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One of the unsolved questions in gamma-ray astronomy is whether the extragalactic gamma-ray background is of the discrete-source origin. To respond to this question, one first needs to reduce the data by differentiating charged particles from gamma rays. This procedure is usually performed on the basis of the detector responses. In this paper, we showed that the geomagnetic shielding effect at GeV energies can, to some extent, be used for this purpose for gamma-ray telescopes in a low Earth orbit. We illustrated this method by applying it to the Fermi-LAT data. To partially decompose the charge-filtered background, we examined the contribution from star-forming galaxies by implying a radio/gamma connection in consideration of next generation radio surveys., Comment: Published in MNRAS. Updated to address typos

Prestellar cores are self-gravitating dense and cold structures within molecular clouds where future stars are born. They are expected, at the stage of transitioning to the protostellar phase, to harbor centrally concentrated dense (sub)structures that will seed the formation of a new star or the binary/multiple stellar systems. Characterizing this critical stage of evolution is key to our understanding of star formation. In this work, we report the detection of high-density (sub)structures on the thousand-astronomical-unit (au) scale in a sample of dense prestellar cores. Through our recent ALMA observations toward the Orion Planck Galactic Cold Clumps, we have found five extremely dense prestellar cores, which have centrally concentrated regions of ∼2000 au in size, and several 107 cm-3 in average density. Masses of these centrally dense regions are in the range of 0.30 to 6.89M⊙. For the first time, our higher resolution observations (0.8' ∼ 320 au) further reveal that one of the cores shows clear signatures of fragmentation; such individual substructures/fragments have sizes of 800-1700 au, masses of 0.08 to 0.84M⊙, densities of 2 - 8 × 107 cm-3, and separations of ∼1200 au. The substructures are massive enough (≳0.1M⊙) to form young stellar objects and are likely examples of the earliest stage of stellar embryos that can lead to widely (∼1200 au) separated multiple systems., L. acknowledges the support from the international partnership program of the Chinese Academy of Sciences through grant No.114231KYSB20200009, National Natural Science Foundation of China (NSFC) through grant NSFC No.12073061, and Shanghai Pujiang Program 20PJ1415500. N.H. acknowledges MoST 108-2112-M-001-017 and MoST 109-2112-M-001-023 grants. G.G. acknowledges support from ANID project AFB 170002. L.B. acknowledges support from ANID project AFB-170002. S.L.Q. is supported by the National Natural Science Foundation of China under grant No. U1631237. D.J. is supported by NRC Canada and by an NSERC Discovery Grant. V.M.P. acknowledges support by the Spanish MINECO under project AYA2017-88754-P, and financial support from the State Agency for Research of the Spanish Ministry of Science and Innovation through the “Unit of Excellence María de Maeztu 2020-2023” award to the Institute of Cosmos Sciences (CEX2019-000918-M). C.W.L. is supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF-2019R1A2C1010851). A.S. acknowledges financial support from the NSF through grant AST-1715876. The research was carried out in part at the Jet Propulsion Laboratory, which is operated for NASA by the California Institute of Technology. D. L. acknowledges support from NSFC No. 11911530226 and 11725313. K.T. was supported by JSPS KAKENHI grant No. 20H05645. J.H. thanks the NSFC grant No. 11873086 and Yunnan Province of China (No. 2017HC018).This work is sponsored (in part) by the Chinese Academy of Sciences (CAS), through a grant to the CAS South America Center for Astronomy (CASSACA) in Santiago, Chile.

We have selected six sources (G209.55–19.68S2, G205.46–14.56S1-A, G203.21–11.20W2, G191.90–11.21S, G205.46–14.56S3, and G206.93–16.61W2) from the Atacama Large Millimeter/submillimeter Array Survey of Orion Planck Galactic Cold Clumps (ALMASOP), in which these sources have been mapped in the CO (J = 2−1), SiO (J = 5−4), and C18O (J = 2−1) lines. These sources have high-velocity SiO jets surrounded by low-velocity CO outflows. The SiO jets consist of a chain of knots. These knots have been thought to be produced by semiperiodic variations in jet velocity. Therefore, we adopt a shock-forming model, which uses such variations to estimate the inclination angle and velocity of the jets. We also derive the inclination angle of the CO outflows using the wide-angle wind-driven shell model and find it to be broadly consistent with that of the associated SiO jets. In addition, we apply this shock-forming model to another three protostellar sources with SiO jets in the literature—HH 211, HH 212, and L1448C(N)—and find that their inclination angle and jet velocity are consistent with those previously estimated from proper-motion and radial-velocity studies.

