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- ID:
- ivo://CDS.VizieR/J/ApJ/854/66
- Title:
- Swift observations of Mrk 421. I. 2005-2008
- Short Name:
- J/ApJ/854/66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present detailed results of Swift observations of the nearby TeV-detected blazar Mrk 421, based on the rich archival data obtained during 2005 March-2008 June. The best fits of the 0.3-10keV spectra were mainly obtained using the log-parabolic model, yielding low spectral curvatures expected in the case of the efficient stochastic acceleration of particles. During strong X-ray flares, the position of the synchrotron spectral energy distribution peak E_p_ was beyond 8keV for 41 spectra, while it sometimes was situated at the UV frequencies in quiescent states. The photon index at 1 keV exhibited a broad range, and the values a<1.70 were observed during the strong flares, hinting at the possible presence of a jet hadronic component. The spectral parameters were correlated in some periods, expected in the framework of the first- and second-order Fermi accelerations of X-ray emitting particles, as well as in the case of turbulence spectrum. The 0.3-10keV flux and spectral parameters sometimes showed very fast variability down to the fluctuations by 6-20% in 180-960s, possibly related to the small-scale turbulent areas containing strongest magnetic fields. X-ray and very high-energy fluxes often showed correlated variability, although several occurrences of more complicated variability patterns are also revealed, indicating that the multifrequency emission of Mrk 421 could not be generated in a single zone.
- ID:
- ivo://CDS.VizieR/J/ApJS/247/27
- Title:
- Swift obs. of Mrk 421. III. 2015 Dec-2018 Apr
- Short Name:
- J/ApJS/247/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from the timing and spectral study of Mrk 421 based mainly on the Swift data in the X-ray energy range obtained during the time interval 2015 December-2018 April. The most extreme X-ray flaring activity on long-term, daily, and intraday timescales was observed during the 2 month period that started in 2017 December, when the 0.3-10keV flux exceeded a level of 5x10^-9^erg/cm^2^/s, recorded only twice previously. While the TeV- band and X-ray variabilities were mostly correlated, the source often varied in a complex manner in the MeV-GeV and radio-UV energy ranges, indicating that the multifrequency emission of Mrk 421 could not always be generated in a single zone. The longer-term flares at X-rays and {gamma}-rays showed a lognormal character, possibly indicating a variability imprint of the accretion disk onto the jet. A vast majority of the 0.3-10keV spectra were consistent with the log-parabolic model, showing relatively low spectral curvature and correlations between the different spectral parameters, predicted in the case of the first- and second-order Fermi processes. The position of the synchrotron spectral energy distribution peak showed an extreme variability on diverse timescales between the energies Ep<0.1 and >15keV, with 15% of the spectra peaking at the hard X-ray, and was related to the peak height as S^p^{propto}E_p_^{alpha}^ with {alpha}~0.6, which is expected for the transition from Kraichnan-type turbulence into the "hard sphere" one. The 0.3-300GeV spectra showed features of the hadronic contribution, jet-star interaction, and upscatter in the Klein-Nishina regime in different time intervals.
- ID:
- ivo://CDS.VizieR/J/ApJ/858/68
- Title:
- Swift obs. of Mrk 421 in selected epochs. II.
- Short Name:
- J/ApJ/858/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from a detailed spectral and timing study of Mrk 421 based on the rich archival Swift data obtained during 2009-2012. Best fits of the 0.3-10keV spectra were mostly obtained using the log-parabolic model showing the relatively low spectral curvature that is expected in the case of efficient stochastic acceleration of particles. The position of the synchrotron spectral energy density peak E_p_ of 173 spectra is found at energies higher than 2keV. The photon index at 1 keV exhibited a very broad range of values a=1.51-3.02, and very hard spectra with a<1.7 were observed during the strong X-ray flares, hinting at a possible hadronic jet component. The spectral parameters varied on diverse timescales and showed a correlation in some periods, which is expected in the case of first- and second-order Fermi acceleration. The 0.3-10keV flux showed strong X-ray flaring activity by a factor of 3-17 on timescales of a few days-weeks between the lowest historical state and that corresponding to a rate higher than 100ct/s. Moreover, 113 instances of intraday variability were revealed, exhibiting shortest flux-doubling/halving times of about 1.2hr, as well as brightenings by 7%-24% in 180-720 s and declines by 68%-22% in 180-900s. The X-ray and very high-energy fluxes generally showed a correlated variability, although one incidence of a more complicated variability was also detected, indicating that the multifrequency emission of Mrk 421 could not be generated in a single zone.
