scholarly journals Empirical estimates of the Galactic halo contribution to the dispersion measures of extragalactic fast radio bursts using X-ray absorption

2020 ◽  
Vol 500 (1) ◽  
pp. 655-662
Author(s):  
Sanskriti Das ◽  
Smita Mathur ◽  
Anjali Gupta ◽  
Fabrizio Nicastro ◽  
Yair Krongold
Keyword(s):  
Galactic Halo ◽  
Dispersion Measure ◽  
Radio Bursts ◽  
X Ray ◽  
Empirical Estimates ◽  
The Galaxy ◽  
Dispersion Measures ◽  
Baryonic Mass ◽  
X Ray Absorption ◽  
Galactic Longitude

ABSTRACT We provide an empirical list of the Galactic dispersion measure (DMGal) contribution to the extragalactic fast radio bursts (FRBs) along 72 sightlines. It is independent of any model of the Galaxy, i.e. we do not assume the density of the disc or the halo, spatial extent of the halo, baryonic mass content, or any such external constraints to measure DMGal. We use 21-cm, UV, EUV, and X-ray data to account for different phases, and find that DMGal is dominated by the hot phase probed by X-ray absorption. We improve upon the measurements of N($\rm{O}\,{\small VII}$) and f$_{\rm O\,{\small VII}}$ compared to previous studies, thus providing a better estimate of the hot phase contribution. The median DMGal = 64$^{+20}_{-23}$ cm−3 pc, with a 68 per cent (90 per cent) confidence interval of 33–172 (23–660) cm−3 pc. The DMGal does not appear to follow any trend with the Galactic longitude or latitude, and there is a large scatter around the values predicted by simple disc + spherical halo models. Our measurements provide more complete and accurate estimates of DMGal independent from the previous studies. We provide a table and a code to retrieve DMGal for any FRB localized in the sky.

scholarly journals Exploring the dispersion measure of the Milky Way halo

2020 ◽  
Vol 496 (1) ◽  
pp. L106-L110 ◽  
Author(s):  
Laura C Keating ◽  
Ue-Li Pen
Keyword(s):  
Milky Way ◽  
External Pressure ◽  
Dispersion Measure ◽  
Radio Bursts ◽  
X Ray ◽  
Additional Information ◽  
Order Of Magnitude ◽  
Dispersion Measures ◽  
Extreme Model ◽  
Milky Way Halo

Abstract Fast radio bursts offer the opportunity to place new constraints on the mass and density profile of hot and ionized gas in galactic haloes. We test here the X-ray emission and dispersion measure predicted by different gas profiles for the halo of the Milky Way. We examine a range of models, including entropy stability conditions and external pressure continuity. We find that incorporating constraints from X-ray observations leads to favouring dispersion measures on the lower end of the range given by these models. We show that the dispersion measure of the Milky Way halo could be less than 10 cm−3 pc in the most extreme model we consider, which is based on constraints from O vii absorption lines. However, the models allowed by the soft X-ray constraints span more than an order of magnitude in dispersion measures. Additional information on the distribution of gas in the Milky Way halo could be obtained from the signature of a dipole in the dispersion measure of fast radio bursts across the sky, but this will be a small effect for most cases.

scholarly journals Finding and characterising WHIM structures using the luminosity density method

2014 ◽  
Vol 11 (S308) ◽  
pp. 368-371
Author(s):  
Jukka Nevalainen ◽  
L. J. Liivamägi ◽  
E. Tempel ◽  
E. Branchini ◽  
M. Roncarelli ◽  
...  
Keyword(s):  
Large Scale ◽  
Real Data ◽  
Sloan Digital Sky Survey ◽  
Physical Parameters ◽  
X Ray ◽  
Galaxy Surveys ◽  
Sky Survey ◽  
The Galaxy ◽  
Hydrodynamical Simulations ◽  
X Ray Absorption

