Swift Bulge Survey: New outbursts from XTE 1739-285 and IGR J17445-2747

ATel #15927; Kashyap, U. (TTU), Maccarone, T. (TTU), Heinke, C. O. (U. Alberta), Rivera Sandoval, L. E. (UTRGV), Bahramian, A. (Curtin U.), on behalf of SBS team
on 3 Mar 2023; 22:27 UT
Credential Certification: Tom Maccarone (thomas.maccarone@ttu.edu)

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We report Neil Gehrels Swift Observatory detections from the Swift Galactic Bulge Survey (Atel #10265) of two known transients, XTE J1739-285 and IGR J17445-2747. The (roughly 120-s) survey observations were made on 2023/02/09 and 2023/02/26.

The neutron star X-ray transient XTE J1739-285 was first discovered in 1999 (Markwardt et al., 1999) and exhibited short outbursts in May 2001 and October 2003. In 2005, the source was detected with INTEGRAL (Atel #592; Atel #615). Since its discovery, multiple outburst events have been reported from XTE J1739-285 (Atel #734; Kaaret et al., 2007, ApJ, 657, L97; Atel #4304; Atel #4804; Bult et al., 2019b, ApJ, 907, 79; Atel #13138; Atel #13473; Atel #13483). Type I X-ray bursts have also been detected from XTE 1739-285 (Galloway et al., 2020, ApJS, 249, 32). The spectrum of XTE J1739-285 was previously described by an absorbed power-law (Atel #13656, #13148) with an additional blackbody component (Atel #13148). We report detection at J2000 coordinates 264.9746, -28.4951, with error radius 3.5’’. The detected count rates are 1.5 c/s and 0.98 c/s, suggesting pile-up (for the Galactic N_H=1.73e22, Bult et al., 2021, ApJ, 907, 79) and unabsorbed 0.5-10 keV flux lower limits (for the Galactic N_H=1.73e22, assuming a power-law with photon index 1.75) of 6.0E-11 ergs/cm^2/s and 3.9E-11 ergs/cm^2/s (not corrected for pile-up).

IGR J17445-2747 was discovered in 2003 by the IBIS/ISGRI gamma-ray telescope onboard INTEGRAL. The transient source was observed with INTEGRAL during an outburst reaching a peak 20-100 keV flux of 4.6e-10 ergs/cm^2/s (Bird et al., 2010, ApJS, 186, 1; Malizia et al., 2010, MNRAS, 408, 975). Swift XRT detected IGR J17445-2747 in 2017 (Atel #10265, #10273). A faint X-ray outburst from IGR J17445-2747 was reported in 2019 (Atel #12843). An X-ray burst has been reported from IGR J17445-2747, indicating that the compact object in the system is a neutron star (Atel #10256, #10265), while the optical counterpart is a giant star, thus likely a symbiotic system (Shaw et al. 2020, MNRAS, 492, 4344). We report detection with Swift/XRT at J2000 coordinates 266.1263, -27.7664, with error radius 4.0’’. We detect IGR J17445-2747 at count rates 0.77 c/s (not correcting for pileup) and 0.08 c/s (for the Galactic N_H=5.6e22, Mereminskiy et al., 2017, Ast. Lett., 43, 656), and 0.5-10 keV unabsorbed flux (for the Galactic N_H=5.6e22, assuming a power-law with photon index 2) of 2.7e-11 ergs/cm^2/s and 2.8e-12 ergs/cm^2/s (not corrected for pile-up, which likely affects only the earlier observation substantially).

We do not detect XTE J1739-285 in our simultaneous UVOT observation (UVW1 filter), and IGR J17445-2747 is outside the UVOT field of view.

We thank the Swift team for scheduling these observations.