Current date: 2022-07-06

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Created/updated limit: 2022-06-29 (7 days ago)

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Number of records retrieved: 454

Keyword score statistics

score 5 -- 1 abstracts

score 4 -- 1 abstracts

score 3 -- 2 abstracts

score 2 -- 8 abstracts

score 1 -- 15 abstracts

in total -- 27 abstracts

Articles that appeared on 2022-07-06

[abstract 1 / 27] Yes (score: 5)
arXiv:2207.02097 [pdf, ps, other]
Title: High-energy neutrinos and gamma rays from winds and tori in active galactic nuclei
Authors: Susumu Inoue, Matteo Cerruti, Kohta Murase, Ruo-Yu Liu,
Comments: 13 pages including supplemental material, for submission to PRL
Subjects: astro-ph.HE astro-ph.CO
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

Powerful winds with wide opening angles, likely driven by accretion disks around BLACK HOLEs (BHs), are observed in the majority of active galactic nuclei (AGN) and can play a crucial role in AGN and galaxy evolution. If protons are accelerated in the wind near the BH via diffusive shock acceleration, p-gamma processes with AGN photons can generate neutrinos as well as pair cascade emission from the gamma-ray to radio bands. The TeV neutrinos tentatively detected by IceCube from the obscured Seyfert galaxy NGC 1068 can be interpreted consistently if the shock velocity is appreciably lower than the local escape velocity, which may correspond to a failed, line-driven wind that is physically well motivated. Although the p-gamma-induced cascade is gamma-gamma-attenuated above a few MeV, it can still contribute significantly to the sub-GeV gamma rays observed from NGC 1068. At higher energies, gamma rays can arise via $pp$ processes from a shock where an outgoing wind impacts the obscuring torus, along with some observable radio emission. Tests and implications of this model are discussed. Neutrinos and gamma rays may offer unique probes of AGN wind launching sites, particularly for objects obscured in other forms of radiation.

[abstract 2 / 27] Yes (score: 4)
arXiv:2207.01980 [pdf, ps, other]
Title: The independence of oscillatory RECONNECTion periodicity from the initial pulse
Authors: Konstantinos Karampelas, James A. McLaughlin, Gert J. J. Botha, Stéphane Régnier,
Comments: 19 pages, 14 figures, accepted for publication in ApJ
Subjects: astro-ph.SR
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

Oscillatory RECONNECTion can manifest through the interaction between the ubiquitous MHD waves and omnipresent null points in the solar atmosphere and is characterized by an inherent periodicity. In the current study, we focus on the relationship between the period of oscillatory RECONNECTion and the strength of the wave pulse initially perturbing the null point, in a hot coronal plasma. We use the PLUTO code to solve the fully compressive, resistive MHD equations for a 2D MAGNETic X-point. Using wave pulses with a wide range of amplitudes, we perform a parameter study to obtain values for the period, considering the presence and absence of anisotropic thermal conduction separately. In both cases, we find that the resulting period is independent of the strength of the initial perturbation. The addition of anisotropic thermal conduction only leads to an increase in the mean value for the period, in agreement with our previous study. We also consider a different type of initial driver and we obtain an oscillation period matching the independent trend previously mentioned. Thus, we report for the first time on the independence between the type and strength of the initializing wave pulse and the resulting period of oscillatory RECONNECTion in a hot coronal plasma. This makes oscillatory RECONNECTion a promising mechanism to be used within the context of coronal seismology.

[abstract 3 / 27] Yes (score: 3)
arXiv:2207.01628 [pdf, ps, other]
Title: A correlation between Ha trough depth and inclination in quiescent X-ray transients: evidence for a low-mass BLACK HOLE in GRO J0422+32
Authors: J. Casares, T. Munõz-Darias, M. A. P. Torres, D. Mata Sanchez, C. T. Britt, M. Armas Padilla, A. Alvarez-Hernandez, V. A. Cuneo, J. I. Gonzalez Hernandez, F. Jimenez-Ibarra, P. G. Jonker, G. Panizo-Espinar, J. Sanchez-Sierras, I. V. Yanes-Rizo,
Comments: Accepted for publication in MNRAS, 21 pages, 15 figures, 6 Tables
Subjects: astro-ph.HE astro-ph.SR
Created: 2022-07-04; Updated: ; Datestamp: 2022-07-06

We present a new method to derive binary inclinations in quiescent BLACK HOLE (BH) X-ray transients (XRTs), based on the depth of the trough (T) from double-peaked Ha emission profiles arising in accretion discs. We find that the inclination angle (i) is linearly correlated with T in phase-averaged spectra with sufficient orbital coverage (>~50 per cent) and spectral resolution, following i (deg)=93.5 x T +23.7. The correlation is caused by a combination of line opacity and local broadening, where a leading (excess broadening) component scales with the de-projected velocity of the outer disc. Interestingly, such scaling allows to estimate the fundamental ratio M1/Porb by simply resolving the intrinsic width of the double-peak profile. We apply the T-i correlation to derive binary inclinations for GRO J0422+32 and SWIFT J1357-0933, two BH XRTs where strong flickering activity has hindered determining their values through ellipsoidal fits to photometric light curves. Remarkably, the inclination derived for GRO J0422+32 (i=55.6+-4.1) implies a BH mass of 2.7+0.7-0.5 Msun thus placing it within the gap that separates BHs from neutron stars. This result proves that low-mass BHs exist in nature and strongly suggests that the so-called "mass gap" is mainly produced by low number statistics and possibly observational biases. On the other hand, we find that SWIFT J1357-0933 contains a 10.9+1.7-1.6 Msun BH seen nearly edge on (i=87.4+2.6-5.6 deg). Such extreme inclination, however, should be treated with caution since it relies on extrapolating the T-i correlation beyond i>~75 deg, where it has not yet been tested.

