X-ray Monitoring Data Research Articles

Classification and Analysis of Solar X-ray Monitoring Data for Intensity Monitoring

Abstract: Scientists have focused on solar flares because they are violent phenomena that take place on the Sun's surface and atmosphere and pose threats to the highly advanced civilization on Earth. Electromagnetic radiation from these eruptions primarily manifests as X-rays, UV light, and sporadically visible light. The energy released by these eruptions is equivalent to that of millions of atomic bombs. The beauty of auroras is enhanced but communication systems are disrupted by geomagnetic storms, which frequently accompany flares via coronal mass ejections (CMEs). Long-distance radio communication is hampered by ionospheric ionization caused by X-rays, and GPS navigation may become less precise, especially in high-latitude areas. Increased radiation levels during solar flares pose a concern to both astronaut safety and satellite operations. Geomagnetic disruptions pose a threat to electrical networks, which could result in widespread blackouts. Complex observatories like the Solar Dynamics Observatory (SDO) and the Solar and Heliospheric Observatory (SOHO) are used to predict and reduce the effects of solar flares. Classifying and analyzing solar flares precisely can assist determine their possible effects, which can range from modest interruptions brought on by Class C flares to major disruptions brought on by X-class flares. This study advances our knowledge of solar-terrestrial interactions and helps with space weather forecasting, both of which are essential in today's highly developed society.

The Relation between Outburst Rate and Orbital Period in Low-mass X-Ray Binary Transients

Abstract We have investigated the outburst properties of low-mass X-ray binary transients (LMXBTs) based on a comprehensive study of the outbursts observed in the past few decades. The outburst rates were estimated based on the X-ray monitoring data from Swift/BAT, RXTE/ASM, and MAXI and previous reports in the literature. We found that almost all LMXBTs with the orbital period below ∼12 hr showed only one outburst in these observations. There are systematic differences in the outburst rate between long-period ( hr) and short-period ( hr) systems. We infer that mass transfer rate is responsible for the systematic difference, since the disk instability model suggested that the mass transfer rate is a key factor affecting the quiescence time. The difference in outburst rate between long-period and short-period LMXBTs is probably due to the different mass transfer mechanism at different evolutionary stages of the donors. Based on the evolutionary tracks of single stars, we derived the critical orbital period for X-ray binaries that harbor a subgiant donor in various metallicities. The critical orbital period ( hr) is consistent with the above orbital period boundary obtained from the statistics of outburst rates. Furthermore, we found a negative correlation between the outburst rate and the orbital period in the samples for which the luminosity class of the donor star is III/IV. The best-fitting power-law index for the black hole subsamples is roughly consistent with the theoretical prediction for those systems with a donor star evolved off the main sequence.

The hypersoft state of Cygnus X–3

Context. Cygnus X–3 is a unique microquasar in the Galaxy hosting a Wolf-Rayet companion orbiting a compact object that most likely is a low-mass black hole. The unique source properties are likely due to the interaction of the compact object with the heavy stellar wind of the companion. Aim. In this paper, we concentrate on a very specific period of time prior to the massive outbursts observed from the source. During this period, Cygnus X–3 is in a so-called hypersoft state, in which the radio and hard X-ray fluxes are found to be at their lowest values (or non-detected), the soft X-ray flux is at its highest values, and sporadic γ-ray emission is observed. We use multiwavelength observations to study the nature of the hypersoft state. Methods. We observed Cygnus X–3 during the hypersoft state with Swift and NuSTAR in X-rays and SMA, AMI-LA, and RATAN-600 in the radio. We also considered X-ray monitoring data from MAXI and γ-ray monitoring data from AGILE and Fermi. Results. We found that the spectra and timing properties of the multiwavelength observations can be explained by a scenario in which the jet production is turned off or highly diminished in the hypersoft state and the missing jet pressure allows the wind to refill the region close to the black hole. The results provide proof of actual jet quenching in soft states of X-ray binaries.