AbstractWe have developed a new method to approach the missing baryons problem. We assume that the missing baryons reside in a form of Warm Hot Intergalactic Medium, i.e. the WHIM. Our method consists of (a) detecting the coherent large scale structure in the spatial distribution of galaxies that traces the Cosmic Web and that in hydrodynamical simulations is associated to the WHIM, (b) mapping its luminosity into a galaxy luminosity density field, (c) using numerical simulations to relate the luminosity density to the density of the WHIM, (d) applying this relation to real data to trace the WHIM using the observed galaxy luminosities in the Sloan Digital Sky Survey and 2dF redshift surveys. In our application we find evidence for the WHIM along the line of sight to the Sculptor Wall, at redshifts consistent with the recently reported X-ray absorption line detections. Our indirect WHIM detection technique complements the standard method based on the detection of characteristic X-ray absorption lines, showing that the galaxy luminosity density is a reliable signpost for the WHIM. For this reason, our method could be applied to current galaxy surveys to optimise the observational strategies for detecting and studying the WHIM and its properties. Our estimates of the WHIM hydrogen column density NH in Sculptor agree with those obtained via the X-ray analysis. Due to the additional NH estimate, our method has potential for improving the constrains of the physical parameters of the WHIM as derived with X-ray absorption, and thus for improving the understanding of the missing baryons problem.

scholarly journals Limits on Hot Galactic Halo Gas from X-Ray Absorption Lines

2007 ◽  
Vol 672 (1) ◽  
pp. L21-L24 ◽  
Author(s):  
Y. Yao ◽  
M. A. Nowak ◽  
Q. D. Wang ◽  
N. S. Schulz ◽  
C. R. Canizares
Keyword(s):  
Galactic Halo ◽  
Absorption Lines ◽  
X Ray ◽  
Halo Gas ◽  
X Ray Absorption

Spectroscopic Observations of Baryons in the Local Universe

2005 ◽  
Vol 216 ◽  
pp. 274-289
Author(s):  
Kenneth R. Sembach
Keyword(s):  
Large Scale ◽  
Intergalactic Gas ◽  
Local Universe ◽  
X Ray ◽  
Spectroscopic Observations ◽  
Spectral Diagnostics ◽  
The Galaxy ◽  
X Ray Absorption ◽  
The Universe ◽  
Velocity Cloud

There is increasing observational evidence that hot, highly-ionized interstellar and intergalactic gas plays a significant role in the evolution of galaxies in the local universe. Recent observations from several ultraviolet and X-ray observatories have been used to study the highly ionized high velocity cloud system in the vicinity of the Galaxy, the hot gaseous corona of the Galaxy, and highly ionized absorption-line systems at low redshift. The primary spectral diagnostics of this warm-hot interstellar/intergalactic medium are ultraviolet and X-ray absorption lines of O vi and O vii. The observational data fit well into the framework of current theories for the evolution of large-scale structure in the universe, which predict that a significant fraction of the baryonic material at low redshift is contained in highly ionized intergalactic gas. In this paper, I summarize some of the recent highlights of spectroscopic observations of the hot baryons in the local universe.

scholarly journals The Hot Galactic Corona and the Soft X-ray Background

1997 ◽  
Vol 166 ◽  
pp. 503-512
Author(s):  
Q. Daniel Wang
Keyword(s):  
Galactic Disk ◽  
Relative Dispersion ◽  
Polytropic Index ◽  
The Sun ◽  
X Ray ◽  
Large Intensity ◽  
The Galaxy ◽  
Electron Density And Temperature ◽  
X Ray Background ◽  
X Ray Absorption