[abstract 4 / 27] Yes (score: 3)
arXiv:2207.01969 [pdf, ps, other]
Title: Discovery of a new supergiant fast X-ray transient MAXI J0709-159 associated with the Be star LY CMa
Authors: M. Sugizaki, T. Mihara, K. Kobayashi, H. Negoro, M. Shidatsu, S. N. Pike, W. Iwakiri, S. Urabe, M. Serino, N. Kawai, M. Nakajima, J. A. Kennea, Z. Liu,
Comments: 13 pages, 10 figures, accepted for publication in PASJ
Subjects: astro-ph.HE
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

We report on the discovery of a new supergiant fast X-ray transient (SFXT), MAXI J0709$-$159, and its identification with LY CMa (also known as HD 54786). On 2022 January 25, a new flaring X-ray object named MAXI J0709$-$159, was detected by Monitor of All-sky X-ray Image (MAXI). Two flaring activities were observed in the two scans of $\sim 3$ hours apart, where the 2-10 keV flux reached $5\times 10^{-9}$ erg cm$^{-2}$ s$^{-1}$. During the period, the source exhibited a large spectral change suggesting that the absorption column density $N_\mathrm{H}$ increased from $10^{22}$ cm$^{-2}$ to $10^{23}$ cm$^{-2}$. NUSTAR follow-up observation on January 29 identified a new X-ray source with a flux of $6\times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ at the position consistent with LY CMa, which has been identified as B supergiant as well as Be star, located at the 3 kpc distance. The observed X-ray activity characterized by the short ($\lesssim$ several hours) duration, the rapid ($\lesssim$ a few seconds) variabilities accompanied with spectral changes, and the large luminosity swing ($10^{32}$-$10^{37}$ erg s$^{-1}$) agree with those of SFXT. On the other hand, optical spectroscopic observations of LY CMa revealed a broad $H\alpha$ emission line, which may indicate the existence of a Be circumstellar disk. These obtained results suggest that the optical companion, LY CMa, certainly has a complex circumstellar medium including dense clumps.

[abstract 5 / 27] (score: 2)
arXiv:2207.01631 [pdf, ps, other]
Title: A 2-hr binary period for the BLACK HOLE transient MAXI J0637-430
Authors: Roberto Soria, Ruican Ma, Lian Tao, Shuang-Nan Zhang,
Comments: 8 pages, 300 kB, accepted by MNRAS on 2022 July 4
Subjects: astro-ph.HE astro-ph.GA
Created: 2022-07-04; Updated: ; Datestamp: 2022-07-06

We revisit various sets of published results from X-ray and optical studies of the Galactic BLACK HOLE (BH) candidate MAXI J0637-430, which went into outburst in 2019. Combining the previously reported values of peak outburst luminosity, best-fitting radii of inner and outer accretion disk, viewing angle, exponential decay timescale and peak-to-peak separation of the He II 4686 disk emission line, we improve the constraints on the system parameters. We estimate a heliocentric distance d = (8.7 +/- 2.3) kpc, a projected Galactocentric distance R = (13.2 +/- 1.8) kpc and a height |z| = (3.1 +/- 0.8) kpc from the Galactic plane. It is the currently known Milky Way BH candidate located farthest from the Galactic Centre. We infer a BH mass M_1 = (5.1 +/- 1.6) M_{sun}, a spin parameter a* <~ 0.25, a donor star mass M_2 = (0.25 +/- 0.07) M_{sun}, a peak Eddington ratio lambda = 0.17 +/- 0.11 and a binary period P_{orb} = 2.2^{+0.8}_{-0.6} hr. This is the shortest period measured or estimated so far for any Galactic BH X-ray binary. If the donor star is a main-sequence dwarf, such a period corresponds to the evolutionary stage where orbital shrinking is driven by gravitational radiation and the star has regained contact with its Roche lobe (low end of the period gap). The three Galactic BHs with the shortest period (<~3 hr) are also those with the highest vertical distance from the Galactic plane (>~2 kpc). This is probably because binaries with higher binding energies can survive faster natal kicks.

[abstract 6 / 27] (score: 2)
arXiv:2207.01743 [pdf, ps, other]
Title: Synthetic Polarization Maps of an Outflow Zone from Magnetohydrodynamic Simulations
Authors: Gianfranco Bino, Shantanu Basu, Masahiro N Machida, Aris Tritsis, Mahmoud Sharkawi, Kundan Kadam, Indrani Das,
Subjects: astro-ph.SR astro-ph.GA
Created: 2022-07-04; Updated: ; Datestamp: 2022-07-06

The canonical theory of STAR FORMATION in a MAGNETized environment predicts the formation of hourglass-shaped MAGNETic fields during the prestellar collapse phase. In protostellar cores, recent observations reveal complex and strongly distorted MAGNETic fields in the inner regions that are sculpted by rotation and outflows. We conduct resistive, nonideal MAGNETohydrodynamic (MHD) simulations of a protostellar core and employ the radiative transfer code POLARIS to produce synthetic POLARIZATION segment maps. Comparison of our mock-POLARIZATION maps based on the toroidal-dominated MAGNETic field in the outflow zone with the observed POLARIZATION vectors of SiO lines in Orion Source I shows a reasonable agreement when the MAGNETic axis is tilted at an angle $\theta = 15^{\circ}$ with respect to the plane-of-sky and if the SiO lines have a net POLARIZATION parallel to the local MAGNETic field. Although the observed POLARIZATION is from SiO lines and our synthetic maps are due to polarized dust emission, a comparison is useful and allows us to resolve the ambiguity of whether the line POLARIZATION is parallel or perpendicular to the local MAGNETic field direction.

