Long-term Light Curve Research Articles

Statistical analysis of the long-term visual light curve parameters of dwarf novae

The long-term visual light curve parameters of 36 dwarf novae are measured. The data is anayzed in search of likely relationships among the light curve parameters and system parameters. New relations of the orbital period with the mean light curve parameters are given. Our ndings for the correlation analysis of individual systems agree with some of the results in previous studies. Almost all of the systems in this study have a bimodal frequency distribution of the outburst duration. By comparing the observational correlations with their theoretical counterparts, we nd that the value of the viscosity parameter of the disk instability model is hot 0:2.

X-ray off states and optical variability in CAL 83

CAL 83 was one of the rst supersoft X-ray binaries (SSBs) to be discovered and is considered to be the prototype of its class. In 15 X-ray observations between 1983{1997 it was observed to have nearly constant X-ray luminosity and temperature, with the exception of one o-state in 1996 (Kahabka et al. 1996). We report on a second X-ray o-state, discovered with a Chandra ACIS-S observation in November 1999. We consider the long-term X-ray and MACHO optical light curves. We nd that, during more than 7 years of monitoring by the MACHO team, CAL 83 has exhibited distinct and well-dened low, intermediate, and high optical states. Transitions between states are not accompanied by color variations. We also nd that both X-ray o states were observed during optical high states and were followed by optical low states within50 days. We discuss possible explanations for the observed optical and X-ray variations. While photospheric adjustments might account for the variations in soft X-ray flux, optical variations can be explained only by invoking changes in the accretion disk, which is the primary source of optical radiation.

LONG-TERM X-RAY VARIABILITIES OF THE SEYFERT GALAXY MCG-2-58-22 : SECULAR FLUX DECREASE AND FLARES

We have studied the long-term X-ray light curve (2$-$10 keV) of the luminous Seyfert 1 galaxy MCG-2-58-22 by compiling data, from various X-ray satellites, which together cover more than 20 years. We have found two distinct types of time variations in the light curve. One is a gradual and secular decrease of the X-ray flux, and the other is the episodic increase of X-ray flux (or flare) by a factor of 2$-$4 compared with the level expected from the secular variation. We detected 3 such flares in total; a representative duration for the flares is $\sim $2 years, with intervening quiescent intervals lasting $\sim 6-8$ years. We discuss a few possible origins for these variabilities. Though a standard disk instability theory may explain the displayed time variability in the X-ray light curve, the subsequent accretions of stellar debris, from a tidal disruption event caused by a supermassive black hole in MCG-2-58-22, cannot be ruled out as an alternative explanation.

Long‐Term Multiwavelength Observations of GRS 1758−258 and the Advection‐dominated Accretion Flow Model

We present a long-term multiwavelength light curve of Galactic black hole candidate GRS 1758-258 by combining previously published and archival data from Granat, ROSAT, the Compton Gamma Ray Observatory, the Rossi X-Ray Timing Explorer, BeppoSAX, ASCA, EXOSAT, and the Very Large Array. In addition, we include the first spectral results from the balloon-borne Gamma-Ray Arcminute Telescope Imaging System (GRATIS). In light of divergent analyses of the 1991-1993 ROSAT observations, we have reanalyzed these data; we find that the soft X-rays track the hard X-rays and that the fits require no blackbody component—indicating that GRS 1758-258 did not go to the high state in 1993. We offer an interpretation of these long-baseline data based on the advection-dominated accretion flow (ADAF) model for a system with crit. We find that the 1990-1993 coeval hard and soft X-ray observations support the ADAF predictions. We discuss a new way to constrain black hole mass with spectral data and the ADAF theory and apply this technique to GRS 1758-258 to find M1 8-9 M☉ at an assumed distance of 8.5 kpc. Further investigations of the ADAF model allow us to evaluate the model critically against the 1996 data and flux-flux diagram of Barret, McClintock, & Grindlay and to understand the limits of the latter's X-ray burster box.

