Coexistence of Superconductivity and Charge Density Wave in SrPt2As2

SrPt2As2 is a novel arsenide superconductor, which crystallizes in the CaBe2Ge2-type structure as a different polymorphic form of the ThCr2Si2-type structure. SrPt2As2 exhibits a charge-density-wave (CDW) ordering at about 470 K and enters into a superconducting state at Tc = 5.2 K. The coexistence of superconductivity and CDW refers to Peierls instability with a moderately strong electron-phonon interaction. Thus SrPt2As2 can be viewed as a nonmagnetic analog of iron-based superconductors, such as doped BaFe2As2, in which superconductivity emerges in close proximity to spin-density-wave ordering.Comment: 4 pages, 5 figure

Effects of an electronic topological transition for anisotropic low-dimensional superconductors

We study the superconducting properties of a two-dimensional superconductor in the proximity to an electronic topological transition (ETT). In contrast to the 3D case, we find that the superconducting gap at T=0, the critical temperature Tc, and the impurity scattering rate are characterized by a nonmonotonic behavior, with maxima occurring close to the ETT. We derive analytical expressions for the value of such maxima both in the s-wave and in the d-wave case. Such expressions are in good qualitative agreement with the phenomenological trend recently observed for Tc^max as a function of the hopping ratio t'/t across several cuprate compounds. We further analyze the effect of an ETT on the Ginzburg-Landau stiffness eta. Instead of vanishing at the ETT, as could be expected, thus giving rise to an increase of the fluctuation effects, in the case of momentum-independent electron-electron interaction, we find eta different from 0, as a result of an integration over the whole Fermi surface.Comment: to be published in Phys. Rev.

MASTER OT J004207.99+405501.1/M31LRN 2015 luminous red nova in M31: Discovery, light curve, hydrodynamics and evolution

We report the discovery and multicolour (VRIW) photometry of the rare explosive star MASTEROT J004207.99+405501.1 - a luminous red nova - in theAndromeda galaxy M31N2015-01a. We use our original light curve acquired with identical MASTER Global Robotic Net telescopes in one photometric system: VRI during the first 30 d and W (unfiltered) during 70 d. Also, we added published multicolour photometry data to estimate the mass and energy of the ejected shell and we discuss the likely formation scenarios of outbursts of this type. We propose an interpretation of the explosion that is consistent with an evolutionary scenario where the merging of stellar components or the disruption of the common envelope of a close binary can explain some luminous red novae. Radiative hydrodynamic simulations of a luminous red nova were carried out in extended parameter space to fit its light curves. We find that the multicolour passband light curves of the luminous red nova are consistent with an initial common envelope radius of 10 R⊙, a merger mass of 3M⊙ and an explosion energy of 3 × 1048 erg. As a result, the phenomenon of novae consists of two classes: classical nuclear novae and more rare events (red novae) connected with the loss of compact common envelopes. © 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society

Multiwavelength observations of GRB 140629A: A long burst with an achromatic jet break in the optical and X-ray afterglow