[abstract 7 / 27] (score: 2)
arXiv:2207.01788 [pdf, ps, other]
Title: Quiet Sun Center to Limb Variation of the Linear Polarization Observed by CLASP2 Across the Mg II h & k Lines
Authors: L. A. Rachmeler, J. Trujillo Bueno, D. E. McKenzie, R. Ishikawa, F. Auchere, K. Kobayashi, R. Kano, T. J. Okamoto, C. W. Bethge, D. Song, E. Alsina Ballester, L. Belluzzi, T. del Pino Aleman, M. Yoshida, T. Shimizu, A. Winebarger, A. R. Kobelski, G. D. Vigil, B. De Pontieu, Y. Suematsu, N. Narukage, M. Kubo, T. Sakao, H. Hara, J. Stepan, M. Carlsson, J. Leenaarts, A. Asensio Ramos,
Comments: 14 pages, 5 figures, to be published in the Astrophysical Journal (ApJ), initially submitted May 2022, revised submission July 2022
Subjects: astro-ph.SR
Created: 2022-07-04; Updated: ; Datestamp: 2022-07-06

The CLASP2 (Chromospheric LAyer SpectroPolarimeter 2) sounding rocket mission was launched on 2019 April 11. CLASP2 measured the four Stokes parameters of the Mg II h & k spectral region around 2800 Angstroms along a 200 arcsecond slit at three locations on the solar disk, achieving the first spatially and spectrally resolved observations of the solar POLARIZATION in this near ultraviolet region. The focus of the work presented here is the center-to-limb variation of the linear POLARIZATION across these resonance lines, which is produced by the scattering of anisotropic radiation in the solar atmosphere. The linear POLARIZATION signals of the Mg II h & k lines are sensitive to the MAGNETic field from the low to the upper chromosphere through the Hanle and MAGNETo-optical effects. We compare the observations to theoretical predictions from radiative transfer calculations in unMAGNETized semi-empirical models, arguing that MAGNETic fields and horizontal inhomogeneities are needed to explain the observed POLARIZATION signals and spatial variations. This comparison is an important step in both validating and refining our understanding of the physical origin of these POLARIZATION signatures, and also in paving the way toward future space telescopes for probing the MAGNETic fields of the solar upper atmosphere via ultraviolet spectropolarimetry.

[abstract 8 / 27] (score: 2)
arXiv:2207.01807 [pdf, ps, other]
Title: Emergence of a new HI 21-cm absorption component at z~1.1726 towards the gamma-ray BLAZAR PKS~2355-106
Authors: Raghunathan Srianand, Neeraj Gupta, Patrick Petitjean, Emmanuel Momjian, Sergei A. Balashev, Francoise Combes, Hsiao-Wen Chen, Jens-Kristian Krogager, Pasquier Noterdaeme, Hadi Rahmani, Andrew J. Baker, Kimberly L. Emig, Gyula I. G. Jozsa, Hans-Rainer Kloeckner, Kavilan Moodley,
Comments: 8 pages, 7 figures and accepted for publication in MNRAS
Subjects: astro-ph.GA
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

We report the emergence of a new HI 21-cm absorption at z_abs = 1.172635 in the damped Lyman-alpha absorber (DLA) towards the gamma-ray BLAZAR PKS 2355-106 (z_em~1.639) using science verification observations (June 2020) from the MeerKAT Absorption Line Survey (MALS). Since 2006, this DLA is known to show a narrow HI 21-cm absorption at z_abs = 1.173019 coinciding with a distinct metal absorption line component. We do not detect significant HI 21-cm optical depth variations from this known HI component. A high resolution optical spectrum (August 2010) shows a distinct Mg I absorption at the redshift of the new HI 21-cm absorber. However, this component is not evident in the profiles of singly ionized species. We measure the metallicity ([Zn/H] = -(0.77\pm0.11) and [Si/H]= -(0.96\pm0.11)) and depletion ([Fe/Zn] = -(0.63\pm0.16)) for the full system. Using the apparent column density profiles of Si II, Fe II and Mg I we show that the depletion and the N(Mg I)/N(Si II) column density ratio systematically vary across the velocity range. The region with high depletion tends to have slightly larger N(Mg I)/N(Si II) ratio. The two HI 21-cm absorbers belong to this velocity range. The emergence of z_abs = 1.172635 can be understood if there is a large optical depth gradient over a length scale of ~0.35 pc. However, the gas producing the z_abs = 1.173019 component must be nearly uniform over the same scale. Systematic uncertainties introduced by the absorption line variability has to be accounted for in experiments measuring the variations of fundamental constants and cosmic acceleration even when the radio emission is apparently compact as in PKS 2355-106.

[abstract 9 / 27] (score: 2)
arXiv:2207.01817 [pdf, ps, other]
Title: Proton Penetration Efficiency over a High Altitude Observatory in Mexico
Authors: S. Miyake, T. Koi, Y. Muraki, Y. Matsubara, S. Masuda, P. Miranda, T. Naito, E. Ortiz, A. Oshima, T. Sakai, T. Sako, S. Shibata, H. Takamaru, M. Tokumaru, J. F. Valdes-Galicia,
Comments: Paper presented in the 21st International Symposium on Very High Energy Cosmic Ray Intercations (ISVHE-CRI 2022) by online
Subjects: astro-ph.SR astro-ph.HE hep-ph
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

In association with a large solar flare on November 7, 2004, the solar neutron detectors located at Mt. Chacaltaya (5,250m) in Bolivia and Mt. Sierra Negra (4,600m) in Mexico recorded very interesting events. In order to explain these events, we have performed a calculation solving the equation of motion of anti-protons inside the MAGNETosphere. Based on these results, the Mt. Chacaltaya event may be explained by the detection of solar neutrons, while the Mt. Sierra Negra event may be explained by the first detection of very high energy solar neutron decay protons (SNDPs) around 6 GeV.

