Published January 1, 2022
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SRG/ART-XC discovery of SRGA J204318.2+443815: Towards the complete population of faint X-ray pulsars
Creators
- Lutovinov, A. A.1
- Tsygankov, S. S.
- Mereminskiy, I. A.1
- Molkov, S., V1
- Semena, A. N.1
- Arefiev, V. A.1
- Bikmaev, I. F.2
- Djupvik, A. A.
- Gilfanov, M. R.
- Karasev, D., I1
- Lapshov, I. Yu1
- Medvedev, P. S.1
- Shtykovsky, A. E.1
- Sunyaev, R. A.
- Tkachenko, A. Yu1
- Anand, S.3
- Ashley, M. C. B.4
- De, K.5
- Kasliwal, M. M.3
- Kulkarni, S. R.3
- Kulkarni, S. R.3
- 1. Russian Acad Sci, Space Res Inst IKI, Prosoyuznaya Ul 84-32, Moscow 117997, Russia
- 2. Kazan Fed Univ, Kremlevskaya Str 18, Kazan, Russia
- 3. CALTECH, Div Phys Math & Astron, Pasadena, CA 91125 USA
- 4. Univ New South Wales, Sch Phys, Sydney, NSW 2052, Australia
- 5. CALTECH, Cahill Ctr Astrophys, Pasadena, CA 91125 USA
Description
We report the discovery of the new long-period X-ray pulsar SRGA J204318.2+443815/SRGe J204319.0+443820 in a Be binary system. The source was found in the second all-sky survey by the Mikhail Pavlinsky ART-XC telescope on board the SRG mission. The followup observations with XMM-Newton, NICER, and NuSTAR allowed us to discover a strong coherent signal in the source light curve with a period of similar to 742 s. The pulsed fraction was found to depend on an increase in energy from similar to 20% in soft X-rays to >50% at high energies, as is typical for X-ray pulsars. The source has a quite hard spectrum with an exponential cutoff at high energies and a bolometric luminosity of L-x similar or equal to 4 x 10(35) erg s(-1). The X-ray position of the source is found to be consistent with the optical transient ZTF18abjpmzf, located at a distance of similar to 8.0 kpc. Dedicated optical and infrared observations with the RTT-150, NOT, Keck, and Palomar telescopes revealed a number of emission lines (H-alpha, He I, and the Paschen and Braket series) with a strongly absorbed continuum. According to the SRG scans and archival XMM-Newton data, the source flux is moderately variable (by a factor of 4-10) on timescales of several months and years. All this suggests that SRGA J204318.2+443815/SRGe J204319.0+443820 is a new quasipersistent low-luminosity X-ray pulsar in a distant binary system with a Be-star of the B0-B2e class. Thus the SRG observatory allowed us to unveil a hidden population of faint objects, including a population of slowly rotating X-ray pulsars in Be systems.
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