its peculiar elongated morphology. Several runs were carried out with different values for the mass loss rate of the jet, the initial radius of the SNR, and the opening angle of the precession cone. We found that our models successfully reproduce the scale and morphology of W50 when the opening angle of the jets is set to 10 or if this angle linearly varies with time. For these models, more realistic runs were made considering that the remnant is expanding into an interstellar medium (ISM) with an exponential density profile (as HI observations suggest). Taking into account all these ingredients, the large scale morphology of the W50-SS 433 system, including the asymmetry between the lobes (formed by the jet-SNR interaction), is well reproduced.Fil: Zavala, Jesús. Universidad Nacional Autónoma de México; MéxicoFil: Velázquez, Pablo F.. Universidad Nacional Autónoma de México; MéxicoFil: Cerqueira, Adriano H. Universidade Estadual de Santa Cruz; BrasilFil: Dubner, Gloria Mabel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin
Multiwavelength Examination of the COS-B Field 2CG 075+00 Yields a Blazar Identification for 3EG J2016+3657
We present a high-energy study of the intriguing COS-B gamma-ray field, 2CG
075+00, in order to search for possible counterparts. New EGRET data show that
the COS-B emission probably corresponds to two localized gamma-ray sources, 3EG
J2016+3657 and 3EG J2021+3716. Spectral fits to these EGRET sources, assuming a
power-law model, yield photon indices of ~ 2 for each object. We examine
archival ROSAT and ASCA X-ray data which overlap both EGRET error boxes, and
find several point sources in the region to a flux limit of approximately 6.5 x
10^{-13} erg cm^{-2} s^{-1}. We conclude that the most probable candidate for
3EG J2016+3657 is the compact, variable, flat-spectrum radio and millimeter
source B2013+370 (G74.87+1.22) which has blazar-like properties. The other
source, 3EG J2021+3716, remains unidentified.Comment: 32 pages, 9 figures, uses aasms4 and epsfig style files. Accepted for
publication in The Astrophysical Journa
3EG J2016+3657: Confirming an EGRET Blazar Behind the Galactic Plane
We recently identified the blazar-like radio source G74.87+1.22 (B2013+370)
as the counterpart of the high-energy gamma-ray source 3EG J2016+3657 in the
Galactic plane. However, since most blazar identifications of EGRET sources are
only probabilistic in quality even at high Galactic latitude, and since there
also exists a population of unidentified Galactic EGRET sources, we sought to
obtain additional evidence to support our assertion that 3EG J2016+3657 is a
blazar. These new observations consist of a complete set of classifications for
the 14 brightest ROSAT X-ray sources in the error circle, of which B2013+370
remains the most likely source of the gamma-rays. We also obtained further
optical photometry of B2013+370 itself which shows that it is variable,
providing additional evidence of its blazar nature. Interestingly, this field
contains, in addition to the blazar, the plerionic supernova remnant CTB 87,
which is too distant to be the EGRET source, and three newly discovered
cataclysmic variables, all five of these X-ray sources falling within 16' of
each other. This illustrates the daunting problem of obtaining complete
identifications of EGRET sources in the Galactic plane.Comment: 16 pages, 6 figures, accepted for publication in The Astrophysical
Journa