adsabs/WIESP2022-NER huggingface dataset:
Paper: 2019ApJ...887..221H (fulltext)
have the same peak value as the sample shown in the same panel. Based on the periodicity of these brightenings, we inquire whether or not they are standing mode MHD waves. They could be standing sausage waves because they can produce spectral profiles with enhancements at both red and blue wings (see, e.g., Tian et al. 2016b ; Shi et al. 2019a , 2019b ). For a loop with a cross section less than 1′′, the period of the sausage mode should be less than 10 s (Nakariakov et al. 2003 ; Nakariakov Verwichte 2005 ), thus the period of the observed phenomena is too large to be a sausage wave. One possibility is a combination of sausage and kink modes, which can occur concurrently in the solar atmosphere (Morton et al. 2012 ). The sausage mode can produce the observed spectral profiles, while the kink mode allows the bright loops to move transversely and thus can provide the observed periodicity. The periodicity of the sausage mode cannot be resolved in the current observations due to the temporal resolution. This leads to the question of whether a flux tube consisting of sausage motions with speeds more than 50 km s −1 is stable. This should be investigated in the future numerical studies. Another explanation is that shocks can be frequently seen in sunspots with periods of about 3 minutes (see Tian et al. 2014 ; Hou et al. 2018 , and references therein). Because shocks could be the result of leakage of p-modes, they can drive quasi-periodic brightenings in the transition region (Yang et al. 2015 ; Hou et al. 2016 , 2018 ). While shocks are propagating along loops, they might drive transverse motions (i.e., kink motions) and lead to repetitive appearances and disappearances of bright loops in the field of view of the spectrograph slit. The observed quasi-periodic brightenings can be the responses of shocks interacting with fine structures in the loop apex. Further theoretical study is required to understand whether and how shocks can produce such phenomena. Another scenario is that they are produced by repetitive magnetic reconnection. Such reconnection can result from magnetic braidings due to the plasma motions of the footpoints of the loops in the photosphere (Parker 1983a , 1983b ). The multiple loop threads seen in the field of view satisfy the basic requirement of this magnetic braiding scenario. Such magnetic reconnection can produce the observed non-Gaussian profiles of Si iv 1394 Å (see e.g., Huang et al. 2017 , 2018b ). Because the driven processes of the magnetic braiding can be modulated by the omnipresent 3 minute oscillations in sunspots, the braiding-induced magnetic reconnection then occurs with a periodicity. It has been demonstrated by numerical simulations that magnetic reconnection modulated by p-mode waves can produce quasi-periodic transition-region explosive events (Chen Priest 2006 ; Heggland et al. 2009 ). Moreover, the periods of the brightenings also agree with standing torsional (Alfvén) modes in a flux tube with lengths
Paper: 2016ApJ...824..110O (fulltext)
a non-zero slope for either half. Similarly, if we split the sample into smaller ranges of group mass, as in Section 4.2 , we are not able to distinguish the slope from zero slope for either half. For our sample, the halfway point at r = 2.06 is at or beyond R 200 (up to almost seven times beyond; see Table 1 ). Therefore, it is not surprising that the gradient in galaxy properties is primarily within this radius. Ideally, with a larger sample, one could find a specific (not necessarily linear) function to describe the change in H i content within R 200 as function of group-centric distance. So far, this has proven to be a challenge; for example, Yoon Rosenberg ( 2015 ) do not detect a radial gradient in H i mass ratio within R 200 at all, using a slightly larger sample (but not including upper limits for galaxies not detected in H i ). 5. CONCLUSIONS AND DISCUSSION In this paper, we take the approach of comparing the H i content at fixed galaxy type and stellar mass in the centers of groups and clusters over a wide range of masses with the H i content in galaxies in control regions out to 4 Mpc surrounding each group or cluster. This process allows us to statistically test for pre-processing in the central systems themselves, including in isolated groups, an approach that complements environmental tests based on local density. Our H i data is from the new catalog, and we use statistical tests from survival analysis in order to include information on upper limits for galaxies not detected in H i . Our primary results are the following. (1) Late-type galaxies in groups lack H i at fixed stellar mass relative to galaxies in a control region extending to 4.0 Mpc surrounding each group. Most of the gradient in galaxy properties out to 4.0 Mpc occurs in the inner 2.0 Mpc. Although this effect is stronger in clusters and large groups (), it is also detectable in groups with . This shows pre-processing of H i gas, not simply at