- ID:
- ivo://CDS.VizieR/J/ApJ/828/3
- Title:
- Swift obs. of the superluminous SNI ASASSN-15lh
- Short Name:
- J/ApJ/828/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present and discuss ultraviolet and optical photometry from the Ultraviolet/Optical Telescope, X-ray limits from the X-Ray Telescope on Swift, and imaging polarimetry and ultraviolet/optical spectroscopy with the Hubble Space Telescope, all from observations of ASASSN-15lh. It has been classified as a hydrogen-poor superluminous supernova (SLSN I), making it more luminous than any other supernova observed. ASASSN-15lh is not detected in the X-rays in individual or co-added observations. From the polarimetry we determine that the explosion was only mildly asymmetric. We find the flux of ASASSN-15lh to increase strongly into the ultraviolet, with an ultraviolet luminosity 100 times greater than the hydrogen-rich, ultraviolet-bright SLSN II SN 2008es. We find that objects as bright as ASASSN-15lh are easily detectable beyond redshifts of ~4 with the single-visit depths planned for the Large Synoptic Survey Telescope. Deep near-infrared surveys could detect such objects past a redshift of ~20, enabling a probe of the earliest star formation. A late rebrightening-most prominent at shorter wavelengths-is seen about two months after the peak brightness, which is itself as bright as an SLSN. The ultraviolet spectra during the rebrightening are dominated by the continuum without the broad absorption or emission lines seen in SLSNe or tidal disruption events (TDEs) and the early optical spectra of ASASSN-15lh. Our spectra show no strong hydrogen emission, showing only Ly{alpha} absorption near the redshift previously found by optical absorption lines of the presumed host. The properties of ASASSN-15lh are extreme when compared to either SLSNe or TDEs.
- ID:
- ivo://CDS.VizieR/J/ApJ/870/123
- Title:
- Swift optical & UV flux of four AGNs
- Short Name:
- J/ApJ/870/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Swift intensive accretion disk reverberation mapping of four AGN yielded light curves sampled ~200-350 times in 0.3-10keV X-ray and six UV/optical bands. Uniform reduction and cross-correlation analysis of these data sets yields three main results: (1) The X-ray/UV correlations are much weaker than those within the UV/optical, posing severe problems for the lamp-post reprocessing model in which variations in a central X-ray corona drive and power those in the surrounding accretion disk. (2) The UV/optical interband lags are generally consistent with {tau}{propto}{lambda}^4/3^ as predicted by the centrally illuminated thin accretion disk model. While the average interband lags are somewhat larger than predicted, these results alone are not inconsistent with the thin disk model given the large systematic uncertainties involved. (3) The one exception is the U band lags, which are on average a factor of ~2.2 larger than predicted from the surrounding band data and fits. This excess appears to be due to diffuse continuum emission from the broad-line region (BLR). The precise mixing of disk and BLR components cannot be determined from these data alone. The lags in different AGN appear to scale with mass or luminosity. We also find that there are systematic differences between the uncertainties derived by Just Another Vehicle for Estimating Lags In Nuclei (JAVELIN) versus more standard lag measurement techniques, with JAVELIN reporting smaller uncertainties by a factor of 2.5 on average. In order to be conservative only standard techniques were used in the analyses reported herein.
- ID:
- ivo://CDS.VizieR/J/ApJ/866/97
- Title:
- Swift X-ray flash & rich gamma-ray bursts in BAT3
- Short Name:
- J/ApJ/866/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We build a comprehensive sample to statistically describe the properties of X-ray flashes (XRFs) and X-ray riches (XRRs) from the third Swift Burst Alert Telescope (BAT3) catalog of Gamma-ray bursts (GRBs). We obtain 81 XRFs, 540 XRRs, and 394 classical GRBs (C-GRBs). We statistically explore the different properties of the {gamma}-ray prompt emission, the X-ray emission, the X-ray light-curve type, the association with supernovae (SNe), and the host galaxy properties for these sources. We confirm that most XRFs/XRRs are long GRBs with low values of peak energy E_peak_^obs^ and they are low-luminosity GRBs. XRFs, XRRs, and C-GRBs follow the same E_X,iso_-E_{gamma},iso_-E_peak,z_ correlations. Compared to the classical GRBs, XRFs are favorable to have the association with SN explosions. We do not find any significant differences of redshift distribution and host galaxy properties among XRFs, XRRs, and C-GRBs. We also discuss some observational biases and selection effects that may affect our statistical results. The GRB detectors with wide energy range and low energy threshold are expected for the XRF/XRR research in the future.
- ID:
- ivo://CDS.VizieR/J/ApJS/197/31
- Title:
- Swift X-ray observations of classical novae. II.
- Short Name:
- J/ApJS/197/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Swift gamma-ray burst satellite is an excellent facility for studying novae. Its rapid response time and sensitive X-ray detector provides an unparalleled opportunity to investigate the previously poorly sampled evolution of novae in the X-ray regime. This paper presents Swift observations of 52 Galactic/Magellanic Cloud novae. We included the X-Ray Telescope (0.3-10keV) instrument count rates and the UltraViolet and Optical Telescope (1700-8000{AA}) filter photometry. Also included in the analysis are the publicly available pointed observations of 10 additional novae the X-ray archives. This is the largest X-ray sample of Galactic/Magellanic Cloud novae yet assembled and consists of 26 novae with Super Soft X-ray emission, 19 from Swift observations.
- 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.
- 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.