The 50 and 100 micron emissions of OJ 287 were detected and upper limits for BL Lac were obtained. These first measurements of two BL Lac objects in the far-infrared show them to be similar to the few quasars previously observed in the far-infrared. In particular, there is no evidence for significant dust emission, and the lambda approximately 100 micron flux density fits on a smooth line joining the near-infrared and millimeter continuum fluxes. The implications of the results for models of the sources are discussed briefly

Harvey, P. M.

Joy, M.

Lester, D. F.

Wilking, B. A.

English

NASA Technical Reports Server

NASA Technical Memorandum 86022 Airborne Astronomy Program 
Medium Altitude Missions Branch 
Preprint Series 023 
NASA-TM-8602219850005392 
Far-Infrared Photometry of 
Compact Extragalactic 
Sources: OJ 287 and 
BL Lac 
Paul M. Harvey, Marshall Joy, 
Daniel F. Lester, and 
Bruce A. Wilking 
October 1984 
NI\SI\ 
National Aeronautics and 
Space Administration 111111111111111111111111111111111111111111111 NF00865 
https://ntrs.nasa.gov/search.jsp?R=19850005392 2020-03-20T20:02:01+00:00Z
NASA Technical Memorandum 86022 Airborne Astronomy Program 
Medium Altitude Missions Branch 
Preprint Series 023 
Far-Infrared Photometry of 
Compact Extragalactic Sources: 
OJ 287 and BL Lac 
Paul M. Harvey 
Marshall Joy 
Daniel F. Lester 
Bruce A. Wilking, University of Texas at Austin, Austin, Texas 
NI\S/\ 
National Aeronautics and 
Space Administration 
Ames Research Center 
Moffett Field. California 94035 
Far-Infrared Photometry of Compact Extragalactic 
Sources: OJ 287 and BL Lac 
by 
Paul M. Harvey, Marshall Joy, Daniel F. Lester, and Bruce A. Wilking 
Astronomy Department, University of Texas at Austin 
Accepted (August 1984) for publication in 
THE ASTROPHYSICAL JOURNAL (LETTERS) 
2 
Abstract 
We have detected the 50 and 100 pm emission of OJ 287 and obtained upper 
limits for BL Lac. These first measurements of two BL Lac objects in the far-
infrared show them to be similar to the few quasars previously observed in the 
far-infrared. In particular there is no evidence for significant dust 
emission, and the A - 100 pm flux density fits on a smooth line joining the 
near-infrared and millimeter continuum fluxes. We briefly discuss the 
implications of the results for models of the sources. 
3 
I. Introduction 
The spectral region between 10 ~m and 1 mm contains information critical 
to our understanding of quasar emission processes. In many models (see e.g. 
Marscher 1980b; K~nigl 1981) this wavelength range reflects the structure in 
the inner parts of the emission region of quasars. This spectral region also 
appears to contain a large fraction of the total luminosity of many quasars 
based on interpolations and extrapolations of observed energy distributions. 
To date only a handful of quasars have been observed at A - 100 ~m (Harvey, 
Wilking, and Joy 1982; Clegg et ala 1983; Neugebauer et al. 1984), although 
the IRAS survey will soon be providing a larger body of data on fluxes of many 
quasars within a narrow range of epochs. We report here on initial 
observations or two optically violently variable (OVV) quasars, OJ 287 and BL 
Lac, as part of a program to study their long-term variability. 
II. Observations 
Our observations were made using NASA's Kuiper Airborne Observatory in 
1983 Oct/Nov. The observations of OJ 287 represent two nights of data, 28 
Oct. and 1 Nov. 1983, totalling 3400 sec integration time, while BL Lac was 
observed for 2600 sec on 29 Oct. 1983. The observations were made with the 6-
channel photometer described by Wilking et ale (1984). The KAO chopper throw 
was set at l' so that one detector at each wavelength was always looking at 
the source while beam-switching. We observed each object simultaneously at 47 
and 95 ~m effective wavelengths with beam sizes of 28 and 40 arcsec 
respectively. The observations were calibrated relative to S140 and IRC+10420 
(Harvey, Wilking and Joy 1984). The absolute calibration is believed accurate 
