J/ApJS/165/439 Interstellar scintillation at 2 and 8GHz (Rickett+, 2006)
Interstellar scintillation observations of 146 extragalactic radio sources.
Rickett B.J., Lazio T.J.W., Ghigo F.D.
<Astrophys. J. Suppl. Ser., 165, 439-460 (2006)>
=2006ApJS..165..439R 2006ApJS..165..439R
ADC_Keywords: BL Lac objects ; Radio sources
Keywords: BL Lacertae objects: general - galaxies: active - ISM: general -
plasmas - quasars: general - scattering
Abstract:
From 1979 to 1996 the Green Bank Interferometer was used by the Naval
Research Laboratory to monitor the flux density from 146 compact radio
sources at frequencies near 2 and 8GHz. We filter the light curves to
separate intrinsic variations on times of a year or more from more
rapid interstellar scintillation (ISS) on times of 550 days. Whereas
the intrinsic variation at 2GHz is similar to that at 8GHz (although
diminished in amplitude), the ISS variation is much stronger at 2 than
at 8GHz. We characterize the ISS variation by an rms amplitude and a
timescale and examine the statistics of these parameters for the 121
sources with significant ISS at 2GHz. We model the scintillations
using the NE2001 Galactic electron model assuming the sources are
brightness-limited.
Description:
Flux density observations with the GBI were made nearly daily from
1979 to 1987 on 46 radio sources, as described by Fiedler et al.
(1987ApJS...65..319F 1987ApJS...65..319F, hereafter F87) and Waltman et al.
(1991ApJS...77..379W 1991ApJS...77..379W, hereafter W91). The sample of sources was
expanded to 146 and the frequency of observations reduced to once
every 2 days during 1988-1996 (Lazio et al. 2001, Cat. J/ApJS/136/265,
hereafter L01). Here we summarize the relevant details of the
Navy-NRAO GBI monitoring program; for complete details see F87, W91,
and L01.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 99 147 Short-term Variations in GBI Flux Density Monitoring
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See also:
J/ApJS/136/265 : Monitoring compact radio sources at 2.5 + 8.2GHz (Lazio+ 2001)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Source name (HHMM+DDD, B1950)
10- 12 I3 deg GLON Galactic longitude
14- 16 I3 deg GLAT Galactic latitude
18- 21 F4.2 kpc Leff Effective length through interstellar plasma
23- 27 F5.2 Jy S2GHz Mean 2GHz flux density
29- 33 F5.2 Jy S8GHz Mean 8GHz flux density
35- 39 F5.3 --- m2 The 2GHz modulation index
41 I1 --- q_m2 Confidence level in m2 (1)
43- 46 F4.1 d tau2 Signal timescale at 2GHz
48- 50 I3 d Tsm Smoothing time
52- 56 F5.3 --- m8 The 8GHz modulation index
58 I1 --- q_m8 Confidence level in m8 (1)
60- 64 F5.1 d tau8 Signal timescale at 8GHz
66- 70 F5.3 --- M2 The 2GHz rms variation on a 300-day
timescale (2)
72- 76 F5.3 --- M8 The 8GHz rms variation on a 300-day
timescale (2)
78- 82 F5.2 --- rho ? Cross correlation coefficient between ISS
at 2 and 8GHz
84- 88 F5.2 --- alpha Spectral index between 2 and 8GHz (3)
90- 93 F4.2 Jy S2.4GHz Most compact component VLBI 2.4GHz flux density
95- 99 F5.2 mas Diam Most compact component VLBI diameter
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Note (1): Confidence level as follows:
2 = convincing evidence for short-term variations (errors 10-20%)
1 = just credible evidence (errors 20-50%)
0 = no credible short-term variations are detected (even though m and
τ were formally estimated)
Note (2): Normalized by the mean flux density. (This quantity was obtained
from the square root of one half of the structure functions of the
low-pass time series at a time lag of 300 days for both 2 and 8GHz).
Note (3): Defined by S∝να.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 14-Dec-2007