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ON LONG-TERM CYG X-1=V1357 CYG VARIABILITY
E.A. Karitskaya, N. G. Bochkarev , V. P. Goranskij and N. V. Metlova Astronomical Institute of RAS, Russia Sternberg Astronomical Institute of Lomonosov Moscow State University , Russia
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Abstract We continue our study of spectral and photometric variability of Cyg X-1 on the base of the 12-year-long series of precision spectral observations and 40-year long series of multicolor photometric observations we have accumulated up to now. In 2006, we revealed for the first time that the temperature of the optical component (О9.7Iab supergiant) was decreasing and its size was increasing over 7 years (1997–2003). Photometry performed at the Crimean Station of the Sternberg Astronomical Institute (Lomonosov Moscow State University) shows that the supergiant’s variability on the time scale of decades continues up to now.
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Cyg X-1 = V1357 Cyg = HDE Cyg X-1 = V1357 Cyg = HDE is an X-ray binary system (with the orbital period P = 5:6 d) whose relativistic component is historically the first candidate black hole (BH) and a prototype of X-ray binaries with black holes. Cyg X-1 is a microquasar having jet during its low “hard” state. It is the brightest object among the high-mass black hole X-ray binaries (mV = 9 mag). The optical component, an O9.7 Iab supergiant, is responsible for about 95% of the system's optical luminosity. The remaining 5% are due to the accretion structure (disk and surrounding gas) near the BH. Intensive investigations of Cyg X-1 are under way for 50 years (more that 4000 paper on Cyg X-1 have already been published), but a lot of phenomena in the system remain unclear.
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Cyg X-1 / V1357 Cyg (история открытия и исследования)
1960-ые – обнаружение рентгеновского источника впервые заподозрил R. Giacconi,H.Gursky,et al,Phys. Rev. Lett. 9, 439 (1962), ракета, баллон кэв, Спутник UHURU в 1970г., быстрая хаотическая переменность 1971 – появился радиоисточник синхронно с ослаблением в X, точные координаты, отождествление с В0 зв. HDE , начало фотометрических набл. В.М.Лютого 1972 – спектр.-дв. с P=5.6d, MXR~10 Mסּ (ч. д.?), опт. P=2.8d 1973 – эффект эллипсоидальности, MXR > 7 Mסּ (Лютый, Сюняев, Черепащук АЖ, 1973) 1983 – прецессионный (?) период 294d в Х и оптике 1991 – кЭв (BATSE), P=5.6d, максимум на фазе 0.5 1996 – радио 2-15 ГГц, запаздывание min (Δφ= ) 1999 – точные элементы Min I=JD E 1999 – корреляция PORB и PPRE в оптике, ИК, Х и радио 2001 – запаздывание Х на 12d относительно оптики 2006 – долговременная var. температуры и радиуса O9.7Iab
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Scheme of X-Ray Binary Cyg X-1
Porb = 5.6d Pprec = 294d scattering gas black hole Mx= 7-10 Msun . hot line accretion disc jet hot spot on the disc tidally distorted supergiant collimated stellar wind MO=20-30 Msun . -- accretion stream Distance d = kpc
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The orbital radial velocity curve Cyg X-1/V1357 Cyg, data 1971-1997:
Psp = (±16), K = 74.9±0.6 кm/s, f(M) = Pph = (±37). The orbit is very near to circle.
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The orbital light curve Cyg X-1/V1357 Cyg (P=5.6d ) - two wave
(the ellipsoidal effect), the full amplitude ~0.04m. The scattering of points is physical variations. Lyuty observations were used
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The ellipsoidality effect-ROCHE model-admissible parameter values for Cyg X-1
40 years ago in our paper Bochkarev N.G. Karitskaya E.A., Shakura N.I., Soviet Astronomy Letters, vol. 1, 1975, p : for A = m, delta A <0.005m, d > 2kpc, Teff < K, f(M)=0.23 Msun the admissible values of Cyg X-1 parameters were obtained: 25°<i<67°; 0.2<q<0.8; 0.8<μ<1; Mo>17Msun; 7Msun<Mx<27Msun D C A B Our admissible values (bold lines) for the mass ratio q as a function of the orbital inclination angle i vs 4 best models A-D from J.A.Orosz et al. Astro-ph, , 18 June 2011, d = 1.86+/-0.12 кpc (Reid et al. 2011).
