ASAS-SN Discovery of an Ongoing, ~3 Magnitude QSO Outburst in SDSS J093052.25+003458.91

ATel #6052; T. W-S. Holoien, K. Z. Stanek (Ohio State), D. Bersier (LJMU), D. Grupe (Swift MOC, PSU), C. S. Kochanek, B. J. Shappee, J. Jencson, U. Basu, B. Danilet, J. F. Beacom (Ohio State), J. L. Prieto (Princeton), D. Szczygiel, G. Pojmanski (Warsaw University Observatory), J. Brimacombe (Coral Towers Observatory)
on 7 Apr 2014; 22:05 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Krzysztof Stanek (stanek.32@osu.edu)

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During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from the quadruple 14-cm "Brutus" telescope in Haleakala, Hawaii, we discovered a new transient source:

 
Object       RA (J2000)   DEC (J2000)      Disc. UT Date   Disc. V mag 
ASASSN-14am  09:30:52.25  +00:34:58.9      2014 Apr. 5.32     16.35 

ASASSN-14am was discovered in images obtained 2014 UT Apr. 5.32 at V~16.35 mag. The object was not detected (V>16.6) in data taken at this location on UT Apr. 4 and earlier. Images obtained on UT Apr. 06 with the LCOGT-1m robotic telescope at the Siding Spring Observatory and with the LT-2m telescope at the Roque de los Muchachos confirm the detection of the new transient. A figure showing the detected source in ASAS-SN images from Apr. 05 as well as non-detections from Apr. 4 and Mar. 24 can be found here. A cross-check of the source position with the SDSS catalog reveals the source of the outburst to be a broadline QSO at redshift 1.77 with m_g ~19.4, see this link. The CRTS database (Drake et al. 2009) indicates this object is variable on the order of ~1 mag and shows one previous partial outburst detected at magnitude 17.9 on 2005 Nov. 28, but nothing as dramatic as the current outburst.

Following ASAS-SN discovery, we obtained a 3ks Swift TOO observation of the transient on UT Apr. 6.99. The UVOT optical/UV magnitudes of the source, measured using a r=5" aperture, were: v=17.17 +/- 0.09, b=17.50 +/- 0.05, u=16.81 +/- 0.05, uvw1=17.26 +/- 0.07, uvm2=18.23 +/- 0.10, uvw2=18.17 +/- 0.08 (uncorrected for extinction). We also detect weak X-ray emission from the source in Swift XRT data, at a rate of roughly 0.012 counts/s. From the Swift and LT measurements and the prediscovery SDSS imaging of the quasar we obtain an SED before and after discovery (see this figure) showing source emission peaking in the (observed) optical range and the emitted flux larger by roughly an order of magnitude in all wavelengths.

In our present follow-up data, the shape of the (optical) SED is little changed, but is 2-3 magnitudes brighter. The quasar was already luminous, with an estimated bolometric luminosity of 2x10^12 solar luminosities based on the NED models of the SDSS data, yet it seems to have brightened by an order of magnitude and then continued to evolve on very short time scales. While such strong and rapid variability is not uncommon in blazars, it is highly unusual, possibly unprecedented, for a luminous quasar such as SDSS J093052.25+003458.91 (e.g., MacLeod et al. 2012).

We thank LCOGT and its staff for their continued support of ASAS-SN. For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.