X-ray spectropolarimetry of the bright atoll Serpens X-1
Journal
Date Issued
2024
Author(s)
•
Gnarini, A.
•
BIANCHI, Simone
•
Bobrikova, A.
•
•
•
•
•
Kaaret, P.
•
Matt, G.
•
Ng, M.
•
Poutanen, J.
•
Ravi, S.
•
Tarana, A.
Abstract
We present simultaneous X-ray polarimetric and spectral observations of the bright atoll source Ser X-1 carried out with the Imaging X-ray Polarimetry Explorer (IXPE), NICER, and NuSTAR. We obtain an upper limit of 2% (99% confidence level) on the polarization degree in the 2–8 keV energy band. We detect four type-I X-ray bursts, two of which during the IXPE observation. This is the first time that has IXPE observed type-I X-ray bursts, and it allows us to place an upper limit on their polarization degree; however, due to the limited total number of counts in each burst, we obtain a relatively high upper limit (80%). We confirm the presence of reflection features in the X-ray spectrum, notably a broad iron line. Fitting the data with a relativistic reflection model, we derive a disk inclination of 25°. The spectral and polarization properties are comparable with other atolls observed by IXPE, suggesting a similar accretion geometry, and the relatively low polarization is consistent with the low inclination.
Volume
690
Start page
A200
Issn Identifier
0004-6361
Ads BibCode
2024A&A...690A.200U
Rights
open.access
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