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Title: Dust Radiative Transfer Modeling of the Infrared Ring around the Magnetar SGR 1900+14

Abstract

A peculiar infrared ring-like structure was discovered by Spitzer around the strongly magnetized neutron star SGR 1900+14. This infrared (IR) structure was suggested to be due to a dust-free cavity, produced by the Soft Gamma-ray Repeaters (SGRs) Giant Flare occurring in 1998, and kept illuminated by surrounding stars. Using a 3D dust radiative transfer code, we aimed to reproduce the emission morphology and the integrated emission flux of this structure assuming different spatial distributions and densities for the dust, and different positions for the illuminating stars. We found that a dust-free ellipsoidal cavity can reproduce the shape, flux, and spectrum of the ring-like IR emission, provided that the illuminating stars are inside the cavity and that the interstellar medium has high gas density ( n {sub H} ∼ 1000 cm{sup −3}). We further constrain the emitting region to have a sharp inner boundary and to be significantly extended in the radial direction, possibly even just a cavity in a smooth molecular cloud. We discuss possible scenarios for the formation of the dustless cavity and the particular geometry that allows it to be IR-bright.

Authors:
 [1]; ; ;  [2];  [3];  [4]
  1. Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE (United Kingdom)
  2. Institute of Space Sciences (IEEC–CSIC), Campus UAB, Carrer de Can Magrans S/N, E-08193 Barcelona (Spain)
  3. Department of Physics, Oregon State University, 301 Weniger Hall, Corvallis, OR 97331 (United States)
  4. Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 (United States)
Publication Date:
OSTI Identifier:
22661343
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 837; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; DENSITY; DUSTS; EMISSION; GAMMA RADIATION; NEUTRON STARS; RADIANT HEAT TRANSFER; RINGS; SIMULATION; SPATIAL DISTRIBUTION; SPECTRA; X RADIATION