to ±20%. The 10 statistical uncertainties of the measurements along with the 
4 
measured flux densities are listed in Table 1. 
III. Discussion 
A. Results 
Figure 1 shows our measured fluxes or upper limits plotted relative to 
measurements at other wavelengths summarized by Jones ~ al (1981). Since 
both OJ 287 and BL Lac are variable at optical and radio wavelengths, the 
details of these energy distributions are uncertain to a factor of -2 • 
Unpublished observations (Glassgold and Bregman, priv. comm.), however, 
suggest that at the time of our observations BL Lac was in a relatively low 
state of power output while OJ 287 was slowly receding from a burst which 
peaked in early 1983. We have, therefore, attempted to plot fluxes in Figure 
1 which were measured at similar levels of activity in the past. 
Two obvious conclusions may be drawn from Figure 1. Following the 
discussion of Harvey, Wilking and Joy (1982) for 3C 345, it is clear that 
thermal dust emission cannot contribute significantly to the total far-
infrared luminosity of OJ 287 and BL Lac because of the very broad and smooth 
energy distribution from infrared to millimeter wavelengths. Like 3C 345, it 
is also clear for OJ 287 that the far-IR spectral region contains a large 
fraction of its total luminosity, since vFv peaks at A - 100~m. The total 
integrated luminosity of OJ 287 at the time of our observations was L - 7 X 
10 12 L@ for z = 0.306 (Miller, French, and Hawley 1978) assuming the fluxes 
plotted in Figure 1. 
B. Implications for Quasar Models 
5 
Ennis, Neugebauer and Werner (1982, hereafter ENW) have shown that many 
BL Lac objects and OVV quasars have similar energy distributions in the sense 
that the ratio of millimeter to near-IR flux density is relatively constant. 
For this class of objects there is a growing body of evidence which suggests, 
in fact, that the entire optical-through-radio energy distribution may be due 
to a single emission mechanism (e.g. ENW; Harvey, Wilking and Joy 1982). Like 
many other BL Lac objects, OJ 287 and BL Lac exhibit relatively flat (in Fv) 
spectra at radio through millimeter wavelengths. At shorter wavelengths their 
spectra turn down in Fv (or flatten in vF v ). In most models the pOint where 
the spectrum turns over in Fv is set by the frequency where 'synch - 1 in the 
inner part of the source at a radius where the density gradient changes 
rapidly (Marscher 1980a,b; ENW; Kellermann and Pauliny-Toth 1981; K~nigl 
1981). In order to account for apparent super-relativistic motions and for 
the lack of evidence for a second turnover in the near-infrared due to 
electron energy losses (Landau ~ ale 1983), it is attractive to explain the 
optical- through-radio continuum as the emission from a relativistic jet which 
is beamed nearly along our line-of-sight (e.g. Blandford and K~nigl 1979; 
Marscher 1980b). In Marscher's model, for instance, the sub-millimeter 
turnover frequency is identified with the synchrotron self-absorption cutoPf-
frequency at the point R+ where the bulk acceleration stops and the particles 
begin to expand freely. 
Our observations place improved limits on the turnover frequency for OJ 
28'7 and BL Lac. From the energy distribution shown in Figure 1, this 
frequency must lie within roughly an octave of 3 x 10 12 Hz or 100 jlm, since 
the flux densities are significantly lower at 100 jlm than at 1 mm. To the 
order of accuracy warranted by the models at this point, this implies R+ is 
6 
similar to that derived by Marscher (1980b) for 3C 345, i.e. 10 1 -10 2 pc, 
assuming Lorentz factors of a few to 10. 
Some of the most important observations to test and limit models for 
quasars will be to study the variability of these objects as a function of 
wavelength. As shown by the measurements reported here, the photometric 
sensitivity on the KAO is now high enough that it is practical to perform such 
a study of OVV quasar variability. Therefore we will be obtaining regular 
measurements Of these and other similar objects in the future to compare with 
data at longer and shorter wavelengths. 