[abstract 10 / 27] (score: 2)
arXiv:2207.01865 [pdf, ps, other]
Title: Ultraviolet Spectropolarimetry: Investigating stellar MAGNETic field diagnostics
Authors: C. P. Folsom, R. Ignace, C. Erba, R. Casini, T. del Pino Alemán, K. Gayley, K. Hobbs, R. Manso Sainz, C. Neiner, V. Petit, M. E. Shultz, G. A. Wade,
Comments: Submitted to Astrophysics and Space Science. arXiv admin note: text overlap with arXiv:2111.06434
Subjects: astro-ph.SR
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

Magnetic fields are important for stellar photospheres and MAGNETospheres, influencing photospheric physics and sculpting stellar winds. Observations of stellar MAGNETic fields are typically made in the visible, although infrared observations are becoming common. Here we consider the possibility of directly detecting MAGNETic fields at ultraviolet (UV) wavelengths using high resolution spectropolarimetry, specifically considering the capabilities of the proposed Polstar mission. UV observations are particularly advantageous for studying wind resonance lines not available in the visible, but they can also provide many photospheric lines in hot stars. Detecting photospheric MAGNETic fields using the Zeeman effect and Least Squares Deconvolution is potentially more effective in the UV due to the much higher density of strong lines. We investigate detecting MAGNETic fields in the MAGNETosphere of a star using the Zeeman effect in wind lines, and find that this could be detectable at high S/N in an O or B star with a strong MAGNETic field. We consider detecting MAGNETic fields using the Hanle effect in linear POLARIZATION, which is complementary to the Zeeman effect, and could be more sensitive in photospheric lines of rapid rotators. The Hanle effect can also be used to infer circumstellar MAGNETism in winds. Detecting the Hanle effect requires UV observations, and a multi-line approach is key for inferring MAGNETic field properties. This demonstrates that high resolution spectropolarimetry in the UV, and the proposed Polstar mission, has the potential to greatly expand our ability to detect and characterize MAGNETic fields in and around hot stars.

[abstract 11 / 27] (score: 2)
arXiv:2207.02069 [pdf, ps, other]
Title: Anatomy of a slow merger: dissecting secularly-driven inspirals of LIGO/Virgo gravitational wave sources
Authors: Chris Hamilton, Roman R. Rafikov,
Comments: 30 pages, 12 figures. To be submitted to ApJ. Comments welcome
Subjects: astro-ph.HE astro-ph.GA
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

The dozens of compact object mergers detected by LIGO/Virgo raise a key theoretical question: how do initially wide binaries shrink sufficiently quickly that they are able to merge via gravitational wave (GW) radiation within a Hubble time? One promising class of answers involves secular driving of binary eccentricity by some external tidal perturbation. This perturbation can arise due to the presence of a tertiary point mass, in which case the system exhibits Lidov-Kozai (LK) dynamics, or it can stem from the tidal field of the stellar cluster in which the binary orbits. While these secular tide-driven mechanisms have been studied exhaustively in the case of no GW emission, when GWs are included the dynamical behavior is still incompletely understood. In this paper we consider compact object binaries driven to merger via high eccentricity excitation by (doubly-averaged, test-particle quadrupole level) cluster tides - which includes LK-driven mergers as a special case - and include the effects of both general RELATIVISTIC precession and GW emission. We provide for the first time an analytical understanding of the different evolutionary stages of the binary's semimajor axis, secular oscillation timescale, and phase space structure all the way to merger. Our results will inform future population synthesis calculations of compact object binary mergers from hierarchical triples and stellar clusters.

[abstract 12 / 27] (score: 2)
arXiv:2207.02106 [pdf, ps, other]
Title: Observational Predictions of LQG Motivated Polymerized Black Holes and Constraints From Sgr A* and M87*
Authors: Rahul Kumar Walia,
Comments: 26 pages, 20 figures and 5 tables
Subjects: gr-qc
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

Loop Quantum Gravity (LQG) inspired partial polymer quantization in four-dimensional theory leads to a single-horizon quantum corrected globally regular BLACK HOLE spacetime. The polymerized BLACK HOLE metric is characterized by the minimum length parameter, $k$, and mimics the Schwarzschild BLACK HOLE in the weak-field limit. We present an analytic and numerical investigation of the strong gravitational lensing and shadow morphology to determine the observational impacts of quantum effects. We calculate the characteristic changes in the lensing observables compared to those for the Schwarzschild BLACK HOLE. It is interesting to note that the deflection angle, the angular separation between the outermost RELATIVISTIC image, and magnification increase with $k$. Using the ray-tracing technique, we simulated the BLACK HOLE shadows under three distinct accretion models: static spherical accretion, radially infalling spherical accretion, and the thin accretion disk model. Polymerized BLACK HOLEs' shadow morphology strongly depends on $k$. Constraints on $k$ are derived for the M87* and Sgr A* black hole shadow observations from the Event Horizon Telescope. Our study suggests that quantum gravity effects are accessible in the astrophysical BLACK HOLEs' observations.