Jets and outflows trace the accretion history of protostars. High-velocity molecular jets have been observed from several protostars in the early Class 0 phase of star formation, detected with the high-density tracer SiO. Until now, no clear jet has been detected with SiO emission from isolated evolved Class I protostellar systems. We report a prominent dense SiO jet from a Class I source G205S3 (HOPS-315: T bol ∼ 180 K, spectral index ∼0.417), with a moderately high mass-loss rate (∼0.59 × 10−6 M ⊙ yr−1) estimated from CO emission. Together, these features suggest that G205S3 is still in a high-accretion phase, similar to that expected of Class 0 objects. We compare G205S3 to a representative Class 0 system G206W2 (HOPS-399) and literature Class 0/I sources to explore the possible explanations behind the SiO emission seen at the later phase. We estimate a high inclination angle (∼40°) for G205S3 from CO emission, which may expose the infrared emission from the central core and mislead the spectral classification. However, the compact 1.3 mm continuum, C18O emission, location in the bolometric luminosity to submillimeter fluxes diagram, outflow force (∼3.26 × 10−5 M ⊙ km s−1 yr−1) are also analogous to that of Class I systems. We thus consider G205S3 to be at the very early phase of Class I, and in the late phase of high accretion. The episodic ejection could be due to the presence of an unknown binary, a planetary companion, or dense clumps, where the required mass for such high accretion could be supplied by a massive circumbinary disk.

A systematic search for cyclical sources of gamma-ray emission on the period range from days to years in the Fermi-LAT sky is performed. Looking for cyclical emission, the sky is binned into equal-area pixels and the generalised Lomb-Scargle periodogram is computed for each of these pixels. The search on the period range between 2.5 and 30 days in the Galactic plane confirms periodicities of three binaries, LSI +61 303, LS 5039, and 1FGL J1018.6-5856. The all-sky search on the period range between 30 days and 2.5 years confirms periodicities of three blazars, PG 1553+113, PKS 2155-304, and BL Lacertae. Evidence for periodic behaviours of four blazars, 4C +01.28, S5 0716+71, PKS 0805-07, and PKS 2052-47, are presented. Three of these blazars, 4C +01.28, PKS 0805-07, and PKS 2052-47, are located at high redshifts. These three sources are potential candidates to binary systems of supermassive black holes provided that major galaxy mergers are more frequent and that galaxies are more gas-rich at high redshifts., Comment: 8 pages, 2 figures, accepted for publication in MNRAS

We develop a method to search for pair haloes around active galactic nuclei (AGN) through a temporal analysis of γ-ray data. The basis of our method is an analysis of the spatial distributions of p ...

We report the detection of four new hot corino sources, G211.47-19.27S, G208.68-19.20N1, G210.49-19.79W and G192.12-11.10 from a survey study of Planck Galactic Cold Clumps in the Orion Molecular Cloud Complex with the Atacama Compact Array (ACA). Three sources had been identified as low mass Class 0 protostars in the Herschel Orion Protostar Survey (HOPS). One source in the lambda Orionis region is firstly reported as a protostellar core. We have observed abundant complex organic molecules (COMs), primarily methanol but also other oxygen-bearing COMs (in G211.47-19.27S and G208.68-19.20N1) and the molecule of prebiotic interest NH2CHO (in G211.47-19.27S), signifying the presence of hot corinos. While our spatial resolution is not sufficient for resolving most of the molecular emission structure, the large linewidth and high rotational temperature of COMs suggest that they likely reside in the hotter and innermost region immediately surrounding the protostar. In G211.47-19.27S, the D/H ratio of methanol ([CH2DOH]/[CH3OH]) and the 12C/13C ratio of methanol ([CH3OH]/[13CH3OH]) are comparable to those of other hot corinos. Hydrocarbons and long carbon-chain molecules such as c-C3H2 and HCCCN are also detected in the four sources, likely tracing the outer and cooler molecular envelopes., 37 pages, 51 figures, to be published in ApJ

Protostellar jets and outflows are signatures of star formation and promising mechanisms for driving supersonic turbulence in molecular clouds. We quantify outflow-driven turbulence through three-dimensional numerical simulations using an isothermal version of the robust total variation diminishing code. We drive turbulence in real-space using a simplified spherical outflow model, analyse the data through density probability distribution functions (PDF), and investigate the Core Formation Rate per free-fall time (CFR_ff). The real-space turbulence driving method produces a negatively skewed density PDF possessing an enhanced tail on the low-density side. It deviates from the log-normal distributions typically obtained from Fourier-space turbulence driving at low densities, but can provide a good fit at high-densities, particularly in terms of mass weighted rather than volume weighted density PDF. Due to this fact, we suggest that the CFR_ff determined from a Fourier-driven turbulence model could be comparable to that of our particular real-space driving model, which has a ratio of solenoidal to compressional components from the resulting turbulence velocity fields of ~0.6., 5 pages, 3 figures, accepted for publication in MNRASL

