- ID:
- ivo://CDS.VizieR/J/ApJS/208/25
- Title:
- Swift X-ray observations of 1FGL sources
- Short Name:
- J/ApJS/208/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed all the archival X-ray data of 134 unidentified (unID) gamma-ray sources listed in the first Fermi/LAT (1FGL) catalog and subsequently followed up by the Swift/XRT. We constructed the spectral energy distributions (SEDs) from radio to gamma-rays for each X-ray source detected, and tried to pick up unique objects that display anomalous spectral signatures. In these analyses, we target all the 1FGL unID sources, using updated data from the second Fermi/LAT (2FGL) catalog on the Large Area Telescope (LAT) position and spectra. We found several potentially interesting objects, particularly three sources, 1FGL J0022.2-1850, 1FGL J0038.0+1236, and 1FGL J0157.0-5259, which were then more deeply observed with Suzaku as a part of an AO-7 program in 2012. We successfully detected an X-ray counterpart for each source whose X-ray spectra were well fitted by a single power-law function. The positional coincidence with a bright radio counterpart (currently identified as an active galactic nucleus, AGN) in the 2FGL error circles suggests these sources are definitely the X-ray emission from the same AGN, but their SEDs show a wide variety of behavior. In particular, the SED of 1FGL J0038.0+1236 is not easily explained by conventional emission models of blazars. The source 1FGL J0022.2-1850 may be in a transition state between a low-frequency peaked and a high-frequency peaked BL Lac object, and 1FGL J0157.0-5259 could be a rare kind of extreme blazar.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/547/A57
- Title:
- Swift X-ray Telescope Cluster Survey
- Short Name:
- J/A+A/547/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new sample of X-ray selected galaxy groups and clusters serendipitously observed with Swift and the X-ray Telescope (XRT). We searched the XRT archive for extended sources among 336 GRB fields with galactic latitude |b|>20{deg}. Our selection algorithm yields a flux-limited sample of 72 X-ray groups and clusters with a well defined selection function and negligible contamination. The sky coverage of the survey goes from the total 40deg^2^ to 1deg^2^ at a flux limit of 10^-14^erg/s/cm^-2 (0.5-2keV). All the X-ray sources are detected in the Swift-XRT soft (0.5-2keV) band.
- ID:
- ivo://CDS.VizieR/J/A+A/567/A89
- Title:
- Swift X-ray Telescope Cluster Survey. II.
- Short Name:
- J/A+A/567/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectral analysis of a new, flux-limited sample of 72 X-ray selected clusters of galaxies identified with the X-ray Telescope (XRT) on board the Swift satellite down to a flux limit of ~10^-14^erg/s/cm2 (SWXCS). We carry out a detailed X-ray spectral analysis with the twofold aim of measuring redshifts and characterizing the properties of the intracluster medium (ICM) for the majority of the SWXCS sources. Optical counterparts and spectroscopic or photometric redshifts for some of the sources are obtained with a cross-correlation with the NASA/IPAC Extragalactic Database. Additional photometric redshifts are computed with a dedicated follow-up program with the Telescopio Nazionale Galileo and a cross-correlation with the SDSS. In addition, we also blindly search for the Hydrogen-like and He-like iron K_{alpha}_ emission line complex in the X-ray spectrum. We detect the iron emission lines in 35% of the sample, and hence obtain a robust measure of the X-ray redshift z_X_ with typical rms error 1-5%. We use z_X_ whenever the optical redshift is not available. Finally, for all the sources with measured redshift, background-subtracted spectra are fitted with a single-temperature mekal model to measure global temperature, X-ray luminosity and iron abundance of the ICM. We perform extensive spectral simulations to accounts for fitting bias, and to assess the robustness of our results. We derive a criterion to select reliable best-fit models and an empirical formula to account for fitting bias. The bias-corrected values are then used to investigate the scaling properties of the X-ray observables.