X-Ray Archival Data Analysis of Time Variabilities in Seyfert Galaxy MCG--2-58-22

We report results from an analysis of the X-ray archival data on MCG-2-58-22 obtained with Ginga, ROSAT and ASCA. By analyzing both short- and long-term light curves, we find clear time variations, ranging widely from, s to more than several years, in the X-ray energy range 0.1 - 10 keV. In addition, a flare is detected in 1991, overlaid on a gradual, secular flux decrease from 1979 to 1993; this flare has a time scale of about 1 year, and the X-ray flux increased by at least a factor of 3. The implications of these observational results are discussed in terms of accretion flow dynamics near a supermassive black hole.

The radial pulsation of AI Aurigae

We present an analysis of eleven years of Stromgren by photometry of the red semiregular variable star AI Aurigae. An early period determination of 63.9 days is confirmed by the long-term light curve behaviour. The light curve shows semi-regular changes with a mean period of 65 days reaching an amplitude of 0.6 mag in some cycles. The b-y colour changes perfectly parallel the V light curve, suggesting radial oscillation to be the main reason for the observed variations. We estimate the main characteristics of the star (mass, radius, effective temperature) that suggest radial pulsation in fundamental or first overtone mode.

The 1997 Outburst of AO 0235+164: Evidence for a Microlensing Event?

We present multiwavelength observations of AO 0235+164 made during a 5 mag outburst in 1997. Detection of the outburst at the observatory of the South Eastern Association for Research in Astronomy prompted a concerted effort by several observatories to monitor the source in the R band. We present V-, R-, and I-band photometry, as well as contemporaneous 850 μm and X-ray measurements. We also use radio measurements from the University of Michigan's World Wide Web site in our analysis. We find that the source varies nearly simultaneously over 6 decades in frequency during this outburst and examine the possibility that the outburst was a result of a microlensing event. The duration of the outburst was on the order of 800 days, and the maximum luminosity was approximately 9.86 × 1047 ergs s-1 (assuming no relativistic beaming). We also analyze the long-term optical light curve and find that, although there is still no evidence for periodicity, the variations are interesting: the timescales between pairs of outbursts are remarkably similar. We suggest that the multifrequency behavior of the 1997 outburst is consistent with microlensing scenarios, while observations of previous outbursts suggest they were not consistent with gravitational microlensing.

Orbital Light Curve of the Peculiar Binary V Sagittae in ExtendedHigh States of Brightness

We have analyzed the orbital modulation of V Sge in two intervals, each several years long, when the long-term light curve was relatively flat, in extended high state of brightness, and displayed just minor fluctuations. We used extensive sets of the visual AAVSO data. The two-sided moving averages with various values of Q were applied to the data folded with the orbital photometric phase – it allowed to pick out the general properties of the orbital component of the variations. We found that the modulation is always present but its shape near the secondary minimum (phase 0.5) remarkably varies for the two respective intervals. The secondary minimum is very prominent in one interval, but is almost absent in other interval. The standard deviation of brightness, computed for each bin of the folded light curve, displays variations through the orbital phase and has its minimum near phase 0.6. All these findings are confirmed for various values of Q. We argue that the source of the scatter of the orbital modulation is located in the lobe of the primary between its center and the L1 point, shifted slightly from the line of centers of the stars.

