Astrophysical Journal Supplement Series, Vol. 120, pp.
95-99, 1999.
Abstract: We show that 22 and 37 GHz total flux density
variations in compact extragalactic radio sources can to a good
accuracy be modeled by superposition of a small number of flare
components. Both the rise and the decay of these flares are
exponential, with a characteristic decay timescale 1.3 times longer
than the rise timescale. The properties of the individual model
flares derived from these flux decompositions are in agreement with
data obtained from VLBI observations of the corresponding new shock
components. The total flux density decompositions can be used to
search correlations between radio and other regimes, to calibrate
and to interpret VLBI observations, and to derive physical
parameters of the amount of Doppler boosting in each source and,
using additional VLBI data, to derive the intrinsic brightness
temperatures, the Lorenz factors and the viewing angles of the
sources.
Watson, D., Hanlon, L., McBreen, B.,
Smith, N., Foley, A.R., Metcalfe, L., Beckmann, V.,
Sánchez, S.F., Teräsranta, H.:
Simultaneous multifrequency observations of the BL Lac MS
0205.7+3509.
Astronomy and Astrophysics, Vol. 345, pp. 414-418,
1999.
Abstract: Radio and optical observations of the possible
microlensed BL Lac source MS0205.7+3509 were obtained
simultaneously with ASCA x-ray measurements in February 1997. A
single power law model, with a photon index f 2.61, is an
adequate fit to the ASCA data, once hydrogenic absorption in
excess of the Galactic value is permitted, confirming a
previous ROSAT measurement. On the basis of our simultaneous
data we have determined MS 0205.7+3509 to be a typical x-ray
select BL-Lac with alphaxox = -0.82. There is
no indication of an inverse Compton (IC) component in the ASCA
spectrum up to 10 keV. No evidence for variability on hour-long
timescales is present in either the x-ray or the optical data.
We discuss these results in the context of a gravitational
microlensing scenario for MS 0205.7+3509.
|
Bloom, S.D., Marscher, A.P., Moore,
E.M., Gear, W., Teräsranta, H., Valtaoja, E., Aller, H.D.,
Aller, M.F.;
Multiwaveband observations of quasars with flat radio spectra
and strong millimeter wave emission.
Astrophysical Journal Supplement Series, Vol. 122, pp.
1-27, 1999.
Abstract: We present multiwaveband observations of a
well-selected sample of 28 quasars and two radio galaxies with
flat radio spectra and strong millimeter-wave emission
(referred to here as FSRQs). The data are analyzed to determine
the radio to infrared and X-ray to gamma-ray properties of
FSRQs and the relationships between them. Specifically, the
synchrotron self-Compton (SSC) process is examined as a likely
common radiation mechanism. For most sources, the broadband
spectra are still incomplete, especially in the far-infrared
and ultraviolet range. Therefore, precise analysis, such as
model fitting of spectra, is not usually possible. To
compensate partially for this, we have taken a statistical
approach and examine the relationship between high- and low-
energy emission by using the data set for the entire
sample.
|
We use very long baseline interferometry (VLBI) at 8.4 and 22
GHz - higher frequencies than those of previous surveys - in
conjunction with nearly simultaneous radio to submillimeter-wave
observations to determine the parameters of the synchrotron
spectrum and to examine the compact angular structure of a subset
of sources from our sample. These parameters are used to predict
the SSC X-ray flux densities. Seven of 30 sources have predicted
self-Compton X-ray flux densities well above the observed flux
densities obtained with the ROSAT satellite unless one assumes
that the radiating plasma experiences bulk relativistic motion
directed toward the observer's line of sight. Three of these
seven sources are detected at gamma-ray frequencies. Model
spectra show that the X-rays are consistent with the first-order
SSC process, with the simultaneous multiwaveband spectrum of the
quasar 0836+710 obtained in 1992 March being very well fitted by
SSC emission from a uniform, relativistically moving source. The
gamma-rays are not produced via second-order self-Compton
scattering but rather by either first-order self-Compton
scattering or some other process.
A comparison of the ROSAT X-ray flux densities and those
obtained earlier with the Einsteim Observatory show that
several FSRQs are X-ray variables on timescales of about a
decade. Several sources that were observed more than once with
ROSAT also show variability on timescales of 1-2 yr, with the
X-ray variability in these cases often associated with
millimeter-wave variability and lower VLBI core-to-jet flux
ratios. Detections at gamma-ray energies also appear to be
related to increases in the radio to millimeter-wave flux
densities.
Statistical analysis shows that the millimeter-wave and x-ray
luminosities for the sample are strongly correlated, with a
linear regression slope ~ 0.65. The peak in the distribution
of X-ray to millimeter spectral indices also indicates a strong
connection between millilmeter-wave and X-ray emission.
Particularly interesting is a correlation between X-ray to
millimeter spectral index and fraction of flux density contained
in the VLBI core. This tendency toward high X-rays fluxes from
sources with stronger jet emission implies that the knots in the
jet are prominent sources of X-rays.
Pietilä, H., Takalo, L.O.,
Tosti, G., Benítez, E., Chiattelli, B., Corradi, R.L.M., Cox,
G., De Diego, J.A., De Francesco, G., Dultzin-Hacyan, D.,
Heinämäki, P., Katajainen, S., Keinänen, P.,
Korhonen, H., Kotilainen, J., Lainela, M., Licandro, J.,
Luciani, M., Nilsson, K., Pursimo, T., Raiteri, C.M., Rekola,
R., Sillanpää, A., Sobrito, G., Teräsranta, H.,
Villata, M., Zurita, A.:
OJ 287 and the predicted fade of 1998;
Astronomy and Astrophysics, Vol. 345, pp. 760-768,
1999.
Abstract: There were predictions that blazar OJ287
should have faded in late 1997 or early 1998. The observational
background for these predictions is the sudden fade of OJ 287
in 1989. Back then, the radio flux decreased steadily for 4-5
months and then the brightness dropped also in the optical
regions suddenly for 2-3 weeks to all time low values, e.g. V=
17.4 mag. The predictions are based on a binary black hole
model, where the companion black hole and its accretion disk
eclipse the emission areas of the primary black hole. We have
made observations of OJ 287 during the time of the predicted
fade. The results show that, in the optical, OJ 287 starts to
fade almost linearly in December 1997 until mid-February 1998,
when it suddenly shows a sharp rise and sharp fade and starts
to get brighter again. The radio observations show no signs of
variability, but the radio flux has been very low since the
1995 outburst. We also have earlier observations since Fall
1993 to Spring 1998, which show that the local minimum reached
in February 1998 was the lowest since 1995. We have made
observations with several telescopes in the optical (UBVRI) and
radio (22 and 37 GHz) bands. We discuss the various events in
the light curves and their implications on the proposed models,
especially the binary black hole model by Lehto & Valtonen
(1996), which was used to make the prediction of the time of
the fade.
