2018 Fiscal Year Annual Research Report
|Research Institution||Kyoto University |
上田 佳宏 京都大学, 理学研究科, 准教授 (10290876)
|Foreign Research Fellow
HU CHIN-PING 京都大学, 理学(系)研究科(研究院), 外国人特別研究員
|Project Period (FY)
2018-11-09 – 2021-03-31
|Keywords||中性子星 / 超臨界降着|
|Outline of Annual Research Achievements
Dr. Hu summarized his previous works on (1) the correlation between the thermal pulse profile and physical quantities and (2) the connection between radiative outburst and timing irregularities in magnetars. Moreover, Dr. Hu developed a code to simulate the pulse profile based on two antipodal hotspots on the surface of a neutron star. It will be helpful for future modeling of the pulse profile of ULPs. These two works were accepted for publication on refereed journals.
We worked on the evolution of spin, orbital, and superorbital modulations of a super-Eddington accretion pulsar SMC X-1. We found that a new excursion event of the superorbital modulation period occurred in MJD 57100. The hardness ratio obtained with Monitor of All-sky X-ray Image (MAXI) suggests an absorption feature during the superorbital transition states. In contrast to the regular epochs, the superorbital profile during the excursion epochs has a shallower and narrower valley, likely caused by a flatter warp of the disk or a ring with a lower opacity. Thanks for the excellent temporal resolution of MAXI, we are able to track the detailed spin period evolution of SMC X-1. We obtain no significant positive correlation between the spin period residual and the superorbital frequency as suggested before. Instead, we observed a hint of anti-correlation. We suggested that the accretion torque could be changed by various origins, including the change of mass accretion rate and the warp angle. The paper has been drafted and will be submitted soon.
|Current Status of Research Progress
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
- Magnetar project: Knowing the properties of magnetars are bases to test the accreting magnetar scenario of ULPs. Dr. Hu has published two papers during the first fiscal year. These works help in understanding the fundamental behaviors of magnetars and provide references when comparing the behaviors of ULPs and magnetars.
- The spin period evolution of super-Eddington accreting pulsar: We have done the work of SMC X-1 in a short timescale and the paper will be submitted soon. When working on the two-dimensional period search with MAXI data, we successfully accelerate the computing speed with the help with a GPU. This technique is helpful for future projects in searching for ULPs. Moreover, this successful experience is helpful for future projects of monitoring Xray pulsars with MAXI.
- Systematically investigating the timing properties of ULXs: The standard operating procedure has been established. Currently, we can generate light curves and power spectra of all the point sources in one galaxy in 0.5-2 days (depending on the number of observations, number of photons, and number of point sources). This procedure could be further optimized by combining part of the procedure with scripts. The corresponding work is ongoing. We expect to find several interesting candidates to deeply investigate their timing and spectral evolutions.
- Search for fast-spinning ultraluminous pulsars: The searching algorithm has been established although no significant periodicity was found yet.
|Strategy for Future Research Activity
- Systematically tracking the pulse period evolution with MAXI: MAXI provides us a unique chance to track the spin period evolution of pulsars owing to its excellent time resolution of 50 microseconds. We will work on LMC X-4 (another super-Eddington accreting pulsar with a 30-day superorbital modulation), 4U 1822-371 (a partial-eclipsing X-ray pulsar), and Her X-1 (an intermediate X-ray binary with a 35-day superorbital modulation) in the upcoming year.
- Systematically investigating the timing properties of ULXs: We will search for interesting candidates with the improved operating procedure. Moreover, we will work on a detailed analysis of two eclipsing candidates in M51 in this year.
- Search for fast-spinning ultraluminous pulsars: We will search for periodicity in ULXs with NuSTAR data. Moreover, we will also try to apply for NICER observations once we find some interesting ULP candidates. Unfortunately, NICER does not have imaging ability and the spatial resolution is poor (3 arcmin). We have to carefully select our candidates that dominate the soft X-ray emission within the field of view.
- Monitoring the superorbital modulations of ultraluminous pulsars: The superorbital modulation of NGC 300 ULX-1 has not yet been well studied. With the accumulation of Swift observation, its superorbital modulation could be revealed in the following two years. Moreover, the long-term stability of the superorbital modulation of NGC 5907 ULX-1 was not well investigated. We will keep monitoring the release of the Swift data and test if they show similar excursion behaviors as SMC X-1.
Research Products (3 results)