Changes in the Long‐Term Intensity Variations in Cygnus X‐2 and LMC X‐3

We report the detection of changes in the long-term intensity variations in two X-ray binaries, Cyg X-2 and LMC X-3. In this work, we have used the long-term light curves obtained with the All-Sky Monitors (ASMs) of the Rossi X-Ray Timing Explorer (RXTE), Ginga, Ariel 5, and Vela 5B and the scanning modulation collimator of HEAO 1. It is found that in the light curves of both the sources, obtained with these instruments at various times over the last 30 years, more than one periodic or quasi-periodic component is always present. The multiple prominent peaks in the periodograms have frequencies unrelated to each other. In Cyg X-2, RXTE-ASM data show strong peaks at 40.4 and 68.8 days, and Ginga-ASM data show strong peaks at 53.7 and 61.3 days. Multiple peaks are also observed in LMC X-3. The various strong peaks in the periodograms of LMC X-3 appear at 104, 169, and 216 days (observed with RXTE-ASM) and 105, 214, and 328 days (observed with Ginga-ASM). The present results, when compared with the earlier observations of periodicities in these two systems, demonstrate the absence of any stable long period. The 78 day periodicity detected earlier in Cyg X-2 was probably due to the short time base in the RXTE data that were used, and the periodicity of 198 days in LMC X-3 was due to a relatively short duration of observation with HEAO 1.

Infrared and optical microvariability observations of TeV blazars

Microvariability observations of two TeV emitting blazars have been made from the Canary Islands International Observatories since 1990. We present a small sample of typical results from the study. We find that, in contrast to the long-term light curve, Mark 501 is more active than Mark 421, suggesting that these, superficially similar objects, are really quite different in characteristics.

Regularities in the long-term optical light curve of the black hole candidate binary A0620 — 00 (V616 Mon)

We have monitored the R and I magnitudes of the black hole candidate system A0620-00 (V616 Mon) in the years 1991-95 at the Wise Observatory. Combining our data with some additional measurements, we analyze a sparsely covered 7 years light curve of the star. We find that the average R-band magnitude is varying on a time scale of a few hundreds days, with a peak to peak amplitude of 0.3 mag. The two maxima in the well known double hump binary cycle, as well as one of the minima between them, vary by a few percent relative to one another in a seemingly random way. One maximum is on the average higher than the other by 0.05 mag. The depth of the second minimum is varying with significantly higher amplitude, in clear correlation with the long term variability of the mean magnitude of the system. It is shallower than the other minimum at times of maximum light, and it becomes deeper at times of minimum system light. According to the commonly acceptable phasing of the binary cycle, the systematically varying minimum corresponds to inferior conjunction of the red dwarf in the system. We cannot suggest any simple geometrical model for explaining the regularities that we find in the long term photometric behaviour of the star.

Long-Term Variability of the Hard X-ray Source GRS 1758-258

The results of hard x-ray observations of GRS 1758-258 in 1990–1997 byGRANAT/SIGMA are presented. The long-term light curve of the source showsvariations in the 40–200 keV luminosity by a factor of more than ~ 7 — from less than 1.5 × 1036 erg s−1 up to 10 × 1036 erg s−1. The average 40–200 keV luminosity is ~ 6 × 1036 erg s−1 and the averaged spectrum has best-fit power-law photon index α = 2.00 ± 0.06 with a steepening above ~ 100 keV. The source long-term light curve and the spectrum are similar to that of 1E1740.7-2942 andCyg X-1.

TT Arietis: Photometric variability from 1985 to 1994

Results of photoelectric observations of TT Ari during the 1985{1994 interval are presented. Observations were carried out at the Rozhen and Belogradchik observatories as part of our programme for the study of anti-dwarf novae. The long-term light curve in the standard UBV system is constructed and peculiar- ities of the long-term behaviour of the star in this time interval are discussed. 21 moments of maxima and 14 mo- ments of minima are added to the list of known maxima and minima of 3.2-hour modulations. The period of 3.2- hour modulations during the 1987/1988, 1989/1990 and 1990/1991 seasons is determined. In our 29 observing runs we searched for 20-min quasi-periodic variations, which were detected in 25 of them. Our results show that in 1989, the 20-min modulation mean period reached a lo- cal maximum of 19.45 min and declined afterwards. The mean brightness variability analysis during the aforemen- tioned seasons conrmed the reliability of the 3: d 8p eriod suspected by Semeniuk et al. (1987).

High-State/Low-State Behavior in the Long-Term Light Curve of V Sagittae

The 1990-1995 light curve of V Sagittae is shown to have brightness transitions lasting several days which separate extended intervals lasting months in a bright or faint state. These transitions recur with semi-regularity at a characteristic period of ∼240 days. Primary and secondary eclipses are conspicuous in the faint state, but are weaker when the system is bright. Our high-state spectra through primary eclipse show no obvious evidence for the rotational disturbance expected from an accretion disk.

