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 an ( isotropic ) luminosity of 2.8 \times 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 \times 10 ^ { 40 } erg s ^ { -1 } , several times higher than any previously reported .