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Klein, K.-L., Chupp, E.L., Trottet,
G., Magun, A., Dunphy, P.P., Rieger, E., Urpo, S.:
Flare-associated energetic particles in the corona and at 1 AU
Astronomy and Astrophysics, Vol. 348, pp. 271-285,
1999.
Abstract: It is widely believed that the longest lasting
and most energetic solar energetic particle events (SEPs)
observed in interplanetary space result from acceleration by
the bow shocks of coronal mass ejections (CMEs). Using
gamma-ray, X-ray and radio diagnostics of interacting particles
and spaceborne and ground-based detection of > 20 MeV
protons at 1 AU during two large events (1989 September 29 and
October 19), we demonstrate that time-extended acceleration
processes in the low and middle corona, far behind the CME,
leave their imprints in the proton intensity time profiles in
interplanetary space for one to several hours after the onset
of the flare: (1) New increases of > 20 MeV proton
fluxes at 1 AU can be traced back to episodes of coronal
acceleration. (2) Increasing richness of relativistic protons
observed at 1 AU in the course of the SEPs is associated with
new coronal particle injection after the impulsive phase. (3)
Particle injection sites enabling a rapid access to the
well-connected magnetic field line, as required by the SEP time
profile, exist in the middle corona even if the nominal
Halpha flare location is far away. These findings
suggest that contrary to the prevalent view acceleration
processes in the low and middle corona supply both interacting
and at least part of the interplanetary particles. The
association of the most proton-rich component of the SEPs with
delayed low-frequency radio emission is consistent with
ionization state studies of SEPs, in that both require
acceleration in a tenuous plasma. We conclude that the
complexity of the corona provides the ingredients for the
acceleration of particles and their injection into a large
range of heliocentric angles. The CME may play the role of a
trigger or even contribute to the buildup of magnetic stresses
in the corona, but its bow shock is not the main accelerator of
the high-energy protons.
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Alcaraz J., Alvisi, D., Alpat, B.,
Ambrosi, G., Anderhub, H., Ao, L., Arefiev, A., Azzarello, P.,
Babucci, E., Baldini, L., Basile, M., Barancourt, D., Barao,
F., Barbier, G., Barreira, G., Battiston, R., Becker, R.,
Becker, U., Bellagamba, L., Béné, P., Berdugo, J., Berges, P.,
Bertucci, B., Biland, A., Bizzaglia, S., Blasko, S., Boella,
G., Bourquin, M., Bruni, G., Buenerd, M., Burger, J.D., Burger,
W.J., Cai, X.D., Cavalletti, R., Camps, C., Cannarsa, P.,
Capell, M., Casadei, D., Casaus, J., Castellini, G., Chang,
Y.H., Chen, H.S., Chen, Z.G., Chernoplekov, N.A., Chiarini, A.,
Chiueh, T.H., Chuang, Y.L., Cindolo, F., Commichau, V., Contin,
A., Cotta-Ramusino, A., Crespo, P., Christinziani, M., da
Cunha, J.P., Dai, T.S., Deus, J.D., Ding, L.K., Dinu, N.,
Djambazov, L., D'Antone, I., Dong, Z.R., Emonet, P., Eppling,
F.J., Eronen, T., Esposito, G., Extermann, P., Favier, J.,
Feng, C.C., Fiandrini, E., Finelli, F., Fisher, P.H., Flaminio,
R., Fluegge, G., Fouque, N., Galaktionov, Yu., Gervasi, M.,
Giusti, P., Gu, W.Q., Guzik, T.G., Hangarter, K., Hasan , A.,
Hermel, V., Hofer, H., Huang, M.A., Hungerford, W., Ionica, M.,
Ionica, R., Isbert, J., Jongmanns, M., Karpinski, W., Kenney,
G., Kenny, J., Kim, W., Klimentov, A., Krieger, J.,
Kossakowski, R., Koutsenko, V., Laborie, G., Laitinen, T.,
Lamanna, G., Laurenti, G., Lebedev, A., Lee, S.C., Levi, G.,
Leytchenko, P., Li, T.P., Liu, C.L., Liu, H.T., Lolli, M.,
Lopes, I., Lu, G., Lu, Y.S., Lübelsmeyer, K., Luckey, D.,
Lustermann, W., Maehlum, G., Mana, C., Margotti, A, Massera,
F., Mayet, F., McNeill, R.R., Meillon, B., Menichelli, M.,
Mezzanotte, F., Mezzenga, R., Mihul, A., Molinari, G., Mourao,
A., Mujunen, A., Palmonari, F., Pancaldi, G., Papi, A., Park,
I.H., Pauluzzi, M., Pauss, F., Perrin, E., Pesci, A., Pevsner,
A., Pilastrini, R., Pimenta, M., Plyaskin, V., Pojidaev, V.,
Postema, H., Prati, E., Produit, N., Rancoita, P.G., Rapin, D.,
Raupach, F., Recupero, S., Ren, D., Ren, Z., Ribordy, M.,
Richeux, J.P., Riihonen, E., Ritakari, J., Roeser, U., Roissin,
C., Sagdeev, R., Santos, D., Sartorelli, G., Schultz von
Drazig, A., Schwering, G., Shoutko, V., Shoumilov, E.,
Siedling, R., Son, D., Song, T., Steuer, M., Sun, G.S., Suter,
H., Tang, X.W., Ting, Samuel, C.C., Ting, S.M., Tenbusch, F.,
Torromeo, G., Torsti, J., Trümper, J., Ulbricht, J., Urpo, S.,
Usoskin, I., Valtonen, E., Vandenhirtz, J., Velikhov, E.,
Verlaat, B., Vetlitsky, I., Vezzu, F., Vialle, J.P., Viertel,
G., Vite, D., Von Gunten, H., Waldmeier Wicki, S., Wallraff.,
W., Wang, B.C., Wang, J.Z., Wang, Y.H., Wefel, J.P., Werner,
E.A., Williams, C., Wu, S.X., Xia, P.C., Yan, J.L., Yan, L.G.,
Yang, C.C.,Yang, M., Yeh, P., Zhang, H.Y., Zhao, D.X., Zhu,
G.Y., Zhu, W.Z., Zhuang, H.L., Zichichi, A.:
Search for Antihelium in Cosmic Rays.
Physics Letters B,
http://hpl3tri1.cern.ch/AMS/Publications/ Vol. 461, pp.
