Browsing by Type "journal articles"

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The 04 – 10 September 2017 Sun–Earth Connection Events: Solar Flares, Coronal Mass Ejections/Magnetic Clouds, and Geomagnetic Storms
(Springer Netherlands, 2019-08-23) Wu, Chin-Chun; Liou, Kan; Lepping, Ronald P.; Hutting, Lynn
In early September 2017, a series of solar flares and coronal mass ejections (CMEs) erupted from the Sun. The Cor2a coronagraph, a unit of the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI), onboard the Solar Terrestrial Relations Observatory (STEREO)-A spacecraft recorded two Sun–Earth-directed CMEs on 4 September (referred to as CME04) and 6 September (referred to as CME06). A few days later, the Wind spacecraft ( ≈212.4 solar radii: R⊙ ) recorded two interplanetary shocks, presumably driven by CME04 and CME06, at ≈22:41 UT on 06 September 2017 (referred to as Shock06) and at ≈22:48 UT on 07 September 2017 (referred to as Shock07), respectively. The travel time of the CME04/Shock06 [ Δtshock-CME@18R⊙ ] and CME06/Shock07 from 18 R⊙ to the Wind spacecraft was 41.52 hours and 32.47 hours, respectively. The propagating speed [ VCME ] of the CME04 and CME06 at ≈18 R⊙ was determined with SECCHI/Cor2a as ≈886 kms−1 and ≈1368 kms−1 , respectively. Assuming a constant velocity after 18 R⊙ , the estimated Δtshock-CME@18R⊙ is 42.45 and 27.5 hours for CME04 and CME06, respectively. This simple estimate of the CME propagation speed provides a satisfactory result for the CME04 event (error ≈2.3% ) but not for the CME06 event (error ≈15.3% ). The second event, CME06, was delayed further due to an interaction with the preceding event (CME04). It is suggested that the CME speed estimated near the Sun with coronagraph images can be a good estimator for the interplanetary CME (ICME) transit time when there is no pre-event. A three-dimensional magnetohydrodynamic simulation is performed to address this issue by providing a panoramic view of the entire process not available from the observations. A southward interplanetary magnetic field [ Bs ] increased sharply to −31.6 nT on 7 September at Wind, followed by a severe geomagnetic storm ( Dst=−124 nT ). The sharp increase of the IMF [ Bs ] was a result of the interaction between Shock07 and the driver of Shock06 (CME04). This study suggests that a severe geomagnetic storm can be caused by the interaction between a MC, with an impinging IP shock from behind, and the Earth’s magnetosphere. The intensity of a geomagnetic storm will likely be stronger for an event associated with ICME–ICME interaction than for a geomagnetic event caused by only a single ICME.
A 0535+26 in the August/September 2005 outburst observed by RXTE and INTEGRAL
(EDP Sciences, 2007-02-20) Caballero, I.; Kretschmar, P.; Santangelo, A.; Staubert, R.; Klochkov, D.; Camero, A.; Ferrigno, C.; Finger, M. H.; Kreykenbohm, I.; McBride, V. A.; Pottschmidt, Katja; Rothschild, R. E.; Schönherr, G.; Segreto, A.; Suchy, S.; Wilms, J.; Wilson, C. A.
Aims. In this Letter we present results from INTEGRAL and RXTE observations of the spectral and timing behavior of the High Mass X-ray Binary A 0535+26 during its August/September 2005 normal (type I) outburst with an average flux F₍₅₋₁₀₀₎ ₖₑᵥ ~ 400 mCrab. The search for cyclotron resonance scattering features (fundamental and harmonic) is one major focus of the paper. Methods. Our analysis is based on data from INTEGRAL and RXTE Target of Opportunity Observations performed during the outburst. The pulse period is determined. X-ray pulse profiles in different energy ranges are analyzed. The broad band INTEGRAL and RXTE pulse phase averaged X-ray spectra are studied. The evolution of the fundamental cyclotron line at different luminosities is analyzed. Results.The pulse period P is measured to be 103.39315(5) s at MJD 53614.5137. Two absorption features are detected in the phase averaged spectra at E₁ ~ 45 keV and E₂ ~ 100 keV. These can be interpreted as the fundamental cyclotron resonance scattering feature and its first harmonic and therefore the magnetic field can be estimated to be B ~4 × 10¹² G.