Long-Term Behavior of Centaurus X-3 Observed with the All Sky Monitor on Board GINGA

view Abstract Citations (18) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Long-Term Behavior of Centaurus X-3 Observed with the All Sky Monitor on Board GINGA Tsunemi, Hiroshi ; Kitamoto, Shunji ; Tamura, Keisuke Abstract The long-term X-ray light curve of Centaurus X-3 and its pulse-period history, which were obtained by the All Sky Monitor on board the Ginga satellite from 1987 February to 1991 October, are presented. The pulse-period history shows a monotonic spin-up overlapping a roughly sinusoidal wave structure with a period of 9.23±0.14 yr. The observed light curve shows no correlation with the spin-up history. Since Cen X-3 is considered to be a disk-fed X-ray pulsar, the mass accretion affects the pulse period by means of angular momentum transfer onto the neutron star. In the absence of a correlation between the light curve and pulse period, we conclude that the observed intensity does not represent the mass accretion rate. Publication: The Astrophysical Journal Pub Date: January 1996 DOI: 10.1086/176652 Bibcode: 1996ApJ...456..316T Keywords: STARS: INDIVIDUAL CONSTELLATION NAME: CENTAURUS X-3; X-RAYS: STARS; STARS: PULSARS: INDIVIDUAL NAME: CENTAURUS X-3; ACCRETION; ACCRETION DISKS full text sources ADS | data products SIMBAD (2)

On the Long-Term Light Curve Behaviour of the Intermediate Polar TX Col

TX Col (1H0547–407; Porb = 5.72 h) is an intermediate polar (IP) with spin and synodic (beat) periods of 1911s and 2106 s respectively (Buckley & Tuohy 1989). EXOSAT observations (Tuohy et al. 1986) showed the beat period dominated at higher energies (ME; 1… 9keV), while the spin period was stronger in softer X-rays (LE1; 0.1… IkeV). The high flux level, and pulse fraction (>70%), of the soft X-rays were unique in an IP at that time. Now three other IPs, recently discovered from the ROSAT survey, have been found to show a true separate soft X-ray component, similar to the polars (Motch & Haberl 1994).The strength of the synodic X-ray period in TX Col was, until the recent discovery of the variable polarised IP, RX J1712.6–2414 (Buckley et al. 1995), unique. This was taken as evidence for direct accretion onto the magnetosphere (e.g. Mason, Rosen & Hellier 1988), through a component of the accretion stream overflowing the disc (Hellier 1992).

Long-Term Brightness Changes of Two CVs

AbstractThe long-term light curves of the AM Her type binary BY Cam and the nova-like variable PG 2133+115 are presented. The BVR observations were carried out at a 0.5 m telescope equipped with a high sensitive TV tube superisocon (Abramenko et al. 1978), the UBV photoelectric data were obtained at 0.6 and 1.25 m telescopes and the photographic estimates were made from the negatives obtained at the 0.4 m astrograph in Crimea.Both stars show high and low brightness states. They show similar behaviour in some respects: the amplitude between high and low states was about two magnitudes in B, but the duration of a low state was approximately two months for BY Cam and 1… 2 years for PG 2133+115.