AbstractI characterize the global distribution of the ¾ keV band background with a simple model of the hot Galactic corona, plus an isotropic extragalactic background. The corona is assumed to be approximately polytropic (index = 5/3) and hydrostatic in the gravitational potential of the Galaxy. The model accounts for X-ray absorption, and is constrained iteratively with the ROSAT all-sky X-ray survey data. Regions where the data deviate significantly from the model represent predominantly the Galactic disk and individual nearby hot superbubbles. The global distribution of the background, outside these regions, is well characterized by the model; the 1σ relative dispersion of the data from the model is ~ 15%. The electron density and temperature of the corona near the Sun are ~ 1.1 × 10−3 cm−3 and ~ 1.7 × 106 K. The same model also explains well the 1.5 keV band background. The model prediction in the ¼ keV band, though largely uncertain, qualitatively shows large intensity and spectral variations of the corona contribution across the sky.

scholarly journals The XXL Survey

2020 ◽  
Vol 638 ◽  
pp. A45
Author(s):  
V. A. Masoura ◽  
I. Georgantopoulos ◽  
G. Mountrichas ◽  
C. Vignali ◽  
E. Koulouridis ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Selection Criteria ◽  
Galactic Nuclei ◽  
Host Galaxy ◽  
Spectral Energy ◽  
Energy Distributions ◽  
X Ray ◽  
Spectral Fitting ◽  
The Galaxy ◽  
X Ray Absorption

The combination of optical and mid-infrared (MIR) photometry has been extensively used to select red active galactic nuclei (AGNs). Our aim is to explore the obscuration properties of these red AGNs with both X-ray spectroscopy and spectral energy distributions (SEDs). In this study, we re-visit the relation between optical/MIR extinction and X-ray absorption. We use IR selection criteria, specifically the W1 and W2 WISE bands, to identify 4798 AGNs in the XMM-XXL area (∼25 deg2). Application of optical/MIR colours (r−W2 >  6) reveals 561 red AGNs (14%). Of these, 47 have available X-ray spectra with at least 50 net (background-subtracted) counts per detector. For these sources, we construct SEDs from the optical to the MIR using the CIGALE code. The SED fitting shows that 44 of these latter 47 sources present clear signs of obscuration based on the AGN emission and the estimated inclination angle. Fitting the SED also reveals ten systems (∼20%) which are dominated by the galaxy. In these cases, the red colours are attributed to the host galaxy rather than AGN absorption. Excluding these ten systems from our sample and applying X-ray spectral fitting analysis shows that up to 76% (28/37) of the IR red AGNs present signs of X-ray absorption. Thus, there are nine sources (∼20% of the sample) that although optically red, are not substantially X-ray absorbed. Approximately 50% of these sources present broad emission lines in their optical spectra. We suggest that the reason for this apparent discrepancy is that the r−W2 criterion is sensitive to smaller amounts of obscuration relative to the X-ray spectroscopy. In conclusion, it appears that the majority of red AGNs present considerable obscuration levels as shown by their SEDs. Their X-ray absorption is moderate with a mean of NH ∼ 1022 cm−2.

scholarly journals Probing the Universe with Fast Radio Bursts

Universe ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 85
Author(s):  
Shivani Bhandari ◽  
Chris Flynn
Keyword(s):  
Energy Parameter ◽  
Hubble Constant ◽  
Host Galaxy ◽  
Dispersion Measure ◽  
Radio Bursts ◽  
Host Galaxies ◽  
Large Samples ◽  
First Results ◽  
Dispersion Measures ◽  
The Universe

Fast Radio Bursts (FRBs) represent a novel tool for probing the properties of the universe at cosmological distances. The dispersion measures of FRBs, combined with the redshifts of their host galaxies, has very recently yielded a direct measurement of the baryon content of the universe, and has the potential to directly constrain the location of the “missing baryons”. The first results are consistent with the expectations of ΛCDM for the cosmic density of baryons, and have provided the first constraints on the properties of the very diffuse intergalactic medium (IGM) and circumgalactic medium (CGM) around galaxies. FRBs are the only known extragalactic sources that are compact enough to exhibit diffractive scintillation in addition to showing exponential tails which are typical of scattering in turbulent media. This will allow us to probe the turbulent properties of the circumburst medium, the host galaxy ISM/halo, and intervening halos along the path, as well as the IGM. Measurement of the Hubble constant and the dark energy parameter w can be made with FRBs, but require very large samples of localised FRBs (>103) to be effective on their own—they are best combined with other independent surveys to improve the constraints. Ionisation events, such as for He ii, leave a signature in the dispersion measure—redshift relation, and if FRBs exist prior to these times, they can be used to probe the reionisation era, although more than 103 localised FRBs are required.