A 100-Gb/s noncoherent silicon receiver for PDM-DBPSK/DQPSK signals
(Optica, 2014) Klamkin, Jonathan; Gambini, Fabrizio; Faralli, Stefano; Malacarne, Antonio; Meloni, Gianluca; Berrettini, Gianluca; Contestabile, Giampiero; Potì, Luca
An integrated noncoherent silicon receiver for demodulation of 100-Gb/s polarization-division multiplexed differential quadrature phaseshift keying and polarization-division multiplexed differential binary phaseshift keying signals is demonstrated. The receiver consists of a 2D surface grating coupler, four Mach-Zehnder delay interferometers and four germanium balanced photodetectors.
The 17 April 2021 widespread solar energetic particle event
(EDP Sciences, 2023-06-09) Dresing, N.; Rodríguez-García, L.; Jebaraj, I. C.; Warmuth, A.; Krupar, Vratislav; da Silva, Daniel ; et al.
Context. A complex and long-lasting solar eruption on 17 April 2021 produced a widespread solar energetic particle (SEP) event that was observed by five longitudinally well-separated observers in the inner heliosphere that covered distances to the Sun from 0.42 to 1 au: BepiColombo, Parker Solar Probe, Solar Orbiter, STEREO A, and near-Earth spacecraft. The event was the second widespread SEP event detected in solar cycle 25, and it produced relativistic electrons and protons. It was associated with a long-lasting solar hard X-ray flare that showed multiple hard X-ray peaks over a duration of one hour. The event was further accompanied by a medium-fast coronal mass ejection (CME) with a speed of 880 km s−1 that drove a shock, an extreme ultraviolet wave, and long-lasting and complex radio burst activity that showed four distinct type III burst groups over a period of 40 min. Aims. We aim to understand the reason for the wide spread of elevated SEP intensities in the inner heliosphere as well as identify the underlying source regions of the observed energetic electrons and protons. Methods. We applied a comprehensive multi-spacecraft analysis of remote-sensing observations and in situ measurements of the energetic particles and interplanetary context to attribute the SEP observations at the different locations to the various potential source regions at the Sun. We used an ENLIL simulation to characterize the complex interplanetary state and its role in the energetic particle transport. The magnetic connection between each spacecraft and the Sun was determined using ballistic backmapping in combination with potential field source surface extrapolations in the lower corona. Using also a reconstruction of the coronal shock front, we then determined the times when the shock establishes magnetic connections with the different observers. Radio observations were used to characterize the directivity of the four main injection episodes, which were then employed in a 2D SEP transport simulation to test the importance of these different injection episodes. Results. A comprehensive timing analysis of the inferred solar injection times of the SEPs observed at each spacecraft suggests different source processes being important for the electron and proton events. Comparison among the characteristics and timing of the potential particle sources, such as the CME-driven shock or the flare, suggests a stronger shock contribution for the proton event and a more likely flare-related source for the electron event. Conclusions. In contrast to earlier studies on widespread SEP events, we find that in this event an important ingredient for the wide SEP spread was the wide longitudinal range of about 110° covered by distinct SEP injections, which is also supported by our SEP transport modeling.
