Multiwavelength observations of the X-ray transient MAXI J1305-704
ATel #4060; C. Sanchez-Fernandez, E. Kuulkers, M. Cadolle-Bel (ESA/ESAC), J. Rodriguez (CEA Saclay), P. D'Avanzo (INAF-OAB), A. Domingo-Garau (CAB, INTA-CSIC), S. Migliari (U. Barcelona)
on 21 Apr 2012; 18:37 UT
Credential Certification: Celia Sanchez-Fernandez (celia.sanchez@sciops.esa.int)
Subjects: Infra-Red, Optical, X-ray, Binary, Black Hole, Neutron Star, Transient
MAXI J1305-704 is a new X-ray transient recently discovered (April 5) by MAXI (ATel #4024, #4030, #4035, #4044). We report here on high energy and optical observations about 2 weeks after the start of the outburst.
INTEGRAL observed the source for 42 ks between April 19 05:00-17:17 (UTC). Quasi-simultaneous Swift observations were executed for 8 ksec between April 19 13:19-18:20 (UTC) and by the REM telescope located in La Silla (Chile) from April 19 05:21 (UTC) for a total duration of 30 minutes.
During this period, the overall emission from MAXI J1305-794, as measured by Swift/XRT (0.1-10 keV band), was rising steadily from ~20 cts/s to ~40 cts/s. The Swift/XRT light curve shows evidence of absorption dips, detected only when the count rate is above ~30 cts/s. It is worth remarking that during this same interval the emission in the 15-50 keV band as measured by Swift/BAT was declining. Our observations do not display evidence of bursting activity, signature of a neutron star compact object.
The source was detected with the following fluxes:
JEM-X (3-10 keV) 15 +/- 1 mCrab;
JEM-X (10-20 keV) 6 +/- 2 mCrab;
ISGRI: (20-40 keV) 6 +/-2 mCrab;
Swift: (2-10 keV) 22 +/- 3 mCrab.
Preliminary join fits to the Swift/XRT data (1.2-8 keV) and JEM-X (3-20 keV) are compatible with a model consistent of a disc blackbody of temperature kT=0.9 +/- 0.1 keV plus a power-law with photon index 2.1 +/- 0.5 for an absorption column density of 1.19 +/- 0.02 x 10^21 cm-2 (reduced chi-sq=1.15). The inclusion of an additional blackbody component does not improve the fit significantly.
The source was not detected by the OMC, with an upper limit of V=16.7mag.
The optical/NIR counterpart of MAXI J1305-704 (ATel #4024) was observed by the REM telescope in imaging mode using the V, R, I, J, H and K filters. The source was detected in all bands. From a preliminary analysis, we estimate a magnitude of R = 16.5 +/- 0.2 (calibrated against the USNOB1.0 catalogue) and H = 15.8 +/- 0.2 (calibrated against the 2MASS catalogue). The above values are in the Vega system and are not corrected for the Galactic extinction.
We thank the Swift, INTEGRAL and REM teams for their prompt scheduling after our TOO requests.