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Published January 1, 2021 | Version v1
Journal article Open

Discovery of thermonuclear Type-I X-ray bursts from the X-ray binary MAXI J1807+132

Creators

  • 1. Univ Southampton, Sch Phys & Astron, Southampton SO17 1BJ, Hants, England
  • 2. Tech Univ Denmark, Natl Space Inst, Elektrovej 327-328, DK-2800 Lyngby, Denmark
  • 3. Chinese Acad Sci, Shanghai Astron Observ, 80 Nandan Rd, Shanghai 200030, Peoples R China
  • 4. NASA, Astrophys Sci Div, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
  • 5. MIT, MIT Kavli Inst Astrophys & Space Res, 77 Massachusetts Ave, Cambridge, MA 02139 USA
  • 6. Texas Tech Univ, Dept Phys & Astron, POB 41051, Lubbock, TX 79409 USA
  • 7. Cosine BV, Oosteinde 36, NL-2361 HE Warmond, Netherlands

Description

MAXI J1807+132 is a low-mass X-ray binary (LMXB) first detected in outburst in 2017. Observations during the 2017 outburst did not allow for an unambiguous identification of the nature of the compact object. MAXI J1807+132 that was detected in outburst again in 2019 and was monitored regularly with Neutron Star Interior Composition Explorer ( NICER). In this paper, we report on 5 days of observations during which we detected three thermonuclear (Type-I) X-ray bursts, identifying the system as a neutron star LMXB. Time-resolved spectroscopy of the three Type-I bursts revealed typical characteristics expected for these phenomena. All three Type-I bursts show slow rises and long decays, indicative of mixed H/He fuel. We find no strong evidence that any of the Type-I bursts reached the Eddington Luminosity; however, under the assumption that the brightest X-ray burst underwent photospheric radius expansion, we estimate a <12.4 kpc upper limit for the distance. We searched for burst oscillations during the Type-I bursts from MAXI J1807+132 and found none (<10 per cent amplitude upper limit at 95 per cent confidence level). Finally, we found that the brightest Type-I burst shows a similar to 1.6 s pause during the rise. This pause is similar to one recently found with NICER in a bright Type-I burst from the accreting millisecond X-ray pulsar SAX J1808.4-3658. The fact that Type-I bursts from both sources can show this type of pause suggests that the origin of the pauses is independent of the composition of the burning fuel, the peak luminosity of the Type-I bursts, or whether the NS is an X-ray pulsar.

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