scholarly journals X-ray observations of PSR J0218+4232 and of PSR B1937+21

1996 ◽  
Vol 160 ◽  
pp. 353-354
Author(s):  
Frank Verbunt ◽  
Helen M. Johnston ◽  
A.G. de Bruyn ◽  
Michiel van der Klis
Keyword(s):  
Magnetic Field ◽  
Minimum Distance ◽  
Electron Distribution ◽  
Rotation Axis ◽  
Dispersion Measure ◽  
Radio Luminosity ◽  
Pulse Period ◽  
X Ray ◽  
The Galaxy ◽  
Low Mass

Navarro et al. (1995) have discovered a 2.3 ms radio pulsar in a 2.0 day orbit around a low-mass companion. An interesting feature of this pulsar, PSR J0218+4232, is that radio emission is discovered throughout the pulse period; this is taken by Navarro et al. as an indication that the pulsar magnetic field is almost aligned with the rotation axis, and may also be related to the rather high radio luminosity of this pulsar,L400MHZ> 2700 mJy kpc2. The dispersion measureDM= 61.25pc cm−3indicates a minimum distance of 5.7 kpc, according to the model for the free electron distribution in the Galaxy by Taylor and Cordes (1993).

scholarly journals The SUrvey for Pulsars and Extragalactic Radio Bursts – IV. Discovery and polarimetry of a 12.1-s radio pulsar

2020 ◽  
Vol 493 (1) ◽  
pp. 1165-1177 ◽  
Author(s):  
V Morello ◽  
E F Keane ◽  
T Enoto ◽  
S Guillot ◽  
W C G Ho ◽  
...  
Keyword(s):  
Position Angle ◽  
Radio Pulsar ◽  
Vector Model ◽  
Dispersion Measure ◽  
Radio Bursts ◽  
Free Electron Density ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Spin Period ◽  
P Parameter

ABSTRACT We report the discovery of PSR J2251−3711, a radio pulsar with a spin period of 12.1 s, the second longest currently known. Its timing parameters imply a characteristic age of 15 Myr, a surface magnetic field of 1.3 × 1013 G, and a spin-down luminosity of 2.9 × 1029 erg s−1. Its dispersion measure of 12.12(1) pc cm−3 leads to distance estimates of 0.5 and 1.3 kpc according to the NE2001 and YMW16 Galactic free electron density models, respectively. Some of its single pulses show an uninterrupted 180-deg sweep of the phase-resolved polarization position angle, with an S-shape reminiscent of the rotating vector model prediction. However, the fact that this sweep occurs at different phases from one pulse to another is remarkable and without straightforward explanation. Although PSR J2251−3711 lies in the region of the $P-\dot{P}$ parameter space occupied by the X-ray isolated neutron stars (XINS), there is no evidence for an X-ray counterpart in our Swift XRT observation; this places a 99 per cent-confidence upper bound on its unabsorbed bolometric thermal luminosity of $1.1 \times 10^{31}~(d / 1~\mathrm{kpc})^2~\mathrm{erg\, s}^{-1}$ for an assumed temperature of 85 eV, where d is the distance to the pulsar. Further observations are needed to determine whether it is a rotation-powered pulsar with a true age of at least several Myr, or a much younger object such as an XINS or a recently cooled magnetar. Extreme specimens like PSR J2251−3711 help bridge populations in the so-called neutron star zoo in an attempt to understand their origins and evolution.

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