Swift monitoring of M51: A 38-day super-orbital period from the ULX7 pulsar and a new transient ULX
Abstract
We present the results from a monitoring campaign made with the Neil Gehrels Swift Observatory of the M51 galaxies, which contain several variable ultraluminous X-ray sources (ULXs). The ongoing campaign started in May 2018, and we report here on ∼ 1 year of observations. The campaign, which consists of 98 observations, has a typical cadence of 3-6 days, has the goal of determining the long-term X-ray variability of the ULXs. Our main result is that ULX7 exhibits a periodic flux modulation on a period of 38 days varying over a magnitude and a half in flux from peak to trough. Since the orbital period of the system is known to be 2 days, the modulation is super-orbital, which is a near-ubiquitous property of ULX pulsars. We also identify a new transient ULX, J132956.8+470852.6, the onset of which occurred during our campaign, reaching a peak luminosity of ∼ 1040 erg s-1, before gradually faded over the next ∼ 200 days until it slipped below the detection limit of our observations. The similarity of the outburst to other transient neutron star ULXs appears to suggest that it is also one of these types of sources.
- Publication:
-
American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23543901B