Serendipitous detection of a new outburst of the HMXB IGR J19294+1816 with XMM-Newton
ATel #13215; Vladimir Domcek (University of Amsterdam), Jakob van den Eijnden (University of Amsterdam), Alicia Rouco Escorial (University of Amsterdam), Juan Hernandez Santisteban (University of St Andrews), Nathalie Degenaar (University of Amsterdam), Rudy Wijnands (University of Amsterdam), Aastha Parikh (University of Amsterdam), Ping Zhou (University of Amsterdam), Jacco Vink (University of Amsterdam)
on 22 Oct 2019; 17:35 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Juan V. Hernandez Santisteban (pantro@gmail.com)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
Referred to by ATel #: 13480
IGR J19294+1816 is an accreting pulsar in high-mass X-ray binary that was discovered by Integral on 31st of March 2009 (ATel #1997). Further studies using Swift/XRT data have found pulsation period of ~12.45s (ATel #1998; #2002) and that it falls within the region of pulse period vs. orbital period parameter space expected for a Be X-ray binary system (ATel #2008).
Here we report the serendipitous detection of an X-ray re-brightening of IGR J19294+1816, during XMM-Newton observation carried out on the 13th of October 2019 in which the source was located in the field of view.
Following Tsygankov et al. (2018), we perform a preliminary fit of the EPIC-pn spectrum using XSPEC's model containing Galactic absorption, a thermal disk component, comptonized emission, and a Gaussian iron line: tbabs x (nthcomp + gauss + diskbb). We fit the spectrum between 1 and 10 keV, obtaining a good fit with reduced chi-squared of 0.997 (for 137 degrees of freedom). We find an absorption column density of N_H ~ (5.09 +/- 0.06)e22 cm^-2, power law index Gamma < 1.05 at 1-sigma upper limit, and disk temperature kT ~ 0.20 +/- 0.01. The iron line has a centroid energy of E ~ 6.374 +/- 0.07 keV and a width of ~ (5.48 +/- 0.01)e-2 keV.
Using the convolution model cflux, we measure an unabsorbed 2-10 keV flux of (2.70 +/- 0.01)e-10 erg/s/cm^2. Assuming an 11 kpc distance (Tsygankov et al. 2018), this translates to an X-ray luminosity of (3.91 +/- 0.01)e36 erg/s.
The onset of the outburst coincides with periastron passage similar to previously reported outburst (ATel #5104). The current periastron passage was predicted to occur on October 16, 2019 (MJD 58772.8), following the ephemeris reported in Tsygankov et al. (2018). Therefore, this outburst is likely a Type-I outburst. The source is also detected in the Swift/BAT data and since our XMM-Newton observation, the source has continued to brighten in the Swift BAT hard X-ray monitor.
To search for pulsations in the XMM-Newton observation, we extracted a barycentred light curve with a 1-second time resolution and folded it on trial periods between 12.3 and 12.6 seconds. We find a spin period of 12.492 +/- 0.001 seconds, where we calculated the error following the method in Brumback et al. (2018a, ApJ, 852, 132; 2018b ApjL, 861, L7). This period is slightly longer than the last reported measurement from 2013 (e.g. 12.457 +/- 0.002 second; ATel #5104).
