Infrared Flares Research Articles

Mid-infrared echoes of ambiguous nuclear transients reveal high dust covering fractions: evidence for dusty tori

ABSTRACT Alongside the recent increase in discoveries of tidal disruption events (TDEs) have come an increasing number of ambiguous nuclear transients (ANTs). These ANTs are characterized by hot blackbody-like UV/optical spectral energy distributions (SEDs) and smooth photometric evolution, often with hard power law-like X-ray emission. ANTs are likely exotic TDEs or smooth flares originating in active galactic nuclei (AGNs). While their emission in the UV/optical and X-ray has been relatively well-explored, their infrared (IR) emission has not been studied in detail. Here, we use the NEOWISE mission and its low-cadence mapping of the entire sky to study mid-IR dust reprocessing echoes of ANTs. We study 19 ANTs, finding significant MIR flares in 18 objects for which we can estimate an IR luminosity and temperature evolution. The dust reprocessing echoes show a wide range in IR luminosities (∼1042–1045 erg s−1) with blackbody temperatures largely consistent with sublimation temperature of graphite grains. Excluding the two sources possibly associated with luminous supernovae (ASASSN-15lh and ASASSN-17jz), the dust covering fractions (fc) for detected IR flares lie between 0.05 and 0.91, with a mean of fc = 0.29 for all ANTs (including limits) and fc = 0.38 ± 0.04 for detections. These covering fractions are much higher than optically selected TDEs and similar to AGNs. We interpret the high covering fractions in ANT host galaxies as evidence for the presence of a dusty torus.

Flares in the Galactic Centre – I. Orbiting flux tubes in magnetically arrested black hole accretion discs

ABSTRACT Recent observations of Sgr A* by the GRAVITY instrument have astrometrically tracked infrared (IR) flares at distances of ∼10 gravitational radii (rg). In this paper, we study a model for the flares based on 3D general relativistic magnetohydrodynamic (GRMHD) simulations of magnetically arrested accretion discs (MADs) that exhibit violent episodes of flux escape from the black hole magnetosphere. These events are attractive for flare modelling for several reasons: (i) the magnetically dominant regions can resist being disrupted via magnetorotational turbulence and shear; (ii) the orientation of the magnetic field is predominantly vertical as suggested by the GRAVITY data; and (iii) the magnetic reconnection associated with the flux eruptions could yield a self-consistent means of particle heating/acceleration during the flare events. In this analysis, we track erupted flux bundles and provide distributions of sizes, energies, and plasma parameter. In our simulations, the orbits tend to circularize at a range of radii from ${\sim} 5\hbox{ to }40\, r_{\rm g}$. The magnetic energy contained within the flux bundles ranges up to ${\sim} 10^{40}\,\rm erg$, enough to power IR and X-ray flares. We find that the motion within the magnetically supported flow is substantially sub-Keplerian, in tension with the inferred period–radius relation of the three GRAVITY flares.

The appearance of a compact jet in the soft–intermediate state of 4U 1543−47

ABSTRACT Recent advancements in the understanding of jet–disc coupling in black hole candidate X-ray binaries (BHXBs) have provided close links between radio jet emission and X-ray spectral and variability behaviour. In ‘soft’ X-ray states the jets are suppressed, but the current picture lacks an understanding of the X-ray features associated with the quenching or recovering of these jets. Here, we show that a brief, ∼4 d infrared (IR) brightening during a predominantly soft X-ray state of the BHXB 4U 1543−47 is contemporaneous with a strong X-ray type B quasi-periodic oscillation, a slight spectral hardening and an increase in the rms variability, indicating an excursion to the soft–intermediate state (SIMS). This IR ‘flare’ has a spectral index consistent with optically thin synchrotron emission and most likely originates from the steady, compact jet. This core jet emitting in the IR is usually only associated with the hard state, and its appearance during the SIMS places the ‘jet line’ between the SIMS and the soft state in the hardness–intensity diagram for this source. IR emission is produced in a small region of the jets close to where they are launched (∼0.1 light-seconds), and the time-scale of the IR flare in 4U 1543−47 is far too long to be caused by a single, discrete ejection. We also present a summary of the evolution of the jet and X-ray spectral/variability properties throughout the whole outburst, constraining the jet contribution to the X-ray flux during the decay.