intermediate densities, but in intermediate-density isolated groups. (2) The gradient in H i content for fixed stellar mass is stronger in larger groups, but the gradient in stellar mass and color does not follow this trend; stellar masses increase and galaxies become bluer with r at similar rates across our four bins of group mass. These difference between H i and optical properties might reflect an additional, rapid mechanism for the removal of gas in the inner regions of larger groups and clusters. Our statistics are insufficient to address whether this is truly a threshold effect, or a gradual change with group mass. (3) Comparing six different environment variables, we find that local density is the best predictor of galaxy properties (including H i content at fixed stellar mass), followed by group-centric radius r and . Considering all combinations of two variables together, we find that fits are improved (higher adjusted R 2 ) only for the addition of group mass M 200 to local density, r , or . We note that
Paper: 2017ApJ...837...19C (fulltext)
faint as 30. They predict for every galaxy a value of L X concordant with the scaling relation with the SFR (approximated by the infrared luminosity) of Basu-Zych et al. ( 2013 ). Without going into details, they estimate L 8–1000μm using photo- z , star-formation rate, UVJ rest-frame colors, and (observed or extrapolated) UV luminosity (). Using their mock catalog, we applied a selection as similar as possible to that of Laigle et al. ( 2016 ) from which we derived our mask. As a result, we find that these galaxies produce a [0.5–2] keV CXB surface brightness of the order of 3.3 × 10 −14 erg cm 2 s −1 deg −2 , which explains about 5% of the nsCXB. By assuming a typical X/O = 0 for AGNs as determined by Civano et al. ( 2012 ) and the i -limiting magnitudes in COSMOS (Scoville et al. 2007b ), we estimate that the undetected AGN [0.5–2] flux is 10 −17 erg cm 2 s −1 . At these low fluxes, star-forming galaxies vastly outnumber AGNs, so we can assume that ordinary AGNs cannot contribute more than galaxies to the soft nsCXB (5%). Being so faint, the sources producing the remaining CXB can be local ( z ∼ 1–3) and of low luminosity. Low-luminosity AGNs are preferentially highly absorbed (Barger et al. 2005 ; Hasinger 2008 ), and therefore we could argue that the hard portion of the nsCXB could be explained by these sources. However, at z ∼ 36, the number density of absorbed sources is still unknown, and we cannot exclude an unpredicted large number of such sources at that redshift. We propose that a large fraction of the remaining emission could arise from still undetected, rapidly accreting black holes at z > 6–7. Assuming the Direct Collapse black hole (DCBH) scenario for the formation of early black hole seeds, Pacucci et al. ( 2015 ) showed that these sources are likely undetected in current deep X-ray/NIR surveys. They compared the emission of DCBHs for two accretion models: radiatively efficient (Standard) and radiatively inefficient (Slim Disk; super-Eddington), in which photon trapping is significant and the outgoing radiation is diminished. In the latter case, the luminosity emitted by these sources is low. These short-lived and fainter black holes are more difficult to detect compared to brighter objects accreting at the Eddington limit (two tentative detections were proposed by Pacucci et al. 2016 ). Indeed, Comastri et al. ( 2015 ) revised the estimate of the local accreted mass density by taking into account that a significant fraction of the local black holes may have grown by radiatively inefficient accretion. From our measurements, the maximum flux produced by accretion onto early black holes is ∼10% of the CXB (see Table 3 ). To place limits on the amount of accretion occurring at , we follow the formalism of Salvaterra et al. ( 2012 ), assuming that the comoving specific emissivity of AGNs can be factorized aswhere is the normalization, , with , is the redshift evolution, and g ( E ) is a (normalized) template spectrum. For these
Paper: 2016ApJ...816...88K (acknowledgments)
This work was supported by a Marie Curie Fellowship and the NASA grants NNX13AI63G / NNX14AQ31G. We thank J.P. Wuelser for providing us with the absolute calibration of IRIS and its temporal evolution. We are very grateful to S. Couvidat for creating hmi.Ic _ 45s _ nrt data for this flare and to P. Scherrer for his explanations of the details of HMI. We thank A. Sainz Dalda for comments on the manuscript and J. Kašparová for her help with adapting the MALI code to account for non-thermal hydrogen collisional rates. We acknowledge helpful discussions that took place at ISSI. S.K. acknowledges the support by the Swiss National Science Foundation (200021-140308), by the European Commission through HESPE (FP7-SPACE-2010-263086), and through NASA contract NAS 5-98033 for RHESSI . P.H. was supported by the FP7 project F-CHROMA under the EC contract no. 606862, by the project RVO:67985815, and by the grant P209/12/1652 of the Grant agency of the Czech Republic.
