INTEGRAL detects renewed activity of the Be/X-ray binary pulsar 1A 0535+262
ATel #14401; I. Caballero (ESA/ESAC), C. Ferrigno (ISDC), E. Kuulkers (ESA/ESTEC), P. Kretschmar (ESA/ESAC), J. Wilms (Remeis Observatory, ECAP), F. Fuerst (ESA/ESAC), J. B. Coley (Howard Univ., NASA GSFC/CRESST), K. Pottschmidt (UMBC, NASA-GSFC/CRESST), R. Rothschild (UCSD), V. Savchenko, E. Bozzo (ISDC), L. Ducci (ISDC; IAAT), I. Kreykenbohm (Remeis Observatory, ECAP)
on 18 Feb 2021; 11:39 UT
Distributed as an Instant Email Notice Transients
Credential Certification: I. Caballero (isabelcaballerod@gmail.com)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
Referred to by ATel #: 14732
INTEGRAL has detected the Be/X-ray binary pulsar 1A 0535+262 at a flux of about 60mCrab in the 28-40 keV range during public Crab calibration observations from 2021-02-13 17:34 to 2021-02-14 06:54. X-ray activity has also been detected by other X-ray instruments (ATel #14392).
The neutron star is in a binary orbit of 111.1 days (Finger et al.2006, BAAS, 38, 359), and the current detection takes place around 20 days before periastron. A giant outburst took place during the previous periastron passage in November/December 2020 (ATel #14227), which could not be observed by INTEGRAL because of visibility constraints.
We performed a preliminary spectral analysis of JEMX-1 and ISGRI data. The data can be fit with a cutoff powerlaw with photon index =1.7+0.3/-0.4 and Ecut=32+18/-9 keV (90% significance), with chi2/d.o.f=27/29. A cyclotron line is not statistically required, but a model including a cyclotron line with E=46.1keV (line parameters fixed to values from Caballero et al. 2007 A&A, 465L, 21C) also describes the data well.
Recurrent normal outbursts at periastron are typically observed after giant ones for this source, therefore additional X-ray activity can be expected during the upcoming periastron passages of the source, during which we encourage multi-wavelength observations.