17β-Estradiol (E2) may be involved in the mode of crustacean female sex hormone (CFSH) action in the blue crab, Callinectes sapidus
(Frontiers, 2022-07-25) Wang, Tao; He, Ke; Blaney, Lee; Chung, J. Sook
17β-estradiol (E2) has been proved to control reproduction, sexual differentiation, and the development of the secondary sexual characteristics of vertebrate females. In decapod crustacean species, crustacean female sex hormone (CFSH), a protein hormone, is required for developing adult-specific ovigerous setae for embryo brooding and gonophores for mating at the blue crab Callinectes sapidus puberty molting. However, it is unclear that whether the mode of CFSH action involves a vertebrate-type sex steroid hormone in crustaceans. To this end, E2 levels were first measured using a competitive ELISA in the hemolymph and the potential CFSH target tissues from both prepuberty and adult females; the presence of E2 was further confirmed with a liquid chromatography tandem mass spectrometry method. Then, the cDNAs of the following genes known to be associated with vertebrate steroidogenic pathways were isolated: StAR-related lipid transfer protein 3 (StAR3); 3β-hydroxysteroid dehydrogenase (3βHSD); two isoforms of 17β-hydroxysteroid dehydrogenase 8 (17βHSD8); and, estradiol-related receptor (ERR). RT-PCR analysis revealed that these genes were widely distributed in the eyestalk ganglia, hepatopancreas, brain, ovary, spermathecae, ovigerous and plumose setae tissues of adult females. The 17βHSD8 transcripts were localized in the follicle cells, the periphery of the nuclear membrane of primary oocytes, and yolk granules of the vitellogenic oocytes using in situ hybridization, and the corresponding protein was detected in the follicle cells and ooplasm of primary oocytes using immunohistochemistry. Furthermore, the adult females injected with CFSH-dsRNA (n = 30 times) had E2 and StAR3 transcripts levels lower in the ovigerous and plumose setae, spermathecae than controls. These results suggested that the mode of CFSH action in C. sapidus might involve E2 in these adult-female-specific tissues.
The 1816 Philadelphia Emma: A Forgotten Edition and Its Readers
(Jane Austen Society of North America, 2016) Wells, Juliette
A 1D fluid model of the Centaurus A jet
(2018-09-27) Wykes, Sarka; Snios, Bradford T.; Nulsen, Paul E. J.; Kraft, Ralph P.; Birkinshaw, Mark; Hardcastle, Martin J.; Worrall, Diana M.; McDonald, Iain; Rejkuba, Marina; Jones, Thomas W.; Stark, David J.; Forman, William R.; Meyer, Eileen T.; Jones, Christine
We implement a steady, one-dimensional flow model for the X-ray jet of Centaurus A in which entrainment of stellar mass loss is the primary cause of dissipation. Using over 260 ks of new and archival Chandra/ACIS data, we have constrained the temperature, density and pressure distributions of gas in the central regions of the host galaxy of Centaurus A, and so the pressure throughout the length of its jet. The model is constrained by the observed profiles of pressure and jet width, and conserves matter and energy, enabling us to estimate jet velocities, and hence all the other flow properties. Invoking realistic stellar populations within the jet, we find that the increase in its momentum flux exceeds the net pressure force on the jet unless only about one half of the total stellar mass loss is entrained. For self-consistent models, the bulk speed only falls modestly, from ~0.67c to ~0.52c over the range of 0.25-5.94 kpc from the nucleus. The sonic Mach number varies between ~5.3 and 3.6 over this range.
2 mm GISMO Observations of the Galactic Center. I. Dust Emission
(The American Astronomical Society, 2019-11-01) Arendt, Richard G; Staguhn, Johannes; Dwek, Eli; Morris, Mark R; Yusef-Zadeh, Farhad; Benford, Dominic J; Kovacs, Attila; Gonzalez-Quiles, Junellie
The Central Molecular Zone (CMZ), covering the inner ∼ 1 ◦ of the Galactic plane has been mapped at 2 mm using the GISMO bolometric camera on the 30 m IRAM telescope. The 2100 resolution maps show abundant emission from cold molecular clouds, from star forming regions, and from one of the Galactic center nonthermal filaments. In this work we use the Herschel Hi-GAL data to model the dust emission across the Galactic center. We find that a single-temperature fit can describe the 160 – 500 µm emission for most lines of sight, if the long-wavelength dust emissivity scales as λ −β with β ≈ 2.25. This dust model is extrapolated to predict the 2 mm dust emission. Subtraction of the model from the GISMO data provides a clearer look at the 2 mm emission of star-forming regions and the brightest nonthermal filament.