387-396, 1999.
Abstract: The Alpha Magnetic Spectrometer (AMS) was
flown on the space shuttle Discovery during flight
ST-91 in a 51.7º orbit at altitudes between 320 and 390
km. A total of 2.86 x 106 helium nuclei were
observed in the rigidity range 1 to 140 GV. No antihelium
nuclei were detected at any rigidity. An upper limit on the
flux ratio of antihelium to helium of < 1.1 x
10-6 is obtained.
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Takalo, L.O., Pursimo, T.,
Sillanpää, A., Hanski, M., Heinämäki, P.,
Katajainen, S., Lainela, M., Nilsson, K., Nurmi, P.,
Pietilä, H., Rekola, R., Riehokainen, A., Valtaoja, E.,
Aller, M., Aller, H., Hughes, P., Cavallone, M., De Francesco,
G., Lanteri, L., Raiteri, C.M., Sobrito, G., Villata, M.,
Efimov, Y, Shakhovskoy, N., Tosti, G., Fiorucci, M.,
Nucciarelli, G., Maesano, M., Massaro, E., Montagni, F., Nesci,
R., D'Alessio, F., Honeycut, R.K., Robertson, J.W., Turner,
G.W., Teräsranta, H., Tornikoski, M., Boltwood, P., Sadun,
A., Poyner, G.:
Radio and optical monitoring of 3C 66A during an extended
outburst. II. 1995-1997.
1999 BLAZAR Data Vol. 1, n. 6, 61 p., 1999.
Abstract: We present new monitoring observations of the
BL Lac object 3C66A, taken between the years 1995-1997. During
this period the object was always observed in an outburst
phase, which started in 1993. Only towards the end of this
observing period the brightness level started to decrease,
suggesting that the outburst is probably over. Characteristic
to the optical light curves are frequent large flares and small
amplitude flickering. The radio data show less violent
variations, with indications of a small amplitude outburst.
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Lähteenmäki, A., Valtaoja,
E.:
Total flux density variations in extragalactic radio sources.
III. Doppler boosting factors, Lorenz factors and viewing
angles for active galactic nuclei.
Astrophysical Journal, Vol. 521, pp. 493-501, 1999.
Abstract: We have calculated Doppler boosting factors
Dvar, for a sample of active galactic nuclei (AGNs)
using total flux density variation monitoring data at 22 and 37
GHz. We argue that this method is more accurate than the other
commonly used methods based on the synchrotron self-Compton
X-ray flux or equipartition of energy. We compare our Doppler
factors with other results and conclude that even if the
average Dvar for a class of sources is very similar
to all others, the variability Doppler factors for individual
objects are more accurate and reliable. An important
application of precise Doppler factors is presented, namely,
calculating the Lorenz factors, gamma, and the viewing angles ,
of relativistic outflows in AGNs. We find that
high-polarization quasars have the greatest Doppler boosting,
while low- polarization quasars and BL Lac objects are less
boosted. The two groups of quasars show different
characteristics because of different combinations of the
Lorentz factor and viewing angle, rather than either a
different gamma or alone.
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Lähteenmäki, A., Valtaoja,
E.:
Optical polarization and imaging of hot spots in radio
galaxies.
Astronomical Journal, Vol. 117, pp. 1168-1174, 1999.
Abstract: We present subarcsecond optical imaging and
polarization observations of five optical hot spot candidates
in the classical double radio sources 3C 111, 3C 303, 3C 351,
3C 390.3, and PKS 2135-147. On the basis of positional
coincidence, optical appearance, and polarization, all four 3C
sources appear to have genuine optical counterparts to radio
hot spots, whereas in PKS 2135-147 the hot spot candidate turns
out to be an unrelated field galaxy. We also confirm the first
ever optical double hot spot in the source 3C 351.
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Alcaraz J., Alvisi, D., Alpat, B.,
Ambrosi, G., Anderhub, H., Ao, L., Arefiev, A., Azzarello, P.,
Babucci, E., Baldini, L., Basile, M., Barancourt, D., Barao,
F., Barbier, G., Barreira, G., Battiston, R., Becker, R.,
Becker, U., Bellagamba, L., Béné, P., Berdugo, J., Berges, P.,
Bertucci, B., Biland, A., Bizzaglia, S., Blasko, S., Boella,
G., Boschini, M., Bourquin, M., Bruni, G., Buenerd, M., Burger,
J.D., Burger, W.J., Cai, X.D., Cavalletti, R., Camps, C.,
Cannarsa, P., Capell, M., Casadei, D., Casaus, J., Castellini,
G., Chang, Y.H., Chen, H.S., Chen, Z.G., Chernoplekov, N.A.,
Chiarini, A., Chiueh, T.H., Chuang, Y.L., Cindolo, F.,
Commichau, V., Contin, A., Cotta-Ramusino, A., Crespo, P.,
Christinziani, M., da Cunha, J.P., Dai, T.S., Deus, J.D., Dinu,
N., Djambazov, L., D'Antone, I., Dong, Z.R., Emonet, P.,
Engelberg, J., Eppling, F.J., Eronen, T., Esposito, G.,
Extermann, P., Favier, J., Feng, C.C., Fiandrini, E., Finelli,
F., Fisher, P.H., Flaminio, R., Fluegge, G., Fouque, N.,
Galaktionov, Yu., Gervasi, M., Giusti, P., Grandi, D., Gu,
W.Q., Hangarter, K., Hasan , A., Hermel, V., Hofer, H., Huang,
M.A., Hungerford, W., Ionica, M., Ionica, R., Jongmanns, M.,
Karlamaa, K., Karpinski, W., Kenney, G., Kenny, J., Kim, W.,
Klimentov, A., Krieger, J., Kossakowski, R., Koutsenko, V.,
Laborie, G., Laitinen, T., Lamanna, G., Liu, H.T., Lolli, M.,
Lopes, I., Lu, G., Lu, Y.S., Lübelsmeyer, K., Luckey, D.,
Lustermann, W., Mana, C., Margotti, A, Massera, F., Mayet, F.,
McNeill, R.R., Meillon, B., Menichelli, M., Mezzanotte, F.,
Mezzenga, R., Mihul, A., Molinari, G., Mourao, A., Mujunen, A.,
Palmonari, F., Pancaldi, G., Papi, A., Park, I.H., Pauluzzi,
M., Pauss, F., Perrin, E., Pesci, A., Pevsner, A., Pilastrini,
R., Pimenta, M., Plyaskin, V., Pojidaev, V., Postema, H.,
Postolache, V., Prati, E., Produit, N., Rancoita, P.G., Rapin,
D., Raupach, F., Recupero, S., Ren, D., Ren, Z., Ribordy, M.,
Richeux, J.P., Riihonen, E., Ritakari, J., Roeser, U., Roissin,
C., Sagdeev, R., Santos, D., Sartorelli, G., Schultz von
Drazig, A., Schwering, G., Seo, E.S., Shoutko, V., Shoumilov,
E., Siedling, R., Son, D., Song, T., Steuer, M., Sun, G.S.,
Suter, H., Tang, X.W., Ting, Samuel, C.C., Ting, S.M.,
Tornikoski, M., Torromeo, G., Torsti, J., Trümper, J.,
Ulbricht, J., Urpo, S., Usoskin, I., Valtonen, E., Vandenhirtz,
J.,Velcea, F., Velikhov, E., Verlaat, B., Vetlitsky, I., Vezzu,
F., Vialle, J.P., Viertel, G., Vite, D., Von Gunten, H.,
Waldmeier Wicki, S., Wallraff., W., Wang, B.C., Wang, J.Z.,
Wang, Y.H., Wiik, K., Wefel, J.P., Werner, E.A., Williams, C.,
Wu, S.X., Xia, P.C., Yan, J.L., Yan, L.G., Yang, C.C., Yang,
M., Ye, S.W., Yeh, P., Xu, Z.Z., Zhang, H.Y., Zhang, Z.P.,
Zhao, D.X., Zhu, G.Y., Zhu, W.Z., Zhuang, H.L., Zichichi,
A.:
Protons in Near Earth Orbit.
