scholarly journals Quasi-periodic behaviour in the optical and γ-ray light curves of blazars 3C 66A and B2 1633+38

2020 ◽  
Vol 492 (4) ◽  
pp. 5524-5539 ◽  
Author(s):  
J Otero-Santos ◽  
J A Acosta-Pulido ◽  
J Becerra González ◽  
C M Raiteri ◽  
V M Larionov ◽  
...  
Keyword(s):  
Light Curve ◽  
Confidence Level ◽  
Light Curves ◽  
Data Set ◽  
Spectrum Radio ◽  
Periodic Behaviour ◽  
Optical Light Curve ◽  
Emission Models ◽  
Γ Ray ◽  
Radio Quasar

ABSTRACT We report on quasi-periodic variability found in two blazars included in the Steward Observatory Blazar Monitoring data sample: the BL Lac object 3C 66A and the Flat Spectrum Radio Quasar B2 1633+38. We collect optical photometric and polarimetric data in V and R bands of these sources from different observatories: St. Petersburg University, Crimean Astrophysical Observatory, WEBT–GASP, Catalina Real-Time Transient Survey, Steward Observatory, STELLA Robotic Observatory, and Katzman Automatic Imaging Telescope. In addition, an analysis of the γ-ray light curves from Fermi–LAT is included. Three methods are used to search for any periodic behaviour in the data: the Z-transform Discrete Correlation Function, the Lomb–Scargle periodogram and the Weighted Wavelet Z-transform. We find pieces of evidence of possible quasi-periodic variability in the optical photometric data of both sources with periods of ∼3 yr for 3C 66A and ∼1.9 yr for B2 1633+38, with significances between 3σ and 5σ. Only B2 1633+38 shows evidence of this behaviour in the optical polarized data set at a confidence level of 2σ–4σ. This is the first reported evidence of quasi-periodic behaviour in the optical light curve of B2 1633+38. Also, a hint of quasi-periodic behaviour is found in the γ-ray light curve of B2 1633+38 with a confidence level ≥2σ, while no periodicity is observed for 3C 66A in this energy range. We propose different jet emission models that could explain the quasi-periodic variability and the differences found between these two sources.

scholarly journals A possible γ-ray quasi-periodic oscillation of ∼314 days in the blazar OJ 287

2020 ◽  
Vol 499 (1) ◽  
pp. 653-658
Author(s):  
Pankaj Kushwaha ◽  
Arkadipta Sarkar ◽  
Alok C Gupta ◽  
Ashutosh Tripathi ◽  
Paul J Wiita
Keyword(s):  
Light Curve ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Periodic Oscillation ◽  
Large Area ◽  
Quasi Periodic Oscillation ◽  
Bl Lacertae ◽  
Emission Models ◽  
Γ Ray ◽  
Blazar Oj 287

ABSTRACT We report the detection of a probable γ-ray quasi-periodic oscillation (QPO) of around 314 d in the monthly binned 0.1–300 GeV γ-ray Fermi-Large Area Telescope light curve of the well-known BL Lacertae blazar OJ 287. To identify and quantify the QPO nature of the γ-ray light curve of OJ 287, we used the Lomb–Scargle periodogram (LSP), REDFIT, and weighted wavelet Z-transform (WWZ) analyses. We briefly discuss possible emission models for radio-loud active galactic nuclei that can explain a γ-ray QPO of such a period in a blazar.

scholarly journals Optical, X-ray, and γ-ray observations of the candidate transitional millisecond pulsar 4FGL J0427.8-6704

2020 ◽  
Vol 494 (3) ◽  
pp. 3912-3926
Author(s):  
M R Kennedy ◽  
R P Breton ◽  
C J Clark ◽  
V S Dhillon ◽  
M Kerr ◽  
...  
Keyword(s):  
Light Curve ◽  
Time Scales ◽  
Periodic Oscillation ◽  
Optical Data ◽  
Data Sets ◽  
Millisecond Pulsar ◽  
X Ray ◽  
State Classification ◽  
Optical Light Curve ◽  
Γ Ray

