We report Swift/BAT survey observations of the Tychos supernova remnant, performed over a period of 104 months since the missions launch. The remnant is detected with high significance (>10 sigma) below 50 keV. We detect significant hard X-ray emissi
on in the 60-85 keV band, above the continuum level predicted by a simple synchrotron model. The location of the observed excess is consistent with line emission from radioactive Titanium-44, so far reported only for Type II supernova explosions. We discuss the implications of these results in the context of the galactic supernova rate, and nucleosynthesis in Type Ia supernova.
We have analyzed the Swift data relevant to the high mass X-ray binary Swift J1816.7-1613. The timing analysis of the BAT survey data unveiled a modulation at a period of P_0=118.5+/-0.8 days that we interpret as the orbital period of the X-ray binar
y system. The modulation is due to a sequence of bright flares, lasting ~30 d, separated by long quiescence intervals. This behavior is suggestive of a Be binary system, where periodic or quasi-periodic outbursts are the consequence of an enhancement of the accretion flow from the companion star at the periastron passage. The position of Swift J1816.7-1613 on the Corbet diagram strengthens this hypothesis. The broad band 0.2-150 keV spectrum is well modeled with a strongly absorbed power-law with a flat photon index Gamma~ 0.2 and a cut-off at ~ 10 keV.
We report on the temporal and spectral properties of the HMXB IGR J16283-4838 in the hard X-ray band. We searched the first 88 months of Swift BAT survey data for long-term periodic modulations. We also investigated the broad band (0.2--150 keV) spec
tral properties of IGR J16283--4838 complementing the BAT dataset with the soft X-ray data from the available Swift-XRT pointed observations. The BAT light curve of IGR J16283-4838 revealed a periodic modulation at P_o=287.6+7-1.7 days (with a significance higher than 4 standard deviations). The profile of the light curve folded at P_o shows a sharp peak lasting ~ 12 d, over a flat plateau. The long-term light curve shows also a ~300 d interval of prolonged enhanced emission. The observed phenomenology is suggestive of a Be nature of IGR J16283-4838, where the narrow periodic peaks and the ~300 d outburst can be interpreted as Type I and Type II outbursts, respectively. The broad band 0.2-150 keV spectrum can be described with an absorbed power-law and a steepening in the BAT energy range.
IGR J18219-1347 is a hard X-ray source discovered by INTEGRAL in 2010. We have analyzed the X-ray emission of this source exploiting the BAT survey data up to March 2012 and the XRT data that include also an observing campaign performed in early 2012
. The source is detected at a significance level of ~14 standard deviations in the 88-month BAT survey data, and shows a strong variability along the survey monitoring, going from high intensity to quiescent states. A timing analysis on the BAT data revealed an intensity modulation with a period of 72.46 days. The significance of this modulation is about 7 standard deviations in Gaussian statistics. We interpret it as the orbital period of the binary system. The light curve folded at P_0 shows a sharp peak covering ~30% of the period, superimposed to a flat level roughly consistent with zero. In the soft X-rays the source is detected only in 5 out of 12 XRT observations, with the highest recorded count rate corresponding to a phase close to the BAT folded light curve peak. The long orbital period and the evidence that the source emits only during a small fraction of the orbit suggests that the IGR J18219-1347 binary system hosts a Be star. The broad band XRT+BAT spectrum is well modeled with a flat absorbed power law with a high energy exponential cutoff at ~11 keV.
In the last years the hard X-ray astronomy has made a significant step forward, thanks to the monitoring of the IBIS/ISGRI telescope on board the INTEGRAL satellite and of the Burst Alert Telescope (BAT) on board of the Swift observatory. This has pr
ovided a huge amount of novel information on many classes of sources. We have been exploiting the BAT survey data to study the variability and the spectral properties of the new high mass X-ray binary sources detected by INTEGRAL. In this letter we investigate the properties of IGR J015712-7259. We perform timing analysis on the 88-month BAT survey data and on the XRT pointed observations of this source. We also report on the broad-band 0.2-150 keV spectral analysis. We find evidence for a modulation of the hard-X-ray emission with period P_o=35.6 days. The significance of this modulation is 6.1 standard deviations. The broad band spectrum is modeled with an absorbed power law with photon index Gamma 0.4 and a steepening in the BAT energy range modeled with a cutoff at an energy of ~13 keV.}
IGR J11305-6256 is one of the numerous sources discovered through the INTEGRAL scan of the Galactic Plane. Thanks to the Swift-BAT survey, that allows the frequent sampling of any sky region, we have discovered in the hard X-ray emission of this sour
ce a modulation with a period of ~120.83 d. The significance of this periodic modulation is ~4 standard deviations in Gaussian statistics. We interpret it as the orbital period of the binary system. We derive an orbital separation between IGR J11305-6256 and its companion star of ~286 R$_{odot}$ corresponding to ~19 times the radius of the companion star. The broadband XRT-BAT (0.3-150 keV) spectrum is described either by the sum of a black-body and a cut-off power-law or by a partially absorbed cut-off power-law. The temporal and spectral characteristics of the source indicate its possible association with the class of persistent, but faint, Be X-ray binary systems.
