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Register a new userMulti-wavelength observations of the Galactic X-ray binaries IGR J20155+3827 and Swift J1713.4-4219
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In recent years, thanks to the continuous surveys performed by INTEGRAL and Swift satellites, our knowledge of the hard X-ray/soft gamma-ray sky has greatly improved. As a result it is now populated with about 2000 sources, both Galactic and extra-galactic, mainly discovered by IBIS and BAT instruments. Many different follow-up campaigns have been successfully performed by using a multi-wavelength approach, shedding light on the nature of a number of these new hard X-ray sources. However, a fraction are still of a unidentified nature. This is mainly due to the lack of lower energy observations, which usually deliver a better constrained position for the sources, and the unavailability of the key observational properties, needed to obtain a proper physical characterization. Here we report on the classification of two poorly studied Galactic X-ray transients IGR J20155+3827 and Swift J1713.4-4219, for which the combination of new and/or archival X-ray and Optical/NIR observations have allowed us to pinpoint their nature. In particular, thanks to XMMNewton archival data together with new optical spectroscopic and archival Optical/NIR photometric observations, we have been able to classify IGR J20155+3827 as a distant HMXB. The new INTEGRAL and Swift data collected during the 2019 X-ray outburst of Swift J1713.4-4219, in combination with the archival optical/NIR observations, suggest a LMXB classification for this source.
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We present simultaneous, multi-wavelength observations of the Small Magellanic Cloud Be/XRB IGR J01217-7257 (=SXP 2.16) during outbursts in 2014, 2015 and 2016. We also present the results of RXTE observations of the Small Magellanic Cloud during which the source was initially discovered with a periodicity of 2.1652$pm$0.0001 seconds which we associate with the spin period of the neutron star. A systematic temporal analysis of long term Swift/BAT data reveals a periodic signal of 82.5$pm$0.7 days, in contrast with a similar analysis of long base line OGLE I-band light curves which reveals an 83.67$pm$0.05 days also found in this work. Interpreting the longer X-ray periodicity as indicative of binary motion of the neutron star, we find that outbursts detected by INTEGRAL and Swift between 2014 and 2016 are consistent with Type I outbursts seen in Be/XRBs, occurring around periastron. Comparing these outbursts with the OGLE data, we see a clear correlation between outburst occurrence and increasing I-band flux. A periodic analysis of subdivisions of OGLE data reveals three epochs during which short periodicities of $sim$1 day are significantly detected which we suggest are non-radial pulsations (NRPs) of the companion star. These seasons immediately precede those exhibiting clear outburst behaviour, supporting the suggested association between the NRPs, decretion disk growth and the onset of Type I outbursts.
We present the results obtained from detailed spectral and timing studies of extra-galactic black hole X-ray binaries LMC~X--1 and LMC~X--3, using simultaneous observations with {it Nuclear Spectroscopic Telescope Array (NuSTAR)} and {it Neil Gehrels Swift} observatories. The combined spectra in the $0.5-30$~keV energy range, obtained between 2014 and 2019, are investigated for both sources. We do not find any noticeable variability in $0.5-30$~keV light curves, with $0.1-10$~Hz fractional rms estimated to be $<2$%. No evidence of quasi-periodic oscillations is found in the power density spectra. The sources are found to be in the high soft state during the observations with disc temperature $T_{rm in}sim 1$~keV, photon index, $Gamma > 2.5$ and thermal emission fraction, $f_{rm disc}>80$%. An Fe K$alpha$ emission line is detected in the spectra of LMC~X--1, though no such feature is observed in the spectra of LMC~X--3. From the spectral modelling, the spins of the black holes in LMC~X--1 and LMC~X--3 are estimated to be in the range of $0.92-0.95$ and $0.19-0.29$, respectively. The accretion efficiency is found to be, $eta sim 0.13$ and $eta sim 0.04$ for LMC~X--1 and LMC~X--3, respectively.