ABSTRACT We present an optical, X-ray, and γ-ray study of 1SXPS J042749.2-670434, an eclipsing X-ray binary that has an associated γ-ray counterpart, 4FGL J0427.8-6704. This association has led to the source being classified as a transitional millisecond pulsar (tMSP) in an accreting state. We analyse 10.5 yr of Fermi LAT data and detect a γ-ray eclipse at the same phase as optical and X-ray eclipses at the >5 σ level, a significant improvement on the 2.8 σ level of the previous detection. The confirmation of this eclipse solidifies the association between the X-ray source and the γ-ray source, strengthening the tMSP classification. However, analysis of several optical data sets and an X-ray observation do not reveal a change in the source’s median brightness over long time-scales or a bi-modality on short time-scales. Instead, the light curve is dominated by flickering, which has a correlation time of 2.6 min alongside a potential quasi-periodic oscillation at ∼21 min. The mass of the primary and secondary stars is constrained to be $M_1=1.43^{+0.33}_{-0.19}$ M⊙ and $M_2=0.3^{+0.17}_{-0.12}$ M⊙ through modelling of the optical light curve. While this is still consistent with a white dwarf primary, we favour the tMSP in a low accretion state classification due to the significance of the γ-ray eclipse detection.

scholarly journals Searching for binary central stars of planetary nebulae with Kepler

2011 ◽  
Vol 7 (S283) ◽  
pp. 344-345
Author(s):  
Dimitri Douchin ◽  
George H. Jacoby ◽  
Orsola De Marco ◽  
Steve B. Howell ◽  
Mattias Kronberger
Keyword(s):  
Initial Data ◽  
Light Curve ◽  
Planetary Nebulae ◽  
Central Star ◽  
Light Curves ◽  
Data Set ◽  
Lunar Cycles ◽  
Near Future ◽  
Central Stars

AbstractThe Kepler Observatory offers unprecedented photometric precision (<1 mmag) and cadence for monitoring the central stars of planetary nebulae, allowing the detection of tiny periodic light curve variations, a possible signature of binarity. With this precision free from the observational gaps dictated by weather and lunar cycles, we are able to detect companions at much larger separations and with much smaller radii than ever before. We have been awarded observing time to obtain light-curves of the central stars of the six confirmed and possible planetary nebulae in the Kepler field, including the newly discovered object Kn 61, at cadences of both 30 min and 1 min. Of these six objects, we could confirm for three a periodic variability consistent with binarity. Two others are variables, but the initial data set presents only weak periodicities. For the central star of Kn 61, Kepler data will be available in the near future.

scholarly journals Light Curve Models for SN 1987A and Diagnosis of Supernova Interior

1988 ◽  
Vol 108 ◽  
pp. 319-334
Author(s):  
Ken’ichi Nomoto ◽  
Toshikazu Shigeyama ◽  
Masa-aki Hashimoto
Keyword(s):  
Light Curve ◽  
Reasonable Agreement ◽  
Light Curves ◽  
Shock Propagation ◽  
Helium Abundance ◽  
X Ray ◽  
Sn 1987A ◽  
Shock Heating ◽  
Helium Stars ◽  
Optical Light Curve

AbstractPresupernova evolution of the progenitor of SN 1987A, hydrodynamics of explosion (shock propagation, explosive nucleosynthesis), optical light curve due to shock heating and 56Co decay, and X-ray and γ-ray light curves are calculated and compared with the observations of SN 1987A. Constraints on the mass of the hydrogen-rich envelope Menv (i.e., mass loss history) and the helium abundance in the envelope are obtained from the progenitor’s blue-red-blue evolution as well as from the light curve. The explosion energy E and the mass and distribution of 56Ni are inferred from the light curves. Models and observations are in reasonable agreement for E/Menv = 1.5 ± 0.5 × 1050 erg/M⊙, Menv = 5 - 10 M⊙, and MNi ∼ 0.07 M⊙. Mixing of 56Ni into the envelope is indicated.Light curves of exploding bare helium stars are also calculated to see whether the observed Type Ib supernova light curves can be accounted for.

scholarly journals Analysis of putative exoplanetary signatures found in light curves of two sdBV stars observed by Kepler

2019 ◽  
Vol 627 ◽  
pp. A86 ◽  
Author(s):  
A. Blokesz ◽  
J. Krzesinski ◽  
L. Kedziora-Chudczer
Keyword(s):  
Fourier Transform ◽  
Light Curve ◽  
Fourier Transforms ◽  
Detection Threshold ◽  
Low Frequency ◽  
Light Curves ◽  
Comparison Star ◽  
Data Set ◽  
Nearby Star ◽  
Lower Amplitude

