X-RAY MONITORING OF ULTRALUMINOUS X-RAY SOURCES

被引：50

作者：

Kaaret, Philip ^{[1
]}

Feng, Hua ^{[2
,3
]}

机构：

[1] Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA

[2] Tsinghua Univ, Dept Engn Phys, Beijing 100084, Peoples R China

[3] Tsinghua Univ, Ctr Astrophys, Beijing 100084, Peoples R China

来源：

ASTROPHYSICAL JOURNAL | 2009年 / 702卷 / 02期

关键词：

black hole physics; galaxies: individual (Holmberg IX; NGC; 5408; 4395); galaxies: stellar content; X-rays: binaries; X-rays: galaxies; SPECTRAL STATES; 2000; OUTBURST; BLACK-HOLES; M82; GALAXY; VARIABILITY; EVOLUTION; GX-339-4; MULTIWAVELENGTH; XTE-J1550-564;

D O I：

10.1088/0004-637X/702/2/1679

中图分类号：

P1 [天文学];

学科分类号：

0704 ;

摘要：

X-ray monitoring observations were performed with the Swift observatory of the ultraluminous X-ray sources Holmberg IX X-1, NGC 5408 X-1, and NGC 4395 X-2 and also of the nuclear X-ray source in NGC 4395. Holmberg IX X-1 remains in the hard X-ray spectral state as its flux varies by a factor of 7 up to a (isotropic) luminosity of 2.8 x 10(40) erg s(-1). This behavior may suggest an unusually massive compact object. We find excess power at periods near 60 days and 28 days in the X-ray emission from Holmberg IX X-1. Additional monitoring is required to test the significance of these signals. NGC 5408 X-1 and NGC 4395 X-2 appear to remain in the soft spectral state found by Chandra and XMM with little variation in spectral hardness even as the luminosity changes by a factor of 9. We found an outburst from the nuclear source in NGC 4395 reaching an X-ray luminosity of 9 x 10(40) erg s(-1), several times higher than any previously reported.

引用

页码：1679 / 1682

页数：4

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