Multi-wavelength Variability Properties of CGRaBS J0733+0456: Identifying a Distant Gamma-Ray Blazar at z = 3.01

Abstract We report on Owens Valley Radio Observatory (OVRO), WISE, Swift and Fermi-LAT observations of the high redshift blazar CGRaBS J0733+0456, from which significant flux variations in radio and infrared (IR), as well as γ-ray domains, are detected. Particularly, the amplitude of long-term IR variation is over one order of magnitude, and the IR variability timescale can be constrained as short as a few hours in the source frame. The IR and γ-ray light curves are found to be rather similar, and the strong quasi-simultaneous IR and γ-ray flares are proven to be unique among the nearby γ-ray sources. This is the first time that a γ-ray blazar at redshift z ≥ 3 with multi-wavelength flux variations (flares) is identified. Broadband spectral energy distributions in different flux states are constructed and theoretically described. The γ-ray flares from some blazars as distant as redshift ∼5 are expected to be detectable for Fermi-LAT.

Uncertainty analysis of the flame temperature determination based on atmospheric absorption effect with optical emission spectroscopy

ABSTRACTFlame temperature, which is an important parameter in combustion diagnostics, provides a better understanding of flame radiative characteristics and can be deduced from the flame emission spectrum. However, in a combustion process with a large-scale flame that requires field measurement, considerable attenuation of the signature from the flame source occurs owing to the absorption of cold molecules in the atmosphere, which produces uncertainties while estimating the flame temperature. We analyze the effect of atmospheric absorption on the flame temperature estimation uncertainty with the optical emission spectroscopic method. We determine the flame temperature of IR (infrared) countermeasure flare combustion by fitting the reference spectrum model applying atmospheric absorption and without applying atmospheric absorption. Line-by-line modeling is conducted using a high-temperature molecular spectroscopic database. The instrument function of the spectrometer is applied, and the atmospheric transmission information is obtained by using the moderate-resolution atmospheric transmission database. In addition, we calculate the estimated flame temperature uncertainty without applying atmospheric absorption when the atmospheric path length, molecular concentration, and flame temperature are varied. Through the analysis, we suggest the wavelength range where the atmospheric absorption is negligible so that the uncertainty is minimized without applying it. Finally, we determine the flame temperature of the IR flare detected with an absolutely calibrated radiometric spectrometer by considering atmospheric absorption. All the fitting results show good agreement with experimental data.

차기 적외선 섬광제 저장수명 예측

This paper shows storage life estimation of next IR(infrared) flare material through accelerated degradation tests. Three temperature conditions for the accelerated degradation tests are 55, 65 and <TEX>$75^{\circ}C$</TEX>. Six performances of IR flare material are burning time, IR peak/continuous Intensity, total energy of near/mid-IR and color ratio, and they were measured after the tests. Storage life of the IR flare material was estimated through both analyzing the degradation data of those performances and applying distribution-based degradation models to the data. Over 30 years of storage life at <TEX>$20^{\circ}C$</TEX> is estimated in terms of IR peak intensity with reliability 0.99 and confidence level 99 %. Additionally, 10 years of storage period at <TEX>$21^{\circ}C$</TEX> would be equivalent to 68 days of accelerated test at <TEX>$65^{\circ}C$</TEX> from the activation energy in Arrhenius model.

Explosive Outflows from Forming Massive Stars

AO imaging of the near IR [Fe ii] and H_2 lines and ALMA CO J = 2 − 1 data confirms the explosive nature of the BN/KL outflow in Orion. N-body interactions in compact groups may be responsible for the production of powerful, explosive protostellar outflows and luminous infrared flares. The Orion event may have been triggered by a protostellar merger. First results of a search for Orion-like events in 200 nearby galaxies with the SPitzer InfraRed Intensive Transients Survey (SPIRITS) are briefly discussed.