- ID:
- ivo://CDS.VizieR/J/ApJ/889/142
- Title:
- Swift/XRT and NICER timing study of MAXI J1820+070
- Short Name:
- J/ApJ/889/142
- Date:
- 03 Dec 2021 13:13:00
- Publisher:
- CDS
- Description:
- We present a detailed timing analysis of the bright black hole X-ray binary MAXI J1820+070 (ASASSN-18ey), during its first detected outburst lasting from 2018 March until 2019 October based on Swift/XRT window timing mode observations, corresponding UVOT data and NICER observations. The light curves clearly show four outbursts, with the source remaining in the hard state during its first outburst, while the rise of the second outburst corresponds with the transition to the soft state. A similar double outburst of GX339-4 has been observed in 2004. Here it is followed by two hard-state only outbursts. In many observations the power density spectra showed type-C quasi-periodic oscillations (QPOs) with characteristic frequencies below 1Hz, which suggests that the source stayed in a state of low effective accretion for large parts of its outburst. The absence of other types of QPOs hinders a precise determination of the state transitions, but from combining NICER and Swift/XRT data, we find that MAXI J1820+070 went from the hard-intermediate to the soft state in less than one day. The covariance ratios derived from NICER data show an increase toward lower energies, which indicate that the source should make a transition to the soft state. This transition finally took place, after MAXI J1820+070 stayed in the hard state at rather constant luminosity for about 116 days. The steepness of the increase of the covariance ratios is not correlated with the amount of rms variability and it does not show a monotonic evolution along the outburst.
- ID:
- ivo://CDS.VizieR/J/ApJS/245/15
- Title:
- Swift XRT follow-up of LIGO/Virgo GW triggers
- Short Name:
- J/ApJS/245/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Neil Gehrels Swift Observatory carried out prompt searches for gravitational-wave (GW) events detected by the LIGO/Virgo Collaboration (LVC) during the second observing run ("O2"). Swift performed extensive tiling of eight LVC triggers, two of which had very low false-alarm rates (GW170814 and the epochal GW170817), indicating a high confidence of being astrophysical in origin; the latter was the first GW event to have an electromagnetic counterpart detected. In this paper we describe the follow-up performed during O2 and the results of our searches. No GW electromagnetic counterparts were detected; this result is expected, as GW170817 remained the only astrophysical event containing at least one neutron star after LVC's later retraction of some events. A number of X-ray sources were detected, with the majority of identified sources being active galactic nuclei. We discuss the detection rate of transient X-ray sources and their implications in the O2 tiling searches. Finally, we describe the lessons learned during O2 and how these are being used to improve the Swift follow-up of GW events. In particular, we simulate a population of gamma-ray burst afterglows to evaluate our source ranking system's ability to differentiate them from unrelated and uncataloged X-ray sources. We find that ~60%-70% of afterglows whose jets are oriented toward Earth will be given high rank (i.e., "interesting" designation) by the completion of our second follow-up phase (assuming that their location in the sky was observed), but that this fraction can be increased to nearly 100% by performing a third follow-up observation of sources exhibiting fading behavior.
- ID:
- ivo://CDS.VizieR/J/ApJ/768/47
- Title:
- Swift/XRT 0.2-10keV observations of SN2009ip
- Short Name:
- J/ApJ/768/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Some supernovae (SNe) show evidence for mass-loss events taking place prior to their explosions. Measuring their pre-outburst mass-loss rates provides essential information regarding the mechanisms that are responsible for these events. Here we present XMM-Newton and Swift X-ray observations taken after the latest, and presumably the final, outburst of SN 2009ip. We use these observations as well as new near-infrared and visible-light spectra and published radio and visible-light observations to put six independent order-of-magnitude constraints on the mass-loss rate of the SN progenitor prior to the explosion. Our methods utilize the X-ray luminosity, the bound-free absorption, the H{alpha} luminosity, the SN rise time, free-free absorption, and the bolometric luminosity of the outburst detected prior to the explosion. Assuming spherical mass loss with a wind-density profile, we estimate that the effective mass-loss rate from the progenitor was between 10^-3^ and 10^-2^M_{sun}_/yr, over a few years prior to the explosion, with a velocity of ~10^3^km/s. This mass-loss rate corresponds to a total circumstellar matter (CSM) mass of ~0.04M_{sun}_, within 6x10^15^cm of the SN. We note that the mass-loss rate estimate based on the H{alpha} luminosity is higher by an order of magnitude. This can be explained if the narrow-line H{alpha} component is generated at radii larger than the shock radius, or if the CSM has an aspherical geometry. We discuss simple geometries which are consistent with our results.