Physics Letters B,
http://hpl3tri1.cern.ch/AMS/Publications/ Vol. 472, pp 215-226,
1999.
Abstract: The proton spectrum in the kinetic energy
range 0.1 to 200 GeV was measured by the Alpha Magnetic
Spectrometer (AMS) during space shuttle flight STS-91 at an
altitude of 380 km. Above the geomagnetic cutoff the observed
spectrum is parameterized by a power law. Below the geomagnetic
cutoff a substantial second spectrum was observed concentrated
at equatorial latitudes with a flux ~ 70
m-2sec-1sr-1. Most of these
second spectrum protons follow a complicated trajectory and
originate from a restricted geographic region.
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Tornikoski, M., Tingay, S.J.,
Mücke, A., Chen, A., Connaughton, V., Jauncey, D.L.,
Johnston-Hollitt, M., Kemp, J., King, E.A., McGee, P.,
Rantakyrö, F., Rayner, D., Reimer, O., Tzioumis, A.K.:
Multiwavelength observations of PKS 2255-282.
Astronomical Journal, Vol. 118, pp. 1161-1168, 1999.
Abstract: During high radio frequency active galactic
nucleus monitoring, we observed a major millimeter wave
outburst from PKS 2255-282 in 1997 and initiated a campaign for
multifrequency radio monitoring and VLBI imaging of the source.
In 1998 January the EGRET instrument on board the Compton
Gamma Ray Observatory detected a bright high-energy
gamma-ray outburst from its direction. Thus we had the unique
opportunity to monitor the source in detail at various radio
frequencies already before the detection of the gamma-ray
outburst. We also initiated multiwavelength follow-up
observations. In this paper we present multiwavelength data for
PKS 2255-282 before and after the gamma-ray outburst. Further,
based on the observations, we estimate some physical parameters
for this source and discuss the various emission mechanisms
possibly involved during this outburst.
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NESTEROV N S, LYUTY V M, VALTAOJA E: Radio
and optical evolution of the Seyfert galaxy NGC 1275; Astronomy
and Astrophysics, Vol 296, pp 628-632, 1995. Abstract: The
results of extensive observations of the Seyfert galaxy NGC
1275 carried out at the radio frequencies 22 GHz, 37 GHz and 87
GHz, and in the optical V band are presented. Two types of
variations in the continuum emission of the galaxy nucleus are
found. Fast outbursts occur at radio frequencies 5-6 years
after the corresponding optical events. These outbursts are
identified with shocks forming in the radio jet. They also
correspond to ejections of new VLBI components from the core.
The second type of variation is caused by a slowly changing
component having a time delay of ( 8 years between radio and
optical domains. We propose that this variation results from a
period of enhanced accretion rate in the nucleus, beginning in
the 1950s and ending around 1980, and leading to the growth and
subsequent decay of the radio emitting jet. Linear
extrapolation of the expansion speeds of these two types of
components indicates that the true galaxy nucleus is located at
a distance of a few parsecs from the radio core (the beginning
of the visible jet). This estimate would place the nucleus
halfway between the 'radio core' and the recently discovered
'counterjet'.
|
MUKHERJEE R, ALLER H D, ALLER M F, BERTSCH D L,
COLLMAR W, DIGEL S W, DINGUS B L, ESPOSITO J A, FICHTEL C E,
HARTMAN R C, HUNTER S D, JOHNSON W N, KANBACH G, KNIFFEN D A,
LIN Y C, MATTOX J R, MAYER-HASSELWANDER H A, MICHELSON P F, VON
MONTIGNY C, NOLAN P L, RAMANAMURTHY P V, SCHNEID E, SREEKUMAR
P, TERÄSRANTA H, THOMPSON D J, WAGNER S J: EGRET gamma-ray
sources: GRO J0744+54 and GRO J0957+65 (=BL Lac Object
0954+658); Astrophysical Journal, Vol 445, pp 189-195, 1995.
Abstract: EGRET detected an unidentified source, GRO J0744+54,
at a significance of 6,5 (, during its observations from 1993
June 28 to July 12. The source was seen again in the following
2 week viewing period and was weakly evident in the earlier
phase 1 of the EGRET observations. Considering the variability
of its gamma-ray flux and its location at high Galactic
latitude, GRO J0744+54 is likely to be a previously undetected
blazar. Its most likely identification is with the radio source
87GB 073840.5+545138. A second source GROJ0957+65, was seen by
EGRET during the same two viewing periods at a combined
significance of 5.7 (. The most probable counterpart of GRO
J0957+65 is the BL Lacertae object 0954+658. The spectra, time
variability, and positions of the two sources are presented.
Multiwavelength observations of 0954+658 are also
presented.
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GRANDI P, MARASCHI L, URRY C M, WEHRLE A E,
ALLER M F, ALLER H D, BALONEK T J, JASON J, McHARDY I M,
HARTMAN R C, PIAN, E, STEVENS J A, SADUN A C, TERÄSRANTA
H, TREVES A: Long term variability of 3C279; Advances in Space
Research, Vol 15, No 5, pp 23-26, 1995. Abstract: Radio, mm,
optical, UV and X-ray light curves of 3C 279 as well as the
(-ray light curve available since 1991 June are considered.