Tidal disruption of asteroids by supermassive black holes

The compact radio source Sgr A ∗ at the centre of our Galaxy harbours a super-massive black hole, and is therefore the nearest laboratory for testing the super-massive black hole astrophysics and environment. Since it is not an active galactic nucleus, it also offers the possibility of observing the capture of low-mass objects, such as comets or asteroids, that may orbit the central black hole. In this paper we discuss conditions for tidal disruption of low-mass objects and predictions of the appearance and light curve of such events, as well as their relevance for the X-ray and infra-red flares detected in Sgr A ∗ . The modelled light curves of such tidal disruption events bear marks of the strong gravitational field: tidal squeezing and elongation of the object, gravitational lensing, aberration of light, and Doppler effects. Finally, we show that this model is able to reproduce and fit X-ray flares.

Variations in the spectral slope of Sgr A* during a NIR flare

We have observed a bright flare of Sgr A* in the near infrared with the adaptive optics assisted integral field spectrometer SINFONI. Within the uncertainties, the observed spectrum is featureless and can be described by a power law. The associated power law index is subject to systematic effects, namely the determination of the background level. We explore these effects and can show that while the absolute value of the spectral power law index is relatively uncertain, our data nevertheless suggest that the spectral index is correlated with the instantaneous flix. Both quantities experience signifbant changes within less than one hour. We argue that the near infrared flares from Sgr A* are due to synchrotron emission of transiently heated electrons, the emission being affected by orbital dynamics and synchrotron cooling, both acting on timescales of ≈20 minutes.

Variations in the Spectral Slope of Sagittarius A* during a Near-Infrared Flare

We have observed a bright flare of Sgr A* in the near infrared with the adaptive optics assisted integral field spectrometer SINFON. Within the uncertainties, the observed spectrum is featureless and can be described by a power law. Our data suggest that the spectral index is correlated with the instantaneous flux and that both quantities experience significant changes within less than one hour. We argue that the near infrared flares from Sgr A* are due to synchrotron emission of transiently heated electrons, the emission being affected by orbital dynamics and synchrotron cooling, both acting on timescales of ~20 minutes.

On the Nature of the Variable Infrared Emission from Sagittarius A*

Recent infrared (IR) observations of the center of our Galaxy indicate that the supermassive black hole (SMBH) source Sgr A* is strongly variable in the IR. The timescale for the variability, ~30 minutes, is comparable to that of the X-ray flares observed by Chandra and XMM-Newton, suggesting a common physical origin. In this paper, we investigate the nature of the IR emission in the context of models recently proposed to interpret the X-ray flares. We show that the IR emission in Sgr A* can be well explained by nonthermal synchrotron emission if a small fraction of the electrons in the innermost region of the accretion flow around the black hole are accelerated into a broken power-law distribution, perhaps through transient events such as magnetic reconnection. The model predicts differences in the variability amplitudes of flares in the IR and X-rays, in general agreement with observations. It also predicts that the IR emission should be linearly polarized, as has indeed been observed during one epoch. IR and X-ray flares analogous to those observed in Sgr A* may be detectable from other accreting SMBHs, provided L 10-8LEdd; at higher luminosities, the flaring emission is dominated by thermal synchrotron self-Compton emission, which is likely to be less variable.

Modeling the radio outbursts in AE Aquarii

AbstractIn this paper we model the non-thermal radio to infra-red flares from AE Aqr. In our model the non-thermal flares originate in highly magnetized (Bblob ≥ 2000 G) blobs that may be among the propeller ejected outflow. It was shown that the condition ß ≤ 1 constrains the frozen-in magnetic field in these blobs to Bblob ≥ 2000 G, which is of the same order of magnitude as the inferred polar field of the secondary. As these magnetized blobs encounter the violent mhd-propeller, processes such as reconnection, magnetic pumping, and shocks will result in continuous acceleration of electrons from (γ = 2 → 30; δ = 2.8 → 2.6) with resultant synchrotron emission. The total radio to infra-red flare spectrum was modelled in terms of such expanding magnetized synchrotron emitting blobs in various stages of their evolution from ρ = (r/r°) = 1 → 400. In terms of our model, the total integrated flux during outbursts, over the wide frequency range from 1 GHz is the result of several (~ 20) synchrotron emitting blobs observed in different stages of their evolution, resulting in a spectrum showing a peak flux of Sv ~ 148 mJy at v ~ 1805 GHz (~ 166 microns), where the spectrum changes from a typical self-absorbed Sv ∝ vα spectrum to Sv ∝ v-(δ-1)/2 spectrum, i.e. where the blobs are combined optically thin.

