Search results for "flare"
showing 10 items of 153 documents
A large X-ray flare from the Herbig Ae star V892 Tau
2003
We report the XMM-Newton observation of a large X-ray flare from the Herbig Ae star V892 Tau. The apparent low mass companion of V892 Tau, V892 Tau NE, is unresolved by XMM-Newton. Nevertheless there is compelling evidence from combined XMM-Newton and Chandra data that the origin of the flare is the Herbig Ae star V892 Tau. During the flare the X-ray luminosity of V892 Tau increases by a factor of ~15, while the temperature of the plasma increases from kT ~ 1.5 keV to kT ~ 8 keV. From the scaling of the flare event, based on hydrodynamic modeling, we conclude that a 500 G magnetic field is needed in order to confine the plasma. Under the assumptions that a dynamo mechanism is required to ge…
Quiescent X-ray emission from an evolved brown dwarf ?
2004
I report on the X-ray detection of Gl569Bab. During a 25ksec Chandra observation the binary brown dwarf is for the first time spatially separated in X-rays from the flare star primary Gl569A. Companionship to Gl569A constrains the age of the brown dwarf pair to ~300-800 Myr. The observation presented here is only the second X-ray detection of an evolved brown dwarf. About half of the observing time is dominated by a large flare on Gl569Bab, the remainder is characterized by weak and non-variable emission just above the detection limit. This emission -- if not related to the afterglow of the flare -- represents the first detection of a quiescent corona on a brown dwarf, representing an impor…
Modeling Non-Confined Coronal Flares: Dynamics and X-Ray Diagnostics
2001
Long-lasting, intense, stellar X-ray flares may approach conditions of breaking magnetic confinement and evolving in open space. We explore this hypothesis with hydrodynamic simulations of flares occurring in a non-confined corona: model flares are triggered by a transient impulsive heating injected in a plane-parallel stratified corona. The plasma evolution is described by means of a numerical 2-D model in cylindrical geometry R,Z. We explore the space of fundamental parameters. As a reference model, we consider a flare triggered by a heating pulse that would cause a 20 MK flare if delivered in a 40000 km long closed loop. The modeled plasma evolution is described. The X-ray emission, spec…
Diagnostics of stellar flares from X-ray observations: from the decay to the rise phase
2007
The diagnostics of stellar flaring coronal loops have been so far largely based on the analysis of the decay phase. We derive new diagnostics from the analysis of the rise and peak phase of stellar flares. We release the assumption of full equilibrium of the flaring loop at the flare peak, according to the frequently observed delay between the temperature and the density maximum. From scaling laws and hydrodynamic simulations we derive diagnostic formulas as a function of observable quantities and times. We obtain a diagnostic toolset related to the rise phase, including the loop length, density and aspect ratio. We discuss the limitations of this approach and find that the assumption of lo…
Post-flare evolution of AR 10923 with Hinode/XRT
2010
Flares are dynamic events which involve rapid changes in coronal magnetic topology end energy release. Even if they may be localized phenomena, the magnetic disturbance at their origin may propagate and be effective in a larger part of the active region. We investigate the temporal evolution of a flaring active region with respect to the loops morphology, the temperature, and emission measure distributions. We consider $Hinode/XRT$ data of a the 2006 November 12th C1.1 flare. We inspect the evolution of the morphology of the flaring region also with the aid of TRACE data. XRT filter ratios are used to derive temperature and emission measure maps and evolution. The analyzed flare includes se…
Chandra study of the eclipsing M dwarf binary, YY Gem
2012
The eclipsing M dwarf binary system, YY Gem, was observed using Chandra covering 140 ks (2Prot) in total, split into two even exposures separated by 0.76 d (0.94 Prot). The system was extremely active: three energetic flares were observed over the course of these observations. The flaring and non-flaring states of the system are analysed in this paper. The activity level increased between the first and second observations even during the quiescent (non-flaring) phases. An analysis of the dynamics of the X-ray-emitting plasma suggests that both components are significantly active. Contemporaneous Hα spectra also suggest that both components show similar levels of activity. The primary star i…
Modeling solar and stellar flares
2003
Abstract The thermal phase of solar X-ray flares has been described as heating-triggered evolution of plasma confined in coronal loops. This paper describes how the modeling of the thermal phase of spatially resolved solar X-ray flares has been extended to investigate spatially unresolved stellar X-ray flares with different scopes, aims and perspectives. Hydrodynamic models are able to describe the evolution of global flare features, such as the X-ray light curves, and to put constraints on heating location. Based on the solar analogy, either detailed hydrodynamic models or approximate analytical descriptions of the decay of flaring coronal loops or loop systems have been extensively applie…
Flare diagnostics from loop modeling of a stellar flare observed with XMM-Newton
2006
Abstract XMM-Newton data of an X-ray flare observed on Proxima Centauri provide detailed and challenging constraints for flare modeling. The comparison of the data with the results of time-dependent hydrodynamic loop modeling of this flare allows us to constrain not only the loop morphology, but also the details of the heating function. The results show that even a complex flare event like this can be described with a relatively few – though constrained – components: two loop systems, i.e., a single loop and an arcade, and two heat components, an intense pulse probably located at the loop footpoints followed by a low gradual decay distributed in the coronal part of the loop. The similarity …
Long-term variability of the Be/X-ray binary A 0535+26 -- I. Optical and UV spectroscopy
1998
The results of a 7-yr optical and UV spectroscopic study of the high-mass X-ray binary A 0535+26 are presented. It was found that throughout the period of the observations the line profile of Hα showed considerable variability. A correlation between the equivalent width of Hα and both V-band magnitude and (B−V) colour excess was observed, albeit with considerable scatter present in the data set. A giant X-ray flare in early 1994 was accompanied by a fading in optical and infrared photometric bands, and a reduction in the equivalent width of Hα. When the star was observed in 1994 September, it was found to have developed a double-peaked Hα profile, and further observations saw the V/R peak r…
Catching the radio flare in CTA 102
2011
Context: The blazar CTA 102 (z=1.037) underwent a historical radio outburst in April 2006. This event offered a unique chance to study the physical properties of the jet. Aims: We used multifrequency radio and mm observations to analyze the evolution of the spectral parameters during the flare as a test of the shock-in-jet model under these extreme conditions. Methods: For the analysis of the flare we took into account that the flaring spectrum is superimposed on a quiescent spectrum. We reconstructed the latter from archival data and fitted a synchrotron self-absorbed distribution of emission. The uncertainties of the derived spectral parameters were calculated using Monte Carlo simulation…