SRG/ART-XC discovery of SRGA J204318.2+443815: towards the complete population of faint X-ray pulsars
astro-ph.HE
/ Authors
A. A. Lutovinov, S. S. Tsygankov, I. A. Mereminskiy, S. V. Molkov, A. N. Semena, V. A. Arefiev, I. F. Bikmaev, A. A. Djupvik, M. R. Gilfanov, D. I. Karasev
and 12 more authors
I. Yu. Lapshov, P. S. Medvedev, A. E. Shtykovsky, R. A. Sunyaev, A. Yu. Tkachenko, S. Anand, M. C. B. Ashley, K. De, M. M. Kasliwal, S. R. Kulkarni, J. van Roestel, Y. Yao
/ Abstract
We report a discovery of a new long-period X-ray pulsar SRGA J204318.2+443815/SRGe J204319.0+443820 in the Be binary system. The source was found in the second all-sky survey by the Mikhail Pavlinsky telescope on board the SRG mission. The follow-up observations with XMM-Newton, NICER and NuSTAR observatories allowed us to discover a strong coherent signal in the source light curve with the period of $\sim742$ s. The pulsed fraction was found to depend on the energy increasing from $\sim20$% in soft X-rays to $>50$% at high energies, as it is typical for X-ray pulsars. The source demonstrate a quite hard spectrum with an exponential cutoff at high energies and bolometric luminosity of $L_X \simeq 4\times10^{35}$ erg/s. Dedicated optical and infrared observations with the RTT-150, NOT, Keck and Palomar telescopes revealed a number of emission lines (H$_α$, HeI, Pashen and Braket series) with the strongly absorbed continuum. All of above suggests that SRGAJ204318.2+443815/ SRGeJ204319.0+443820 is a new persistent low luminosity X-ray pulsar in a distant binary system with a Be-star of the B0-B2e class. Thus the SRG observatory allow us to unveil the hidden population of faint persistent objects including the population of slowly rotating X-ray pulsars in Be systems.