Daily Monitoring of TeV Gamma-Ray Emission from Mrk 421, Mrk 501, and the Crab Nebula with HAWC

Abstract We present results from daily monitoring of gamma-rays in the energy range from ∼0.5 to ∼100 TeV with the first 17 months of data from the High Altitude Water Cherenkov (HAWC) Observatory. Its wide field of view of 2 steradians and duty cycle of % are unique features compared to other TeV observatories that allow us to observe every source that transits over HAWC for up to ∼6 hr each sidereal day. This regular sampling yields unprecedented light curves from unbiased measurements that are independent of seasons or weather conditions. For the Crab Nebula as a reference source, we find no variability in the TeV band. Our main focus is the study of the TeV blazars Markarian (Mrk) 421 and Mrk 501. A spectral fit for Mrk 421 yields a power-law index and an exponential cut-off TeV. For Mrk 501, we find an index and exponential cut-off TeV. The light curves for both sources show clear variability and a Bayesian analysis is applied to identify changes between flux states. The highest per-transit fluxes observed from Mrk 421 exceed the Crab Nebula flux by a factor of approximately five. For Mrk 501, several transits show fluxes in excess of three times the Crab Nebula flux. In a comparison to lower energy gamma-ray and X-ray monitoring data with comparable sampling, we cannot identify clear counterparts for the most significant flaring features observed by HAWC.

The AGILE monitoring of Cygnus X-3: transient gamma-ray emission and spectral constraints

We present the AGILE-GRID monitoring of Cygnus X-3, during the period between November 2007 and July 2009. We report here the whole AGILE-GRID monitoring of Cygnus X-3 in the AGILE "pointing" mode data-taking, to confirm that the gamma-ray activity coincides with the same repetitive pattern of multiwavelength emission and to analyze in depth the overall gamma-ray spectrum by assuming both leptonic and hadronic scenarios. Seven intense gamma-ray events were detected in this period, with a typical event lasting one or two days. These durations are longer than the likely cooling times of the gamma-ray emitting particles, implying we see continuous acceleration rather than the result of an impulsive event such as the ejection of a single plasmoid which then cools as it propagates outwards. Cross-correlating the AGILE-GRID light curve with X-ray and radio monitoring data, we find that the main events of gamma-ray activity have been detected while the system was in soft spectral X-ray states (RXTE/ASM count rate > 3 counts/s), that coincide with local and often sharp minima of the hard X-ray flux (Swift/BAT count rate < 0.02 counts/cm^2/s), a few days before intense radio outbursts. [...] These gamma-ray events may thus reflect a sharp transition in the structure of the accretion disk and its corona, which leads to a rebirth of the microquasar jet and subsequent enhanced radio activity. [...] Finally, we examine leptonic and hadronic emission models for the gamma-ray events and find that both scenarios are valid. In the leptonic model - based on inverse Compton scatterings of mildly relativistic electrons on soft photons from the Wolf-Rayet companion star and from the accretion disk - the emitting particles may also contribute to the overall hard X-ray spectrum, possibly explaining the hard non-thermal power-law tail sometimes seen during special soft X-ray states in Cygnus X-3.

Influence of natural convection on microstructure evolution during the initial solidification transient: comparison of phase-field modeling with in situ synchrotron X-ray monitoring data

The influence of natural convection on the evolution of the solid-liquid (s/l) interface during the initial transient of upward directional solidification was studied on Al-4 wt.% Cu alloy by coupling the two dimensional quantitative phase-field model with the Navier-Stokes equations. The simulations were compared with in situ and real-time synchrotron X-ray monitoring data. The origin of natural convection in experiment was the presence of a small unavoidable horizontal temperature gradient. Due to the stringent requirement on the phase-field interface width parameters, the simulated domain could not be chosen as large as the size of the experimental sample. As the calculated fluid flow strength would be weakened by using a smaller domain, a horizontal temperature gradient ten times larger than the estimated experimental value was applied in simulation to recover a fluid flow washing the s/l interface similarly to experiments. Direct comparison to experimental measurements demonstrated that the phase-field simulations with convection qualitatively reproduced the evolution of all the characteristic parameters measured in experiments. Based on these results, the effects of natural convection on the growth dynamics of the s/l interface during directional solidification of alloy were further clarified.