Context. We investigate the validity of the claim that invokes two extreme exoplanetary system candidates around the pulsating B-type subdwarfs KIC 10001893 and KIC 5807616 from the primary Kepler field. Aims. Our goal was to find characteristics and the source of weak signals that are observed in these subdwarf light curves. Methods. To achieve this, we analyzed short- and long-cadence Kepler data of the two stars by means of a Fourier transform and compared the results to Fourier transforms of simulated light curves to which we added exoplanetary signals. The long-cadence data of KIC 10001893 were extracted from CCD images of a nearby star, KIC 10001898, using a point spread function reduction technique. Results. It appears that the amplitudes of the Fourier transform signals that were found in the low-frequency region depend on the methods that are used to extract and prepare Kepler data. We demonstrate that using a comparison star for space telescope data can significantly reduce artifacts. Our simulations also show that a weak signal of constant amplitude and frequency, added to a stellar light curve, conserves its frequency in Fourier transform amplitude spectra to within 0.03 μHz. Conclusions. Based on our simulations, we conclude that the two low-frequency Fourier transform signals found in KIC 5807616 are likely the combined frequencies of the lower amplitude pulsating modes of the star. In the case of KIC 10001893, the signal amplitudes that are visible in the light curve depend on the data set and reduction methods. The strongest signal decreases significantly in amplitude when KIC 10001898 is used as a comparison star. Finally, we recommend that the signal detection threshold is increased to 5σ (or higher) for a Fourier transform analysis of Kepler data in low-frequency regions.

GRB 070311: A COMMON ORIGIN FOR THE PROMPT AND AFTERGLOW EMISSION

2008 ◽  
Vol 17 (09) ◽  
pp. 1359-1362 ◽  
Author(s):  
◽  
S. D. VERGANI ◽  
C. GUIDORZI
Keyword(s):  
Light Curve ◽  
Power Law ◽  
Time Profile ◽  
Common Origin ◽  
Light Curves ◽  
X Ray ◽  
Γ Ray ◽  
Prompt Emission

GRB 070311 was a long burst that triggered INTEGRAL. We present prompt γ-ray, early NIR/optical, late optical and X-ray data on this burst and its afterglow. Interestingly, the H-band light curve acquired with REM exhibits two pulses at 80 and 140 s after the peak of the γ-ray burst, with possible evidence for a contemporaneous faint γ-ray tail. The late optical and X-ray afterglow underwent a rebrightening between 3 × 104 and 2 × 105 s after the burst with energy comparable with that of the prompt emission extrapolated in the X-ray band. After fitting the early γ-ray and optical light curves, we modelled the time profile of the late rebrightening as the time-rescaled version of the prompt γ-ray pulse over an underlying power law. This result supports a common origin for both prompt and late X-ray/optical afterglow rebrightening of GRB 070311 within the external shock scenario.

scholarly journals The dual nature of blazar fast variability: Space and ground observations of S5 0716+714

2020 ◽  
Vol 501 (1) ◽  
pp. 1100-1115
Author(s):  
C M Raiteri ◽  
M Villata ◽  
D Carosati ◽  
E Benítez ◽  
S O Kurtanidze ◽  
...  
Keyword(s):  
Light Curve ◽  
Time Scales ◽  
Light Curves ◽  
Spectral Variability ◽  
Short Term ◽  
Dual Nature ◽  
X Ray ◽  
Geometric Origin ◽  
Optical Light Curve ◽  
Doppler Factor

ABSTRACT Blazar S5 0716+714 is well-known for its short-term variability, down to intraday time-scales. We here present the 2-min cadence optical light curve obtained by the TESS space telescope in 2019 December–2020 January and analyse the object fast variability with unprecedented sampling. Supporting observations by the Whole Earth Blazar Telescope Collaboration in B, V, R, and I bands allow us to investigate the spectral variability during the TESS pointing. The spectral analysis is further extended in frequency to the UV and X-ray bands with data from the Neil Gehrels Swift Observatory. We develop a new method to unveil the shortest optical variability time-scales. This is based on progressive de-trending of the TESS light curve by means of cubic spline interpolations through the binned fluxes, with decreasing time bins. The de-trended light curves are then analysed with classical tools for time-series analysis (periodogram, autocorrelation, and structure functions). The results show that below 3 d there are significant characteristic variability time-scales of about 1.7, 0.5, and 0.2 d. Variability on time-scales $\lesssim 0.2$ d is strongly chromatic and must be ascribed to intrinsic energetic processes involving emitting regions, likely jet substructures, with dimension less than about 10−3 pc. In contrast, flux changes on time-scales $\gtrsim 0.5$ d are quasi-achromatic and are probably due to Doppler factor changes of geometric origin.

