Search results for "Light curve"
showing 10 items of 155 documents
Optical and X-ray Observations of M31N 2007-12b: An Extragalactic Recurrent Nova with a Detected Progenitor?
2009
We report combined optical and X-ray observations of nova M31N 2007-12b. Optical spectroscopy obtained 5 days after the 2007 December outburst shows evidence of very high ejection velocities (FWHM H$\alpha \simeq 4500$ km s$^{-1}$). In addition, Swift X-ray data show that M31N 2007-12b is associated with a Super-Soft Source (SSS) which appeared between 21 and 35 days post-outburst and turned off between then and day 169. Our analysis implies that $M_{\rm WD} \ga 1.3 $M$_{\odot}$ in this system. The optical light curve, spectrum and X-ray behaviour are consistent with those of a recurrent nova. Hubble Space Telescope observations of the pre-outburst location of M31N 2007-12b reveal the prese…
Study of a sample of faint Be stars in the exofield of CoRoT. II. Pulsation and outburst events: Time series analysis of photometric variations
2018
Context. The class of Be stars are the epitome of rapid rotators in the main sequence. These stars are privileged candidates for studying the incidence of rotation on the stellar internal structure and on non-radial pulsations. Pulsations are considered possible mechanisms to trigger mass-ejection phenomena required to build up the circumstellar disks of Be stars. Aims. Time series analyses of the light curves of 15 faint Be stars observed with the CoRoT satellite were performed to obtain the distribution of non-radial pulsation (NRP) frequencies in their power spectra at epochs with and without light outbursts and to discriminate pulsations from rotation-related photometric variations. Met…
AGingaObservation of the X‐Ray Pulsar 4U 0352+30
1996
4U 0352 + 30 (X Persei) is a low-luminosity binary X-ray pulsar with a pulse period of 835 s. We present timing and spectral analysis of a Ginga observation of X Persei from 1990 January 26 to January 29. The observation shows the peculiar spectral behavior of X Persei: the pulse-averaged hardness ratio exhibits a sharp hardening episode at phase minimum of the light curve. In order to explain the shape of the observed hardness ratio, we discuss the possible geometry of the emitting region. Simple models of fan emission from a hollow accretion column can reproduce the qualitative features of the observed light curve and hardness ratio.
A 60-night campaign on dwarf novae. - I. Photometric variability of SU UMa and YZ Cnc
1994
A 60-night campaign on SU UMa, YZ Cnc and some secondary targets was carried out during 1988 December and 1989 January at the Observatorio del Roque de Los Muchachos (the 1988 International Time Project). The aim was to study the behaviour of these dwarf novae through their outburst cycle. Here we present the overall light curves of the main targets, SU UMa and YZ Cnc, which show that the optical fluxes continue to decrease after the end of the outburst. For YZ Cnc we find that, during quiescence, orbital variability is present, which may be interpreted as modulation caused by the bright-spot region. Near the end of an outburst, a weak, sinusoidal variation is observed; we discuss the possi…
Disappearance of Hard X-Ray Emission in the Last BeppoSAX Observation of the Z Source GX 349+2
2003
We report on the results from two BeppoSAX observations of the Z source GX 349+2 performed in February 2001 and covering the broad energy range 0.12-200 keV. The light curve obtained from these observations shows a large flaring activity, the count rate varying from ~130 to ~260 counts/s, indicating that the source was in the flaring branch during these observations. The average spectrum is well described by a soft blackbody and a Comptonized component. To well fit the energy spectrum three gaussian lines are needed at 1.2 keV, 2.6 keV, and 6.7 keV with corresponding equivalent widths of 13 eV, 10 eV, and 39 eV, probably associated to L-shell emission of Fe XXIV, Ly-alpha S XVI, and Fe XXV,…
SIMULATIONS OF DYNAMICS AND EMISSION FROM MAGNETIZED GRB AFTERGLOWS
2010
The role of magnetic fields in the GRB flow is still controversial. The afterglow emission, particularly the early phases, may provide a probe into the magnetization of the outflow. Using ultrahigh resolution relativistic MHD simulations, the interaction between radially expanding magnetized ejecta with the interstellar medium is studied. We explore the effect of the magnetic field strength of the ejecta on the afterglow structure, particularly regarding the presence and strength of a reverse shock. We compute synthetic afterglow light curves to quantify the effect of the magnetization of the flow on observed radiation.
XMM-Newton observations of the young open cluster Blanco 1. II. X-ray time variability and flares.
2005
We study the X-ray variability of the young open cluster Blanco 1 observed with the EPIC camera on board the XMM-Newton X-ray observatory. The time coverage of EPIC observations has allowed us to address short time scale (hours) variability, while the comparison with previous ROSAT observations has allowed us to investigate the variability on time scale of six years. On the time scale of hours, dM stars of the cluster are more variable than solar-mass stars. The main features of X-ray light curves in dM stars appear to be essentially flare-like events with a typical duration of the order of a few ks, while dF-dG stars show smooth variations. Two intense flares were observed in the ZS76 clus…
Eclipsed X-ray flares in binary stars: geometrical constraints on the flare's location and size
2007
The observation of eclipses during X-rays flares taking place in active cool stars binaries allows us to calculate the position and size of the flares. This information cannot be derived by analyzing the decay of the flares, a frequently used approach in the literature that requires the assumption of a physical model. We make use of the eclipsing light curve to constrain the set of possible solutions, from the geometrical point of view, in two flares of Algol, and one flare in VW Cep. We make use of a technique developed with the system SV Cam (i~90 deg) and generalize it to binary systems with arbitrary inclination. The method simulates all possible geometrical situations that can produce …
Detection of a Hard Tail in the X-Ray Spectrum of the Z Source GX 349+2
2001
We present the results of a BeppoSAX observation of the Z source GX 349+2 covering the energy range 0.1-200 keV. The presence of flares in the light curve indicates that the source was in the flaring branch during the BeppoSAX observation. We accumulated energy spectra separately for the non-flaring intervals and the flares. In both cases the continuum is well described by a soft blackbody ($k T_{BB} \sim 0.5$ keV) and a Comptonized spectrum corresponding to an electron temperature of $k T_e \sim 2.7$ keV, optical depth $\tau \sim 10$ (for a spherical geometry), and seed photon temperature of $k T_W \sim 1$ keV. All temperatures tend to increase during the flares. In the non-flaring emissio…
The long time-scale X-ray variability of the radio-quiet quasar PG 0804+761
2003
We present the results from a study of the timing properties and the energy spectrum of the radio-quiet quasar PG0804+761, based on monitoring RXTE PCA observations that lasted for a year. This is a systematic study of the X-ray variations on time scales of weeks/months of the most luminous radio-quiet quasar studied so far. We detect significant variations in the 2-10 keV band of an average amplitude of ~15%. The excess variance of the light curve is smaller than that of Seyfert galaxies, entirely consistent with the relationship between variability amplitude and luminosity defined from the Seyfert data alone. The power spectrum of the source follows a power-like form of slope ~ -1. Howeve…