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A = f1 (q,i,μ,β,u) deltaA = f2 (q,i,μ,β,u) deltaP/P = f3 (q,i,μ)
Эффект эллипсоидальности, модель Роша, допустимые значения параметров для Cyg X-1 40 лет назад в нашей работе Бочкарев Н. Г., Карицкая Е. А., Шакура Н. И., 1975, Эффект эллипсоидальности и параметры двойных рентгеновских систем Cyg X-1 и Cen X-3. ПАЖ 1, №6, 12-17 Бочкарев Н. Г., Карицкая Е. А., Шакура Н. И., , Расчет эффекта эллипсоидальности в тесных двойных системах с одним оптическим компонентом. АЖ 56, № 1, Коэффициент гравитационного потемнения =1/4 A = f1 (q,i,μ,β,u) deltaA = f2 (q,i,μ,β,u) deltaP/P = f3 (q,i,μ) (по теореме Фон Цейпеля) Коэффициент потемнения к краю u=0.4 Для Cyg X-1 : deltaP/P = 0 Функция масс =0.23
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J.A.Orosz et al. ApJ , 742, Dec 2011 J.A.Orosz et al. ApJ , 742, Dec 2011 V.М.Lyuty, гг. Модель D Модель А V-bund , cooperative program, FSU V.М.Lyuty,
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J.A.Orosz et al. ApJ , 742, Dec 2011 Model D
Table 2 Cygnus X-1 Final Parameters Parameter Value i (deg) ± 0.76 Ω ± 0.084 e ± 0.003 ω (deg) ± 5.3 Mopt (M) ± 1.90 Ropt (R) ± 0.68 log g (cgs) ± 0.018 M (M) ± 0.98 J. Zi´ołkowski, 2014 talked about the contradiction of Msun value to theory of evolution – mass-luminosity relation for massive core hydrogen burning. His most probable estimation for the star and black hole are 27 Msun and 16 Msun. If the hydrogen content of the supergiant decreases to 0.6, the stellar mass get smaller from 27 to 24 Msun. J. Cˇechura, S. D. Vrtilek and P. Hadrava, 2015 adopted the values 24 и 8.7 Msun (q=0.36)
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Other methods are needed
For example new method of 2D Doppler tomograms for the component mass ratio q determination we have developed and obtained 1/4 < q < 1/3 (Karitskaya E. A., Agafonov M. I., Bochkarev N. G. et al. 2005, 2007) -red line Abubekerov et al (2004) have puted limits on inclinational angle i<44 deg by the shape of radial velocity curve (green line) D C A B
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Accumulated observational material
40-year long series of multicolor photometric observations – UBVR observations by Lyuty, Metlova et.al from 1971 to present times (Crimea laboratory, Sternberg Inst.) Observational data from different observatories during two cooperative programs of X-ray sources in former Soviet Union (including ours) + James Kemp observations, including linear polarisation In the frame of the international campaign “Optical Monitoring of Unique Astrophysical Objects", 2258 UBVR observations of Cyg X-1 were performed during 407 nights. 12-year-long series of precision spectral observations X-ray RXTE ASM observation archive ( )
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High-resolution spectral observations from 2002
Peak Terskol Observatory (Central Caucasus, Russia): 2-m telescope echelle-spectrographs: - Coude Focus: R = 45000, Å; -- Cassegrain Focus: R = 13000, 3800 – 7600 Å. BOAO Observatory (South Korea): 1.84 m telescope fiber echelle-spectrograph: R = & 30000, 3800 – Å. During 33 nights in spectra were obtained.
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Spectral observations
BTA NES eshelle spectrograph (2k x 2k) CCD camera 21 nights гг spectra Sum. expos. 50 hours R=60000 (5 кm/s) S/N ~ 330 (up to 500 for resolution element) Mexican Guillermo Haro Observatory, Cananea, Sonora 2.1 m tel., R = 13000 CFHT, ESPaDOnS, Havaii, 3.6 m tel., А, S/N ~ 700, R=65000, 12 Sept , 1 spectrum, exposition 80 min.