2 mm GISMO Observations of the Galactic Center. II. A Nonthermal Filament in the Radio Arc and Compact Sources
(The American Astronomical Society, 2019-11-01) Staguhn, Johannes; Arendt, Richard G; Dwek, Eli; Morris, Mark R; Yusef-Zadeh, Farhad; Benford, Dominic J; Kovacs, Attila; Gonzalez-Quiles, Junellie
We have used the Goddard IRAM 2-Millimeter Observer (GISMO) with the 30 m IRAM telescope to carry out a 2 mm survey of the Galaxy’s central molecular zone (CMZ). These observations detect thermal emission from cold ISM dust, thermal free-free emission from ionized gas, and nonthermal synchrotron emission from relatively flat-spectrum sources. Archival data sets spanning 3.6 µm to 90 cm are used to distinguish different emission mechanisms. After the thermal emission of dust is modeled and subtracted, the remaining 2 mm emission is dominated by free-free emission, with the exception of the brightest nonthermal filament (NTF) that runs though the middle of the bundle of filaments known as the Radio Arc. This is the shortest wavelength at which any NTF has been detected. The GISMO observations clearly trace this NTF over a length of ∼ 0.2 ◦ , with a mean 2 mm spectral index which is steeper than at longer wavelengths. The 2 mm to 6 cm (or 20 cm) spectral index steepens from α ≈ −0.2 to −0.7 as a function distance from the Sickle H II region, suggesting that this region is directly related to the NTF. A number of unresolved (at 21′′) 2 mm sources are found nearby. One appears to be thermal dust emission from a molecular cloud that is associated with an enigmatic radio point source whose connection to the Radio Arc is still debated. The morphology and colors at shorter IR wavelengths indicate other 2 mm unresolved sources are likely to be compact H II regions.
20 years of change in tundra NDVI from coupled field and satellite observations
(IOP Publishing, 2023-08-17) Huemmrich, Karl; Gamon, John; Campbell, Petya Entcheva; Mora, Marianna; Vargas Z, Sergio; Almanza, Brenda; Tweedie, Craig
In 2022 we resampled normalized difference vegetation index (NDVI) along a 100 m transect in tundra near Utqiagvik, AK that had been previously measured through the 2000–2002 growing seasons, providing an opportunity to examine a 20 year NDVI change at a 1 m resolution in a region that is experiencing increased warming and precipitation over this period. Multidecadal NDVI change was spatially variable across the transect with nearly half of the transect showing greening, about a third not showing conclusive change, and about 20% browning. In wet areas, greening (increased NDVI) was associated with increased green leaf area index, while in drier areas greening was related to changes in species cover. Browning was not related to change in species cover and appeared to be due to increased coverage of standing dead material in graminoid dominated canopies. These types of detailed observations provide insights into the interpretation of satellite based NDVI trends and emphasize the importance of microtopography and hydrology in mediating vegetation change in a warming Arctic.