Recent high-resolution high-sensitivity observations of protostellar jets have shown many to possess deviations to their trajectories. HH 211 is one such example where sub-mm observations with the SMA have revealed a clear reflection-symmetric wiggle. The most likely explanation is that the HH 211 jet source could be moving as part of a protobinary system. Here we test this assumption by simulating HH 211 through 3D hydrodynamic jet propagation simulations using the PLUTO code with a molecular chemistry and cooling module, and initial conditions based on an analytical model derived from SMA observations. Our results show the reflection-symmetric wiggle can be recreated through the assumption of a jet source perturbed by binary motion at its base, and that a regular sinusoidal velocity variation in the jet beam can be close to matching the observed knot pattern. However, a more complex model with either additional heating from the protostar, or a shorter period velocity pulsation may be required to account for enhanced emission near the source, and weaker knot emission downstream. Position velocity diagrams along the pulsed jet beam show a complex structure with detectable signatures of knots and show caution must be exercised when interpreting radial velocity profiles through observations. Finally, we make predictions for future HH 211 observations with ALMA., Comment: 11 pages, 6 figures

High-resolution imaging of the Sunyaev–Zel'dovich (SZ) effect opens new possibilities for testing the presence of various high-energy particle populations in clusters of galaxies. A detailed X-ray analysis of the ‘Bullet cluster’ (1E 0657−56) with Chandra has revealed the presence of additional X-ray spectral components beyond a simple, single-temperature plasma in its X-ray spectra. X-ray methods alone are insufficient to elucidate the origins of these spectral components. We show that the morphology and magnitude of the SZ effect at high frequencies are critically dependent upon the mechanism by which the additional X-ray spectra are created. We examine the differences between the predicted SZ effect emission maps at 600 GHz assuming the X-ray spectra are composed of thermal gas with a steep power-law index component and also thermal gas with a significant contribution of strongly heated gas. A two-temperature model with a hot (kT ≃ 30–40 keV) second component is the most consistent with existing SZ data at high frequencies. However, significant morphological differences remain. High-angular-resolution SZ intensity maps at high frequencies in combination with deep X-ray data provide a new window into understanding particle energization processes in the hottest, massive merging galaxy clusters.

The properties of bipolar outflows depend on the structure in the environment as well as the nature of the jet. To help distinguish between the two, we investigate here the properties pertaining to the ambient medium. We execute axisymmetric hydrodynamic simulations, injecting continuous atomic jets into molecular media with density gradients (protostellar cores) and density discontinuities (thick swept-up sheets). We determine the distribution of outflowing mass with radial velocity (the mass spectrum) to quantify our approach and to compare to observationally determined values. We uncover a sequence from clump entrainment in the flanks to bow shock sweeping as the density profile steepens. We also find that the dense, highly supersonic outflows remain collimated but can become turbulent after passing through a shell. The mass spectra vary substantially in time, especially at radial speeds exceeding 15 km s -1 . The mass spectra also vary according to the conditions: both envelope-type density distributions and the passage through dense sheets generate considerably steeper mass spectra than a uniform medium. The simulations suggest that observed outflows penetrate highly non-uniform media.

Recent high-resolution, high-sensitivity observations of protostellar jets have shown many to possess an underlying ‘wiggle’ structure. HH 211 is one such example where recent sub-mm observations revealed a clear reflection-symmetric wiggle. An explanation for this is that the HH211 jet source is moving as part of a protobinary system. Here we test this assumption by simulating HH211 through 3D hydrodynamic simulations using the pluto code with a molecular chemistry and cooling module, and initial conditions based on an analytical model derived from SMA observations. Molecular chemistry allows us to accurately plot synthetic molecular emission maps and position-velocity diagrams for direct comparison to observations, enabling us to test the observational assumptions and put constraints on the physical parameters of HH211. Our preliminary results show that the reflection-symmetric wiggle can be recreated through the assumption of a jet source being part of a binary system.

In order to understand the formation of the multipolar structures of the pre-planetary nebula (PPN) CRL 618, we perform 3D simulations using a multi-directional bullet model. The optical lobes of CRL 618 and fast molecular outflows at the tips of the lobes have been found to have similar expansion ages of ~ 100 yr. Additional fast molecular outflows were found near the source along the outflow axes with ages of ~ 45 yr, suggesting a second episode of bullet ejections. Thus, in our simulations, two episodes of bullet ejections are assumed. The shaping process is simulated using the ZEUS-3D hydrodynamics code that includes molecular and atomic cooling. In addition, molecular chemistry is also included to calculate the CO intensity maps. Our results show the following: (1) Multi-epoch bullets interacting with the toroidal dense core can produce the collimated multiple lobes as seen in CRL 618. The total mass of the bullets is ~ 0.034 solar mass, consistent with the observed high-velocity CO emission in fast molecular outflows. (2) The simulated CO J=3-2 intensity maps show that the low-velocity cavity wall and the high-velocity outflows along the lobes are reasonably consistent with the observations. The position-velocity diagram of the outflows along the outflow axes shows a linear increase of velocity with distance, similar to the observations. The ejections of these bullets could be due to magneto-rotational explosions or nova-like explosions around a binary companion.