SUPERHUMPS IN CATACLYSMIC BINARIES. VIII. V1159 ORIONIS

ABSTRACT We report photometry of the cataclysmic variable V1159 Orionis for ~400 hours over 168 nights during 1992-4. The long-term light curves show that this is a dwarf nova of the SU UMa class, with normal outbursts recurring on a mean period of 4.0 days, and superoutbursts recurring on a period of 47.6 days. These periods wander slightly, as is typical of the class. High-speed photometry at minimum light, far from superoutbursts, reveals a weak photometric signal at 89.83 ± 0.10 min, which is presumably the underlying orbital period of the binary. During superoutburst, large-amplitude superhumps are observed with P=92.4 min. The superhumps appear very suddenly on the rising branch. In a few days they fade to a full amplitude of 0.1 mag and become more complex in waveform. However, they can be traced throughout the decline phase to quiescence, and even apparently succeed in enduring to the next normal eruption. In fact, we note the occasional existence of superhumps at essentially all phases of the eruption cycle--not merely at supermaxima, where they are very common and downright famous. The "positive" (P>Porb) superhumps resemble in detail the common superhumps seen in the best-known SU UMa stars, and can be reasonably interpreted as arising from an eccentric accretion disk with an advancing line of apsides. But additional subtle details are detected in V1159 Ori. In one superoutburst the frequencies of the high harmonics are slighly higher than expected, and in another they are far lower than expected. And on two occasions there appeared "negative" superhumps (P<Porb) with a period of 82.7 ± 0.2 min. We discuss these features in terms of the disk-precession model, but without any convincing resolution. Two other periodic signals, of unknown origin, were detected: rapid oscillations ("DNOs") with a period increasing from 29 to 34 s over 7 days in mid-decline from a superoutburst; and a probable signal near 8 c/day, appearing mainly in quiescence.

TIMESCALES OF LONG-TERM OPTICAL BASE-LEVEL FLUCTUATIONS IN THREE CLASSES OF AGN

ABSTRACT The long-term optical light curves of many active galactic nuclei (AGN) disply smooth, cyclical changes in level on timescales of years. Earlier work by Smith et al. (1993) estimated the timescales of this previously undiscussed phenomenon for a sample of 60 classical radio-loud quasars. The present study extends the analysis to three additional groups of AGN: the BL Lacertids, the compact galaxies, and the radio-quiet quasars. The average timescale of the BL Lacertids is approximately equal to that of the classical quasars, lending credence to unified models of these objects. The long-term fluctuations of the compact galaxies and the radio-quiet quasars are slower. Our analysis tends to support the division of the BL Lacertids into two populations.

Do We See Magnetic Effects in Dwarf Nova Outbursts?

Many observations indicate that fast rotating late type stars show magnetic activity. We therefore argue that some of the secondary stars in cataclysmic binaries might also have magnetic fields. Such magnetic fields would reach over the accretion disk around the white dwarf primary. We investigate their effect on dwarf nova outbursts. The magnetic field lines will penetrate the disk and remove angular momentum. This shifts the accumulation of mass towards the inner disk, closer to the white dwarf, and therefore leads to a different outburst behaviour, which can be recognized in observed light curves of dwarf novae. If a magnetic field of the order 50 - 100 gauss is acting on the accretion disk, we expect narrower and more frequent outbursts as compared to the non-magnetic case. Outburst records of three dwarf novae above the period gap (P &gt; 3h), whose long-term light curves are well covered, were used to search for traces of magnetic activity. All three cases display a pronounced bimodality in the distribution of their outburst width, i.e. either narrow or wide outbursts occur. We found evidence for a cyclic behaviour in one case, SS Aur: possible “magnetic episodes” repeating every 18 years reveal epochs with abnormally frequent narrow outbursts and nearly or totally missing wide ones. There are also indications for a similar behaviour of SS Cyg with a 7-years cycle, but with less pronounced periodicity. The third case, U Gem, does not show clear evidence of magnetic activity although we found some indications for a transitory oscillation of the width of wide outbursts after 1926, with a period of 13.6 years. The behaviour of SS Aur and SS Cyg resembles the theoretical predictions, there is, however, an important difference: Throughout the entire cycle, marked by the “magnetic episodes”, neither wide nor narrow outbursts alter their mean light curves: magnetic fields seem to affect only the observed proportion in the frequency of both outburst types without altering the light curves of individual outbursts. Remarkably, most of the “anomalous outbursts” (which are characterized by an abnormally slow rising branch to an outburst) occur also at or near the “magnetic episodes”.