Strong flux correlations are found between the X-ray and the
radio-optical region. Variations at 100 MeV are well correlated
to the optical and X-ray bands. The variability amplitude, as
measured by an average logarithmic dispersion of the available
measurements is small in the radio and increases systematically
with increasing frequency up to the (-ray band, with the
possible exception of the X-ray amplitude.
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VALTAOJA E, TERÄSRANTA H: Gamma
radiation from radio schocks in AGN jets; Astronomy and
Astrophysics, Vol 297, pp L13-L16, 1995. Abstract: We compare
the Phase 1 gamma-ray detections and nondetections of active
galactic nuclei by the EGRET instrument of Compton Gamma Ray
Observatory with Metsähovi 22 GHz and 37 GHz radio flux
curves. We find a good correlation between the type of the
source, the radio state of the source, and the gamma-ray
emission. With few exceptions, gamma-rays are detected when,
and only when, a quasar with high optical polarization is in
the initial phases of a high radio frequency outburst. Other
types of sources - low polarization quasars, BL Lac objects,
radio galaxies - are rarely detected in gamma-rays, even when
in a similar state of radio activity. Our results limit viable
gamma-ray production mechanisms to those involving strongly
beamed gamma-rays from radio-emitting shocks in jets oriented
close to our line of sight.
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LAGERQVIST C-I, ERIKSON A, DEBEHOGNE H,
FESTIN L, MAGNUSSON P, MOTTOLA S, OJA T, DeANGELIS G, BELSKAYA
I N, DAHLGREN M, GONANO-BEURER M, LAGERROS J, LUMME K,
POHJOLAINEN S: Physical studies of asteroids. XXIX. Photometry
and analysis of 27 asteroids; Astronomy and Astrophysics
Supplement Series, Vol 113, No 1, pp 115-129,1995. Abstract:
The asteroid 153 Hilda was studied by photometric,
spectroscopic and polarimetric observations during the
apparition in 1992. The rotation period was determined to 5.11
hours with a lightcurve amplitude of 0.05 magnitudes. From our
spectrum we find 153 Hilda to be of taxonomic type P. The
polarization value of -0.23 at a phase angle of 3.2 degrees
seems normal for a P-type asteroid. Long term integrations of
the orbit shows that it is stable over time intervals of
several million years.
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STEVENS J.A., LITCHFIELD S J, ROBSON E I, GEAR
W K, TERÄSRANTA H, TORNIKOSKI M, VALTAOJA E: The spectral
evolution of high frequency radio outbursts in the blazar PKS
0420-014; Monthly Notices of the Royal Astronomical Society,
Vol 275, pp 1146-1154, 1995. Abstract: Multifrequency
monitoring data between 375 and 22 GHz are used to investigate
the spectral evolution of radio outbursts in the blazar
0420-014. It is shown that, after subtraction of the underlying
'quiescent' emission, the flare spectrum can be described by a
simple homogeneous self-absorbed synchrotron component. The
evolution of this spectrum is found to be qualitatively
consistent with the shock model of Marscher & Gear, although
not totally so in detail. Some of the discrepancies can
possibly be resolved if the proposed relativistic jet, which is
initially oriented close to the line-of-sight, bends away. The
optically thin spectrum of the flare emission, however, is
found to be flatter than allowed by the model. Strong
correlations are found between the 90-22 GHz twopoint spectral
index and the logarithm of the 90-GHz flux. These trends are
reconciled with the evolution of the synchrotron spectrum
during the flares.
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PIAN E, EDELSON R A, WAGNER S J, BREGMAN J,
GEORGE I, TREVES A, WAMSTEKER W, BOCK H, CARINI M, COURVOISIER
T, DONAHUE M, EFIMOV Y, FILIPPENKO A, FINK H, HEIDT J, LAWRENCE
A, MARSCHI L, MILLER H R, PIKE G, QUIRRENBACH A, SHAKHOVSKOY N,
SILLANPÄÄ A, SITKO M, SMITH P, TAKALO L,
TERÄSRANTA H, VALTAOJA E, WARD M, WARWICK R: Simultaneous
UV, optical and radio monitoring of the BL LAC object OJ 287 in
March 1993; 30th COSPAR meeting, Hamburg, July 11-21, 1994,
Advances in Space Research, Vol 16, No 3, pp (3)57-(3)60, 1995.
Abstract: The BL Lacertae object OJ 287 was intensively
monitored with the IUE satellite from 1993 March 15 to 20 in
the 2000-3000 wavelength region. The very low emission state
of the source hampered the detection during part of the 23
performed exposures. The light curve at 2650 constructed with
the 11 best images exhibits a variable trend with a factor ( 2
enhancement of the flux in about 3 hours. Simultaneous ground
based observations show an optical flux variability of smaller
amplitude, but correlated with the UV light curve without any
apparent lag. The radio light curve is nearly constant. The UV
emission state is the weakest observed in 15 years for this
flaring blazar, being a factor of ( 20 lower than the maximum
recorded one.
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LEPPÄNEN K J, ZENSUS J A, DIAMOND
P J: Linear Polarization Imaging with Very Long Baseline
Interferometry at High Frequencies; Astronomical Journal, Vol
110, No 5, pp 2479-2492, 1995. Abstract: We describe a new
method to self-calibrate the instrumental polarization
characteristics in polarimetric very long baseline
interferometry (VLBI) observations. The method is especially
useful at high frequencies where no suitable calibrator sources
with known polarization properties are available. In a test
experiment with the Very Long Baseline Array (VLBA), the feed
polarization parameters (D-factors) were calibrated to within
0.2 % RMS using a compact continuum source. This made possible
measuring the fractional polarization with a maximum accuracy
of 0.15 %. Higher calibration accuracy could be obtained with
H20-maser sources. We demonstrate that the electric vector
orientation can be calibrated internally with the VLBA at 22
GHz. Therefore, VLBP observations without calibrator sources
are possible at this frequency. We applied the method to VLBA
observations of three active galactic nuclei (AGN) and imaged
the linear polarization structure of AGN for the first time at
22 GHz. In 3C 345 and 3C 279 the inferred magnetic field is
predominantly perpendicular in the jet. In 3C 273 the magnetic
field is approximately longitudinal within 2 milliarcsecond of
the core; at larger distances the field is random. The core
polarization is low in all three quasars (<3 %), whereas the
jet components are up to 30 % polarized. The polarization
properties of 3C 345 and 3C 279 are largely consistent with a
general model based on strong plane-perpendicular shocks in the
jet plasma; the properties of 3C 273 cannot be easily explained
by simple shock models.
