0Assigned ID: 1170
----- Attempting Submission 1 (Tue Oct 01 10:41:35 GMT 2019) -----Updated Visit 04 for the repeat observation.1746723135----- Attempting Submission 1 (Tue Oct 08 19:52:33 GMT 2019) -----
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----- Attempting Submission 2 (Tue Dec 03 10:13:48 GMT 2019) -----Caught in the Act: Closest TDE Discovered Before Peak LightWide-field optical transient surveys have discovered about a dozen of tidal disruption events (TDEs), which
belong to a rare class of transient phenomena that occur when an unlucky star is tidally disrupted by a
supermassive black hole (SMBH). In recent years, two emission mechanisms (circularization v.s. reprocessing)
have been put forward to explain the excess in the UV and optical emission in TDEs, which is unexpected
according to the classical TDE framework. Albeit timely observations have only been made for ~5 TDEs so far,
UV spectroscopy is critical to disentangling these scenarios, as most strong atomic features fall in this band.
These emission and absorption line diagnostics can shine light on the physical state (velocity, density,
composition) of the emitting gas (in analogy with quasars).
Being the closest and earliest TDE discovered and classified to date, AT2019qiz (at z=0.0151) is being intensively monitored by observations across the electromagnetic spectrum as it offers the first-ever opportunity to probe the early-time properties of a TDE. Here we propose to obtain 3 epochs of FUV and NUV observations of AT2019qiz at t_peak - 1 month, t_peak, and t_peak + 1 month with HST. These observations will allow us to test whether outflow is ubiquitous amongst TDEs and constrain its early evolution for the first time.We request 3 epochs of UV spectroscopy of the TDE AT2019qiz, over the wavelength range
from 1200-3000A. Assuming a typical rise time of 50 days for TDEs, our designed cadence will be sampling AT2019qiz at t = tpeak - 1 month, tpeak, and tpeak + 1 month, respectively.
We use the most recent inferred blackbody temperature from the Swift-UVOT pho-
tometry (T~22,000 K) as the input spectrum to estimate the expected SNR in different
instrumental congurations. Assuming an orbital visibility of 53 minutes, we find that we can obtain ~35 min of on-source exposure
in a single orbit. We can achieve the best SNR in the near-UV (NUV) using
STIS with the NUV-MAMA detector. Therefore, we also choose to use STIS with the FUV-
MAMA detector for the far-UV (FUV) spectroscopy to avoid switching instruments during
the same visit.
We request 1 orbit of HST time for each proposed epoch. We estimate the SNR con-
servatively by employing the most recent r-band magnitude (~16 mag). We can achieve a SNR per resolution element of >20 for the far UV with the G140L grating
(over the range from 1150-1700A and a SNR per resolution element of >30 for the near
UV (1650-3150A) for the continuum emission within 1 ks and ~500s exposure time, respectively. Even in the case where
the TDE declines rapidly, the 1 ks exposure time will still yield a SNR~5 in the FUV and
SNR~8 in the NUV at r = 20 mag.Dr. Hung, Dr. Gezari, Dr. Cenko, and Dr. van Velzen are experienced observers with
expertise in analyzing and interpreting TDE spectroscopic data (15+ papers analyzing multi- wavelength
observations of TDEs). Dr. Cenko has led two previously approve HST programs (13853, 15331) to obtain UV
spectra of TDEs and has led the analysis and the interpretation of the HST STIS spectra of TDE ASASSN-14li.
Dr. Hung has been approved a HST program (15679) to observe TDE ZTF18abxftqm and has led the analysis and the interpretation of the HST STIS spectra of TDE AT2018zr (with Dr. Foley). Dr. Roth is
an expert in theoretical modeling of TDE spectra (2 first-author publication in the past 3 years) and has led the
theoretical interpretation of the HST STIS spectra of TDEs AT2018zr and ASASSN-14li.Massive Black Holes And Their Host Galaxies0falseSUPPORTEDGALAXYACCRETION DISKDISKNUCLEUSWINDJ2000J2000STIS/FUV-MAMASpectroscopicNoNoG140L1425STIS/NUV-MAMASpectroscopicNoNoG230L2376STIS/FUV-MAMASpectroscopicNoNoG140L1425STIS/NUV-MAMASpectroscopicNoNoG230L2376STIS/FUV-MAMASpectroscopicNoNoG140L1425STIS/NUV-MAMASpectroscopicNoNoG230L2376POS-TARGDITHER0.55LINEfalsefalse390.0STIS-ALONG-SLIT1falseTiming link suitability includes constraints ([02 After 01 by 25.0 to 40.0 days])The scheduling data was generated by CASM 27.2.CASM was run in Phase II mode.1571669628000293.2383368664932(Tic-Visit
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