The ‘harder when brighter’ X-ray behaviour of the low-luminosity active galactic nucleus NGC 7213

We present the first robust evidence of an anti-correlation between the X-ray photon index, \Gamma, and the X-ray luminosity in a single low luminosity active galactic nuclei (LLAGN), NGC 7213. Up to now, such anti-correlation trends have been seen only in large samples of LLAGN that span a wide range of X-ray fluxes, although the opposite behaviour (i.e. a positive correlation between \Gamma and X-ray luminosity) has been extensively studied for individual X-ray bright active galactic nuclei. For NGC 7213, we use the long-term X-ray monitoring data of Rossi X-ray Timing Explorer (RXTE), regularly obtained on average every two days from March 2006 to December 2009. Based on our X-ray data, we derive the \Gamma versus flux and the hardness ratio versus flux relations, indicating clearly that NGC 7213 follows a `harder when brighter' spectral behaviour. Additionally, by analysing radio and optical data, and combining data from the literature, we form the most complete spectral energy distribution (SED) of the source across the electromagnetic spectrum yielding a bolometric luminosity of 1.7*10^43 erg s^-1. Phenomenologically, the SED of NGC 7213 is similar to that of low-ionization nuclear emission-line region. The robust anti-correlation trend that we find between \Gamma and X-ray luminosity together with the low accretion rate of the source, 0.14 per cent that of Eddington limit, make NGC 7213 the first LLAGN exhibiting a similar spectral behaviour with that of black hole X-ray binaries in `hard state'.

AGILE detection of Cygnus X-3γ-ray active states during the period mid-2009/mid-2010

Cygnus X-3 (Cyg X-3) is a well-known microquasar producing variable emission at all wavelengths. Cyg X-3 is a prominent X-ray binary producing relativistic jets, and studying its high energy emission is crucial for the understanding of the fundamental acceleration processes in accreting compact objects. Aims. Our goal is to study extreme particle acceleration and {\gamma}-ray production above 100 MeV during special spectral states of Cyg X- 3 usually characterized by a low hard X-ray flux and enhanced soft X-ray states. We observed Cyg X-3 with the AGILE satellite in extended time intervals from 2009 Jun.-Jul., and 2009 Nov.-2010 Jul. We report here the results of the AGILE {\gamma}-ray monitoring of Cyg X-3 as well as the results from extensive multiwavelength campaigns involving radio (RATAN-600, AMI-LA and Mets\"{a}hovi Radio Observatories) and X-ray monitoring data (XTE and Swift). We detect a series of repeated {\gamma}-ray flaring activity from Cyg X-3 that correlate with the soft X-ray states and episodes of decreasing or non-detectable hard X-ray emission. Furthermore, we detect {\gamma}-ray enhanced emission that tends to be associated with radio flares greater than 1 Jy at 15 GHz, confirming a trend already detected in previous observations. The source remained active above 100 MeV for an extended period of time (almost 1.5 months in 2009 Jun.-Jul. and 1 month in 2010 May). We study in detail the short timescale {\gamma}-ray flares that occurred before or near the radio peaks. Our results confirm the transient nature of the extreme particle acceleration from the microquasar Cyg X-3. A series of repeated {\gamma}-ray flares shows correlations with radio and X-ray emission confirming a well established trend of emission. We compare our results with Fermi-LAT and MAGIC TeV observations of Cyg X-3.