Paper: 2016ApJ...833...31B (acknowledgments)
We thank Naomi McClure-Griffiths for providing the new H i terminal-velocity measurements from McClure-Griffiths Dickey ( 2016 ) in electronic form and the anonymous referee for a constructive report. J.B. and A.B. received financial support for this project from the Natural Sciences and Engineering Research Council of Canada. J.B. also received partial support from an Alfred P. Sloan Fellowship. T.F. and N.K. are supported by the NSF CAREER award 1455260. The MCMC analyses in this work were run using emcee (Foreman-Mackey et al. 2013 ).
Paper: 2020MNRAS.491.2576W (fulltext)
large sample of AGNs and obtain some different results. (1) A few sources exhibit a hint of saturation at high flux levels, but about half of the sources do not show a clear evidence of saturation in our data (e.g. Ark120, Mrk110, Figs A5 and B3 ). (2) Different sources follow different tracks (i.e. different slopes of the correlation) in the L X / L Edd diagram rather than a common relation (i.e. a single slope of the correlation). (3) Using the sample of AGNs instead of individual source, we can explore the spectral evolution in a much larger X-ray Eddington ratio range (4 orders of magnitude, Fig. 1 ). (4) We introduce the slope of the correlation to parametrize the increase speed of as a function of flux, and find for an anticorrelation between and the X-ray Eddington ratio. Globally, the increasing tendency of with increasing X-ray luminosity becomes slower, but there is no saturation effect observed even when the X-ray Eddington ratio increases by four orders of magnitude (Fig. 1 ). 4 DISCUSSION It is well known that the observed is governed by the absorption, the reflection effects, and the Comptonization process itself. The X-ray flux can change significantly within a time-scale as short as 10 3 10 4 s; however, neither the column density nor the covering factor is expected to vary so fast. On the other hand, the variation of X-ray flux can affect the ionization state and the opacity of absorber, resulting in variable absorption. In this way, the observed increases with increasing the X-ray flux, but the derived relation is much shallower than the data of most sources (Sobolewska Papadakis 2009 ). Moreover, such absorption effect should be prominent at high luminosity, that is in conflict with the anticorrelation between and the X-ray Eddington ratio shown in Fig. 2 . The reflection component could offer a significant fraction of X-ray emissions, and tend to flatten the spectrum below 10keV, reducing the observed . However, the reflection is unimportant in the power-law fitting with the RXTE /PCA data due to their low energy resolution. Investigating the RXTE data of 10 AGNs (all in our sample), Sobolewska Papadakis ( 2009 ) argued that a constant reflection component plus a power-law component, which is variable in flux but constant in profile, failed to account for the spectral evolution. It is unclear whether the spectral softening behaviour can be interpreted as the decreasing of the relative contribution of the reflection component with increasing the X-ray flux. Recently, observations with XMMNewton and NuSTAR have been made on several objects in our sample (e.g. MCG-6-30-15 and Ark120; Parker etal. 2014 ; Porquet etal. 2018 ), and these data have sufficient statistics and spectral resolution to separate out the intrinsic power-law and reflection components. A quantitative estimation on the influence of the reflection effect at different flux levels could be accomplished with next generation of X-ray missions in the future (e.g.
