Abstract
Abstract We demonstrate the use of the AKARI FIS All-Sky Survey maps in the study of extragalactic objects. A quick but reliable estimate of the Galactic foreground is essential for extragalactic research in general. We explored the galactic foreground and calculated hydrogen column densities using AKARI FIS and other recent all-sky survey data, and compared our results to former estimates. Our AKARI-FIS-based foreground values were then used toward gamma-ray burst (GRB) sources as input for X-ray afterglow spectrum fitting. From those fits the intrinsic column densities at the GRB sources were derived. The high-angular-resolution AKARI-FIS-based Galactic foreground hydrogen column densities are statistically very similar, but for most of the tested directions somewhat lower than previous estimates based on low-resolution data. This is due to the low filling factor of high-density enhancements in all galactic latitudes. Accordingly, our AKARI-FIS-based new intrinsic hydrogen column densities are usually higher or similar compared to the values calculated based, e.g., on the low-resolution Leiden/Argentine/Bonn survey data and listed in the Leicester database. The variation, however, is typically smaller than the error of the estimate from the fits of the X-ray afterglow spectra. There are a number of directions where the improvement of the foreground estimates resulted in an overestimate of magnitude or higher increment of the derived intrinsic hydrogen column densities. We concluded that most of the GRBs with formerly extremely low intrinsic hydrogen column densities are in fact normal, but we confirmed that GRB050233 is indeed a non-enveloped long GRB.
Highlights
It is always a challenge to accurately estimate the column density of the galactic foreground interstellar medium in the direction of extragalactic sources
We investigated the X-ray spectra of gamma-ray burst (GRB) observed by the X-Ray Telescope (XRT) of the Swift satellite
The AKARI-Far-Infrared Surveyor (FIS)-based foreground hydrogen column density estimates typically agree fairly well with the LABsurvey-based values in the Leicester archive, and are typically slightly smaller. This is mainly due to the fact that the filling factor of the low column densities is higher than the high columnm density ones
Summary
It is always a challenge to accurately estimate the column density of the galactic foreground interstellar medium in the direction of extragalactic sources. It is one of the important parameters when calculating the physical parameters of gamma-ray burst (GRB) host galaxies. The duration of the gamma-ray emission is measured as the time interval during which a given fraction of the total observed counts have been detected. Additional types are intermediate (Horvath 2009; Horvath & Toth 2016) and ultra-long (Boer et al 2015) GRBs. Longduration GRBs are associated with the explosions of massive stars (see, e.g., Stanek et al 2003), while short ones are associated with binary mergers
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