XMMSL1 J152535.1+174859 in active state

ATel #8630; J. Greiner, T. Kruehler, C. Delvaux (all MPE Garching)
on 3 Feb 2016; 18:55 UT
Distributed as an Instant Email Notice Transients
Credential Certification: J. Greiner (jcg@mpe.mpg.de)

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XMM-Newton detected a bright X-ray source during slew 9295300004, performed between 2016-01-24 01:52-03:42 UT (http://xmm.esac.esa.int/external/xmm_products/slew_results/web_9295300004.shtml), at coordinates RA(2000.0) = 15:25:35.09, Decl.(2000.0) = 17:48:59.7 (+-8 arcsec), henceforth XMMSL1 J152535.1+174859. The measured count rate of 1.4+-0.4 cts/s corresponds to an increase in flux by a factor of about 5 with respect to the ROSAT all-sky survey (1RXS J152532.2+174912, Voges et al. 1999).

We observed the field of XMMSL1 J152535.1+174859 simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile). We obtained 140 sec of total exposure in g'r'i'z′ and 240 sec in JHK at a midtime of 08:58 UT on 2016-02-02, at a seeing of 1.1 arcsec and at an airmass of 1.9.

We find two sources within the 8 arcsec error circle:

Source 1: RA = 15:25:35.45, Decl = 17:48:55.2

Source 2: RA = 15:25:34.59, Decl = 17:49:00.0

with an error of +-0.2" each.

In comparison to SDSS (measured in 2004), Source 1 is constant to within 0.02 mag, while Source 2 has increased in brightness by 0.30 mag in g', 0.23 mag in r', 0.23 mag in i' and 0.13 mag in z'. We therefore suggest source 2 as counterpart of XMMSL1 J152535.1+174859, despite the non-simultaneity of the optical/NIR and X-ray measurements.

In detail, we measure the following magnitudes (all in AB)

 
g' = 18.24 +- 0.02 mag,  
r' = 18.11 +- 0.02 mag,  
i' = 17.49 +- 0.02 mag,  
z' = 17.74 +- 0.02 mag,  
J  = 17.56 +- 0.07 mag,  
H  = 17.15 +- 0.09 mag, and  
K  = 16.68 +- 0.17 mag.  

The given magnitudes are derived based on calibrating the images against SDSS and 2MASS field stars and are not corrected for the Galactic foreground extinction corresponding to a reddening of E(B-V)= 0.04 mag in the direction of the burst (Schlafly & Finkbeiner 2011).

Historically, this object was even another magnitude brighter, at 16.96 mag (POSS-I E, 103a-E).

SDSS DR12 provides a spectrum, resulting in a classification of a QSO "starburst broadline" at a redshift of 0.1254. We note that with our astrometry, Source 2 corresponds to SDSS J152534.58+174900.0, while the above XMM slew survey page suggests SDSS J152535.44+174855.2 as counterpart. We also note that NED lists the redshift of SDSS J152534.58+174900.0 as 0.145.