Aims. We investigate the long gamma-ray burst (GRB) 140629A through multiwavelength observations to derive the properties of the dominant jet and its host galaxy. Methods. The afterglow and host galaxy observations were taken in the optical (Swift/UVOT and various facilities worldwide), infrared (Spitzer), and X-rays (Swift/XRT) between 40 s and 3 yr after the burst trigger. Results. Polarisation observations by the MASTER telescope indicate that this burst is weakly polarised. The optical spectrum contains absorption features, from which we confirm the redshift of the GRB as originating at z = 2.276 ± 0.001. We performed spectral fitting of the X-rays to optical afterglow data and find there is no strong spectral evolution. We determine the hydrogen column density NH to be 7.2 × 1021 cm−2 along the line of sight. The afterglow in this burst can be explained by a blast wave jet with a long-lasting central engine expanding into a uniform medium in the slow cooling regime. At the end of energy injection, a normal decay phase is observed in both the optical and X-ray bands. An achromatic jet break is also found in the afterglow light curves ∼0.4 d after trigger. We fit the multiwavelength data simultaneously with a model based on a numerical simulation and find that the observations can be explained by a narrow uniform jet in a dense environment with an opening angle of 6.7◦ viewed 3.8◦ off-axis, which released a total energy of 1.4 × 1054 erg. Using the redshift and opening angle, we find GRB 140629A follows both the Ghirlanda and Amati relations. From the peak time of the light curve, identified as the onset of the forward shock (181s after trigger), the initial Lorentz factor (Γ0) is constrained in the range 82-118. Fitting the host galaxy photometry, we find the host to be a low mass, star-forming galaxy with a star formation rate of log (SFR) = 1.1+−00.94 M yr−1. We obtain a value of the neutral hydrogen density by fitting the optical spectrum, log NHI = 21.0 ± 0.3, classifying this host as a damped Lyman-alpha. High ionisation lines (N v, Si iv) are also detected in the spectrum. © ESO 2019.China Scholarship Council, CSCNational Science Foundation, NSFNational Basic Research Program of China (973 Program): DST/IMRCD/BRICS/Pilotcall/ProFCheap/2017, 2018YFA0404204, NSFC-1183300317-52-80133Agenzia Spaziale Italiana, ASI: 2015-046-R.0Ministry of Education and Science of the Russian Federation, Minobrnauka: 2019-05-595-0001-2496, 2019-05-592-0001-729317-52-80139 BRICS-aAgenzia Spaziale Italiana, ASI201406660015Leverhulme TrustEuropean Regional Development Fund, FEDER: AYA-2015-71718-RNational Research Foundation, NRF: 2018R1A2A1A05022685Horizon 2020 Framework Programme, H2020: 654215★ Research supported by the China Scholarship Council. † Deceased.7 IRAF is distributed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc. under cooperative agreement with the National Science Foundation. http://ast.noao.edu/data/softwareAcknowledgements. Acknowledge the support by the program of China Scholarships Council (CSC) under the Grant no. 201406660015. We also acknowledge support from the Spanish MINEICO ministry and European FEDER funds AYA-2015-71718-R. SRO gratefully acknowledges the support of the Leverhulme Trust Early Career Fellowship. RS-R acknowledges support from ASI (Italian Space Agency) through the Contract no. 2015-046-R.0 and from European Union Horizon 2020 Programme under the AHEAD project (grant agreement no. 654215). MASTER equipment is supported by Lomonosov MSU Development Program and by Moscow Union OPTIKA. VL,EG, NT, VK are supported by BRICS RFBR grant 17-52-80133. MASTER-Tunka equipment is supported of Russian Federation Ministry of Science and High Education (grants 2019-05-592-0001-7293 and 2019-05-595-0001-2496). B.-B.Z. acknowledges support from the National Key Research and Development Program of China (2018YFA0404204), and NSFC-11833003. S.B.P. acknowledges BRICS grant DST/IMRCD/BRICS/Pilotcall/ProFCheap/2017(G) for this work. I.D. acknowledges L. Piro his invitation and financial support to visit and work at IAPS (Rome). We also acknowledge the use of the public data from the Swift data archive. We thank the excellent support form the GTC staff which is located at Observatorio del Roque de los Muchachos at Canary Islands (Spain). Thanks to the data support by NASA with Spitzer Space Telescope. SP and RB acknowledge support from RBRF grant 17-52-80139 BRICS-a. IHP acknowledges support from NRF 2018R1A2A1A05022685. Finally, we want to thank the anonymous referee for his/her comments, which have substantially improved the manuscript

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

Multi-messenger Observations of a Binary Neutron Star Merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ∼ 1.7 {{s}} with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of {40}-8+8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 {M}ȯ . An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ∼ 40 {{Mpc}}) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ∼ 9 and ∼ 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.</p