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TOTH L V, HAIKALA L, LILJESTRÖM T,
MATTILA K: L1780: a cometary globule associated with Loop I;
Astronomy and Astrophysics, Vol 295, pp 755-766, 1995.
Abstract: 12CO, 13CO and C18O J = 1 ( 0 observations of the
L1778/L 1780 high latitude (b = 36(.7) dark cloud have been
carried out using the Gornergrat 3m and SEST 15m telescopes.
The observations revealed a cometary cloud structure: a dense
core asymmetrically surrounded by a diffuse outer layer. The
mass of the cloud calculated from the CO observations is 21.6
M(. The compact 13CO core has a mass of 8.3M( and is found to
be in virial equilibrium. The CO data have been compared to
previous optical, H I, and IRS observations. We suggest that
the structure and the morphology of L 1780 have been influenced
by two large scale environmental effects: (1) the asymmetric
interstellar UV radiation field and (2) a shock front, both
caused by the high mass stars of the Sco - Cen OB
association.
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TORNIKOSKI M, VALTAOJA E, TERÄSRANTA H,
KARLAMAA K, LAINELA M, NILSSON K, KOTILAINEN J, LAINE S,
LÄHTEENMÄKI A, KNEE L B G, BOTTI L C L: SEST
Observations of extragalactic radio sources at 3 mm and 1.3 mm;
Astronomy and Astrophysics Supplement Series, Vol 116, pp
157-165, 1996. Abstract: Flux densities of 155 extragalactic
radio sources observed with the SEST telescope at 3 mm and 1.3
mm are presented. The observations were performed from October
1987 to June 1994. In addition to the flux density tables we
have plotted the flux density curves for some of the most
frequently observed sources.
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GRANDI P, URRY C M, MARASCHI L, WEHRLE A E,
MADEJSKI G M, ALLER M F, ALLER H D, BAILYN C D, BALONEK T J,
BOCK T H, GLASS I S, McHARDY I M, MULCHAYE J S, LITCHFIELD S J,
REUTER H P, SADUN A C, SHERRY W, STEPPE H, STEVENS J A,
TERÄSRANTA H, TORNIKOSKI, M, WAGNER S J: 3C 279
multiwavelength monitoring: II. Ground-based campaign; The
Astrophysical Journal, Vol 459, pp. 73-81, 1996. Abstract: The
optical violently variable quasar 3C 279 was monitored
simultaneously from radio to g-ray frequencies in 1992 December
- 1993 January. We report a detailed study of the ground-based
resluts from radio to optical wavelengths. These data show that
3C 279 has a typical blazar spectrum, slightly rising at radio
frequency and then progressively steeper above a first turnover
frequency between 37 and 90 GHz. In the millimeter wavelength
region, a simple power law is not an adquate description of the
spectrum. We suggest that the millimeter "shoulder" corresponds
to an additional emission component, self-absorbed between 150
and 375 GHz, possibly associated with the detachment of a new
VLBI knot and with the start of radio flare. A flux increase of
20 % over 20 days was observed at 37 and 90 GHz, while
conteporaneously the R-band flux doubled in about two weeks.
The lack of strong variability in contemporaneous X-ray light
curves (possible X-ray variations are less than 30 %) implies
no direct (i.e., zero lag) correlations between the optical and
X-ray fluxes. If X-rays are produced by inverse-Compton
scattering of relativistic electrons on some seed photons, the
above results exclude that the optical band are responsible for
the scattering to X-ray energies. We suggest that the X-rays
are instead produced through the inverse-Compton process by
electrons of lower energy, which radiate via synchrotron in the
radio millimeter wave bands and which scatter either on the
synchrotron photons themselves or on external photons.
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BRAJSA R, POHJOLAINEN S, RUZDJAK V, SAKURAI T,
URPO S, VRSNAK B, WÖHL H: Helium 10830 measurements of
the Sun; Solar Physics, Vol 163, pp 79-91, 1996. Abstract:
Measurements of theSun in the near-infrared He I 10830
absorption line were performed using the echelle spectrograph
with a dispersion of 6.71 m per pixel at the Vacuum Tower
Telescope (German Solar Telescopes, Teide Observatory, Izana,
Tenerife, Spain) on May 26, 1993. These measurements were
compared with full-disc soft X-ray images of the Sun (Japanese
solar satellite Yohkoh), full-disc solar images in Ha (Big Bear
Solar Observatory), full-disc solar images in the He I 10830
line (National Solar Observatory, Kitt Peak) and with full-disc
microwave solar maps at 37 GHz (MetsÄhovi Radio Research
Station). In the He 10830 line the Sun displays a
limbdarkening similar to that in the visible part of the
spectrum. Active regions and Ha filaments show a strong
absorption in the He 10830 line, whereas the absorption is
weak in coronal holes.
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POHJOLAINEN S, URPO S, HERRMANN R: A
multi-wavelength study of a series of solar flares on June 11,
1991; 30th COSPAR Scientific Assembly, Hamburg, Germany, July
11-21, 1994, Advances in Space Research, Vol 17, No 4/5, pp
139-142, 1996. Abstract: On June 11, 1991, at 8:00-9:30 UT,
several flares were observed in the active region 6659
(N38W24). We have studied the time development,
fine-structures, spectral features, polarization , and
correlation between different wavelengths of each of these
events. The data used in the analysis are Metsähovi and
Bern microwave data, GOES7 soft X-ray data, and other
wavelength information from the Solar Geophysical Data.
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ESKELINEN P, ENGELBERG J: Tests on a 3 GHz
ground plane yagi; IEEE Aerospace and Electronic Systems
Magazine, Vol 11, No 2, pp 37-40, 1996. Abstract: Classical
dimensioning of a ground plane yagi antenna for 3 GHz leads to
a gain which is 2-3 dB less than predicted, but this can be
overcome to some extent by additional directors. The impedance
matching strongly depends on the size of the reflector, which
should be by a factor of 1.2 longer than given by classical
theory. The shape and size of the ground plane itself can be
varied considerably with little or no effect on either the
radiation pattern or the impedance characteristics but, on the
other hand, inaccurate mutual positioning of the individual
elements has a drastic influence. Material conductivity is not
of prime concern.