[abstract 13 / 27] (score: 1)
arXiv:2207.01636 [pdf, ps, other]
Title: A new formulation of strong-field MAGNETohydrodynamics for neutron stars
Authors: Shreya Vardhan, Sašo Grozdanov, Samuel Leutheusser, Hong Liu,
Comments: 6+7 pages, 3 figures
Subjects: astro-ph.HE hep-ph nucl-th physics.plasm-ph
Created: 2022-07-04; Updated: ; Datestamp: 2022-07-06

We present a formulation of MAGNETohydrodynamics which can be used to describe the evolution of strong MAGNETic fields in neutron star interiors. Our approach is based on viewing MAGNETohydrodynamics as a theory with a one-form global symmetry and developing an effective field theory for the hydrodynamic modes associated with this symmetry. In the regime where the local velocity and temperature variations can be neglected, we derive the most general constitutive relation consistent with symmetry constraints for the electric field in the presence of a strong MAGNETic field. This constitutive relation not only reproduces the phenomena of Ohmic decay, ambipolar diffusion, and Hall drift derived in a phenomenological model by Goldreich and Reisenegger, but also reveals new terms in the evolution of the MAGNETic field which cannot easily be seen from such microscopic models. This formulation gives predictions for novel diffusion behaviors of small perturbations around a constant background MAGNETic field, and for the two-point correlation functions among various components of the electric and MAGNETic fields.

[abstract 14 / 27] (score: 1)
arXiv:2207.01639 [pdf, ps, other]
Title: Mean-field analysis on large-scale MAGNETic fields at high Reynolds numbers
Authors: Ryota Shimada, Hideyuki Hotta, Takaaki Yokoyama,
Comments: 17 pages, 20 figures, Accepted for publication in ApJ
Subjects: astro-ph.SR
Created: 2022-07-04; Updated: ; Datestamp: 2022-07-06

Solar MAGNETic fields comprise an 11-year activity cycle, represented by the number of sunspots. The maintenance of such a solar MAGNETic field can be attributed to fluid motion in the convection zone, i.e. a dynamo. This study conducts the mean-field analyses of the global solar dynamo simulation presented by Hotta et al. (2016). Although the study succeeds in producing coherent large-scale MAGNETic fields at high Reynolds numbers, the detailed physics of the maintenance of this field have not been fully understood. This study extracts the alpha-tensor and the turbulent MAGNETic diffusivity tensor through mean-field analyses. The turbulent MAGNETic diffusivity exhibits a significant decrease towards high Reynolds numbers. The decrease in the turbulent MAGNETic diffusivity suppresses the energy conversion of large-scale field to small-scale field. This implies that the decrease in the turbulent MAGNETic diffusivity contributes to the maintenance of a large-scale MAGNETic field at high Reynolds numbers. A significant downward turbulent pumping is observed; it is enhanced in the weak phase of the large-scale field. This study proposes a cyclic reversal process of a large-scale field which is dominantly driven by the alpha-effect and is possibly triggered by downward pumping.

[abstract 15 / 27] (score: 1)
arXiv:2207.01641 [pdf, ps, other]
Title: Photon emission from an excited string
Authors: Maurizio Firrotta, Vladimir Rosenhaus,
Comments: 32 pages
Subjects: hep-th
Created: 2022-07-04; Updated: ; Datestamp: 2022-07-06

We compute the amplitude for an excited string in any precisely specified state to decay into another excited string in any precisely specified state, via emission of a tachyon or photon. For generic and highly excited string states, the amplitude is a complicated function of the outgoing kinematic angle, sensitive to the precise state. We compute the square of this amplitude, averaged over POLARIZATIONs of the ingoing string and summed over POLARIZATIONs of the outgoing string. The seeming intractability of these calculations is made possible by extracting amplitudes involving excited strings from amplitudes involving tachyons and a large number of photons; the number of photons grows with the complexity of the excited string state. Our work is in the spirit of the broad range of recent studies of statistical mechanics and chaos for quantum many-body systems. The number of different excited string states at a given mass is exponentially large, and our calculation gives the emission amplitude of a single photon from each of the microstates -- which, through the Horowitz-Polchinski correspondence principle, are in correspondence with BLACK HOLE microstates.

[abstract 16 / 27] (score: 1)
arXiv:2207.01648 [pdf, ps, other]
Title: Giant RADIO GALAXies in the LoTSS Bo\"otes deep field
Authors: Marco Simonte, Heinz Andernach, Marcus Brüggen, Dominik Schwarz, Isabella Prandoni, Anthony G. Willis,
Comments: Accepted for publication in MNRAS. 23 pages, 16 figures, 3 tables
Subjects: astro-ph.GA astro-ph.CO
Created: 2022-07-04; Updated: ; Datestamp: 2022-07-06

Giant RADIO GALAXies (GRGs) are RADIO GALAXies that have projected linear extents of more than 700 kpc or 1 Mpc, depending on definition. We have carried out a careful visual inspection in search of GRGs of the Bootes LOFAR Deep Field (BLDF) image at 150 MHz. We identified 74 GRGs with a projected size larger than 0.7 Mpc of which 38 are larger than 1 Mpc. The resulting GRG sky density is about 2.8 (1.43) GRGs per square degree for GRGs with linear size larger than 0.7 (1) Mpc. We studied their radio properties and the accretion state of the host galaxies using deep optical and infrared survey data and determined flux densities for these GRGs from available survey images at both 54 MHz and 1.4 GHz to obtain integrated radio spectral indices. We show the location of the GRGs in the P-D diagram. The accretion mode onto the central BLACK HOLEs of the GRG hosts is radiatively inefficient suggesting that the central engines are not undergoing massive accretion at the time of the emission. Interestingly, 14 out of 35 GRGs for which optical spectra are available show a moderate STAR FORMATION rate. Based on the number density of optical galaxies taken from the DESI DR9 photometric redshift catalogue, we found no significant differences between the environments of GRGs and other RADIO GALAXies, at least for redshift up to z = 0.7.

