We report on two superoutbursts of the AM CVn-type object CR Boo in 2014 April–March and 2015 May–June. A precursor outburst accompanied both of these superoutbursts. During the rising branch of the ...main superoutburst in 2014, we detected growing superhumps (stage A superhumps) whose period was 0.017669(24) d. Assuming that this period reflects the dynamical precession rate at the radius of the 3:1 resonance, we could estimate the mass ratio (q = M
2/M
1) of 0.101(4) by using the stage A superhump period and the orbital period of 0.0170290(6) d. This mass ratio is consistent with that expected from the theoretical evolutionary model of AM CVn-type objects. The detection of precursor outbursts and stage A superhumps is the second case in AM CVn-type objects. There are two interpretations of the outbursts of AM CVn-type objects. One is a dwarf nova (DN) outbursts analogy, which suggets that the outbursts are caused by thermal and tidal instabilities. Another is the VY Scl-type variation, which suggests that the outbursts are caused by the variation of the mass-transfer rate of the secondary.This detection of the superhump variations strongly supports the former interpretation.
Abstract We present a photometric study of NY Ser, an in-the-gap SU UMa-type nova, in 2002 and 2013. We determined the duration of its superoutburst and the mean period of its superhump are 18 d and ...0.10458 d, respectively. We detected in 2013 that NY Ser showed two distinct states separated by a superoutburst. A state of rather infrequent normal outbursts lasted at least 44 d before the superoutburst, and a state of frequent outbursts started immediately after the superoutburst and lasted at least 34 d. Unlike a typical SU UMa star with a bimodal distribution of outburst duration, NY Ser displayed a diversity of normal outbursts. In the state of infrequent outbursts, we detected a wide ∼ 12 d outburst accompanied by 0.098 d orbital modulation but without superhumps ever established in NY Ser. We classified this as a “wide normal outburst.” The orbital period was dominant both in quiescence and during normal outbursts in this state. In the state of the most frequent normal outbursts, the 0.10465 d positive superhump period was dominant and coexisted with the orbital modulation. In 2002 we detected the normal outburst of “intermediate” 5–6 d duration that was also accompanied by orbital modulations.
Abstract
We present results of optical polarimetric and multi-band photometric observations for γ-ray loud, narrow-line Seyfert 1 galaxy 1H 0323+342. This object has been monitored by the 1.5-m ...Kanata telescope since 2012 September, but following a γ-ray flux enhancement detected by Fermi Large Area Telescope (Fermi-LAT) on MJD 56483 (2013 July 10), dense follow-up was performed by 10 0.5–2.0-m telescopes in Japan over one week. The 2-yr RC-band light curve showed clear brightening corresponding to the γ-ray flux increase, and then decayed gradually. The high state as a whole lasted for ∼ 20 d, during which we clearly detected optical polarization from this object. The polarization degree (PD) of the source increased from 0%–1% in quiescence to ∼ 3% at maximum and then declined to the quiescent level, with the duration of the enhancement being less than 10 d. The moderate PD around the peak allowed us to precisely measure the daily polarization angle (PA). As a result, we found that the daily PAs were almost constant and aligned to the jet axis, suggesting that the magnetic field direction at the emission region is transverse to the jet. This implies either a presence of helical/toroidal magnetic field or transverse magnetic field compressed by shock(s). We also found small-amplitude intra-night variability during the 2-hr continuous exposure on a single night. We discuss these findings based on the turbulent multi-zone model recently advocated by Marscher (2014, ApJ, 780, 87). Optical to ultraviolet (UV) spectrum showed a rising shape in the higher frequency and the UV magnitude measured by Swift/UVOT (UV and Optical Telescope) was steady even during the flaring state, suggesting that thermal emission from accretion disk is dominant in that band.
We report on photometric observations of two WZ Sge-type dwarf novae, MASTER OT J211258.65+242145.4 and MASTER OT J203749.39+552210.3, which underwent outbursts in 2012. Early superhumps were ...recorded in both systems. During the superoutburst plateau, ordinary superhumps with a period of 0.060291(4) d (MASTER J211258) and with 0.061368(11) d (MASTER J203749) on average were observed. MASTERJ211258 and MASTERJ203749 exhibited eight post-superoutburst rebrightenings and more than four, respectively. In the final part of the superoutburst, an increase in superhump period was seen in both systems. We made a survey of WZSge-type dwarf novae with multiple rebrightenings, and confirmed that the superhump periods of WZSge-type dwarf novae with multiple rebrightenings were longer than those of WZSge-type dwarf novae without a rebrightening. Although WZSge-type dwarf novae with multiple rebrightenings have been thought to be likely candidates for period bouncers based on their low mass ratio (q), inferred from the period of fully grown (stage B) superhumps, our new method of using the period of growing superhumps (stage A superhumps), however, implies higher q's than those expected from stage B superhumps. These q values appear to be consistent with the duration of the stage A superoutbursts, which likely reflects the growth time of the 3W1 resonance. We present a working hypothesis that the small fractional superhump excesses for stage B superhumps in these systems may be explained by a gas pressure effect that works more efficiently in these systems than in ordinary SU UMa-type dwarf novae. This result forms a new picture that WZSge-type dwarf novae with multiple rebrightenings and SU UMa-type ones without a rebrightening (they are not period bouncers) are located in the same place on the evolutionary track.
