We report here on the longest deep X-ray observation of a SFXT outside outburst, with an average luminosity level of 1E33 erg/s (assuming 3 kpc distance). This observation was performed with Suzaku in December 2009 and was targeted on IGRJ08408-4503, with a net exposure with the X-ray imaging spectrometer (XIS, 0.4-10 keV) and the hard X-ray detector (HXD, 15-100 keV) of 67.4 ks and 64.7 ks, respectively, spanning about three days. The source was caught in a low intensity state characterized by an initially average X-ray luminosity level of 4E32 erg/s (0.5-10 keV) during the first 120 ks, followed by two long flares (about 45 ks each) peaking at a flux a factor of about 3 higher than the initial pre-flare emission. Both XIS spectra (initial emission and the two subsequent long flares) can be fitted with a double component spectrum, with a soft thermal plasma model together with a power law, differently absorbed. The spectral characteristics suggest that the source is accreting matter even at this very low intensity level. From the HXD observation we place an upper limit of 6E33 erg/s (15-40 keV; 3 kpc distance) to the hard X-ray emission, which is the most stringent constrain to the hard X-ray emission during a low intensity state in a SFXT, to date. The timescale observed for the two low intensity long flares is indicative of an orbital separation of the order of 1E13 cm in IGRJ08408-4503.
We present the first direct evidence for dense clumps of matter in the companion wind in a Supergiant Fast X-ray Transient (SFXT) binary. This is seen as a brief period of enhanced absorption during one of the bright, fast flares that distinguish these systems. The object under study was IGR J17544-2619, and a total of 236 ks of data were accumulated with the Japanese satellite Suzaku. The activity in this period spans a dynamic range of almost 10000 in luminosity and gives a detailed look at SFXT behavior.
We report on a 250 ks long X-ray observation of the supergiant fast X-ray transient (SFXT) IGR J16479-4514 performed with Suzaku in 2012 February. About 80% of the short orbital period (Porb=3.32 days) was covered as continuously as possible for the first time. The source light curve displays variability of more than two orders of magnitude, starting with a very low emission state lasting the first 46 ks (1E-13 erg/cm2/s, 1-10 keV), consistent with being due to the X-ray eclipse by the supergiant companion. The transition to the uneclipsed X-ray emission is energy dependent. Outside the eclips…
The eclipsing hard X-ray source IGR J16479-4514 is the Supergiant Fast X-ray Transient (SFXT) with the shortest orbital period (3.32 days). This allowed us to perform a 250 ks long X-ray observation with Suzaku in 2012 February, covering most of its orbit, including the eclipse egress. Outside the eclipse, the source luminosity is around a few 1E34erg/s. The X-ray spectrum can be fit with an absorbed power law together with a neutral iron emission line at 6.4 keV. The column density is constant at 1E23 cm-2 outside the X-ray eclipse. During the eclipse it is lower, consistent with a scattering…
Suzaku observations are presented for the high-mass X-ray binaries IGR J16207-5129 and IGR J17391-3021 (=XTE J1739-302). For IGR J16207-5129, we provide the first X-ray broadband (0.5--60 keV) spectrum from which we confirm a large intrinsic column density (nH = 1.6e23 /cm2), and we constrain the cutoff energy for the first time (Ec = 19 keV). A prolonged (> 30 ks) attenuation of the X-ray flux was observed which we tentatively attribute to an eclipse of the probable neutron star by its massive companion, in a binary system with an orbital period between 4 and 9 days, and inclination angles > …
Supergiant Fast X-ray Transients are a class of Galactic High Mass X-ray Binaries with supergiant companions. Their extreme transient X-ray flaring activity was unveiled thanks to INTEGRAL/IBIS observations. The SFXTs dynamic range, with X-ray luminosities from 1E32 erg/s to 1E37 erg/s, and long time intervals of low X-ray emission, are puzzling, given that both their donor star properties and their orbital and spin periodicities seem very similar to those displayed by massive binaries with persistent X-ray emission. Clumpy supergiant winds, accretion barriers, orbital geometries and wind anis…
The X-ray binary 4U 1954+31 has been classified as a Low Mass X-ray Binary (LMXB) containing a M giant and a neutron star (NS). It has also been included in the rare class of X-ray symbiotic binaries (SyXB). The Gaia parallax, infrared colors, spectral type, abundances, and orbital properties of the M star demonstrate that the cool star in this system is not a low mass giant but a high mass M supergiant. Thus, 4U 1954+31 is a High Mass X-ray Binary (HMXB) containing a late-type supergiant. It is the only known binary system of this type. The mass of the M I is 9$^{+6}_{-2}$ M$_\odot$ giving an…
