The magnetic field in intergalactic space gives important information about magnetogenesis in the early universe. The properties of this field can be probed by searching for radiation of secondary ...e+e− pairs created by TeV photons that produce GeV range radiation by Compton-scattering cosmic microwave background photons. The arrival times of the GeV "echo" photons depend strongly on the magnetic field strength and coherence length. A Monte Carlo code that accurately treats pair creation is developed to simulate the spectrum and time-dependence of the echo radiation. The extrapolation of the spectrum of powerful gamma-ray bursts (GRBs) like GRB 130427A to TeV energies is used to demonstrate how the intergalactic magnetic field can be constrained if it falls in the 10−21-10−17 G range for a 1 Mpc coherence length.
Optical counterparts of ULXs in NGC 1672 Allak, S; Akyuz, A; Sonbas, E ...
Monthly notices of the Royal Astronomical Society,
08/2022, Letnik:
515, Številka:
3
Journal Article
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ABSTRACT
In this work, we deploy archival data from Hubble Space Telescope, Chandra, XMM–Newton, and Swift-XRT, to probe the nature of nine candidate ultraluminous X-ray sources (ULXs) in NGC 1672. ...Specifically, our study focuses on using the precise source positions obtained via improved astrometry based on Chandra and Hubble Space Telescope observations to search for and identify potential optical counterparts for these ULXs. Unique optical counterparts are identified for two of the ULX candidates, i.e. X2 and X6; for three of the candidates, i.e. X1, X5, and X7, we found two potential counterparts for each source within the respective error radii. No optical counterparts were found for the remaining four sources. The spectral energy distribution of X2 is fitted to a blackbody spectrum with a temperature of ∼104 K and the spectral class of the source is determined to be B7−A3, a supergiant donor star. We used colour–magnitude diagrams to investigate ages of the counterparts. Of all the sources studied, X9 exhibits the most variability whereby the X-ray flux varies by a factor of ∼50 over a time period spanning 2004–2019, and also traces a partial q-curve-like feature in the hardness–intensity diagram, hinting at possible spectral transitions.
ABSTRACT
The results of a temporal analysis of observations for a sample of nine low-mass X-ray binaries (LMXBs) are presented. Of these sources, five host a neutron star (NS) primary (4U1608−52, Aql ...X-1, 4U1705−44, GX17+2-, and Cyg X-2), and four host a black hole (BH) (GX339-4, XTE J1859+226, H1743−322, and MAXI J1659−152). The NS group includes three Atolls and two Z-type sources. We utilized archival Proportional Counter Array (PCA)/RXTE data to construct high-resolution light-curves. A wavelet transform of the light curves is deployed to extract a minimal time-scale (MTS) associated with the spectral state of the sources. The MTS, together with the fractional root-mean-square (rms) and hardness ratios, is used to construct RMS–MTS and hardness–MTS diagrams that enable a direct comparison of the evolution of spectral transitions in the target sources. Observations with high fractional rms and high hardness cluster in a broad region occupied jointly by BH and NS sources. For low fractional rms observations, the Atolls exhibit large MTS whereas Z-type sources exhibit small MTS. This new feature raises the possibility of discriminating between these two types of sources. Moreover, in the hardness–MTS plane, BH sources are the sole occupiers of the low-hardness and small-MTS domain thus potentially signalling a unique property for distinguishing BH and NS hosts in LMXBs.
Spectral lag, the time difference between the arrival of high-energy and low-energy photons, is a common feature in gamma-ray bursts (GRBs). Norris et al. reported a correlation between the spectral ...lag and the isotropic peak luminosity of GRBs based on a limited sample. More recently, a number of authors have provided further support for this correlation using arbitrary energy bands of various instruments. In this paper, we report on a systematic extraction of spectral lags based on the largest Swift sample to date of 31 GRBs with measured redshifts. We extracted the spectral lags for all combinations of the standard Swift hard X-ray energy bands: 15-25 keV, 25-50 keV, 50-100 keV, and 100-200 keV and plotted the time dilation corrected lag as a function of isotropic peak luminosity. The mean value of the correlation coefficient for various channel combinations is -0.68 with a chance probability of {approx}0.7 x 10{sup -3}. In addition, the mean value of the power-law index is 1.4 +- 0.3. Hence, our study lends support to the existence of a lag-luminosity correlation, albeit with large scatter.