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HARTMAN RC, WEBB J R, MARSCHER A P, TRAVIS J P,
DERMER C D, ALLER M F, ALLER H D, BALONEK T J, BENNETT K, BLOOM
S D, FUJIMOTO R, HERMSEN W, HUGHES P, KII T, KURFESS J D,
MAKINO F, MATTOX J R, VON MONTIGNY C, OHASHI T, ROBSON I, RYAN
J, SADUN A, SCHÖNFELDER V, SMITH A G, TERÄSRANTA H,
TORNIKOSKI M, TURNER M J L: Simultaneous multiwavelength
spectrum and variability of 3C 279 from 109 to 1024 Hz;
Astrophysical Journal, Vol 461, pp 698-712, 1996. Abstract:
Data from a number of monitoring programs have been combined
with data from the Compton Gamma Ray Observatory and the Ginga
X-ray satellite to construct a spectrum covering nearly 15
decades in frequency during or near the time of the 3 C 279
g-ray flare observed by EGRET in 1991 June. A much less
complete spectrum is presented for 1991 October. Light curves
from early 1991 to mid-1992 are presented for radio,
millimeter, submillimeter, infrared, optical and g-rays.
Although the temporal coverage is incomplete, the only evidence
for correlation in variability between the g-rays and lower
frequencies is a flare in the optical R-band that peaks within
~ 1 day of the maximum in the g-ray light curve. The
variability shows higher relative amplitude in g-rays than in
the R band. We present spectral fits to the overall multi-wave
band spectrum averaged over the 1991 June flare corresponding
to two models: (i) synchrotron self-Compton (SSC) emission from
a relativistic jet and (ii) inverse Compton scattering of seed
photons originating external to the jet (ECS) by the
synchrotron-emitting relativistic electrons in the jet. Either
model can fit the observed spectra satisfactorily. The higher
amplitude of the g-ray variations is as predicted by the SSC
model and can be accomodated within the ECS model of the flare
is caused by a temporary change in the bulk Lorentz factor of
the g-ray emitting plasma.
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POHJOLAINEN S, VALTAOJA E, URPO S: Solar microwave
burst classification and correlation with soft X-rays;
Astronomy and Astrophysics, Vol 306, pp. 973-980, 1996.
Abstract: A large sample of microwave bursts observed at the
Metsähovi Radio Research Station during 1989-1992 was
analysed and the corresponding active regions were classified.
The burst-producing active regions could be divided into three
types according to their burst features. The bursts recorded at
37 GHz (8 mm wavelength) were also compared with the GOES soft
X-ray data. The gradual rise and fall type burst fluxes showed
almost linear correlation with soft X-ray fluxes, but no common
denominator could be found for those radio bursts that lacked a
counterpart at soft X-rays. Most of the impulsive microwave
bursts were found to start and peak just before the soft X-ray
maximum, while many of the gradual bursts started soon after
the X-ray onset and peaked after the X-ray maximum. The X-ray
flux rise before microwave onset was found to correlate with
the maximum X-ray flux, in both impulsive and gradual burst
events, the correlation coefficient depending on the soft X-ray
flux.
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ÖSTENSEN R, REFSDAL S, STABELL R,
TEUBER J, EMANUELSEN P I, FESTIN L, FLORENTIN-NIELSEN R, GAHM
G, GULLBRING E, GRUNDAHL F, HJORTH J, JABLONSKI M, JAUNSEN A O,
KAAS A A, KARTTUNEN H, KOTILAINEN J, LAURIKAINEN E, LINDGREN H,
MÄHÖNEN P, NILSSON K, OLOFSSON G, OLSEN Ö,
PETTERSEN B R, PIIROLA V, SÖRENSEN A N, TAKALO L, THOMSEN
B, VALTAOJA E, VESTERGAAR M, av VIANBORG T: Monitoring of the
Einstein cross with the Nordic Optical Telescope; Astronomy and
Astrophysics, Vol 309, pp 59-64, 1996. Abstract: We report
results from five years of monitoring of the Einstein Cross
(QSO 2237+00305) with the Nordic Optical Telescope. The
photometry, mainly in the R and I bands, has been performed by
a PSF fitting and 'cleaning' procedure, in which the four image
components as well as the host galaxy and its nucleus are
iteratively removed. The resulting lightcurves exhibit several
microlensing features; one event may have a timescale as short
as 14 days. Variations on timescales of several years are found
in all four images. This becomes even mores convincingwhen our
data are combined with data published for 1986-89. No clear
high amplification event was observed during the period. A
brightening of all four components during 1994 is interpreted
as intrisic variation.
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MUKHERJEE R, DINGUS B L, GEAR W K, HARTMAN R C,
HUNTER S D, MARSCHER A P, MOORE E M, ROBSON E I, SREEKUMAR P,
STEVENS J A, TERÄSRANTA H, TORNIKOSKI M, WAGNER S J, ZHANG
Y F: EGRET observations of the 1993 March gamma-ray flare from
PKS 0528+134; Astrophysical Journal, Vol 470, pp 831-838, 1996.
Abstract: EGRET observation of PKS 0528+134 during the 1993
March flare in gamma-rays is presented here. During the flare
gamma-rays were detected at a level approximately three times
greater than the observed intensity in earlier observations.
Spectra of the source during the flare, as well as during the
nonflaring state are presented. The flux history of PKS
0528+134 as observed from the start of the Compton Gamma Ray
Observatory (CGRO) mission up to the end of Phase 3 (1993
October) is given. Multiwavelength observations of PKS 0528+134
during the flare are also presented. A detailed relativistic
SSC jet model agrees well with the 1993 March Multiwavelength
spectrum; the data, however, are insufficient to discriminate
between this and other emission models.
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POHJOLAINEN S, VALTAOJA E, URPO S: Solar
microwave burst emission relation to X-ray radiation; Astronomy
and Astrophysics, Vol 314, pp 947-956, 1996. Abstract: We have
calculated the thermal bremsstrahlung component for 87
microwave burst observed at a near-millimeter wavelength (37
GHz), using a well-known procedure for computing the plasma
temperature and emission measure from the GOES soft X-ray data.
The calculated values showed good correlation with the observed
fluxes in gradual rise and fall-type bursts. In the majority of
impulsive type bursts a bremsstrahlung component was found to
be present, often as a post-burst increase. Some bursts without
a thermal component were found and they could be connected with
higher energy electrons producing hard X-ray radiation and
gyrosynchrotron emission at microwaves. Those microwave bursts
that were recorded at hard X-rays during CGRO-BATS observing
times are discussed in more detail.