The 2001 Superoutburst of WZ Sagittae
(IOP, 2002-06-10) Patterson, Joseph; Masi, Gianluca; Richmond, Michael W.; Martin, Brian; Beshore, Edward; Skillman, David R.; Kemp, Jonathan; Vanmunster, Tonny; Rea, Robert; Allen, William; Davis, Stacey; Davis, Tracy; Henden, Arne A.; Starkey, Donn; Foote, Jerry; Oksanen, Arto; Cook, Lewis M.; Fried, Robert E.; Husar, Dieter; Novák, Rudolf; Campbell, Tut; Robertson, Jeff; Krajci, Thomas; Pavlenko, Elena; Mirabal, Nestor; Niarchos, Panos G.; Brettman, Orville; Walker, Stan
We report the results of a worldwide campaign to observe WZ Sagittae during its 2001 superoutburst. After a 23 yr slumber at V = 15.5, the star rose within 2 days to a peak brightness of 8.2, and showed a main eruption lasting 25 days. The return to quiescence was punctuated by 12 small eruptions, of ~1 mag amplitude and 2 day recurrence time; these "echo outbursts" are of uncertain origin, but somewhat resemble the normal outbursts of dwarf novae. After 52 days, the star began a slow decline to quiescence. Periodic waves in the light curve closely followed the pattern seen in the 1978 superoutburst: a strong orbital signal dominated the first 12 days, followed by a powerful common superhump at 0.05721(5) day, 0.92(8)% longer than Porb. The latter endured for at least 90 days, although probably mutating into a "late" superhump with a slightly longer mean period [0.05736(5) day]. The superhump appeared to follow familiar rules for such phenomena in dwarf novae, with components given by linear combinations of two basic frequencies: the orbital frequency ωo and an unseen low frequency Ω, believed to represent the accretion disk's apsidal precession. Long time series reveal an intricate fine structure, with ~20 incommensurate frequencies. Essentially all components occurred at a frequency nωo - mΩ, with m = 1, ..., n. But during its first week, the common superhump showed primary components at nωo - Ω, for n = 1, 2, 3, 4, 5, 6, 7, 8, 9 (i.e., m = 1 consistently); a month later, the dominant power shifted to components with m = n - 1. This may arise from a shift in the disk's spiral‐arm pattern, likely to be the underlying cause of superhumps. The great majority of frequency components are redshifted from the harmonics of ωo, consistent with the hypothesis of apsidal advance (prograde precession). But a component at 35.42 cycles day⁻¹ suggests the possibility of a retrograde precession at a different rate, probably N = 0.13 ± 0.02 cycles day⁻¹. The eclipses permit measuring the location and brightness of the mass‐transfer hot spot. The disk must be very eccentric and nearly as large as the white dwarf's Roche lobe. The hot‐spot luminosity exceeds its quiescent value by a factor of up to 60. This indicates that enhanced mass transfer from the secondary plays a major role in the eruption.
THE 2010 MAY FLARING EPISODE OF CYGNUS X-3 IN RADIO, X-RAYS, AND γ-RAYS
(IOP Publishing, 2011-05-05) Williams, Peter K. G.; Tomsick, John A.; Bodaghee, Arash; Bower, Geoffrey C.; Pooley, Guy G.; Pottschmidt, Katja; Rodriguez, Jérôme; Wilms, Jörn; Migliari, Simone; Trushkin, Sergei A.
In 2009, Cygnus X-3 (Cyg X-3) became the first microquasar to be detected in the GeV γ-ray regime, via the satellites Fermi and AGILE. The addition of this new band to the observational toolbox holds promise for building a more detailed understanding of the relativistic jets of this and other systems. We present a rich data set of radio, hard and soft X-ray, and γ-ray observations of Cyg X-3 made during a flaring episode in 2010 May. We detect a ∼3 day softening and recovery of the X-ray emission, followed almost immediately by a ∼1 Jy radio flare at 15 GHz, followed by a 4.3σ γ-ray flare (E > 100 MeV) ∼1.5 days later. The radio sampling is sparse, but we use archival data to argue that it is unlikely the γ-ray flare was followed by any significant unobserved radio flares. In this case, the sequencing of the observed events is difficult to explain in a model in which the γ-ray emission is due to inverse Compton scattering of the companion star's radiation field. Our observations suggest that other mechanisms may also be responsible for γ-ray emission from Cyg X-3.
2011 Report From the Student Affiliates of Seventeen (SAS)
(The Counseling Psychologist, 2012) Lantz, Melanie M.; Shaffer, Katharine S.
The Student Affiliates of Seventeen (SAS) is the student-run representative body for the Society of Counseling Psychology (SCP) student members. Our primary purpose is to keep student members informed of current events in SCP and APA, and to represent the collective student voice to SCP. SAS is currently hosted by the University at Albany Counseling Psychology doctoral program, and we have just concluded our first of three years as the host institution. Our 15-member executive board has worked hard during our initial transition year, and we are excited to share our accomplishments and vision for our term with TCP readers.
