16 research outputs found
Profound optical flares from the relativistic jets of active galactic nuclei
Intense outbursts in blazars are among the most extreme phenomena seen in
extragalactic objects. Studying these events can offer important information
about the energetic physical processes taking place within the innermost
regions of blazars, which are beyond the resolution of current instruments.
This work presents some of the largest and most rapid flares detected in the
optical band from the sources 3C 279, OJ 49, S4 0954+658, Ton 599, and PG
1553+113, which are mostly TeV blazars. The source flux increased by nearly ten
times within a few weeks, indicating the violent nature of these events. Such
energetic events might originate from magnetohydrodynamical instabilities near
the base of the jets, triggered by processes modulated by the magnetic field of
the accretion disc. We explain the emergence of flares owing to the injection
of high-energy particles by the shock wave passing along the relativistic jets.
Alternatively, the flares may have also arisen due to geometrical effects
related to the jets. We discuss both source-intrinsic and source-extrinsic
scenarios as possible explanations for the observed large amplitude flux
changes.Comment: 8 pages, 2 figures, 38th International Cosmic Ray Conference
(ICRC2023) proceeding
Catching profound optical flares in blazars
Flaring episodes in blazars represent one of the most violent processes
observed in extra-galactic objects. Studies of such events shed light on the
energetics of the physical processes occurring in the innermost regions of
blazars, which cannot otherwise be resolved by any current instruments. In this
work, we present some of the largest and most rapid flares captured in the
optical band in the blazars 3C 279, OJ 49, S4 0954+658, TXS 1156+295 and PG
1553+113. The source flux was observed to increase by nearly ten times within a
timescale of a few weeks. We applied several methods of time series analysis
and symmetry analysis. Moreover, we also performed searches for periodicity in
the light curves of 3C 279, OJ 49 and PG 1553+113 using the Lomb-Scargle method
and found plausible indications of quasi-periodic oscillations (QPOs). In
particular, the 33- and 22-day periods found in 3C 279, i.e. a 3:2 ratio, are
intriguing. These violent events might originate from magnetohydrodynamical
instabilities near the base of the jets, triggered by processes modulated by
the magnetic field of the accretion disc. We present a qualitative treatment as
the possible explanation for the observed large amplitude flux changes in both
the source-intrinsic and source-extrinsic scenarios.Comment: 11 pages, 6 figures, MNRAS accepte
Spitzer Observations of the Predicted Eddington Flare from Blazar OJ 287
Binary black hole (BH) central engine description for the unique blazar OJ
287 predicted that the next secondary BH impact-induced bremsstrahlung flare
should peak on 2019 July 31. This prediction was based on detailed general
relativistic modeling of the secondary BH trajectory around the primary BH and
its accretion disk. The expected flare was termed the Eddington flare to
commemorate the centennial celebrations of now-famous solar eclipse
observations to test general relativity by Sir Arthur Eddington. We analyze the
multi-epoch Spitzer observations of the expected flare between 2019 July 31 and
2019 September 6, as well as baseline observations during 2019 February-March.
Observed Spitzer flux density variations during the predicted outburst time
display a strong similarity with the observed optical pericenter flare from OJ
287 during 2007 September. The predicted flare appears comparable to the 2007
flare after subtracting the expected higher base-level Spitzer flux densities
at 3.55 and 4.49 m compared to the optical R-band. Comparing the 2019 and
2007 outburst lightcurves and the previously calculated predictions, we find
that the Eddington flare arrived within 4 hours of the predicted time. Our
Spitzer observations are well consistent with the presence of a nano-Hertz
gravitational wave emitting spinning massive binary BH that inspirals along a
general relativistic eccentric orbit in OJ 287. These multi-epoch Spitzer
observations provide a parametric constraint on the celebrated BH no-hair
theorem.Comment: 8 pages, 4 figures, 1 table, to appear in ApJ
The morphology of the asteroidal dust around White Dwarf Stars : optical and near-infrared pulsations in G29-38
More than 36 yr have passed since the discovery of the infrared excess from circumstellar dust orbiting the white dwarf G29-38, which at 17.5 pc it is the nearest and brightest of its class. The precise morphology of the orbiting dust remains only marginally constrained by existing data, subject to model-dependent inferences, and thus fundamental questions of its dynamical origin and evolution persist. This study presents a means to constrain the geometric distribution of the emitting dust using stellar pulsations measured at optical wavelengths as a variable illumination source of the dust, which reradiates primarily in the infrared. By combining optical photometry from the Whole Earth Telescope with 0.7–2.5 μm spectroscopy obtained with SpeX at NASA’s Infrared Telescope Facility, we detect luminosity variations at all observed wavelengths, with variations at most wavelengths corresponding to the behavior of the pulsating stellar photosphere, but toward the longest wavelengths the light curves probe the corresponding time variability of the circumstellar dust. In addition to developing methodology, we find the pulsation amplitudes decrease with increasing wavelength for principal pulsation modes, yet increase beyond ≈2 μm for nonlinear combination frequencies. We interpret these results as combination modes derived from the principal modes of identical ℓ values and discuss the implications for the morphology of the warm dust. We also draw attention to some discrepancies between our findings and theoretical expectations for the results of the nonlinearity imposed by the surface convection zone on mode–mode interactions and on the behavior of the first harmonic of the highest-amplitude pulsation mode
Apophis planetary defense campaign
We describe results of a planetary defense exercise conducted during the close approach to Earth by the near-Earth asteroid (99942) Apophis during 2020 December–2021 March. The planetary defense community has been conducting observational campaigns since 2017 to test the operational readiness of the global planetary defense capabilities. These community-led global exercises were carried out with the support of NASA's Planetary Defense Coordination Office and the International Asteroid Warning Network. The Apophis campaign is the third in our series of planetary defense exercises. The goal of this campaign was to recover, track, and characterize Apophis as a potential impactor to exercise the planetary defense system including observations, hypothetical risk assessment and risk prediction, and hazard communication. Based on the campaign results, we present lessons learned about our ability to observe and model a potential impactor. Data products derived from astrometric observations were available for inclusion in our risk assessment model almost immediately, allowing real-time updates to the impact probability calculation and possible impact locations. An early NEOWISE diameter measurement provided a significant improvement in the uncertainty on the range of hypothetical impact outcomes. The availability of different characterization methods such as photometry, spectroscopy, and radar provided robustness to our ability to assess the potential impact risk
Polarization and Spectral Energy Distribution in OJ 287 during the 2016/17 Outbursts
We report optical photometric and polarimetric observations of the
blazar OJ 287 gathered during 2016/17. The high level of activity,
noticed after the General Relativity Centenary flare, is argued to be
part of the follow-up flares that exhibited high levels of polarization
and originated in the primary black hole jet. We propose that the
follow-up flares were induced as a result of accretion disk
perturbations, traveling from the site of impact towards the primary
SMBH. The timings inferred from our observations allowed us to estimate
the propagation speed of these perturbations. Additionally, we make
predictions for the future brightness of OJ 287.</p