We present late-time multi-wavelength observations of Swift J1644+57, suggested to be a relativistic tidal disruption flare (TDF). Our observations extend to >4 years from discovery, and show that 1.4 years after outburst the relativistic jet switched-off on a timescale less than tens of days, corresponding to a power-law decay faster than $t^{-70}$. Beyond this point weak X-rays continue to be detected at an approximately constant luminosity of $L_X sim 5 times 10^{42}$ erg s$^{-1}$, and are marginally inconsistent with a continuing decay of $t^{-5/3}$, similar to that seen prior to the switch-off. Host photometry enables us to infer a black hole mass of $M_{BH}=3 times 10^6$ M$_{odot}$, consistent with the late time X-ray luminosity arising from sub-Eddington accretion onto the black hole in the form of either an unusually optically faint AGN or a slowly varying phase of the transient. Optical/IR observations show a clear bump in the light curve at timescales of 30-50 days, with a peak magnitude (corrected for host galaxy extinction) of $M_R sim -22-23$. The luminosity of the bump is significantly higher than seen in other, non-relativistic TDFs and does not match any re-brightening seen at X-ray or radio wavelengths. Its luminosity, light curve shape and spectrum are broadly similar to those seen in superluminous SNe, although subject to large uncertainties in the correction of the significant host extinction. We discuss these observations in the context of both TDF and massive star origins for Swift J1644+5734 and other candidate relativistic tidal flares.
We summarize the results of our long-running campaign to help understand the nature of high-mass X-ray binaries (HMXBs), emphasizing recent Suzaku observations of IGR J16207-5129 and IGR J17391-3021. Thanks to the expanding ranks of HMXBs in our Galaxy, we are able to perform more reliable statistical analyses on the three currently-known sub-classes of HMXB: those with supergiant companions (SGXBs); those with Be companions (BEXBs); and the enigmatic Supergiant Fast X-ray Transients (SFXTs). We discuss new diagnostic tools, akin to the Corbet diagram, in which HMXBs tend to segregate based on their dominant accretion mechanism. We show how SFXTs span across the divided populations of BEXBs and SGXBs, bolstering the intriguing possibility that some SFXTs represent an evolutionary link. The use of HMXBs as tracers of recent massive star formation is revisited as we present the first ever spatial correlation function for HMXBs and OB star-forming complexes. Our results indicate that at distances less than a few kpc from a given HMXB, it is more likely to have neighbors that are known massive-star forming regions as opposed to objects drawn from random distributions. The characteristic scale of the correlation function holds valuable clues to HMXB evolutionary timescales.
In this paper we report on a long multi-wavelength observational campaign of the supergiant fast X-ray transient prototype IGR J17544-2619. A 150 ks-long observation was carried out simultaneously with XMM-Newton and NuSTAR, catching the source in an initial faint X-ray state and then undergoing a bright X-ray outburst lasting about 7 ks. We studied the spectral variability during outburst and quiescence by using a thermal and bulk Comptonization model that is typically adopted to describe the X-ray spectral energy distribution of young pulsars in high mass X-ray binaries. Although the statistics of the collected X-ray data were relatively high we could neither confirm the presence of a cyclotron line in the broad-band spectrum of the source (0.5-40 keV), nor detect any of the previously reported tentative detection of the source spin period. The monitoring carried out with Swift/XRT during the same orbit of the system observed by XMM-Newton and NuSTAR revealed that the source remained in a low emission state for most of the time, in agreement with the known property of all supergiant fast X-ray transients being significantly sub-luminous compared to other supergiant X-ray binaries. Optical and infrared observations were carried out for a total of a few thousands of seconds during the quiescence state of the source detected by XMM-Newton and NuSTAR. The measured optical and infrared magnitudes were slightly lower than previous values reported in the literature, but compatible with the known micro-variability of supergiant stars. UV observations obtained with the UVOT telescope on-board Swift did not reveal significant changes in the magnitude of the source in this energy domain compared to previously reported values.
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