DISCOVERY OF ENERGY-DEPENDENT X-RAY MICROLENSING IN Q2237+0305

We present our long term Chandra X-ray monitoring data for the gravitationally lensed quasar Q2237+0305 with 20 epochs spanning 10 years. We easily detect microlensing variability between the images in the full (0.2--8 keV), soft (0.2--2 keV), and hard (2--8 keV) bands at very high confidence. We also detect, for the first time, chromatic microlensing differences between the soft and hard X-ray bands. The hard X-ray band is more strongly microlensed than the soft band, suggesting that the corona above the accretion disk thought to generate the X-rays has a non-uniform electron distribution, in which the hotter and more energetic electrons occupy more compact regions surrounding the black holes. Both the hard and soft X-ray bands are more strongly microlensed than the optical (restframe UV) emission, indicating that the X-ray emission is more compact than the optical, confirming the microlensing results from other lenses.

Fast optical and X-ray variability in the UCXB 4U0614+09⋆

We present results from several years of fast optical photometry of 4U0614+091 (V1055 Orionis), a candidate ultracompact X-ray binary most likely consisting of a neutron star and a degenerate secondary. We find evidence for strong accretion-driven variability at all epochs, that manifests itself as red noise. This flickering produces transient peaks in the observed power spectrum in the 15-65 min period range. Only in one of our 12 optical datasets can we see evidence for a period that cannot be reproduced using the red noise model. This period of 51 minutes coincides with the strongest period detected by Shahbaz et al. (2008) and can thus be taken as the prime candidate for the orbital period of the system. Furthermore, we find some tentative evidence for the X-ray vs. optical flux anticorrelation discovered by Machin et al. (1990) using our data together with the all-sky X-ray monitoring data from RXTE/ASM. We propose that the complex time series behaviour of 4U0614+09 is a result of drastic changes in the accretion disc geometry/structure on time scales from hours to days. Finally we want to draw attention to the interpretation of moderately strong peaks in the power spectra of, especially accreting, sources. Many of such "periods" can probably be attributed to the presence of red noise (i.e. correlated events) in the data.

Recent discoveries of supersoft X‐ray sources in M 31

AbstractClassical novae (CNe) have recently been reported to represent the major class of supersoft X‐ray sources (SSSs) in the central area of our neighbouring galaxy M 31. This paper presents a review of results from recent X‐ray observations of M 31 with XMM‐Newton and Chandra. We carried out a dedicated optical and X‐ray monitoring program of CNe and SSSs in the central area ofM 31. We discovered the first SSSs in M 31 globular clusters (GCs) and their connection to the very first discovered CN in a M 31 GC. This result may have an impact on the CN rate in GCs. Furthermore, in our optical and X‐ray monitoring data we discovered the CN M3 1N 2007‐11a, which shows a very short SSS phase of 29–52 days. Short SSS states (durations ≤ 100 days) of CNe indicate massive white dwarfs (WDs) that are candidate progenitors of supernovae type Ia. In the case of M31N 2007‐11a, the optical and X‐ray light curves suggest a binary containing a WD with MWD &gt; 1.0 M⊙. Finally, we present the discovery of the SSS counterpart of the CN M31N 2006‐04a. The X‐ray light curve of M31N 2006‐04a shows short‐time variability, which might indicate an orbital period of about 2 hours (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

X-ray variability of NGC 3227 and 5506 and the nature of active galactic nucleus 'states'

