Abstract
We report on the X-ray spectral analysis and time evolution of GRS 1739−278 during its 2014 outburst, based on MAXI/GSC and Swift/XRT observations. Over the course of the outburst, a ...transition from the low/hard state to the high/soft state and then back to the low/hard state was seen. During the high/soft state, the innermost disk temperature mildly decreased, while the innermost radius estimated with the multi-color disk model remained constant at ∼18 (D/8.5 kpc)(cos i/cos 30°)−1/2 km, where D is the source distance and i is the inclination of observation. This small innermost radius of the accretion disk suggests that the central object is more likely to be a Kerr black hole rather than a Schwardzschild black hole. Applying a relativistic disk emission model to the high/soft state spectra, a mass upper limit of 18.3 M⊙ was obtained based on the inclination limit i < 60° for an assumed distance of 8.5 kpc. Using the empirical relation of the transition luminosity to the Eddington limit, the mass is constrained to 4.0–18.3 M⊙ for the same distance. The mass can be further constrained to be no larger than 9.5 M⊙ by adopting the constraints based on the fits to the NuSTAR spectra with relativistically blurred disk reflection models (Miller et al. 2015, ApJ, 799, L6).
We report on the detection and follow-up multi-wavelength observations of the new X-ray transient MAXI J1807+132 with the MAXI/GSC, Swift, and ground-based optical telescopes. The source was first ...recognized with the MAXI/GSC on 2017 March 13. About a week later, it reached maximum intensity (∼10 mCrab in 2-10 keV), and then gradually faded in ∼10 days by more than one order of magnitude. Time-averaged Swift/X-ray Telescope spectra in the decaying phase can be described by a blackbody with a relatively low temperature (0.1-0.5 keV), plus a hard power-law component with a photon index of ∼2. These spectral properties are similar to those of neutron star low-mass X-ray binaries (LMXBs) in their dim periods. The blackbody temperature and the radius of the emission region varied in a complex manner as the source became dimmer. The source was detected in the optical wavelength on March 27-31 as well. The optical flux decreased monotonically as the X-ray flux decayed. The correlation between the X-ray and optical fluxes is found to be consistent with those of known neutron star LMXBs, supporting the idea that the source is likely to be a transient neutron star LMXB.
Abstract
The long gamma-ray burst GRB 161017A was detected by Fermi and Swift, and its afterglow was observed by the MITSuME 50 cm optical telescope promptly, about 50 s after the burst. Early ...optical observations revealed that the optical light curve exhibits a plateau and rebrightening in the early afterglow phase about 500 and 5000 s after the trigger, respectively. By investigating the behavior of the spectral and temporal flux variation, it was found that the plateau and rebrightening cannot be explained in the context of the simple standard afterglow model. These observational features can be explained with two independent refreshed shocks, which indicate the long-acting central engine. We evaluated the physical parameters of the subsequent shells, and we then determined the kinetic energy ratios of the two colliding shells to the leading shell to be roughly 1 and 8, respectively. In addition, two prominent X-ray flares about 200 s after the trigger may be signatures of delayed ejections of the energetic jets responsible for the refreshed shocks. Such late activity of the central engine and X-ray flares play a crucial role in understanding the mechanisms for jet formation and photon emission.
A soft X-ray lag detected in Centaurus A Tachibana, Yutaro; Kawamuro, Taiki; Ueda, Yoshihiro ...
Publications of the Astronomical Society of Japan,
06/2016, Letnik:
68, Številka:
SP1
Journal Article
Recenzirano
Odprti dostop
We performed time-lag analysis on the X-ray light curves of Centaurus A (Cen A) obtained by the Gas Slit Camera (GSC) aboard the Monitor of All-sky X-ray Image (MAXI) in three energy bands (2–4 keV, ...4–10 keV, and 10–20 keV). We discovered a soft X-ray lag relative to higher energies (soft lag) on a timescale of days in a flaring episode by employing the discrete correlation function (DCF) and the z-transformed discrete correlation function (ZDCF) method. In the episode, a peak and a centroid in the DCF and the ZDCF was observed at a soft lag of ∼ 5 d in 2–4 keV versus 4–10 keV and in 4–10 keV versus 10–20 keV, and ∼ 10 d in 2–4 keV versus 10–20 keV. We found it difficult to explain the observed X-ray variation by a single energy injection with the one-zone synchrotron self-Compton (SSC) model, in which the soft lags in these three energy bands reflect the different cooling times of the relativistic electrons, by assuming the magnetic field and minimum Lorentz factor estimated from a broad-band spectral energy distribution. Alternatively, if the phenomenon is interpreted as cooling of Comptonizing electrons in a corona covering the accretion disk, the temperature of the corona producing the variable X-rays should be ∼ 10 keV for reconciliation with the soft lag in the energy range of 2–20 keV.
Abstract
The black hole binary V404 Cygni (= GS 2023+338) had an outburst on 2015 June 15 after 26 years of its quiescence. We report on the multi-color optical observation (g΄, RC, and IC) of this ...object at the beginning of its outburst performed by the MITSuME 50 cm telescope in Akeno, Yamanashi, and the MURIKABUSHI 105 cm telescope at Ishigakijima Astronomical Observatory. Through time domain analysis of the multi-color light curves, we successfully decomposed the optical variations into two components: a highly variable and a less-variable component. The loci of the less-variable component in the color–color diagram are consistent with that of multi-temperature blackbody radiation, while those of the highly variable component trace out a power-law spectrum with a spectral index α ∼ 0.6–1.0. For the less-variable component, we argue that an irradiated disk with the innermost temperature higher than ∼2.0 × 104 K and the outermost temperature lower than ∼6.5 × 103 K is the most plausible source. The gradual rising trend of the light curve during our observation is probably due to the growing of the less-variable component. The observed spectral energy distribution from optical to ultraviolet can be expressed by a model consisting of a power-law component and an irradiated disk component.