We thank the entire staff of the Kuiper Airborne Observatory for their 
continued dedication which made these observations possible. This research 
was supported by NASA grant NAG 2-67. 
7 
References 
Blandford, R.D., and K5nigl, A. 1979, A£. ~., 232, 34. 
Clegg, P.L. ~ al. 1983, Ap. ~., ~Z~, 58. 
Ennis, D., Neugebauer, G., and Werner, M.W. 1982, A£. ~., 262, 460. 
Harvey, P.M., Wilking, B.A., and Joy, M. 1982, Ap. ~. (Letters), 254, L29. 
Harvey, P.M., Wilking, B.A., and Joy, M. 1984, Nature, 307, 441. 
Jones, T.W., Rudnick, L., Owen, F.N., Puschell, J.J., Ennis, D.J., and Werner, 
M.W. 1981, A£. ~., ~~~, 97. 
Kellermann, K.I. and Pauliny-Toth, I.I.K. 1981, Ann. Rev Astr. Ap., ~2, 373. 
K5nigl, A. 1981, A£. ~., ~~~, 700. 
Landau, R. et al. 1983, Ap. J., 268, 68. 
-- - - ---
Marscher, A.P. 1980a, Nature, 286, 12. 
Marscher, A.P. 1980b, A£. ~., 235, 386. 
Miller, J.S., French, H.B., and Hawley,S.A. 1978, in Pittsburgh Conference on 
BL Lac Objects, ed. A.M. Wolfe (Pittsburgh:~niversity of Pittsburgh 
Press), , p. 176. 
Neugebauer, G. et al. 1984, A£. ~.(Letters), ~7~' L83. 
Wilking, B.A., Harvey, P.M., Lada, C.J., Joy, M.,and Doering, C. 1984, A£. ~., 
279, 291. 
OJ 287 
BL Lac 
8 
Table 
Observed Flux Densities (Jy) 
50 pm 
0.62 ± 0.23 
0.18 ± 0.25 
100 pm 
1.53 ± 0.31 
0.40 ± 0.32 
Figure Caption 
Figure 1 - The optical-through-radio energy distributions of OJ 287 and 
BL Lac. The points from this study are at 3 and 6 x 10 12 Hz. The 
other data are taken from Jones ~ al.(1981). The OJ 287 data 
are from an epoch when the source was roughly a factor of two 
brighter than in its quiescent state while the BL Lac fluxes are 
from an epoch when it was in its quiescent state. The energy 
distribution is given in terms of vFv which shows energy per 
octave. 
10 
Authors' Postal Addresses 
P.M. Harvey, M. Joy, D.F. Lester, B.A. Wilking 
Astronomy Department 
University of Texas 
Austin, TX 78712 
11 
• 
r 
LO 
/ 
• x \ I u ..... q-
• X 0 CD ..J N 
..J ., 
m 0 
• X rt> 
-,- N I 
-X'" ~ 
C\J 
g 
..J 
X • 
'" 
X ~ 
X • 
~ 0 X. 
rt> ¢ LO (,() 
-I iJ.?N- I 
~'E 
~;:: 0_ 
..J 
1. Report No. I 2. Government Accession No. 3. Recipient's Catalog No. 
NASA TM-86022 
4. Title and Subtitle 5. Report Date 
FAR-INFRARED PHOTOMETRY OF COMPACT EXTRAGALACTIC November 1984 
SOURCES: OJ 287 and BL Lac 6. Performing Organization Code 
7. Author(s) 8. Performing Organization Report No. 
Paul M. Harvey, Marshall Joy, Daniel F. Lester, and 85016 
Bruce A. Wilkin2: 10. Work Unit No. 
9. Performing Organization Name and Address 
University of Texas at Austin 11. Contract or Grant No. 
Austin, TX 78712 
13. Type of Report and Period Covered 
12. Sponsoring Agency Name and Address Technical Memorandum 
National Aeronautics and Space Administration 14. Sponsoring Agency Code 
Washington, DC 20546 352-02-03 
15. Supplementary Notes 
Preprint Series #23. Supported by NASA grants. Point of contact: L. C. 
Haughney, Ames Research Center, MiS 211-12, Moffett Field, CA 94035, 
(415) 965 ·5339 ETS L"M~ .')iiQ 
16 Abstract 
We have detected the 50 and 100 )lm emission of OJ 287 and obtained 
upper limits for BL Lac. These first measurements of two BL Lac objects 
in the far-infrared show them to be similar to the few quasars previously 
observed in the far-infrared. In particular there is no evidence for 
significant dust emission, and the /.. - 100 )lm flux density fits on a 
smooth line joining the near-infrared and millimeter continuum fluxes. 
We briefly discuss the implications of the results for models of the 
sources. 
17. Key Words (Suggested by Author(s)) 18. Distribution Statement 
Quasars: far-infrared emission Unlimited 
Subj ect category - 089 
19. Security Classif. (of thisreport) 20. Security Classif. (of this page) 21. No. of Pages 22. Price' 
Unclassified Unclassified 13 A03 
'For sale by the National Technical Information Service, Springfield, Virginia 22161 
End of Document 


Far-infrared photometry of compact extragalactic sources: OJ 187 and BL Lac

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server