NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Studying the Accretion Geometry of EXO 2030+375 at Luminosities Close to the Propeller RegimeThe Be X-ray binary EXO2030+375 was in an extended low-luminosity state during most of 2016. We observed this state with NuSTAR and Swift, supported by INTEGRAL observations and optical spectroscopy with the Nordic Optical Telescope (NOT). We present a comprehensive spectral and timing analysis of these data here to study the accretion geometry and investigate a possible onset of the propeller e ect. The H data show that the circumstellar disk of the Be-star is still present. We measure equivalent widths similar to values found during more active phases in the past, indicating that the low-luminosity state is not simply triggered by a smaller Be disk. The NuSTAR data, taken at a 3-78 keV luminosity of 6:8 1035 erg s-1 (for a distance of 7.1 kpc), are nicely described by standard accreting pulsar models such as an absorbed power law with a high-energy cuto. We find that pulsations are still clearly visible at these luminosities, indicating that accretion is continuing despite the very low mass transfer rate. In phaseresolved spectroscopy we find a peculiar variation of the photon index from 1.5 to 2.5 over only about 3% of the rotational period. This variation is similar to that observed with XMM-Newton at much higher luminosities. It may be connected to the accretion column passing through our line of sight. With Swift/XRT we observe luminosities as low as 1034 erg s-1 where the data quality did not allow us to search for pulsations, but the spectrum is much softer and well described by either a blackbody or soft power-law continuum. This softer spectrum might be due to the accretion being stopped by the propeller e ect and we only observe the neutron star surface cooling.
Document ID
20180006574
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Fürst, F.
(European Space Astronomy Centre (ESAC) Madrid, Spain)
Kretschmar, P.
(European Space Astronomy Centre (ESAC) Madrid, Spain)
Kajava, J. J. E.
(Turku Univ. Finland)
Alfonso-Garzón, J.
(Centro de Astrobiología Madrid, Spain)
Kühnel, M.
(Remeis Sternwarte Bamberg, Germany)
Sanchez-Fernandez, C.
(European Space Astronomy Centre (ESAC) Madrid, Spain)
Blay, P.
(Instituto de Astrofisica de Canarias La Laguna, Tenerife, Spain)
Wilson-Hodge, C. A.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Jenke, P.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Kreykenbohm, I.
(Remeis Sternwarte Bamberg, Germany)
Pottschmidt, K.
(Maryland Univ. Baltimore County Baltimore, MD, United States)
Wilms, J.
(Remeis Sternwarte Bamberg, Germany)
Rothschild, R. E.
(California Univ. San Diego, CA, United States)
Date Acquired
October 18, 2018
Publication Date
October 19, 2017
Publication Information
Publication: Astronomy & Astrophysics
Publisher: EDP Sciences
Volume: 606
ISSN: 0004-6361
e-ISSN: 1432-0746
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN60527
Funding Number(s)
CONTRACT_GRANT: NNG08FD60C
CONTRACT_GRANT: 295114
CONTRACT_GRANT: 80GSFC17M0002
CONTRACT_GRANT: 268740
Distribution Limits
Public
Copyright
Other

Available Downloads

There are no available downloads for this record.
No Preview Available