ABSTRACT
Black hole transients are known to undergo spectral transitions that form q-shaped tracks on a hardness intensity diagram. In this work, we use the archival Rossi X-ray Timing Explorer data ...to extract a characteristic minimal time-scale for the spectral states in GX 339−4 for the 2002–2003 and 2010 outbursts. We use the extracted time-scale to construct an intensity variability diagram for each outburst. This new diagram is comparable to the traditional hardness intensity diagram and offers the potential for probing the underlying dynamics associated with the evolution of the relevant emission regions in black hole transients. We confirm this possibility by connecting the minimal time-scale with the inner disc radius, Rin (estimated from spectral fits), and demonstrate a positive correlation between these variables as the system evolves through its spectral transitions. Furthermore, we probe the relation between the minimal time-scale and the break frequencies extracted from the power spectral densities. Lastly, we examine a possible link between the extracted time-scale and a traditional measure of variability, i.e. the root mean square, determined directly from the power spectra.
ABSTRACT
We report the results of new transit observations for the three hot Jupiter-like planets, HATP-36b, HATP-56b, and WASP-52b, respectively. Transit timing variations (TTVs) are presented for ...these systems based on observations that span the period 2016–2020. The data were collected with the 0.6-m telescope at Adiyaman University (ADYU60, Turkey) and the 1.0 m telescope at TÜBİTAK National Observatory (TUG, Turkey). Global fits were performed to the combined light curves for each system along with the corresponding radial velocity (RV) data taken from the literature. The extracted parameters (for all three systems) are found to be consistent with the values from previous studies. Through fits to the combined mid-transit times data from our observations and the data available in the literature, an updated linear ephemeris is obtained for each system. Although a number of potential outliers are noted in the respective O-C diagrams, the majority of the data are consistent within the 3σ confidence level implying a lack of convincing evidence for the existence of additional objects in the systems studied.
ABSTRACT Spectral lag, which is defined as the difference in time of arrival of high- and low-energy photons, is a common feature in gamma-ray bursts (GRBs). Previous investigations have shown a ...correlation between this lag and the isotropic peak luminosity for long duration bursts. However, most of the previous investigations used lags extracted in the observer frame only. In this work (based on a sample of 43Swift long GRBs with known redshifts), we present an analysis of the lag-luminosity relation in the GRB source frame. Our analysis indicates a higher degree of correlation -0.82 ± 0.05 (chance probability of 5.5 × 10-5) between the spectral lag and the isotropic peak luminosity,L iso, with a best-fitting power-law index of -1.2 ± 0.2, such thatL isolag-1.2. In addition, there is an anticorrelation between the source-frame spectral lag and the source-frame peak energy of the burst spectrum,E pk(1 +z ). PUBLICATION ABSTRACT
ABSTRACT
We present the results of a temporal and spectral analysis of the transient source ULX-4 in the galaxy M51. The data used were drawn from Chandra, XMM–Newton, and Swift-XRT archives, ...spanning the years 2000–2019.. The X-ray flux of the source is seen to vary by two orders of magnitudes within a month but a short-term variability was not observed over the time intervals of 100–2000 s in the 0.3–10 keV energy band. We find some evidence for the existence of bi-modality feature in the flux distribution of ULX-4. We identified two optical sources as possible counterparts within an error radius of 0${_{.}^{\prime\prime}}$18 at 95 ${{\ \rm per\ cent}}$ confidence level for ULX-4 based on the archival Hubble Space Telescope (HST)/ACS and HST/WFC3 data. Blackbody fits of the spectral energy distributions (SEDs) indicate the spectral type to be B-type stars. One of these counterparts exhibits a low-amplitude optical periodicity of 264 ± 37 d in the F606W filter; if we assume this apparent periodicity is associated with the orbital motion of the donor, then it is more likely that the donor is a red supergiant satisfying the long periodicity and accretion via Roche lobe overflow. Consequently, the SED would then have to be interpreted as a superposition of emissions from a cold donor and a hot flow component, most likely from an accretion disc. If, on the other hand, the periodicity is superorbital in nature i.e. due to possible interactions of the compact object with a circumstellar disc, the donor could then be a Be/X star hosting a neutron star.
ABSTRACT
Similar to black hole X-ray binary transients, hysteresis-like state transitions are also seen in some neutron-star X-ray binaries. Using a method based on wavelets and light curves ...constructed from archival Rossi X-ray Timing Explorer observations, we extract a minimal timescale over the complete range of transitions for 4U 1608-52 during the 2002 and 2007 outbursts and the 1999 and 2000 outbursts for Aql X-1. We present evidence for a strong positive correlation between this minimal timescale and a similar timescale extracted from the corresponding power spectra of these sources.
We have investigated the time variations in the light curves from a sample of long and short Fermi/GBM gamma-ray bursts (GRBs) using an impartial wavelet analysis. The results indicate that in the ...source frame, the variability time-scales for long bursts differ from that for short bursts, variabilities of the order of a few milliseconds are not uncommon and an intriguing relationship exists between the minimum variability time and the burst duration.
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