The X-Ray Telescope (XRT) on board Swift was mainly designed to provide detailed position, timing and spectroscopic information on Gamma-Ray Burst (GRB) afterglows. During the mission lifetime the fraction of observing time allocated to other types o
f source has been steadily increased. In this paper, we report on the results of the in-flight calibration of the timing capabilities of the XRT in Windowed Timing read-out mode. We use observations of the Crab pulsar to evaluate the accuracy of the pulse period determination by comparing the values obtained by the XRT timing analysis with the values derived from radio monitoring. We also check the absolute time reconstruction measuring the phase position of the main peak in the Crab profile and comparing it both with the value reported in literature and with the result that we obtain from a simultaneous Rossi X-Ray Timing Explorer (RXTE) observation. We find that the accuracy in period determination for the Crab pulsar is of the order of a few picoseconds for the observation with the largest data time span. The absolute time reconstruction, measured using the position of the Crab main peak, shows that the main peak anticipates the phase of the position reported in literature for RXTE by ~270 microseconds on average (~150 microseconds when data are reduced with the attitude file corrected with the UVOT data). The analysis of the simultaneous Swift-XRT and RXTE Proportional Counter Array (PCA) observations confirms that the XRT Crab profile leads the PCA profile by ~200 microseconds. The analysis of XRT Photodiode mode data and BAT event data shows a main peak position in good agreement with the RXTE, suggesting the discrepancy observed in XRT data in Windowed Timing mode is likely due to a systematic offset in the time assignment for this XRT read out mode.
We present an overview of our Supergiant Fast X-ray Transients (SFXT) project, that started in 2007, by highlighting the unique observational contribution Swift is giving to this exciting new field. By means of outburst detection with Swift/BAT and f
ollow-up with Swift/XRT, we demonstrated that while the brightest phase of the outburst only lasts a few hours, further significant activity is observed at lower fluxes for a considerably longer (weeks) time. After intense monitoring with Swift/XRT, we now have a firm estimate of the time SFXTs spend in each phase. The 4 SFXTs we monitored for 1-2 years spend between 3 and 5 % of the time in bright outbursts. The most most probable flux level at which a random observation will find these sources, when detected, is F(2-10 keV) ~ 1-2E-11 erg cm^{-2} s^{-1} (unabsorbed), corresponding to luminosities of a few 10^{33} to a few 10^{34} erg s^{-1}. Finally, the duty-cycle of inactivity ranges between 19 and 55 %.
Swift is the only observatory which, due to its unique fast-slewing capability and broad-band energy coverage, can detect outbursts from Supergiant Fast X-ray Transients (SFXTs) from the very beginning and study their evolution panchromatically. Than
ks to its flexible observing scheduling, which makes monitoring cost-effective, Swift has also performed a campaign that covers all phases of the lives of SFXTs with a high sensitivity in the soft X-ray regime, where most SFXTs had not been observed before. Our continued effort at monitorning SFXTs with 2-3 observations per week (1-2 ks) with the Swift X-Ray Telescope (XRT) over their entire visibility period has just finished its second year. We report on our findings on the long-term properties of SFXTs, their duty cycle, and the new outbursts caught by Swift during the second year.
We present two years of intense Swift monitoring of three SFXTs, IGR J16479-4514, XTE J1739-302, and IGR J17544-2619 (since October 2007). Out-of-outburst intensity-based X-ray (0.3-10keV) spectroscopy yields absorbed power laws with by hard photon i
ndices (G~1-2). Their outburst broad-band (0.3-150 keV) spectra can be fit well with models typically used to describe the X-ray emission from accreting NSs in HMXBs. We assess how long each source spends in each state using a systematic monitoring with a sensitive instrument. These sources spend 3-5% of the total in bright outbursts. The most probable flux is 1-2E-11 erg cm^{-2} s^{-1} (2-10 keV, unabsorbed), corresponding to luminosities in the order of a few 10^{33} to 10^{34} erg s^{-1} (two orders of magnitude lower than the bright outbursts). The duty-cycle of inactivity is 19, 39, 55%, for IGR J16479-4514, XTE J1739-302, and IGR J17544-2619, respectively. We present a complete list of BAT on-board detections further confirming the continued activity of these sources. This demonstrates that true quiescence is a rare state, and that these transients accrete matter throughout their life at different rates. X-ray variability is observed at all timescales and intensities we can probe. Superimposed on the day-to-day variability is intra-day flaring which involves variations up to one order of magnitude that can occur down to timescales as short as ~1ks, and whichcan be explained by the accretion of single clumps composing the donor wind with masses M_cl~0.3-2x10^{19} g. (Abridged)