The 2013 FLEX—US Airborne Campaign at the Parker Tract Loblolly Pine Plantation in North Carolina, USA
(MDPI, 2017-06-16) Middleton, Elizabeth M.; Rascher, Uwe; Corp, Lawrence A.; Huemmrich, Karl; Cook, Bruce D.; Noormets, Asko; Schickling, Anke; Pinto, Francisco; Alonso, Luis; Damm, Alexander; Guanter, Luis; Colombo, Roberto; Campbell, Petya Entcheva; Landis, David R.; Zhang, Qingyuan; Rossini, Micol; Schuettemeyer, Dirk; Bianchi, Remo
The first European Space Agency (ESA) and NASA collaboration in an airborne campaign to support ESA’s FLuorescence EXplorer (FLEX) mission was conducted in North Carolina, USA during September–October 2013 (FLEX-US 2013) at the Parker Tract Loblolly Pine (LP) Plantation (Plymouth, NC, USA). This campaign combined two unique airborne instrument packages to obtain simultaneous observations of solar-induced fluorescence (SIF), LiDAR-based canopy structural information, visible through shortwave infrared (VSWIR) reflectance spectra, and surface temperature, to advance vegetation studies of carbon cycle dynamics and ecosystem health. We obtained statistically significant results for fluorescence, canopy temperature, and tower fluxes from data collected at four times of day over two consecutive autumn days across an age class chronosequence. Both the red fluorescence (F685) and far-red fluorescence (F740) radiances had highest values at mid-day, but their fluorescence yields exhibited different diurnal responses across LP age classes. The diurnal trends for F685 varied with forest canopy temperature difference (canopy minus air), having a stronger daily amplitude change for young vs. old canopies. The Photochemical Reflectance Index (PRI) was positively correlated with this temperature variable over the diurnal cycle. Tower measurements from mature loblolly stand showed the red/far-red fluorescence ratio was linearly related to canopy light use efficiency (LUE) over the diurnal cycle, but performed even better for the combined morning/afternoon (without midday) observations. This study demonstrates the importance of diurnal observations for interpretation of fluorescence dynamics, the need for red fluorescence to understand canopy physiological processes, and the benefits of combining fluorescence, reflectance, and structure information to clarify canopy function versus structure characteristics for a coniferous forest.
The 2019 outburst of the 2005 classical nova V1047 Cen: a record breaking dwarf nova outburst or a new phenomenon?
(2021-08-17) Aydi, E.; Sokolovsky, K. V.; Bright, J. S.; Tremou, E.; Nyamai, M. M.; Evans, A.; Strader, J.; Chomiuk, L.; Myers, G.; Hambsch, F-J.; Page, K. L.; Buckley, D. A. H.; Woodward, C. E.; Walter, F. M.; Mróz, P.; Vallely, P. J.; Geballe, T. R.; Banerjee, D. P. K.; Gehrz, R. D.; Fender, R. P.; Gromadzki, M.; Kawash, A.; Knigge, C.; Mukai, K.; Munari, U.; Orio, M.; Ribeiro, V. A. R. M.; Sokoloski, J. L.; Starrfield, S.; Udalski, A.; Woudt, P. A.
We present a detailed study of the 2019 outburst of the cataclysmic variable V1047 Cen, which hosted a classical nova eruption in 2005. The peculiar outburst occurred 14 years after the classical nova event, lasted for more than 400 days, and reached an amplitude of around 6 magnitudes in the optical. Early spectral follow-up revealed what could be a dwarf nova (accretion disk instability) outburst in a classical nova system. However, the outburst duration, high velocity (>2000 km s⁻¹) features in the optical line profiles, luminous optical emission, and the presence of prominent long-lasting radio emission, together suggest a phenomenon more exotic and energetic than a dwarf nova outburst. There are striking similarities between this V1047 Cen outburst and those of "combination novae" in classical symbiotic stars. We suggest that the outburst may have started as a dwarf nova that led to the accretion of a massive disk, which in turn triggered enhanced nuclear shell burning on the white dwarf and eventually led to generation of a wind/outflow. From optical photometry we find a \bf{possible} orbital period of 8.36 days, which supports the combination nova scenario and makes the system an intermediate case between typical cataclysmic variables and classical symbiotic binaries. If true, such a phenomenon would be the first of its kind to occur in a system that has undergone a classical nova eruption and is intermediate between cataclysmic variables and symbiotic binaries.
