Support ATel At Patreon

[ Previous | Next | ADS ]

Swift/XRT observation of Swift J151857.0-572147 indicates that the source likely made a transition to the soft state

ATel #16519; Melania Del Santo, Thomas D. Russell (INAF/IASF Palermo), Alessio Marino (ICE/CSIC), Sara Motta (INAF/OAB)
on 10 Mar 2024; 13:34 UT
Credential Certification: Melania Del Santo (melania@ifc.inaf.it)

Subjects: X-ray, Transient

Referred to by ATel #: 16524, 16538

Following the recent report of a bright radio flare from the new X-ray transient Swift J151857.0-572147 observed with the Australia Telescope Compact Array (ATCA; ATel #16518), we triggered a ToO X-ray campaign with Swift/XRT. The first XRT pointing began on March 10 at 07:29:00 UT, and lasted approximately 1000 s.

The observed 0.5-10 keV count rate was on average approximately 330 ct/s. The X-ray spectrum is significantly softer than in the previous XRT observation (ATel #16500). The X-ray spectrum can be well described by an absorbed disk black-body plus a power-law model with a reduced chi^2=1.07 (618 d.o.f.). We find an equivalent hydrogen column of (4.4 +/- 0.3)E22 cm^-2, a photon index of 2.2(-0.4, +0.3) and an inner disk temperature of 0.81 +/- 0.06 keV. The derived 0.5-10 keV flux was 2.1 E-10 erg cm^-2 s^-1, while the corresponding 2-10 keV unabsorbed flux is roughly 3.5 E-8 erg cm^-2 s^-1 .

These parameters are consistent with those of a typical Galactic black hole X-ray binary in a soft or soft/intermediate state. The results of the spectral fitting indicate that Swift J151857.0-572147 likely just made a state transition from the hard to the soft state, as suggested by the bright radio flare observed by ATCA.

Further MW observations are already planned.

We thank the Swift PI and the ODS for the rapid scheduling of Swift ToO observation.