We present the results from analyses of Suzaku observations of the supergiant X-ray binaries IGR J16207-5129 and IGR J17391-3021. For IGR J16207-5129, we provide the first broadband (0.5--60 keV) spectrum from which we confirm a large intrinsic column density (nH = 16e22 /cm2), and constrain the cutoff energy for the first time (Ec = 19 keV). We observed a prolonged (> 30 ks) attenuation of the X-ray flux which we tentatively attribute to an eclipse of the probable neutron star by its massive companion. For IGR J17391-3021, we witnessed a transition from quiescence to a low-activity phase punc…
X-ray reverberation lags from the vicinity of supermassive black holes have been detected in almost 30 AGN. The soft lag, which is the time delay between the hard and soft X-ray light curves, is usually interpreted as the time difference between the direct and reflected emission, but is alternatively suggested to arise from the direct and scattering emission from distant clouds. By analysing the archival Suzaku observations totalling an exposure time of ~ 770 ks, we discover a soft lag of $10\pm3.4$ ks at $9.58\times10^{-6}$ Hz in the luminous quasar PDS 456, which is the longest soft lag and …
We present the results obtained from broadband spectroscopy of the high mass X-ray binary 4U 1700-37 using data from a Suzaku observation in 2006 September 13-14 covering 0.29-0.72 orbital phase range. The light curves showed significant and rapid variation in source flux during entire observation. We did not find any signature of pulsations in the light curves. However, a quasi-periodic oscillation at ~20 mHz was detected in the power density spectrum of the source. The 1-70 keV spectrum was fitted with various continuum models. However, we found that the partially absorbed high energy cutoff…
We present an analysis of a 37-ks observation of the supergiant fast X-ray transient (SFXT) IGR J17391-3021 (=XTE J1739-302) gathered with Suzaku. The source evolved from quiescence to a low-activity level culminating in three weak flares lasting ~3 ks each in which the peak luminosity is only a factor of 5 times that of the pre-flare luminosity. The minimum observed luminosity was 1.3x10^33 erg/s (d/2.7 kpc)^2 in the 0.5--10 keV range. The weak flares are accompanied by significant changes in the spectral parameters including a column density (nH = (4.1+-0.5)x10^22 /cm^2) that is ~2--9 times …
We present a broadband spectral analysis of accreting neutron stars using data from XIS and PIN onboard \emph{Suzaku}. From spectral fits of these sources with a single continuum model including a powerlaw and high energy cut-off, cyclotron lines (where required), we studied the correlation between various spectral parameters. Among 39 sources we studied, 16 are those where the existence of a cyclotron line is known in literature, and 29 need a cutoff energy. Among these 29 sources, 18 have cutoff energy bunched in a range of 3-10 keV while for 11 sources, it spreads over 12-25 keV. This bi-mo…
We present the first dedicated X-ray study of the supernova remnant (SNR) G32.8-0.1 (Kes 78) with Suzaku. X-ray emission from the whole SNR shell has been detected for the first time. The X-ray morphology is well correlated with the emission from the radio shell, while anti-correlated with the molecular cloud found in the SNR field. The X-ray spectrum shows not only conventional low-temperature (kT ~ 0.6 keV) thermal emission in a non-equilibrium ionization state, but also a very high temperature (kT ~ 3.4 keV) component with a very low ionization timescale (~ 2.7e9 cm^{-3}s), or a hard non-th…
We present X-ray flux and spectral analyses of the three pointed Suzaku observations of the TeV high synchrotron peak blazar Mrk 421 taken throughout its complete operational duration. The observation taken on 5 May 2008 is, at 364.6 kiloseconds (i.e., 101.3 hours), the longest and most evenly sampled continuous observation of this source, or any blazar, in the X-ray energy 0.8 - 60 keV until now. We found large amplitude intra-day variability in all soft and hard bands in all the light curves. The discrete correction function analysis of the light curves in soft and hard bands peaks on zero l…
We present broad-band pulsation and spectral characteristics of the accreting X-ray pulsar OAO 1657--415 with a 2.2 d long \emph{Suzaku} observation carried out covering its orbital phase range $\sim$ 0.12--0.34, with respect to the mid-eclipse. During the last third of the observation, the X-ray count rate in both the X-ray Imaging Spectrometer (XIS) and the HXD-PIN instruments increased by a factor of more than 10. During this observation, the hardness ratio also changed by a factor of more than 5, uncorrelated with the intensity variations. In two segments of the observation, lasting for $\…