2021 Effective Area calibration of the Nuclear Spectroscopic Telescope ARray (NuSTAR)
(SPIE, 2021-10-21) Madsen, Kristin; Forster, Karl; Grefenstette, Brian W.; Harrison, Fiona A.; Miyasaka, Hiromasa
We present here the updated calibration of The Nuclear Spectroscopic Telescope ARray NuSTAR, which was performed using data on the Crab accumulated over the last 9 years in orbit. The basis for this new calibration contains over 250ks of focused Crab (imaged through the optics) and over 500ks of stray-light Crab (not imaged through optics). We measured an epoch averaged Crab spectrum of the stray-light Crab data and define a canonical Crab spectrum of Gamma = 2.103 +- 0.001 and N = 9.69 +- 0.02 keV-1 cm-2 s-1 at 1 keV, which we use as our calibration standard. The new calibration, released in the CALDB update 20211020, provides significant updates to: 1) the detector absorption component, 2) the detector response function, and 3) the effective area vignetting function. The calibration improves agreement between FPMA and FPMB across detectors with a standard deviation of 1.7% for repeat observations between off-axis angles of 1-4 arcmin, and the measured flux has increased by 5-15%, with 5% below 1 arcmin off-axis angle, 10% between 1-2 arcmin, and 15 above 4arcmin.
The 21-cm signal from the Cosmic Dawn: metallicity dependence of high mass X-ray binaries
(2022-03-21) Kaur, Harman Deep; Qin, Yuxiang; Mesinger, Andrei; Pallottini, Andrea; Fragos, Tassos; Basu-Zych, Antara
X-rays from High-Mass X-ray Binaries (HMXBs) are likely the main source of heating of the intergalactic medium (IGM) during Cosmic Dawn (CD), before the completion of reionization. This Epoch of Heating (EoH; z∼10−15) should soon be detected via the redshifted 21-cm line from neutral hydrogen, allowing us to indirectly study the properties of HMXBs in the unseen, first galaxies. Low-redshift observations, as well as theoretical models, imply that the integrated X-ray luminosity to star formation rate of HMXBs (LX/SFR) should increase in metal-poor environments, typical of early galaxies. Here we study the impact of the metallicity (Z) dependence of LX/SFR during the EoH. For our fiducial models, galaxies with star formation rates of order 10⁻³−10⁻¹ M⊙ yr⁻¹ and metallicities of order 10⁻³−10⁻² Z⊙ are the dominant contributors to the X-ray background (XRB) during this period. Different LX/SFR-Z relations result in factors of ∼ 3 differences in these ranges, as well as in the mean IGM temperature and the large-scale 21-cm power, at a given redshift. We compute mock 21-cm observations adopting as a baseline a 1000h integration with the upcoming Square Kilometer Array (SKA), for two different LX/SFR-Z relations. We perform inference on these mock observations using the common simplification of a constant LX/SFR, finding that constant LX/SFR models can recover the IGM evolution of the more complicated LX/SFR-Z simulations only during the EoH. At z<10, where the typical galaxies are more polluted, constant LX/SFR models over-predict the XRB and its relative contribution to the early stages of the reionization.
The 27-day rotational variations in total solar irradiance observations: From SORCE/TIM, ACRIMSAT/ACRIM III, and SOHO/VIRGO
(Elsevier, 2015-07-09) Lee, Jae N.; Cahalan, Robert F.; Wu, Dong L.