[abstract 17 / 27] (score: 1)
arXiv:2207.01654 [pdf, ps, other]
Title: First gravitational-wave search for intermediate-mass BLACK HOLE mergers with higher order harmonics
Authors: Koustav Chandra, Juan Calderón Bustillo, Archana Pai, Ian Harry,
Comments: 15 pages, 8 figures
Subjects: gr-qc
Created: 2022-07-04; Updated: ; Datestamp: 2022-07-06

Current matched-filter searches for gravitational waves from binary black-hole mergers compare the calibrated detector data to waveform templates that omit the higher-order mode content of the signals predicted by General Relativity. However, higher-order emission modes become important for highly inclined asymmetric sources with masses above $\simeq 100 M_\odot$, causing current searches to be ill-suited at detecting them. We present a new gravitational-wave search that implements templates including higher-order modes, adapted signal-glitch discriminators and trigger-ranking statistics to specifically target signals displaying strong higher modes, corresponding to nearly edge-on sources with total redshifted masses in the intermediate-mass black-hole range $M_T(1+z) \in (100,500) M_\odot$ and mass-ratios $q\in(1,10)$. Our search shows a volumetric sensitivity gain of up to 450\% to these signals compared to existing searches omitting higher-order modes. We deploy our search on public data from the third observing run of Advanced LIGO. While we find no statistically significant candidates beyond those already reported elsewhere, our search sets the stage to search for higher-mode rich signals in future observing runs. The efficient detection of such signals is crucial to performing detailed tests of General Relativity, observing strong-field phenomena, and maximising the chances of observing the yet uncharted realm of intermediate-mass BLACK HOLE binaries.

[abstract 18 / 27] (score: 1)
arXiv:2207.01694 [pdf, ps, other]
Title: Weak cosmic censorship conjecture for the (2+1)-dimensional charged BTZ BLACK HOLE in the Einstein-Gauss-Bonnet Gravity
Authors: Ayyesha K. Ahmed, Sanjar Shaymatov, Bobomurat Ahmedov,
Comments: 8 pages, no figures
Subjects: gr-qc
Created: 2022-07-04; Updated: ; Datestamp: 2022-07-06

It is well known that ($2+1$) dimensional charged BTZ (Banados, Teitelboim, Zanelli) BLACK HOLE can be overcharged by a charged scalar field and a charged particle in contrast to their analogues in ($3+1$) and higher dimensions. In this regard, it may play an important role to understand more deeply the properties of the ($2+1$)-dimensional charged BLACK HOLE in the Einstein-Gauss-Bonnet (EGB) gravity. In this paper, we test the validity of the weak cosmic censorship conjecture for the ($2+1$)-dimensional charged black hole in novel EGB theory derived recently by Henniger et. al (2021). We show that the minimum energy that particle can have at the horizon becomes negative for both an extremal and nearly-extremal BTZ BLACK HOLEs in EGB gravity. It is proven that both extremal and nearly-extremal $(2+1)$ dimensional BTZ black hole could be overcharged in EGB theory, leading to the violation of the weak cosmic censorship conjecture (WCCC), which is in good agreement with the results obtained for the classical BTZ BLACK HOLE.

[abstract 19 / 27] (score: 1)
arXiv:2207.01713 [pdf, ps, other]
Title: Introducing the notion of tensors through a variation of a Feynman didactic approach
Authors: Lucas Queiroz, Edson C. M. Nogueira, Danilo T. Alves,
Comments: 16 pages, 46 figures
Subjects: physics.ed-ph
Created: 2022-07-04; Updated: ; Datestamp: 2022-07-06

In one of his books [$\textit{The Feynmann Lectures on Physics}$, vol. 2], Feynman presents a didactic approach to introduce basic ideas about tensors, using, as a first example, the dependence of the induced POLARIZATION of a crystal on the direction of the applied electric field, and also presenting the energy ellipsoid as a way of visualizing the POLARIZATION tensor. In the present paper, we propose some variations on Feynman's didactic approach, considering as our basic models a single ground-state atom and a carbon dioxide ($\text{CO}_{2}$) molecule, instead of crystals, and introducing a visual representation of tensors based on the ideas of the Lam\'e stress ellipsoid, instead of the energy ellipsoid. With these changes, the resulting didactic proposal presents a reduction in the prerequisites of physical and mathematical concepts if compared to Feynman's original approach, requiring, for example, no differential calculus and only introductory vector algebra. The text is written so that it can be used directly as a learning tool for students (even those in the beginning of the undergraduate course), as well as for teachers interested in preparing their own materials.

[abstract 20 / 27] (score: 1)
arXiv:2207.01959 [pdf, ps, other]
Title: Determining AGN luminosity histories using present-day outflow properties: a neural-network based approach
Authors: Kastytis Zubovas, Jonas Bialopetravičius, Monika Kazlauskaitė,
Comments: 15 pages, 6 figures in main text. Accepted for publication in MNRAS
Subjects: astro-ph.GA astro-ph.IM
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

Large-scale outflows driven by ACTIVE GALACTIC NUCLEi (AGN) can have a profound influence on their host galaxies. The outflow properties themselves depend sensitively on the history of AGN energy injection during the lifetime of the outflow. Most observed outflows have dynamical timescales longer than the typical AGN episode duration, i.e. they have been inflated by multiple AGN episodes. Here, we present a neural-network based approach to inferring the most likely duty cycle and other properties of AGN based on the observable properties of their massive outflows. Our model recovers the AGN parameters of simulated outflows with typical errors $< 25\%$. We apply the method to a sample of 59 real molecular outflows and show that a large fraction of them have been inflated by AGN shining with a rather high duty cycle $\delta_{\rm AGN} > 0.2$. This result suggests that nuclear activity in galaxies is clustered hierarchically in time, with long phases of more frequent activity composed of many short activity episodes. We predict that $\sim \! 19\%$ of galaxies should have AGN-driven outflows, but half of them are fossils - this is consistent with currently available data. We discuss the possibilities to investigate AGN luminosity histories during outflow lifetimes and suggest ways to use our software to test other physical models of AGN outflows. The source code of all of the software used here is made public.