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Main spectral features: the supergiant absorption lines:
-- HI, HeI, HeII, -- strong CNO l4640Å blend, -- multiple lines of heavy elements (C, N, O, Ne, Mg, Si, S, Fe, Zn), strong emission components in Hα and HeII l4686Å with complex profiles. Sequences HeII 4686 Å и HeI 4713 Å profiles against the orbital period phases X-ray “soft” June 2003 HeII 4686 Å HeI 4713 Å X-ray “hard” 2002 X-ray “soft” 2002 The Figure shows series of fragments of Cyg X-1 optical spectra against the orbital phase. HeI 4713 A absorption line Doppler shift corresponds to the optical component (supergiant) orbital motion. HeII 4686 A line profile variability encloses information on the gas fluxes in the system and on how they are affected by the X-ray radiation variability.
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The X-ray Flare of June 13, 2003 The line profile variations:
According to RXTE/ASM data, the X-ray flux F( keV) increased by a factor of 1.7 in 3.7 hours (the time-interval between the expositions) The line profile variations: F=0.79 F=0.79 F=0.76 F=0.76 Ф is orbital phase Intensity of HeII 4686A line was increased and Hα line was decreased. So circumstellar gas ionization was increased during the X-ray flare.
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Model atmosphere of Cyg X-1 optical star
The main results are reported in: Karitskaya, E. A.; Agafonov, M. I.; Bochkarev, N. G.; Bondar, A. V.; Galazutdinov, G. A.; Lee, B.-C.; Musaev, F. A.; Sapar, A. A.; Sharova, O. I.; Shimanskii, V. V., 2005, Astronomical and Astrophysical Transactions, vol. 24, Issue 5, p Karitskaya E.A., Lyuty V.M., Bochkarev N.G., Shimanskii V. V., Tarasov A. E., Bondar A. V., Galazutdinov G. A., Lee B.-C., Metlova N.V., Long-Term Variations of the Supergiant in the X-Ray Binary Cyg X-1. Inf. Bull. Var. Stars, No. 5678, 2006, p. 1-4. Karitskaya, E. A.; Shimanskii, V. V.; Sakhibullin, N. A.; Bochkarev, N. G., Peculiarities of the Chemical Composition of the Optical Component of Cyg X-1. In: Why Galaxies Care about AGB Stars: their Importance as Actors and Probes. ASP Conf. Series, V. 378, Eds.: F.Kerschbaum, C.Charbonell & R.F.Wing, 2007, p Shimanskii, V. V.;Karitskaya E.A., et.al Astronomical Rep. 2012
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By comparing the observed high-resolution spectra to model non-LTE ones, it becomes possible to put limitations on the parameters of the O supergiant (the optical component of Cyg X-1): Teff = /- 500K, log g =3.31 +/- 0.07, element abundance excess: from 0.4 dex to 1.0 dex for He, N, Ne, Mg, Si, that is, products of CNO- and alpha-processes. It looks like the mixing of matter ought to be far more effective in that object than in the single star alpha Cam, due, in all probability to tidal interaction and mass exchange with the relativistic component at the preceding and present stages of the system evolution.
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Cyg X-1 spectra simulation technique
The SPECTR code (Sakhibullin, Shimanskii, 1997): 1) Illuminated atmosphere models with heating and cooling balance (Ivanova et al., 2002); 2) Equipotential shape of a star that almost fills its Roche lobe (Shimanskii, 2002); 3) Two types of outer illumination spectra “soft” - “hard” (A.Zdziarski, M.Gierlinski, (Prog. Theor. Phys. Suppl. No.155, 2004); 4) A synthetic spectrum based on spectral lines (Shimanskii et al., 2003); 5) Direct computation of non-LTE effects for HI, HeI, MgII, SiIV with influence of outer illumination (Ivanova et al., 2004).
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The obtained results: O-star fundamental parameters:
Teff = /- 500K, log g =3.31 +/- 0.07, [He/H] = 0.43+/- 0.06, Chromosphere with a temperature excess up to 5000K is formed during the “soft” state of Cyg X-1 only. X-ray radiation of any type causes no sensible effect on HI, HeI, MgII, CII, etc. profiles. P Cyg emission components in HeI λλ4387, 4471, 4713, 4921, 5876 Å profiles; Hot wind outflow from the O-star surface at optical depth log τ < -2.0. erg/s theor theory obs Obs
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Chemical composition conclusions
Cyg X-1 supergiant atmosphere shows a high (from 0.4 dex to 1.0 dex) excess of He, N, Ne, Mg, Si, that is, the elements affected by CNO– and alpha--processes. It looks like the mixing of matter ought to be far more effective in that object than in the single star alpha Cam, due, in all probability to tidal interaction and mass exchange with the relativistic component at the preceding and present stages of the system evolution. Cyg X-1 star chemical composition is anomalous. It demonstrates an influence of matter transformation as in CNO – cycle and in alpha – processes. The detected peculiarities of the chemical composition of Cyg X-1 optical component atmosphere may serve as landmarks for the system evolution recuperation.