scholarly journals An investigation of 56Ni shells as the source of early light curve bumps in type Ia supernovae

2020 ◽  
Vol 642 ◽  
pp. A189
Author(s):  
M. R. Magee ◽  
K. Maguire
Keyword(s):  
Light Curve ◽  
Light Curves ◽  
Radioactive Material ◽  
Type Ia Supernovae ◽  
Spectral Evolution ◽  
Strong Suppression ◽  
Shell Models ◽  
Type Ia ◽  
Optical Light Curve ◽  
Ia Supernovae

An excess of flux (i.e. a bump) in the early light curves of type Ia supernovae has been observed in a handful of cases. Multiple scenarios have been proposed to explain this excess flux. Recently, it has been shown that for at least one object (SN 2018oh) the excess emission observed could be the result of a large amount of 56Ni in the outer ejecta (∼0.03 M⊙). We present a series of model light curves and spectra for ejecta profiles containing 56Ni shells of varying masses (0.01, 0.02, 0.03, and 0.04 M⊙) and widths. We find that even for our lowest mass 56Ni shell, an increase of >2 magnitudes is produced in the bolometric light curve at one day after explosion relative to models without a 56Ni shell. We show that the colour evolution of models with a 56Ni shell differs significantly from those without and shows a colour inversion similar to some double-detonation explosion models. Furthermore, spectra of our 56Ni shell models show that strong suppression of flux between ∼3700–4000 Å close to maximum light appears to be a generic feature for this class of model. Comparing our models to observations of SNe 2017cbv and 2018oh, we show that a 56Ni shell of 0.02–0.04 M⊙ can match shapes of the early optical light curve bumps, but the colour and spectral evolution are in disagreement. Our models also predict a strong UV bump that is not observed. This would indicate that an alternative origin for the flux excess is necessary. In addition, based on existing explosion scenarios, producing such a 56Ni shell in the outer ejecta as required to match the light curve shape, without the presence of additional short-lived radioactive material, may prove challenging. Given that only a small amount of 56Ni in the outer ejecta is required to produce a bump in the light curve, such non-monotonically decreasing 56Ni distributions in the outer ejecta must be rare, if they were to occur at all.

scholarly journals Variability characteristics of Blazar 0J 287

1996 ◽  
Vol 175 ◽  
pp. 45-46
Author(s):  
L.O. Takalo ◽  
A. Sillanpää ◽  
T. Pursimo ◽  
H.J. Lehto ◽  
K. Nilsson ◽  
...  
Keyword(s):  
Light Curve ◽  
Time Scales ◽  
Light Curves ◽  
Data Archive ◽  
Extragalactic Object ◽  
Optical Light Curve ◽  
Blazar Oj 287

Blazar OJ 287 is one of the best observed extragalactic objects. It's historical light curve goes back to 1890′s. Based on the historical behaviour Sillanpää et al. (1988) showed that OJ 287 displays large periodic outbursts, with a period of 11.7 years. We have monitored OJ 287 intensively for two years, during the OJ-94 project. This project was created for monitoring OJ 287 during its predicted new outburst in 1994. In the data archive we have over 7000 observations on OJ 287, in the radio, infrared and optical bands. This data archive contains the best ever obtained light curves for any extragalactic object. The optical light curve shows continuous variability down to time scales of tens of minutes. The variability observed in OJ 287 can be broken down to (at least) four different categories:

scholarly journals OJ 287: A Blazar with Everything

1994 ◽  
Vol 159 ◽  
pp. 409-409
Author(s):  
L.O. Takalo
Keyword(s):  
Correlation Analysis ◽  
Light Curve ◽  
Observational Data ◽  
Light Curves ◽  
Simple Correlation ◽  
Data Set ◽  
Preliminary Results ◽  
Blazar Oj 287

We have collected all the observations available to us of blazar OJ 287. Here we will present preliminary results from our investigation of these data. The photometric light curves show large outbursts occuring (quasi)simultaneously in all frequences. The largest outbursts occured during 1972 and 1983. The B-band light curve can be extended to the year 1894. This being the longest available observational data set of all blazars. Polarization light curves in optical show random variations in all timescales. In the radio bands the polarization observations show well defined structure in the light curves. Light curves and simple correlation analysis based on the light curves on different frequences will be presented.

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