NuSTAR observation of GRO J1744−28 at low mass accretion rate

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dc.contributor.authorKönig, O.
dc.contributor.authorFürst, F.
dc.contributor.authorKretschmar, P.
dc.contributor.authorBallhausen, R.
dc.contributor.authorSokolova-Lapa, E.
dc.contributor.authorDauser, T.
dc.contributor.authorSánchez-Fernández, C.
dc.contributor.authorHemphill, P. B.
dc.contributor.authorWolff, M. T.
dc.contributor.authorPottschmidt, Katja
dc.contributor.authorWilms, J.
dc.date.accessioned2020-11-03T19:06:55Z
dc.date.available2020-11-03T19:06:55Z
dc.date.issued2020-11-13
dc.description.abstractWe present the spectral analysis of the LMXB GRO J1744-28 using ∼29 ks of NuSTAR data taken in 2017 February at a low luminosity of 3.2×10³⁶ erg/s (3-50 keV). The continuum spectrum is modeled with an absorbed power-law with exponential cut-off, and an additional iron line component. We find no obvious indications for a CRSF and therefore perform a detailed cyclotron line search using statistical methods on the pulse phase-averaged as well as phase-resolved spectra. The previously detected Type II X-ray bursts are absent. Clear pulsations at a period of 2.141124(9) Hz are detected. The pulse profile shows an indication of a secondary peak, which was not seen at higher flux. The 4σ upper limit for the strength of a CRSF in the 3-20 keV band is 0.07 keV, lower than the strength of the line found at higher luminosity. The detection of pulsations shows that the source did not enter the "propeller" regime, even though the source flux of 4.15×10⁻¹⁰ erg/cm2/s was almost one order of magnitude below the threshold for the propeller regime claimed in previous studies on this source. The transition into the propeller regime in GRO J1744-28 must therefore be below a luminosity of 3.2×10³⁶ erg/s, which implies a surface magnetic field ≲2.9×10¹¹ G and mass accretion rate ≲1.7×10¹⁶ g/s. A change of the CRSF depth as function of luminosity is not unexpected and has been observed in other sources. This result possibly implies a change in emission geometry as function of mass accretion rate to reduce the depth of the line below our detection limit.en_US
dc.description.sponsorshipOK thanks the ESAC Trainee Program (https://www.cosmos.esa.int/web/esac-trainees) which initiated this analysis, and the ERASMUS+ fellowship program for their financial support. RB acknowledges funding by Deutsches Zentrum für Luft- und Raumfahrt under contract 50 OR 1606. MTW is supported by the NuSTAR Guest Investigator Program. This research has made use of ISIS functions (ISISscripts) provided by ECAP/Remeis observatory and MIT (http://www.sternwarte.uni-erlangen.de/isis/). This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA).en_US
dc.description.urihttps://www.aanda.org/articles/aa/full_html/2020/11/aa39064-20/aa39064-20.htmlen_US
dc.format.extent9 pagesen_US
dc.genrejournal articlesen_US
dc.identifierdoi:10.13016/m2pgnl-7aqn
dc.identifier.citationKönig, O., “NuSTAR observation of GRO J1744-28 at low mass accretion rate”, Astronomy and Astrophysics, vol. 643, 2020. doi:10.1051/0004-6361/202039064.en_US
dc.identifier.urihttp://hdl.handle.net/11603/20004
dc.identifier.urihttps://doi.org/10.1051/0004-6361/202039064
dc.language.isoen_USen_US
dc.publisherEDP Sciences
dc.relation.isAvailableAtThe University of Maryland, Baltimore County (UMBC)
dc.relation.ispartofUMBC Center for Space Sciences and Technology
dc.relation.ispartofUMBC Faculty Collection
dc.relation.ispartofUMBC Physics Department
dc.rightsThis work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
dc.rightsPublic Domain Mark 1.0
dc.rights.urihttps://creativecommons.org/publicdomain/mark/1.0/
dc.titleNuSTAR observation of GRO J1744−28 at low mass accretion rateen_US
dc.typeTexten_US
dcterms.creatorhttps://orcid.org/0000-0002-4656-6881

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