Abstract
We report on a superoutburst of the AM CVn-type object SDSS J090221.35+381941.9 J0902; orbital period 0.03355(6) d in 2014 March–April. The entire superoutburst consisted of a precursor ...outburst and the main superoutburst, followed by a short rebrightening. During the rising phase of the main superoutburst, we detected growing superhumps (stage A superhumps) with a period of 0.03409(1) d. During the plateau phase of the superoutburst, superhumps with a shorter period (stage B superhumps) were observed. Using the orbital period and the period of stage A superhumps, we were able to measure the dynamical precession rate of the accretion disk at the 3:1 resonance, and obtained a mass ratio (q) of 0.041(7). This is the first successful measurement of the mass ratio in an AM CVn-type object accomplished by the recently developed stage A superhump method. The value is generally in agreement with that based on the theoretical evolutionary model. The orbital period of J0902 is the longest among those of the outbursting AM CVn-type objects, and a period on the borderline between the outbursting system and the system with a stable cool disk appears to be longer than one supposed.
CTA 102, classified as a flat spectrum radio quasar at z = 1.037, produced an exceptionally bright optical flare in 2012 September. Following the Fermi Large Area Telescope detection of enhanced ...gamma -ray activity, we closely monitored this source in the optical and near-infrared bands for the 10 subsequent nights using 12 telescopes in Japan and South Africa. On MJD 56197 (2012 September 27, four to five days after the peak of bright gamma -ray flare), polarized flux showed a transient increase, while total flux and polarization angle (PA) remained almost constant during the "orphan polarized-flux flare." We also detected an intra-night and prominent flare on MJD 56202. The total and polarized fluxes showed quite similar temporal variations, but the PA again remained constant during the flare. Interestingly, the PAs during the two flares were significantly different from the jet direction. The emergence of a new emission component with a high polarization degree (PD) up to 40% would be responsible for the observed two flares, and such a high PD indicates the presence of a highly ordered magnetic field at the emission site. We argue that the well-ordered magnetic field and even the observed directions of the PA, which is grossly perpendicular to the jet, are reasonably accounted for by transverse shock(s) propagating down the jet.
We present monitoring campaign observations at optical and near-infrared (NIR) wavelengths for a radio-loud active galactic nucleus (AGN) at z = 0.840, SDSSJ110006.07+442144.3 (hereafter, ...J1100+4421), which was identified during a flare phase in late 2014 February. The campaigns consist of three intensive observing runs from the discovery to 2015 March, mostly within the scheme of the OISTER collaboration. Optical-NIR light curves and simultaneous spectral energy distributions (SEDs) are obtained. Our measurements show the strongest brightening in 2015 March. We found that the optical-NIR SEDs of J1100+4421 show an almost steady shape despite the large and rapid intranight variability. This constant SED shape is confirmed to extend to similar to 5 mu m in the observed frame using the archival WISE data. Given the lack of absorption lines and the steep power-law spectrum of alpha(upsilon) similar to -1.4, where f(v) proportional to v(alpha upsilon), synchrotron radiation by a relativistic jet with no or small contributions from the host galaxy and the accretion disk seemsmost plausible as an optical-NIR emission mechanism. The steep optical-NIR spectral shape and the large amplitude of variability are consistent with this object being a low.peak jet-dominated AGN. In addition, sub-arcsecond resolution optical imaging data taken with Subaru Hyper Suprime-Cam does not show a clear extended component and the spatial scales are significantly smaller than the large extensions detected at radio wavelengths. The optical spectrum of a possible faint companion galaxy does not show any emission lines at the same redshift, and hence a merging hypothesis for this AGN-related activity is not supported by our observations.
Young solar-type stars are known to show frequent "superflares", which may
severely influence the habitable worlds on young planets via intense radiations
and coronal mass ejections. Here we report ...an optical spectroscopic and
photometric observation of a long-duration superflare on the young solar-type
star EK Draconis (50-120 Myr age) with the Seimei telescope and $Transiting$
$Exoplanet$ $Survey$ $Satellite$ ($TESS$). The flare energy
2.6$\times$10$^{34}$ erg and white-light flare duration 2.2 hr are much larger
than those of the largest solar flares, and this is the largest superflare on a
solar-type star ever detected by optical spectroscopy. The H$\alpha$ emission
profile shows no significant line asymmetry, meaning no signature of a filament
eruption, unlike the only previous detection of a superflare on this star
(Namekata et al. 2021, $Nat.Astron$). Also, it did not show significant line
broadening, indicating that the non-thermal heating at the flare footpoints are
not essential or that the footpoints are behind the limb. The time evolution
and duration of the H$\alpha$ flare are surprisingly almost the same as those
of the white-light flare, which is different from general M-dwarf
(super-)flares and solar flares. This unexpected time evolution may suggest
that different radiation mechanisms than general solar flares are predominant,
as follows: (1) radiation from (off-limb) flare loops, and (2) re-radiation via
radiative backwarming, in both of which the cooling timescales of flare loops
could determine the timescales of H$\alpha$ and white light.
Solar flares are often accompanied by filament/prominence eruptions (\(\sim10^{4}\) K and \(\sim 10^{10-11}\) cm\(^{-3}\)), sometimes leading to coronal mass ejections (CMEs) that directly affect the ...Earth's environment. `Superflares' are found on some active solar-type (G-type main-sequence) stars, but the association of filament eruptions/CMEs has not been established. Here we show that our optical spectroscopic observation of the young solar-type star EK Draconis reveals the evidence for a stellar filament eruption associated with a superflare. This superflare emitted a radiated energy of \(2.0\times10^{33}\) erg, and blue-shifted hydrogen absorption component with a large velocity of \(-510\) km s\(^{-1}\) was observed shortly after. The temporal changes in the spectra greatly resemble those of solar filament eruptions. Comparing this eruption with solar filament eruptions in terms of the length scale and velocity strongly suggests that a stellar CME occurred. The erupted filament mass of \(1.1\times10^{18}\) g is 10 times larger than those of the largest solar CMEs. The massive filament eruption and an associated CME provide the opportunity to evaluate how they affect the environment of young exoplanets/young Earth and stellar mass/angular-momentum evolution.
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