During the last decade, observations from SORCE (Solar Radiation and Climate Experiment)/TIM (Total Irradiance Monitor), ACRIMSAT (Active Cavity Radiometer Irradiance Monitor Satellite)/ACRIM III, and SOHO (Solar and Heliospheric Observatory)/VIRGO (Variability of IRradiance and Gravity Oscillations Sun PhotoMeter) provided Total Solar Irradiance (TSI) measurements with unprecedented accuracy and stability to determine the amount of solar irradiance reaching the top of the atmosphere and how solar irradiance varies on different time scales. These three independent measurements are analyzed using the EEMD (Ensemble Empirical Mode Decomposition) method to characterize the phase and amplitude of the 27-day solar rotational variation in TSI. The mode decomposition clearly identifies a 27-day solar rotational signature on TSI measurements. The rotational variations of TSI from the three independent observations are generally consistent with each other, despite different mean TSI values. During the declining phase of solar cycle 23, the amplitude of TSI 27-day variations is as high as 0.8 W/m² (~0.05%), while during the rising phase of solar cycle 24, the amplitude is up to 0.4 W/m² (~0.04%). During the minimum phase (2008–2009), the amplitude of the rotational mode is only ~0.1 W/m². The correlation of this rotational mode between TIM and ACRIM III is ~0.92 and the slope of the local peak values is ~0.98. The correlation between TIM and VIRGO is ~0.96 and the slope of the local peak values is ~0.98, very similar to the slope with ACRIM III.
2FHL: THE SECOND CATALOG OF HARD FERMI-LAT SOURCES
(IOP, 2016-01-14) Mirabal, N.; Buson, S.; et al.
We present a catalog of sources detected above 50 GeV by the Fermi-Large Area Telescope (LAT) in 80 months of data. The newly delivered Pass 8 event-level analysis allows the detection and characterization of sources in the 50 GeV–2 TeV energy range. In this energy band, Fermi-LAT has detected 360 sources, which constitute the second catalog of hard Fermi-LAT sources (2FHL). The improved angular resolution enables the precise localization of point sources (~1farcm7 radius at 68% C. L.) and the detection and characterization of spatially extended sources. We find that 86% of the sources can be associated with counterparts at other wavelengths, of which the majority (75%) are active galactic nuclei and the rest (11%) are Galactic sources. Only 25% of the 2FHL sources have been previously detected by Cherenkov telescopes, implying that the 2FHL provides a reservoir of candidates to be followed up at very high energies. This work closes the energy gap between the observations performed at GeV energies by Fermi-LAT on orbit and the observations performed at higher energies by Cherenkov telescopes from the ground.
2MASS J10274572+0629104: the very short period young M6 dwarf binary system identified in K2 data
(Oxford University Press, 2019-04-13) Paudel, Rishi R; Gizis, John E.; Burgasser, Adam J.; Hsu, Chih-Chun
We report the identification of a very low mass new binary system 2MASS J10274572+0629104, based on Kepler K2 photometry and Gaia DR2 astrometry. The K2 light curve is consistent with a beat pattern of two periodic signals, and using Lomb-Scargle periodogram, we find two rotation periods of 0.2114±0.0002 day and 0.2199±0.0003 day. We conclude that these rotation periods arise from two stars with similar spectral types of M6, and have near equal luminosity. It is the first ultracool binary system to be identified based on beat patterns in the light curve. Near-infrared spectroscopy yields RV = -9.8±0.6 km s⁻¹, v sin i =21.5±1.1 km s⁻¹, Tₑᶠᶠ = 3110±40 K, and log g = 5.2±0.2. The motions are consistent with a young age, as are the rotation periods, but the source does not appear to be part of any known moving group. Furthermore, we detected three strong white light flares in the K2 light curve, with estimated total bolometric (UV/optical/IR) energies to be 2.8 × 10³³, 5.2 × 10³³ and 3.8 × 10³³ erg respectively

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