We use X-ray monitoring data obtained over a broad range of time-scales to measure the broad-band power spectral density functions (PSDs) of two Seyfert galaxies: the broadline Seyfert 1 NGC 3227 and the Seyfert 2 NGC 5506, which has recently been identified as an obscured narrow-line Seyfert 1 (NLS 1). Using a Monte Carlo fitting technique, we demonstrate that both PSDs are reminiscent of the PSD of black hole X-ray binaries (BHXRBs) in the high/soft state, and specifically rule out a low/hard-state PSD shape in NGC 3227. This result demonstrates that, at least where variability is concerned, broad-line Seyferts with hard X-ray spectra (photon index � ∼ 1.6) are not simply the analogues of the low/hard state in BHXRBs, and the dichotomy of NLS 1 and broad-line Seyferts cannot be simply interpreted in terms of the two states. We show that the PSD normalization in NGC 3227 is strongly energy-dependent, with larger variability amplitudes at lower energies, unlike NGC 5506 which shows little energy dependence of variability. We demonstrate that this difference is caused by spectral pivoting of the continuum in NGC 3227 at high energies, which is probably also related to the large amplitude of variability seen in the 2‐10 keV band in this active galactic nucleus (AGN). Using the new PSD data and new results in the literature, we replot the PSD break time-scale versus mass plot for all AGNs with PSD breaks measured so far, and demonstrate that higher accretion rate AGNs appear to have relatively shorter break time-scales for their black hole mass than lower accretion rate AGNs. Ke yw ords: methods: statistical ‐ galaxies: active ‐ galaxies: individual: NGC 3227 ‐ galaxies: individual: NGC 5506 ‐ galaxies: Seyfert ‐ X-rays: galaxies.

Long-term properties of accretion discs in X-ray binaries -- I. The variable third period in SMC X-1

Long-term X-ray monitoring data from the Rossi X-Ray Timing Explorer (RXTE) All-Sky Monitor (ASM) and the Compton Gamma Ray Observatory (CGRO) Burst And Transient Source Experiment (BATSE) reveal that the third (superorbital) period in SMC X-1 is not constant, but varies between 40 and 60 d. A dynamic power spectrum analysis indicates that the third period has been present continuously throughout the five years of ASM observations. This period changed smoothly from 60 to 45 d and then returned to its former value, on a time-scale of approximately 1600 d. During the nearly 4 yr of overlap between the CGRO and RXTE missions, the simultaneous BATSE hard X-ray data confirm and extend this variation in SMC X-1. Our discovery of such an instability in the superorbital period of SMC X-1 is interpreted in the context of recent theoretical studies of warped, precessing accretion discs. We find that the behaviour of SMC X-1 is consistent with a radiation-driven warping model.

Multiwavelength monitoring of the BL Lacertae object PKS 2155-304. 4: Multiwavelength analysis

Simultaneous X-ray, ultraviolet, optical, infrared, and radio monitoring data were used to test and constrain models of continuum emission from the BL Lacertae object PKS 2155-304. Intensively sampled ultraviolet and soft X-ray light curves showed a clear temporal correlation with the X-rays leading the ultraviolet by 2-3 hr. This lag was found to be significantly different from zero after an exhaustive comparison of four different techniques for measuring temporal correlations. Variations in the ultraviolet trough optical wave bands were also strongly correlated, with no measurable lag down to limiting timescales of approximately less than 1-2 hr. This strong correlation extends to the near-infrared, but the less intensive sampling precludes measurement of any lag beyomnd an upper limit of approximately less than 1 day. These lags and limits of the order of hours are much shorter than most rapid observed single-band variations. Because of the very sparse radio sampling, it was not possible to measure quantitatively the correlation and lag with shorter wavelengths, but the data do suggest that the radio may lag the optical/ultraviolet by approximately 1 week, with longer delays and weaker variations to longer radio wavelengths. The epoch-folding Q(exp 2) statistic was used to test for periodicity, and no evidence for strict or quasi-periodicity was found in any of the light curves. Because they lead the lower frequencies, the soft X-rays (approximately less than 1 keV) cannot arise from synchrotron self-Compton scattering. These results also rule out the accretion disk model, which predicts a measurable lag between ultraviolet/optical wavelength bands and a correlation between hardness and brightness, neither of which were seen. They are consistent with the entire radio through X-ray continuum arising from direct synchrotron emission from a relativistic jet. However, the tapered jet model, in which the X-ray emission is produced closer in, has problems explaining the magnitude of the ultraviolet/X-ray lag, because the X-ray-emitting electrons have very short lifetimes (t(sub 1/2) much less than 1 s). The result that the lag is much smaller than the variability timescale suggests instead that the radiation may be produced in a flattened region such as a shock front.