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TAKALO L O, SILLANPÄÄ A, PURSIMO T,
LEHTO H J, NILSSON K, TEERIKORPI P, HEINÄMÄKI P,
LAINELA M, KIDGER M, DE DIEGO J A, GONZçLEZ-PÄREZ,
RODRÊGUEZ-ESPINOSA J-M, MAHONEY T, BOLTWOOD P, DULTZIN-HACYAN
D, BENÕTEZ E, TURNER G W, ROBERTSON J W, HONEYCUT R K, EFIMOV
YU S, SHAKHOSKOY N, CHARLES P A, SCHRAMM K J, BORGEEST U, LINDE
J V, WENEIT W, KÖHL D, SCHRAMM T, SADUN A, GRASHUIS R,
HEIDT J, WAGNER S, BOCK H., KMMEL M, PFEIFFER M, HEINES A,
FIORUCCI M, TOSTI G, GHISELLINI G, RAITERI C M, VILLATA M, DE
FRANCESCO G, BOSIO S, LATINI G, POYNER G, ALLER M F, ALLER H D,
HUGHES P, VALTAOJA E, TERÄSRANTA H, TORNIKOSKI M:
"Monitoring of 3C 66A during an extended outburst. I The light
curves; Astronomy and Astrophysics Supplement Series, Vol 120,
pp 313-321, 1996. Abstract: We present results from a two year
intensive monitoring of BL Lac object 3C 66A (PKS 0219+428).
This object was observed in outburst during these two years. It
reached the brightest ever observed magnitude on V=13.59
(1.2.1995) and on K=10.59 (15.2.1994). The optical and infrared
light curves are characterised by randomly distributed fast
flares, lasting a few days and well defined outbursts lasting a
week or two. On top of these flares we can occasionally se
small amplitude microvariability. No clear correlation can be
found between the spectral behaviour and the occurrence of
these flares. In the radio bands 3C 66A was quite faint and
very stable compared to the optical variations. The light
curves will be presented with preliminary analysis and
discussions on the possible causes for the observed
variations.
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VALTAOJA E, TERÄSRANTA H: The relationsship
between gamma emission and radio flares in AGN; Astronomy and
Astrophysics Supplement Series, Vol 120, pp 491-494, 1996.
Abstract: A comparison between Phase 1 EGRET data and
Metsähovi total flux density monitoring at 22 GHz and 37
GHz shows that gamma-rays are likely to be detected only in
quasars with high optical polarization, and even them only
during the initial stages of a high radio frequency outburst.
Other types of sources, including BL Lacs, are rarely detected.
There also appears to be a correlation between the radio flare
strength, rapidity, and the detected gamma-ray flux. Taken
together, these results indicate that gamma-rays are produced
by the synchrotron self-Compton mechanism in the shocked
regions of the jet, with both the relativistic electrons and
the seed photons originating in the same shock far away from
the core and the accretion disk.
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BRAJSA B, RUZDJAK V, VRSNAK B, WÖHL H,
POHJOLAINEN S, URPO S: A new method for numerical data
reduction of solar microwave measurements; Hvar Observatory
Bulletin, Vol 20, pp 15-40, 1996. Abstract: Numerical data
reduction of full-disk solar measurements taken in the
microwave part of the spectrum (37 GHz) at the Metsähovi
Radio Research Station is described. The basic parameteer
distinguishing between various features on the microwave solar
maps is the brightness temperature. Regions on the Sun with a
lower brightness temperature than the quiet Sun level are
called Low Temperature Regions (LTRs), and in the present paper
mainly LTRs are considered. On the other hand, High Temperature
Regions (HTRs) have a brightness temperature higher than the
quiet Sun level. The data reduction includes: to obtain a
circular solar picture, to construct twelve radial vectors from
the preliminary solar disk center in order to determine the
coordinates of the solar limb, to remove "erroneous" limb
points, to determine a circle through the limb points by the
least-squares method, to obtain corrected coordinates of the
solar disk center and the radius and to repeat the procedures
using the obtained results as input parameters. The quiet Sun
level was determined as the mean value of all data points on
the disk for every map separately. Several numerical criteria
were tested, and the minima of relative intensities for all
data points were determined. taking these minima as centers,
circles of different radii were drawn with the criterion that
the mean value inside the circle is less than the quiet Sun
level. The latitudinal distribution of LTRs, as well as the
solar rotation rate is determined by the LTRs, were
investigated using automatic numerical procedures. It was
established how the parameters which describe the solar
rotation rate and corresponding errors depend upon various
numerical criteria including: definition of LTR's size,
allowing different deviations of LTR's position and rotation
rate, confining the set of obtained rotation rates according to
each error of the rotation rate and confining the set of
obtained rotation rates according to allowance of a specific
rotation rate at a specific latitude.
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LILJESTRÖM T, OLOFSSON G: Evidence for
infall toward Z Canis Majoris from radio and near-infrared
spectroscopy;Astrophysical Journal, Vol 478, pp 1997.Abstract:
We report radio line observations of CO(1-0), 13CO(1-0),
CS(5-4), CS(2-1), C34S(2-1), H13CO+(1-0), HCS+(2-1), and
N2H+(1-0) and near-infrared spectroscopy (in the K, L, and M
bands) of Z CMa and its surroundings. Our results show that the
CS(2-1) cloud around Z CMa is in approximate virial equilibrium
and has a mass of some 42 M. The CS(5-4), C34S(2-1), and
H13CO+(1-0) data reveal a centrally condensed and flattened
inner cloud core structure perpendicular to the CO(1-0)
outflow, which has a dynamical timescale of some
(2*10^3)-(1*10^4) yr. The mass of the CS(5-4) core is 8.0-15 M,
which is close to the magnetic critical mass. Along the major
axis of the CS(5-4) core there is a velocity gradient, which
can be interpreted as a superposition of initial cloud rotation
and infall. Evidence for an infalling inner cloud core with a
temperature gradient, an r^-1.5 density law, and an r^-0.5
velocity law is provided by the redshgift self-absorption
feature in the H13CO+ profile, present in a very compact region
oriented perpendicularly to the CO(1-0) outflow of Z CMa.
Motivated by these signs of infall in the inner cluod core, we
probe with our observational data the inside-out collapse model
of Shu and the predictions of Galli & Shu for the collapse of a
magnetized cloud core.
Our medium-resolution K-band spectrum shows besides the
redshift, very marginal Brgamma line four vibrationally excited
first-overtone CO band heads in absorption. The slopes seen in
the K-band spectrum are intrinsic to the FU Orionis-type disk
of Z CMa and suggest the presence of the vibration-rotation
bands of water vapor, implying a temperature around 2000 K and
a hydrogen nuclei density on the order of 10^12 cm^-3 at 2.2
micrometre. The likely cause of these water-band wings is the
strong heating produced by the mass accretion through the inner
disk onto the star. Our L band does not show the 3.08
micrometre water ice feature. Instead, our spectrum suggests
the presence of a 2.9 micrometre feature, probably due to
stretching vibrations of OH, or a shift of the water ice band
to 2.9 micrometre, caused by large grains when scattering
dominates. |
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