Paper: 2016ApJ...829...54B (fulltext)
are denoted by black vertical lines. In all cases of Figure 1 a spectral break is observed at the largest of the three scales, i.e., the scale corresponding to the lowest ion frequency . This result is consistent with the observations in the solar wind (Chen et al. 2014 ). However, in the range , where is the frequency corresponding to the smallest ion scale, the power spectra are modified by ion instabilities: while a power law seems to develop after the break in the case of very high beta (Figure 1 , top panel), the onset of the cascade is shifted toward higher frequencies (Figure 1 , middle and bottom panels) by the formation of a broader “knee” and develops at . For example, in the bottom panel, we observe a local bump at the break, which has been identified in this particular event (see Alexandrova et al. 2006 ) as the signature of Alfvén vortices, controlled by . Each case presents a different slope α in this range, as shown by the compensated spectra depicted by red lines in each panel (the spectral index α is indicated in each panel on the right). Kinetic instabilities can modify the power spectrum at ion scales and affect the fluctuations in the small-scale range. Therefore, the identification of kinetic instabilities is important and it is the subject of investigation in the following section. 3. SMALL-SCALE TURBULENCE ANISOTROPY AND SPECTRAL INDEX In this section we study in detail the effects of mirror modes and AIC waves, which are observed to dominate in the magnetosheath (Schwartz et al. 1996 ), on the spectral index and anisotropy of fluctuations in the small-scale range, i.e., f ∈ [0.2–10] Hz in our case. To do so, we choose four time intervals of about 3–5 minutes each (i.e., PSDs at frequencies 0.025 Hz are not reliable) and we sort them out depending on the nature of the present waves. The selected cases are chosen as follows: (1) no waves are dominating the spectrum (2008 March 17, 12:30–12:35 UTC); (2) only strong mirror modes are observed (2008 March 25, 07:01–07:05 UTC); (3) strong AIC waves dominate (2008 March 30, 01:35–01:39 UTC); and (4) a mixture of the mirror and AIC waves is observed (2008 March 25, 06:51–06:56 UTC). These intervals are selected during periods of low v ( v ≈ 50 km s −1 ) so that the effects of the Doppler shift due to the plasma flow past the spacecraft (i.e., increase of δB y ) are minimized (Sahraoui et al. 2006 ; Alexandrova et al. 2008b ). Because of the low bulk velocity Taylor's hypothesis could be violated (see, e.g., Klein et al. 2014 ), thus we performed three tests to ensure that this hypothesis holds in the selected cases. First, we determined the turbulence intensity ( v 0 being the mean bulk velocity and v rms the root mean square of v fluctuations) to be in the range [0.04–0.09] (i.e., I ≪ 1); then, we found that the relation is fulfilled (for a detailed description of the test, see Sahraoui et al. 2012 ); and finally, we found good agreement between the probability density
Paper: 2017A&A...597A.100M (fulltext)
be considered constant between all the observations. A simple light-travel argument can then put constraints on the distance between the central source and the reflector. For an edge-on view of the system, , and yr, depending on when the source switched on (between the beginning of 1996 and the beginning of 2001). In this case, the distance between the source and the reflector is pc. First a fading, and then an increase in reflection is then expected to occur in the future, and monitoring of the source is the only way to keep track of its changes. Monitoring could also shed new light on the role of the X-ray absorber, which varies on much shorter temporal scales and seems to be associated with broad line region (BLR) clouds (see Risaliti et al. 2010) . If this is the case, the physical interpretation of our result applying the decoupled MYTorus model is straightforward: the l.o.s. is intercepting the variable (and presumably compact) Compton-thin absorber, while the reflector is located on larger scales and the photons reflecting back to our l.o.s. are “seeing” a Compton-thick column of gas. Risaliti et al. (2010) suggest that the absorber is a BLR cloud, assuming a central black hole (BH) mass of . In this picture, a second “screen” is required to obscure the broad lines in the optical spectrum, which is instead likely showing an outflow, resulting in the classification of Mrk 1210 as a Seyfert 2 (Mazzalay Rodríguez-Ardila 2007) . However, if the reflection component comes from photons reflecting off the far inner wall of the torus, delayed with respect to the intrinsic emission, a rather distant torus edge is needed with respect to the dust sublimation radius , which is usually thought to mark the inner wall of the torus, and in this case is 0.2 pc ( Gandhi et al. 2009 , and references therein, and adopting a bolometric correction of 20; Lusso et al. 2012 ). Table 3 ASCA best fit parameters compared with NuSTAR pexrav+zgauss only model. Notes. The NuSTAR