[abstract 21 / 27] (score: 1)
arXiv:2207.01977 [pdf, ps, other]
Title: Figuring the fine structure of the BLACK HOLE at the Galactic Center with extremely large mass-ratio inspirals
Authors: Shu-Cheng Yang, Huijiao Luo, Wen-Biao Han, Yuan-Hao Zhang,
Comments: 16 pages, 8 figures
Subjects: gr-qc
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

In the Galaxy, extremely large mass-ratio inspirals(X-MRIs) composed of brown dwarfs and the massive BLACK HOLE (MBH) at the Galactic Center could be potential gravitational wave(GW) sources for space-borne detectors. The estimated event rate is considerable, making X-MRIs a promising class of targets for future GW missions. With a few X-MRI observations, astronomers could determine the fine structure of the central MBH with incredible accuracy. In this work, using a waveform model for axisymmetric BLACK HOLEs, we simulate the GWs from twenty X-MRI systems with varied parameters. We find that the mass, spin, and deviation parameters of the Kerr BLACK HOLE could be determined accurately ($\sim 10^{-5} - 10^{-6} $ ) with only one X-MRI event with high a signal-to-noise ratio(SNR). The measurement of the above parameters could be improved with more X-MRI observations.

[abstract 22 / 27] (score: 1)
arXiv:2207.01990 [pdf, ps, other]
Title: Accretion in massive colliding wind binaries and the effect of wind momentum ratio
Authors: Amit Kashi, Amir Michaelis, Yarden Kaminetsky,
Comments: Accepted for publication in MNRAS
Subjects: astro-ph.SR astro-ph.HE
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

We carry out a numerical experiment of ejecting winds in a massive colliding wind binary system, and quantifying the accretion onto the secondary star under different primary mass loss rates. We set a binary system comprising a Luminous Blue Variable (LBV) as the primary and a Wolf-Rayet (WR) star as the secondary, and vary the mass loss rate of the LBV to obtain different values of wind momentum ratio $\eta$. Our simulations include two sets of cases: one where the stars are stationary, and one that includes the orbital motion. As $\eta$ decreases the colliding wind structure moves closer to the secondary. We find that for $\eta \lesssim 0.05$ the accretion threshold is reached and clumps which originate by instabilities are accreted onto the secondary. For each value of $\eta$ we calculate the mass accretion rate and identify different regions in the $\dot{M}_{\rm acc}$ - $\eta$ diagram. For $0.001 \lesssim \eta \lesssim 0.05$ the accretion is sub- Bondi-Hoyle-Lyttleton (BHL) and the average accretion rate satisfies the power-law $\dot{M}_{\rm acc} \propto \eta^{-1.73}$ for static stars. The accretion is not continuous but rather changes from sporadic to a larger duty cycle as $\eta$ decreases. For $\eta\lesssim0.001$ the accretion becomes continuous in time and the accretion rate is BHL, up to a factor of 0.4--0.8. The simulations that include the orbital motion give qualitatively similar results, with the steeper power law $\dot{M}_{\rm acc} \propto \eta^{-1.86}$ for the sub-BHL region and lower $\eta$ as an accretion threshold.

[abstract 23 / 27] (score: 1)
arXiv:2207.02011 [pdf, ps, other]
Title: The radial distribution function reveals the underlying mesostructure of the AdS BLACK HOLE
Authors: Conghua Liu, Jin Wang,
Subjects: gr-qc
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

Based on the equations of state, one can infer the underlying interaction potentials among the BLACK HOLE molecules in the case of Schwarzschild-AdS and charged AdS BLACK HOLEs. The microscopic molecules with the interaction potential arrange in a specific way to form the mesostructure, whose size is between the macro (BLACK HOLE system) and the micro (BLACK HOLE molecules). As a result, the mesostructure leads to the emergence of the macroscopic phase. However, the information about the mesostructure of the AdS BLACK HOLE are still elusive. In this Letter, the radial distribution function is introduced to probe the mesostructure of the AdS BLACK HOLE. We find that the mesostructure of the Schwarzschild-AdS BLACK HOLE behaves as the ideal gas when the temperature is high. Furthermore, we find the mesostructure for the liquid-like (gas-like) phase of the small (large) charged AdS BLACK HOLE. A sudden change of the mesostructure emerges from the liquid-like phase to the gas-like phase when the charged AdS BLACK HOLE undergoes a phase transition from the small to large BLACK HOLE, consistent with the viewpoint that the phase transition of the charged AdS BLACK HOLE is reminiscent of that of the vdW fluid. This study provides a new angle towards understanding the BLACK HOLE from its mesostructure.