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Multiwavelength photometry Photometric observations and comparison with X-ray data
The main results are reported in: Kemp J., Karitskaya E.A., Kumsiashvili et al. 1987, Astron.Rep., Karitskaya E.A., Goranskij V.P., Grankin E.N. et al.: 2000, Astronomy Letters, 26, 22. (Pis'ma v Astron.Zh., 26, 27); Karitskaya A.A., Voloshina I.B., Goranskij V.P. et al.: 2001, Astron.Rep., 45, 350.(Astron.Zh., 78, 408); In Kemp et al. we confurmed the existence of the 294-day period in optical variations revealed by Priedhorsky et.al in X-ray. The observational material included a many-year series of photoelectric observations of Cyg X-1 obtained in the frame of a cooperative program to study X-ray systems, conducted in the USSR.
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Optical manifestations of 294-day period
In Kemp J., Karitskaya E.A., Kumsiashvili et al. 1987 1912 B photometrical points were collected Obtained in the frame of a cooperative program to study X-ray systems, conducted in the USSR + observations by J. Kemp The “precession” period P=294 day The variations of average brightness level by 0.01 mag Variations of the shape of the orbital light curve with the phase of P=294 day- the running hamp along the orbital light curve with the amplitude 0.01 mag in the the direction of the orbital phase increasing - the direction of the disk precession coincides with that of the orbital motion. agree well with the model of a tilted (j =10-15 grad) precessing accretion disk, which radiates in the optical range and also scattering and reprocessing the radiation of the supergiant. F=0.0 F=0.5 Опт В X набл
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Результаты наших исследований переменности линейной поляризации
1) Модель наклонного прецессирующего диска, имеющего собственное излучение, рассеивающего и переизлучающего свет сверхгиганта может объяснить меньше половины переменности поляризации (все амплитуды Фурье гармоник, за исключением амплитуды 2-й гармоники) при параметрах Rзв = a; Rd= a; i=55°- 65°; j=15°- 20° Размеры аккреционного диска не превышают 60% полости Роша Х компонента. Прецессия происходит в сторону орбитального движения и может быть обусловлена моментом сил, переносимым газовой струей на наклонный диск. 2) Переменность линейной поляризации обусловлена в основном рассеянием в газе, расположенном несимметрично относительно линии, соединяющей компоненты, например, в асимметричном звездном ветре.
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In Karitskaya. et al.: 2000, 2001: In the frame of the international campaign ”Optical Monitoring of Unique Astrophysical Objects” (Georgia, Kazakhstan, Russia, Uzbekistan, and Ukraine) in : 2258 UBVR observations made during 407 nights Comparison with ASM/RXTE ( keV) data – 1806 daily points
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The orbital light curve P=5.6 d
ASM RXTE X-Ray 1996 г. V-band The amplitude A=0.045+/ mag The difference minima depth deltaA=0.003+/ mag
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Besides the orbital variation in optics and X-rays there are:
The average level variation of brightness, “precessional” period 147/294 дн. In X-rays “hard” –”soft” state transition - years The flares of several day duration ~0.04 mag, for example June, 2 and Oct., 9 in 1996 , coinciding with 20% Х –ray weakening of the same duration. The flares of from several hours to one day ~0.025 зв.в. correlating with Х –ray flares and not depending with orbital phase. Dips, including week-long fading on ~0.04 mag in UBVR, which correlates with 20% Х –ray weakening early November, JD ; short - time weakening JD
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X-ray variations delays in respect to the optical ones
The correspondence between optical and Х-ray variations. Cross-correlation analysis of the X-ray and optical mean brightness shows significant correlation. The X-ray variations delays in respect to the optical one - 7 d delay in 1996 and 12 d - in (the main 1996 X-ray outburst and the mean orbital optical and X-ray light curves were subtracted from the X-ray and optical data). For we derived a correlation, with the X-ray light curve lagging 12 +/-- 2 days relative to the optical light curve, with a significance level substantially exceeding 99.99% (Karitskaya et al. 2001). Evidences of mass transfer instability
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Evidences of instability of matter flowing between the components
1. The shape variations of X-ray orbital light curve. 2. Unusual optical deep fading in November,1996. 3. Several-day-long optical flares coincided with X-ray dips. The suggested scenario of flares and dips The scenario of observed X-ray delays and several-day-long optical flares coinciding with X-ray dips was suggested (Karitskaya 1998). According to this scenario, matter flows from time to time in separate portions from the supergiant towards the accretion structure, forming separate clots. Every clot produces a shock wave and a bump at the outer rim of the accretion structure, which, in their turn, produce a prolonged optical flare, while the scattered matter produces additional absorption of the soft X-ray flux (dip). The remaining matter, after the time interval necessary to cross the accretion structure (disk), produces an X-ray flare. The characteristic time of the matter transfer through the accretion disk was about 7 days in Summer and Autumn 1996 and 12 days in contradict to standard disk accretion theory . Accretion go through high altitudes.