line equivalent width is calculated with respect to the reflection continuum. Fig. 9 Observed 1040 keV flux ( top panel ) and iron line flux ( bottom panel ) of Mrk 1210, as a function of time. 4.2. Eclipsing event The ASCA data cannot distinguish between a Compton-thick eclipsing event and an intrinsic low-flux state of the central engine. A random pass of a Compton-thick cloud (or an alignment of clouds along the l.o.s.) during the ASCA observation is consistent with the known clumpiness of the gas surrounding obscured AGN. During the two observations by ASCA in 1995, separated by 25 days, Mrk 1210 was in a low-flux state. In an eclipsing scenario, this means that the putative eclipsing event lasted for at least 25 days. Assuming Keplerian motion of the clump, the linear size eclipsed by a moving Compton-thick cloud in a given time interval can be written as cm, where is the distance from the center in parsecs, and is the eclipse time interval in units of 25 days. This implies that the
Paper: 2016ApJ...820...37Y (acknowledgments)
This work is supported by the National Natural Science Foundation of China through grants of 11503035, 11573036, 11373009, 11433008, and 11403040, the China Ministry of Science and Technology under State Key Development Program for Basic Research through the grant of 2012CB821800, the International ST Cooperation Program of China through the grant of 2010DFA02710, the Beijing Natural Science Foundation through the grant of 1144015, and the Young Researcher Grant of National Astronomical Observatories, Chinese Academy of Sciences. K.W. acknowledges support from the ESO fellowship and grant WA3628-1/1 through the DFG priority programme 1573 “Physics of the Interstellar Medium” ( http://www.ism-spp.de ). We give our thanks to the staff at the Qinghai Station of Purple Mountain Observatory for their hospitable assistance during the observations and the Key Laboratory for Radio Astronomy of Chinese Academy of Sciences for partial support in the operation of the telescope.
Paper: 2018MNRAS.474L..71B (fulltext)
ratio of Y e = 0.30, for the assumed distance of 40 Mpc. We also present photometry of AT 2017gfo over a period 10 d post detection, in optical ( B, V and R ) and infrared ( J, H and K ), derived from the MASTER-SAAO and IRSF telescopes at Sutherland, respectively. We again compare these results to the respective kilonova model predictions, and conclude that either the Y e = 0.25 or 0.30 wind models are qualitatively similar to the observed magnitudes. 2 SALT AND SAAO OBSERVATIONS Following the detection of AT 2017gfo, the optical counterpart to GW170817, director’s discretionary time observations (programme 2017-1-DDT-009) were undertaken on 2017 August 18 and 19 on the Southern African Large Telescope (SALT; Buckley et al. 2006 ). The observations were taken with the prime focus Robert Stobie spectrograph (Burgh et al. 2003 ), beginning in twilight and proceeding until the end of the available telescope track time. A third attempt on August 20 resulted in no meaningful data being obtained due to the sky brightness coupled with the degree of fading of the kilonova. The observational details are included in Table 1 , and preliminary reports on the results are presented in Shara et al. ( 2017 ), Abbott et al. ( 2017b ), McCully et al. ( 2017 ) and Andreoni et al. ( 2017 ). Table 1. Observing details. Notes. a Transparency; seeing. b Since GW trigger time: 2017 August 17, 12h41m04s UTC. The low-resolution PG300 surface relief transmission grating was used, rotated to an angle of 5.75°, with a long slit of width 2 arcsec, which implies an ∼88 per cent slit throughput in the given seeing conditions. The spectra had a resolution which varied from R ∼ 150 (at ∼3750 Å) to ∼400 (at ∼9600 Å), with a mean of R ∼ 380. The observations were reduced using the PySALT package (Crawford et al. 2010 ), which accounts for basic CCD characteristics (cross-talk, bias and gain correction) and removal of cosmic rays, wavelength calibration, and relative flux calibration. Additional reductions to account for accurate sky and galaxy background removal were done using standard iraf routines. Because of the SALT design, which has a moving, field-dependent and underfilled entrance pupil, absolute flux calibration with SALT is difficult to achieve with a good degree of accuracy, which at best is ± 20 per cent. Observations were taken in morning twilight on 2017 August 18 of the spectrophotometric standard star EG21, which was used to determine a relative flux calibration on both nights. The spectral fluxes were then corrected by convolving the observed spectra with standard Johnson–Cousins B and R filters and comparing the results with B and R observations taken simultaneously with the MASTER-SAAO facility, which are included in Table 1 , corrected for Milky Way extinction, as presented in Lipunov et al. ( 2017 ). This comparison implied that the spectra were required to be adjusted in flux by a multiplicative constant of 2.04 and 2.4, respectively, on the