We present optical, X-ray and gamma-ray observations of GRB 111209A, at a redshift of z = 0.677. We show that this event was active in its prompt phase for about 25000 seconds, making it the longest burst ever observed. This rare event could have been detected up to z ~ 1.4. Compared to other long GRBs, GRB 111209A is a clear outlier in the energy-fluence and duration plane. The high-energy prompt emission shows no sign of a strong black body component, as expected if the event was caused by a tidal disruption event or a supernova shock breakout. Given the extreme longevity of this event, and …
We present a comparative study of stellar winds in classical supergiant high mass X-ray binaries (SgXBs) and supergiant fast X-ray transients (SFXTs) based on the analysis of publicly available out-of-eclipse observations performed with Suzaku and XMM-Newton. Our data-set includes 55 observations of classical SgXBs and 21 observations of SFXTs. We found that classical SgXBs are characterized by a systematically higher absorption and luminosity compared to the SFXTs, confirming the results of previous works in the literature. Additionally, we show that the equivalent width of the fluorescence K…
Swift recently discovered an unusual gamma-ray and x-ray transient (Sw 1644+57) that was initially identified as a long-duration gamma-ray burst (GRB). However, the ~ 10 keV x-ray emission has persisted for over a month with a luminosity comparable to its peak value. The astrometric coincidence of the source with the center of its host galaxy, together with other considerations, motivated the interpretation that Sw 1644+57 was produced by an outburst from a 10^{6-7} M_sun black hole at the center of the galaxy. Here we consider the alternate possibility that Sw 1644+57 is indeed a long-duratio…
Context. About 120 Be/X-ray binaries (BeXBs) are known in the Small Magellanic Cloud (SMC); about half of them are pulsating with periods from a few to hundreds of seconds. SXP 1323 is one of the longest-period pulsars known in this galaxy. Aims. SXP 1323 is in the field of view of a large set of calibration observations that we analyse systematically, focusing on the time analysis, in search of periodic signals. Methods. We analyse all available X-ray observations of SXP 1323 from Suzaku, XMM-Newton, and Chandra, in the time range from 1999 to the end of 2016. We perform a Lomb-Scargle period…
Molecular clouds are predicted to emit nonthermal X-rays when they are close to particle-accelerating supernova remnants (SNRs), and the hard X-ray source AX J1714.1-3912, near the SNR RX J1713.7-3946, has long been considered a candidate for diffuse nonthermal emission associated with cosmic rays diffusing from the remnant to a closeby molecular cloud. We aim at ascertaining the nature of this source by analyzing two dedicated X-ray observations performed with Suzaku and Chandra. We extracted images from the data in various energy bands, spectra, and light curves and studied the long-term evo…
The "ultra-long" Gamma Ray Burst GRB 111209A at redshift z=0.677, is so far the longest GRB ever observed, with rest frame prompt emission duration of ~4 hours. In order to explain the bursts exceptional longevity, a low metallicity blue supergiant progenitor has been invoked. In this work, we further investigate this peculiar burst by performing a multi-band temporal and spectral analysis of both the prompt and the afterglow emission. We use proprietary and publicly available data from Swift, Konus Wind, XMM-Newton, TAROT as well as from other ground based optical and radio telescopes. We fin…
We report the results of a high-energy multi-instrumental campaign with INTEGRAL, RXTE, and Swift of the recently discovered INTEGRAL source IGR J19294+1816. The Swift/XRT data allow us to refine the position of the source to RA= 19h 29m 55.9s Dec=+18deg 18' 38.4" (+- 3.5"), which in turn permits us to identify a candidate infrared counterpart. The Swift and RXTE spectra are well fitted with absorbed power laws with hard (Gamma ~ 1) photon indices. During the longest Swift observation, we obtained evidence of absorption in true excess to the Galactic value, which may indicate some intrinsic ab…
This study presents the temporal and spectral analysis of the prompt emission of two high-redshift gamma-ray bursts (GRBs), 120521C at $z\sim6$ and 130606A at $z\sim5.91$, which were performed using the Swift-XRT/BAT and the Suzaku-WAM simultaneously. Based on follow-up XRT observations, the longest durations of the prompt emissions were approximately $80$ s (120521C) and $360$ s (130606A) in the rest frame of each GRB, which are categorized as long-duration GRBs, but are insufficiently long compared with the predicted duration of GRBs that originate from first-generation stars. Because of the…