- ID:
- ivo://CDS.VizieR/J/ApJ/808/144
- Title:
- Swift/XRT 0.5-10keV obs. of MAXI J1659-152
- Short Name:
- J/ApJ/808/144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an energy dependent X-ray variability study of the 2010 outburst of the black hole X-ray binary MAXI J1659-152 with the Swift X-ray Telescope (XRT). The broadband noise components and the quasi-periodic oscillations (QPO) observed in the power spectra show a strong and varied energy dependence. Combining Swift XRT data with data from the Rossi X-ray Timing Explorer, we report, for the first time, an rms spectrum (fractional rms amplitude as a function of energy) of these components in the 0.5-30keV energy range. We find that the strength of the low-frequency component (<0.1Hz) decreases with energy, contrary to the higher frequency components (>0.1Hz) whose strengths increase with energy. In the context of the propagating fluctuations model for X-ray variability, we suggest that the low-frequency component originates in the accretion disk (which dominates emission below ~2keV) and the higher frequency components are formed in the hot flow (which dominates emission above ~2keV). As the properties of the QPO suggest that it may have a different driving mechanism, we investigate the Lense-Thirring precession of the hot flow as a candidate model. We also report on the QPO coherence evolution for the first time in the energy band below 2keV. While there are strong indications that the QPO is less coherent at energies below 2keV than above 2keV, the coherence increases with intensity similar to what is observed at energies above 2keV in other black hole X-ray binaries.
18488. Swift-XRT long GRB durations
- ID:
- ivo://CDS.VizieR/J/ApJ/800/16
- Title:
- Swift-XRT long GRB durations
- Short Name:
- J/ApJ/800/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The discovery of a number of gamma-ray bursts (GRBs) with duration exceeding 1000s has opened the debate on whether these bursts form a new class of sources, the so-called ultra-long GRBs, or if they are rather the tail of the distribution of the standard long GRB duration. Using the long GRB sample detected by Swift, we investigate the statistical properties of long GRBs and compare them with the ultra-long burst properties. We compute the burst duration of long GRBs using the start epoch of the so-called "steep decay" phase detected with Swift/XRT. We discuss also the differences observed in their spectral properties. We find that ultra-long GRBs are statistically different from the standard long GRBs with typical burst duration less than 100-500s, for which a Wolf-Rayet star progenitor is usually invoked. Together with the presence of a thermal emission component we interpret this result as indication that the usual long GRB progenitor scenario cannot explain the extreme duration of ultra-long GRBs, their energetics, as well as the mass reservoir and size that can feed the central engine for such a long time.
- ID:
- ivo://CDS.VizieR/J/MNRAS/397/1177
- Title:
- Swift-XRT observations of GRBs
- Short Name:
- J/MNRAS/397/1177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a homogeneous X-ray analysis of all 318 Gamma Ray Bursts detected by the X-ray Telescope on the Swift satellite up to 2008 July 23; this represents the largest sample of X-ray GRB data published to date. In Sections 2-3 we detail the methods which the Swift-XRT team has developed to produce the enhanced positions, light curves, hardness ratios and spectra presented in this paper. Software using these methods continues to create such products for all new GRBs observed by the Swift-XRT. We also detail web-based tools allowing users to create these products for any object observed by the XRT, not just GRBs. In Sections 4-6 we present the results of our analysis of GRBs, including probability distribution functions of the temporal and spectral properties of the sample. We demonstrate evidence for a consistent underlying behaviour which can produce a range of light curve morphologies, and attempt to interpret this behaviour in the framework of external forward shock emission. We find several difficulties, in particular that reconciliation of our data with the forward shock model requires energy injection to continue for days to weeks.
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/945
- Title:
- Swift/XRT obs. of unidentified IBIS sources
- Short Name:
- J/MNRAS/403/945
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The most recent IBIS/ISGRI survey, i.e. the fourth one, lists 723 hard X-ray sources, many still unidentified, i.e. lacking an X-ray counterpart or simply not studied at lower energies, i.e. below 10keV. In order to overcome this lack of X-ray information, we cross-correlated the list of IBIS sources included in the fourth IBIS catalogue with the Swift/X-ray Telescope (XRT) data archive, finding a sample of 20 objects, not yet reported in the literature, for which XRT data could help in the search for the X-ray and hence optical counterpart and/or, for the first time, in the study of the source spectral and variability properties below 10keV. 16 of these objects are new INTEGRAL detections, while four were already listed in the third survey but not yet observed in X-rays.