Citation Formats

Natale, G., Rea, N., Torres, D. F., Girart, J. M., Lazzati, D., and Perna, R., E-mail: gnatale@uclan.ac.uk. Dust Radiative Transfer Modeling of the Infrared Ring around the Magnetar SGR 1900+14. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA5C82.
Natale, G., Rea, N., Torres, D. F., Girart, J. M., Lazzati, D., & Perna, R., E-mail: gnatale@uclan.ac.uk. Dust Radiative Transfer Modeling of the Infrared Ring around the Magnetar SGR 1900+14. United States. doi:10.3847/1538-4357/AA5C82.
Natale, G., Rea, N., Torres, D. F., Girart, J. M., Lazzati, D., and Perna, R., E-mail: gnatale@uclan.ac.uk. Wed . "Dust Radiative Transfer Modeling of the Infrared Ring around the Magnetar SGR 1900+14". United States. doi:10.3847/1538-4357/AA5C82.
@article{osti_22661343,
title = {Dust Radiative Transfer Modeling of the Infrared Ring around the Magnetar SGR 1900+14},
author = {Natale, G. and Rea, N. and Torres, D. F. and Girart, J. M. and Lazzati, D. and Perna, R., E-mail: gnatale@uclan.ac.uk},
abstractNote = {A peculiar infrared ring-like structure was discovered by Spitzer around the strongly magnetized neutron star SGR 1900+14. This infrared (IR) structure was suggested to be due to a dust-free cavity, produced by the Soft Gamma-ray Repeaters (SGRs) Giant Flare occurring in 1998, and kept illuminated by surrounding stars. Using a 3D dust radiative transfer code, we aimed to reproduce the emission morphology and the integrated emission flux of this structure assuming different spatial distributions and densities for the dust, and different positions for the illuminating stars. We found that a dust-free ellipsoidal cavity can reproduce the shape, flux, and spectrum of the ring-like IR emission, provided that the illuminating stars are inside the cavity and that the interstellar medium has high gas density ( n {sub H} ∼ 1000 cm{sup −3}). We further constrain the emitting region to have a sharp inner boundary and to be significantly extended in the radial direction, possibly even just a cavity in a smooth molecular cloud. We discuss possible scenarios for the formation of the dustless cavity and the particular geometry that allows it to be IR-bright.},
doi = {10.3847/1538-4357/AA5C82},
journal = {Astrophysical Journal},
number = 1,
volume = 837,
place = {United States},
year = {Wed Mar 01 00:00:00 EST 2017},
month = {Wed Mar 01 00:00:00 EST 2017}
}
  • We present results from high-resolution infrared observations of magnetars SGR 1806-20 and SGR 1900+14 over 5 years using laser-supported adaptive optics at the 10 m Keck Observatory. Our measurements of the proper motions of these magnetars provide robust links between magnetars and their progenitors and provide age estimates for magnetars. At the measured distances of their putative associations, we measure the linear transverse velocity of SGR 1806-20 to be 350 {+-} 100 km s{sup -1} and of SGR 1900+14 to be 130 {+-} 30 km s{sup -1}. The transverse velocity vectors for both magnetars point away from the clusters ofmore » massive stars, solidifying their proposed associations. Assuming that the magnetars were born in the clusters, we can estimate the braking index to be {approx}1.8 for SGR 1806-20 and {approx}1.2 for SGR 1900+14. This is significantly lower than the canonical value of n = 3 predicted by the magnetic dipole spin-down suggesting an alternative source of dissipation such as twisted magnetospheres or particle winds.« less
  • Quasi-periodic oscillations (QPOs) observed in the giant flares of magnetars are of particular interest due to their potential to open up a window into the neutron star interior via neutron star asteroseismology. However, only three giant flares have been observed. We therefore make use of the much larger data set of shorter, less energetic recurrent bursts. Here, we report on a search for QPOs in a large data set of bursts from the two most burst-active magnetars, SGR 1806-20 and SGR 1900+14, observed with Rossi X-ray Timing Explorer. We find a single detection in an averaged periodogram comprising 30 burstsmore » from SGR 1806–20, with a frequency of 57 Hz and a width of 5 Hz, remarkably similar to a giant flare QPO observed from SGR 1900+14. This QPO fits naturally within the framework of global magneto-elastic torsional oscillations employed to explain giant flare QPOs. Additionally, we uncover a limit on the applicability of Fourier analysis for light curves with low background count rates and strong variability on short timescales. In this regime, standard Fourier methodology and more sophisticated Fourier analyses fail in equal parts by yielding an unacceptably large number of false-positive detections. This problem is not straightforward to solve in the Fourier domain. Instead, we show how simulations of light curves can offer a viable solution for QPO searches in these light curves.« less
  • We present the results of a LIGO search for short-duration gravitational waves (GWs) associated with the 2006 March 29 SGR 1900+14 storm. A new search method is used, 'stacking' the GW data around the times of individual soft-gamma bursts in the storm to enhance sensitivity for models in which multiple bursts are accompanied by GW emission. We assume that variation in the time difference between burst electromagnetic emission and potential burst GW emission is small relative to the GW signal duration, and we time-align GW excess power time-frequency tilings containing individual burst triggers to their corresponding electromagnetic emissions. We usemore » two GW emission models in our search: a fluence-weighted model and a flat (unweighted) model for the most electromagnetically energetic bursts. We find no evidence of GWs associated with either model. Model-dependent GW strain, isotropic GW emission energy E{sub GW}, and {gamma} {identical_to} E{sub GW}/E {sub EM} upper limits are estimated using a variety of assumed waveforms. The stacking method allows us to set the most stringent model-dependent limits on transient GW strain published to date. We find E {sub GW} upper limit estimates (at a nominal distance of 10 kpc) of between 2 x 10{sup 45} erg and 6 x 10{sup 50} erg depending on the waveform type. These limits are an order of magnitude lower than upper limits published previously for this storm and overlap with the range of electromagnetic energies emitted in soft gamma repeater (SGR) giant flares.« less
  • Using radiative transfer methods described in the previous papers of this series, dust-emission models of the bright planetary nebula NGC 7027 have been calculated. An analysis of the infrared continuum of NGC 7027 based upon these calculations shows the following: If the spatial dust distribution coincides with the ionized gas distribution as given by Scott in 1973 (within approx.3.2'' from the center), the infrared continuum may be produced by an unknown substance whose infrared emissivity declines with increasing wavelength to about 50 $mu$ and then rises. If there exists a cool outer dust shell beyond 5''-6'' from the central source,more » the observed infrared continuum may be produced by iron grains of radius 1 $mu$ or by a mixture of smaller iron and graphite grains. (AIP)« less