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Cyg X-1 system supergiant variability
The 35-year long series of observations performed by V.M.Lyuty at SAI Crimean Laboratory revealed the supergiant light variation on the time-scale tens of years.
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Cyg X-1 system supergiant variability
E.A. Karitskaya, V.M. Lyuty, N.G. Bochkarev, V.V. Shimanskii, et al., 2006a, Long-Term Variations of the Supergiant in the X-Ray Binary Cyg X-1, IBVS, No.5678, pp.1-4. Spectral observations at Crimean Astrophysical Observatory in 1997 performed in the Coude focus of the 2.6 m telescope R=35000, λλ A June 15-August 16, 1997. 20 spectra were obtained. Brightness variations in U-band and X-ray activity There is the correlation between U brightness fading and X-ray activity increasing according ASM/RXTE !!! The data were compared with the data obtained at Terskol Observatory and at BOAO (South Korea).
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HeI 4713 A line profile: 1997 vs 2004 data
The 1997 line profile is different – less deep than the one. One example of non-LTE computation for 1997 data is given. Log g =3.32 is found not to be in agreement with the photometric changes. Therefore combined analysis of photometric and spectral variability has been performed.
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The star radius has increased by 1-4%,
Averaged magnitude differences for 2004 vs 1997 according to V.M.Lyuty’s photometric observations: deltaU 0.065±0.003 m, deltaB 0.031±0.003 m, deltaV 0.029±0.003 m. Simultaneous matching of non-LTE simulation of the photometric variability and HeI 4713 A line profiles against the observed ones shows that from 1997 to : The star radius has increased by 1-4%, The temperature has decreased by K. X-ray activity increasing after 1996 is believed to be a result of the supergiant parameter changes.
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Continuation of the history of Cyg X-1 variations
After the death of V. M. Lyuty the unique UBV observational series was extended by N.V.Metlova with the same equipment on SAI 60-cm telescope, Crimea. The brightness dropping in the whole continues to this day, although separate maxima sometimes take place. The very blue flare in 2009 is very interesting
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Colour variations
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X-ray variation from 2003 to 2014
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The orbital light curve reflects overall brightness falling
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increasing corresponds to X-ray flare. It may be connected with
High “soft” states Abrupt U brightness increasing corresponds to X-ray flare. It may be connected with the appearance of hot gas with large emission mearsurment EM.
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U and X-ray flare in 2009
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Long time variations of HeI4713A profile
Variations of depth is connected with V mag average level variations !
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H-beta profile variation
=0.03 -250 250 Vr km/s In H-beta profile on the orbital phase =0.03 the gas component was appeared in 2007 year.
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Conclusions of last investigations
The mean level of brightness changes – from 1999 year the brightness decreases on average. Time scale of year variations are imposed on this falling. Connection of variability in X-ray with variability in optics which is in agreement with the idea that as brightness decreases the supergiant temperature decreases while its radius increases approaching a critical Roch lobe. It makes the matter flowing unstable which leads to frequent, non irregular “hard” – “soft” X-ray state changes. Signs of presence at the system of an variable optically thin gas components may appear. During X-ray flare in 2009 year the increasing of hot optically thin gas took place. This has led to a flare in U band only.
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