Probing the physical properties of the intergalactic medium using blazars. (arXiv:2109.06632v1 [astro-ph.HE])

<a href="http://arxiv.org/find/astro-ph/1/au:+Dalton_T/0/1/0/all/0/1">Tony Dalton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Morris_S/0/1/0/all/0/1">Simon L. Morris</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fumagalli_M/0/1/0/all/0/1">Michele Fumagalli</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gatuzz_E/0/1/0/all/0/1">Efrain Gatuzz</a>

We use Swift blazar spectra to estimate the key intergalactic medium (IGM)

properties of hydrogen column density(Nhxigm), metallicity and temperature over

a redshift range of 0.03 leq z leq 4.7, using a collisional ionisation

equilibrium(CIE) model for the ionised plasma. We adopted a conservative

approach to the blazar continuum model given its intrinsic variability and use

a range of power law models. We subjected our results to a number of tests and

found that the Nhxigm parameter was robust with respect to individual exposure

data and co-added spectra for each source, and between Swift and XMM-Newton

source data. We also found no relation between Nhxigm and variations in source

flux or intrinsic power laws. Though some objects may have a bulk

Comptonisation component which could mimic absorption, it did not alter our

overall results. The Nhxigm from the combined blazar sample scales

as(1+z)^1.8+-0.2. The mean hydrogen density at z = 0 is n0 = (3.2+-0.5) x

10^-7 cm^-3. The mean IGM temperature over the full redshift range is log(TK)

= 6.1+-0.1 and the mean metallicity is [XH] = -1.62+-0.04 (Z sim0.02) When

combining with the results with a gamma-ray burst (GRB) sample, we find the

results are consistent over an extended redshift range of 0.03 leq z leq 6.3.

Using our model for blazars and GRBs, we conclude that the IGM contributes

substantially to the total absorption seen in both blazar and GRB spectra.

We use Swift blazar spectra to estimate the key intergalactic medium (IGM)

properties of hydrogen column density(Nhxigm), metallicity and temperature over

a redshift range of 0.03 leq z leq 4.7, using a collisional ionisation

equilibrium(CIE) model for the ionised plasma. We adopted a conservative

approach to the blazar continuum model given its intrinsic variability and use

a range of power law models. We subjected our results to a number of tests and

found that the Nhxigm parameter was robust with respect to individual exposure

data and co-added spectra for each source, and between Swift and XMM-Newton

source data. We also found no relation between Nhxigm and variations in source

flux or intrinsic power laws. Though some objects may have a bulk

Comptonisation component which could mimic absorption, it did not alter our

overall results. The Nhxigm from the combined blazar sample scales

as(1+z)^1.8+-0.2. The mean hydrogen density at z = 0 is n0 = (3.2+-0.5) x

10^-7 cm^-3. The mean IGM temperature over the full redshift range is log(TK)

= 6.1+-0.1 and the mean metallicity is [XH] = -1.62+-0.04 (Z sim0.02) When

combining with the results with a gamma-ray burst (GRB) sample, we find the

results are consistent over an extended redshift range of 0.03 leq z leq 6.3.

Using our model for blazars and GRBs, we conclude that the IGM contributes

substantially to the total absorption seen in both blazar and GRB spectra.

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