Faint Infrared Flares from the Microquasar GRS 1915+105.

We present simultaneous infrared and X-ray observations of the Galactic microquasar GRS 1915+105 using the Palomar 5 m telescope and Rossi X-Ray Timing Explorer on 1998 July 10 UT. Over the course of 5 hr, we observed six faint infrared (IR) flares with peak amplitudes of approximately 0.3-0.6 mJy and durations of approximately 500-600 s. These flares are associated with X-ray soft-dip/soft-flare cycles, as opposed to the brighter IR flares associated with X-ray hard-dip/soft-flare cycles seen in 1997 August by Eikenberry et al. Interestingly, the IR flares begin before the X-ray oscillations, implying an "outside-in" origin of the IR/X-ray cycle. We also show that the quasi-steady IR excess in 1997 August is due to the pileup of similar faint flares. We discuss the implications of this flaring behavior for understanding jet formation in microquasars.

Evidence for a Disk-Jet Interaction in the Microquasar GRS 1915+105

We report simultaneous X-ray and infrared (IR) observations of the Galactic microquasar GRS1915+105 using XTE and the Palomar 200-inch telescope on August 13-15, 1997 UTC. During the last two nights, the microquasar GRS 1915+105 exhibited quasi-regular X-ray/infrared (IR) flares with a spacing of $\sim 30$ minutes. While the physical mechanism triggering the flares is currently unknown, the one-to-one correspondence and consistent time offset between the X-ray and IR flares establish a close link between the two. At late times in the flares the X-ray and IR bands appear to ``decouple'', with the X-ray band showing large-amplitude fast oscillations while the IR shows a much smoother, more symmetrical decline. In at least three cases, the IR flare has returned to near its minimum while the X-rays continue in the elevated oscillatory state, ruling out thermal reprocessing of the X-ray flux as the source of IR flare. Furthermore, observations of similar IR and radio flares by Fender et al. (1997) imply that the source of the IR flux in such flares is synchrotron emission. The common rise and subsequent decoupling of the X-ray and IR flux and probable synchrotron origin of the IR emission is consistent with a scenario wherein the IR flux originates in a relativistic plasma which has been ejected from the inner accretion disk. In that case, these simultaneous X-ray/IR flares from a black-hole/relativistic-jet system are the first clear observational evidence linking of the time-dependent interaction of the jet and the inner disk in decades of quasar and microquasar studies.

On negative infrared flares of flare stars

The basic formulation of the so-called fast electron hypothesis is presented. According to this hypothesis, the optical flares of UV Cet-type stars are caused by the inverse compton effect, i.e., nonthermal interactions of infrared photons with fast electrons (E equal to about 1.5 MeV), as well as nonthermal bremsstrahlung. The spontaneous appearance of fast electrons on the outer regions of the star is the essence of the flare. The fast electron hypothesis elicits two important predictions: (1) the possibility of X-ray emission during the stellar flares and (2) the inevitability of negative infrared flares. Both predictions are confirmed by direct observations. The importance of negative infrared flares is especially striking; it may be taken as convincing evidence that the inverse Compton effect may really work in the stellar atmospheres. 25 references.

On the infrared observations of stellar flares

In connection with the appearance of the first results of infrared observations of stellar flares, a more elaborate analysis ofnegative infrared flares as a phenomenon, predicted by the fastelectron hypothesis, has been carried out. As a result, the wavelength regions of negative flares are established for the stars of different spectral types as well as the calculated amplitudes of the negative flares (Tables I and II).