ABSTRACT We present simultaneous optical and near-infrared (NIR) polarimetric results for the black hole binary V404 Cyg spanning the duration of its seven-day-long optically brightest phase of its ...2015 June outburst. The simultaneous R- and Ks-band light curves showed almost the same temporal variation except for the isolated (∼30-minute duration) orphan Ks-band flare observed at MJD 57193.54. We did not find any significant temporal variation of polarization degree (PD) and position angle (PA) in both R and Ks bands throughout our observations, including the duration of the orphan NIR flare. We show that the observed PD and PA are predominantly interstellar in origin by comparing the V404 Cyg polarimetric results with those of the surrounding sources within the 7′ × 7′ field of view. The low intrinsic PD (less than a few percent) implies that the optical and NIR emissions are dominated by either disk or optically thick synchrotron emission, or both. We also present the broadband spectra of V404 Cyg during the orphan NIR flare and a relatively faint and steady state by including quasi-simultaneous Swift/XRT and INTEGRAL fluxes. By adopting a single-zone synchrotron plus inverse-Compton model as widely used in modeling of blazars, we constrained the parameters of a putative jet. Because the jet synchrotron component cannot exceed the Swift/XRT disk/corona flux, the cutoff Lorentz factor in the electron energy distribution is constrained to be <102, suggesting that particle acceleration is less efficient in this microquasar jet outburst compared to active galactic nucleus jets. We also suggest that the loading of the baryon component inside the jet is inevitable based on energetic arguments.
V404 Cygni went into an outburst again on June 15, 2015 after 26 years of quietness. Soon after the notifications, we started intense optical observation campaign of this source. The spectral index ...between RC and IC-band was stable over the outburst, whereas that between g′ and RC-band varied violently. With the time domain analysis of the multi-color optical light curves, we successfully decomposed optical variations into three components: highly-variable component (HVC), little-variable component (LVC). The loci of the LVC in the color-color diagram is consistent with that of a single temperature blackbody radiation or a multi-color blackbody radiation from a standard accretion disk, while those of the HVC trace that of power-law spectra.
In the digital ecosystem, the internet is overflowing with a myriad of content, from blogs to engaging videos, compelling media outlets to devise strategies that maximize viewership and revenue. It ...becomes essential to understand the patterns of user engagement, which are shaped by daily routines and timings. Our study leverages Wikipedia's access logs to unveil two innovative methods for dissecting the temporal dynamics of content consumption. The first method utilizes natural language processing to categorize articles into genres, pinpointing those that garner peak interest at specific moments. The second approach employs Independent Component Analysis (ICA) to delve into viewing trends, thereby uncovering user lifestyle patterns and elucidating when and how content is consumed. These methodologies equip content creators and media strategists with the tools to fine-tune publication schedules, boost engagement, and customize content according to audience preferences, offering a strategic edge in the competitive digital sphere.
ABSTRACT Multi-wavelength observations of the black widow binary system 2FGL J2339.6-0532 are reported. The Fermi gamma-ray source 2FGL J2339.6-0532 was recently categorized as a black widow in which ...a recycled millisecond pulsar (MSP) is evaporating the companion star with its powerful pulsar wind. Our optical observations show clear sinusoidal light curves due to the asymmetric temperature distribution of the companion star. Assuming a simple geometry, we constrained the range of the inclination angle of the binary system to , which enables us to discuss the interaction between the pulsar wind and the companion in detail. The X-ray spectrum consists of two components: a soft, steady component that seems to originate from the surface of the MSP, and a hard, variable component from the wind-termination shock near the companion star. The measured X-ray luminosity is comparable to the bolometric luminosity of the companion, meaning that the heating efficiency is less than 0.5. In the companion orbit, 1011 cm from the pulsar, the pulsar wind is already in the particle-dominant stage with a magnetization parameter of . In addition, we precisely investigated the time variations of the X-ray periodograms and detected a weakening of the orbital modulation. The observed phenomenon may be related to unstable pulsar wind activity or weak mass accretion, both of which can result in the temporal extinction of the radio pulse.
Kiso Supernova Survey (KISS): Survey strategy Morokuma, Tomoki; Tominaga, Nozomu; Tanaka, Masaomi ...
Publications of the Astronomical Society of Japan,
12/2014, Letnik:
66, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Abstract
The Kiso Supernova Survey (KISS) is a high-cadence optical wide-field supernova (SN) survey. The primary goal of the survey is to catch the very early light of a SN, during the shock ...breakout phase. Detection of SN shock breakouts combined with multi-band photometry obtained with other facilities would provide detailed physical information on the progenitor stars of SNe. The survey is performed using a 2 $_{.}^{\circ}$2 × 2 $_{.}^{\circ}$2 field-of-view instrument on the 1.05-m Kiso Schmidt telescope, the Kiso Wide Field Camera (KWFC). We take a 3-min exposure in g-band once every hour in our survey, reaching magnitude g ∼ 20–21. About 100 nights of telescope time per year have been spent on the survey since 2012 April. The number of the shock breakout detections is estimated to be of the order of 1 during our three-year project. This paper summarizes the KISS project including the KWFC observing setup, the survey strategy, the data reduction system, and CBET-reported SNe discovered so far by KISS.
PDF
