Refereed journal article or data article (A1)

Observations of 4U 1626-67 with the Imaging X-Ray Polarimetry Explorer

List of AuthorsMarshall H.L., Ng M., Rogantini D., Heyl J., Tsygankov S.S., Poutanen J., Costa E., Zane S., Malacaria C., Agudo I., Antonelli L.A., Bachetti M., Baldini L., Baumgartner W.H., Bellazzini R., Bianchi S., Bongiorno S.D., Bonino R., Brez A., Bucciantini N., Capitanio F., Castellano S., Cavazzuti E., Ciprini S., De Rosa A., Monte E.D., Gesu L.D., Lalla N.D., Marco A.D., Donnarumma I., Doroshenko V., Dovčiak M., Ehlert S.R., Enoto T., Evangelista Y., Fabiani S., Ferrazzoli R., Garcia J.A., Gunji S., Hayashida K., Iwakiri W., Jorstad S.G., Karas V., Kitaguchi T., Kolodziejczak J.J., Krawczynski H., Monaca F.L., Latronico L., Liodakis I., Maldera S., Manfreda A., Marin F., Marinucci A., Marscher A.P., Matt G., Mitsuishi I., Mizuno T., Muleri F., Ng C.Y., O’Dell S.L., Omodei N., Oppedisano C., Papitto A., Pavlov G.G., Peirson A.L., Perri M., Pesce-Rollins M., Petrucci P.O., Pilia M., Possenti A., Puccetti S., Ramsey B.D., Rankin J., Ratheesh A., Romani R.W., Sgrò C., Slane P., Soffitta P., Spandre G., Tamagawa T., Tavecchio F., Taverna R., Tawara Y., Tennant A.F., Thomas N.E., Tombesi F., Trois A., Turolla R., Vink J., Weisskopf M.C., Wu K., Xie F., Chakrabarty D., Schulz N.S.

PublisherIOP Publishing

Publication year2022

JournalAstrophysical Journal

Journal name in sourceAstrophysical Journal

Volume number940

Issue number1




Self-archived copy’s web address


We present measurements of the polarization of X-rays in the 2–8 keV band from the pulsar in the ultracompact low-mass X-ray binary 4U 1626–67 using data from the Imaging X-Ray Polarimetry Explorer (IXPE). The 7.66 s pulsations were clearly detected throughout the IXPE observations as well as in the NICER soft X-ray observations, which we used as the basis for our timing analysis and to constrain the spectral shape over the 0.4–10 keV energy band. Chandra HETGS high-resolution X-ray spectra were also obtained near the times of the IXPE observations for firm spectral modeling. We found an upper limit on the pulse-averaged linear polarization of <4% (at 95% confidence). Similarly, there was no significant detection of polarized flux in pulse phase intervals when subdividing the bandpass by energy. However, spectropolarimetric modeling over the full bandpass in pulse phase intervals provided a marginal detection of polarization of the power-law spectral component at the 4.8% ± 2.3% level (90% confidence). We discuss the implications concerning the accretion geometry onto the pulsar, favoring two-component models of the pulsed emission.

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Last updated on 2023-20-01 at 13:08