[abstract 24 / 27] (score: 1)
arXiv:2207.02021 [pdf, ps, other]
Title: Exploring physical properties of minimally deformed strange star model and constraints on maximum mass limit in $f(\mathcal{Q})$ gravity
Authors: S. K. Maurya, G. Mustafa, M. Govender, Ksh. Newton Singh,
Comments: 11 Figures and 3 Tables
Subjects: gr-qc
Created: 2022-07-02; Updated: ; Datestamp: 2022-07-06

In this work we take our cue from the observations of gravitational waves of the GW190814 event which suggests that source of the signals can be ascribed to a compact binary coalescence of a 22.2 to 24.3$ M_{\odot}$ BLACK HOLE and a compact object endowed with a mass of 2.50 to 2.67$M_{\odot}$. In the current exposition, we are concerned with modeling of the lower mass component of the coalescence pair. We utilise the $f(\mathcal{Q})$ gravity together with Minimum Geometric Deformation (MGD) technique to obtain compact stellar objects with masses aligned with the GW190814 event. Starting off with the Tolman IV ansatz for one of the metric functions, together with a MIT Bag model equation of state we are able to reduce the problem of fully describing the gravitational behaviour of the seed solution to a quadrature. Through the MGD technique, we introduce anisotropy by deforming the radial part of the gravitational potential. This enables us to obtain two new classes of solutions which depend on the metricity parameter, $\cal Q$ and the deformation constant, $\beta$. We show that these two parameters play a crucial role in determining the thermodynamical behaviour and stability of our models. In particular, we show that the interplay between the metricity parameter and the deformation constant leads to predicted mass of the progenitor articulating as the secondary component of GW190814.

[abstract 25 / 27] (score: 1)
arXiv:2207.02130 [pdf, ps, other]
Title: Physical Implications of Pure Lovelock Geometry on Stellar Structure
Authors: Ksh. Newton Singh, Megandhren Govender, Sudan Hansraj, Farook Rahaman,
Comments: 11 Pages, 16 Figures, 1 Table
Subjects: gr-qc astro-ph.HE
Created: 2022-07-02; Updated: ; Datestamp: 2022-07-06

We construct an exact anisotropic star model with a linear barotropic equation of state and with Finch-Skea potential within the framework of pure Lovelock gravity. A comparison with the corresponding Einstein model in a suitable limit is easily deduced. Evidently higher curvature effects induced by the Lovelock contributions generate lower densities, pressures, surface tensions and anisotropy factors when compared to its Einstein counterpart. The maximum moment of inertia is attained for the Einstein case and hence it may be inferred that Lovelock effects soften the equation of state. The model satisfies various stability tests.

[abstract 26 / 27] (score: 1)
arXiv:2207.02135 [pdf, ps, other]
Title: Impact of spatially correlated fluctuations in sunspots on metrics related to MAGNETic twist
Authors: C. Baumgartner, A. C. Birch, H. Schunker, R. H. Cameron, L. Gizon,
Comments: accepted in A&A
Subjects: astro-ph.SR
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

The twist of the MAGNETic field above a sunspot is an important quantity in solar physics. For example, MAGNETic twist plays a role in the initiation of flares and coronal mass ejections (CMEs). Various proxies for the twist above the photosphere have been found using models of uniformly twisted flux tubes, and are routinely computed from single photospheric vector MAGNETograms. One class of proxies is based on $\alpha_z$, the ratio of the vertical current to the vertical MAGNETic field. Another class of proxies is based on the so-called twist density, $q$, which depends on the ratio of the azimuthal field to the vertical field. However, the sensitivity of these proxies to temporal fluctuations of the MAGNETic field has not yet been well characterized. We aim to determine the sensitivity of twist proxies to temporal fluctuations in the MAGNETic field as estimated from time-series of SDO/HMI vector MAGNETic field maps. To this end, we introduce a model of a sunspot with a peak vertical field of 2370 Gauss at the photosphere and a uniform twist density $q= -0.024$ Mm$^{-1}$. We add realizations of the temporal fluctuations of the MAGNETic field that are consistent with SDO/HMI observations, including the spatial correlations. Using a Monte-Carlo approach, we determine the robustness of the different proxies to the temporal fluctuations. The temporal fluctuations of the three components of the MAGNETic field are correlated for spatial separations up to 1.4 Mm (more than expected from the point spread function alone). The Monte-Carlo approach enables us to demonstrate that several proxies for the twist of the MAGNETic field are not biased in each of the individual MAGNETograms. The associated random errors on the proxies have standard deviations in the range between $0.002$ and $0.006$ Mm$^{-1}$, which is smaller by approximately one order of magnitude than the mean value of $q$.

[abstract 27 / 27] (score: 1)
arXiv:2207.02142 [pdf, ps, other]
Title: Observation of S4716 -- a Star with a 4 yr Orbit around Sgr A*
Authors: Florian Peißker, Andreas Eckart, Michal Zajaček, Silke Britzen,
Comments: 33 pages, 23 figures, published at ApJ
Subjects: astro-ph.GA astro-ph.SR
Created: 2022-07-05; Updated: ; Datestamp: 2022-07-06

The ongoing monitoring of the Galactic center and Sgr A*, the central supermassive BLACK HOLE, produces surprising and unexpected findings. This goes hand in hand with the technical evolution of ground- and space-based telescopes and instruments, but also with the progression of image filter techniques such as the Lucy Richardson algorithm. As we continue to trace the members of the S cluster close to Sgr A* on their expected trajectory around the supermassive BLACK HOLE, we present the finding of a new stellar source, which we call S4716. The newly found star orbits SgrA* in about 4.0 yr and can be detected with NIRC2 (Keck), OSIRIS (Keck), SINFONI (VLT), NACO (VLT), and GRAVITY (VLTI). With a periapse distance of about 100 au, S4716 shows an equivalent distance toward Sgr A* as S4711. These fast-moving stars undergo a similar dynamical evolution, since S4711-S4716 share comparable orbital properties. We will furthermore draw a connection between the recent finding of a new faint star called S300 and the data presented here. Additionally, we observed a blend-star event with S4716 and another newly identified S star S148 in 2017.