Cannot find file /Users/nrt3/Desktop/Proposals/HSTc29/210905A_mid/HST210905Av4.pdf0Assigned ID: 2686
----- Attempting Submission 1 (Mon Jan 31 20:36:39 GMT 2022) -----
HST Phase I Proposal 2686 successfully submitted.
Receipt: # 2686-1
----- Attempting Submission 2 (Mon Jan 31 23:24:10 GMT 2022) -----
HST Phase I Proposal 2686 successfully submitted.
Receipt: # 2686-2
----- Attempting Submission 3 (Mon Jan 31 23:35:23 GMT 2022) -----New version of phase 2, with two orbits switched from WFC3/IR to WFC3/UVIS as per approved PCR 92450.
UVIS observations defined in a new visit, since they don't need to be obtained at same time as WFC3/IR obs.621294033----- Attempting Submission 1 (Tue Mar 29 16:27:53 GMT 2022) -----
----- Attempting Submission 2 (Fri Mar 10 14:24:44 GMT 2023) -----The afterglow and host of GRB 210905A at z=6.3The recently discovered GRB 210905A is the highest redshift GRB for which an early, high-S/N, mid-high resolution afterglow spectrum has been obtained. In addition to providing the redshift, this spectrum exhibits numerous metal lines and a complex velocity structure spanning ~360 km/s, and blueshifted by ~1000 km/s from a tentative Ly-a emission line. Modelling of the Lyman-alpha damping wing reveals the host column density, and puts constraints on the neutral fraction of the surrounding intergalactic medium. Analysis of the abundances gives an average metallicity Z~Zsol/20. In addition, the afterglow of this GRB started bright and has declined slowly, implying a late jet break. This suggests a wide jet and hence a particularly high energy event, perhaps indicative of an unusual progenitor star. Here we seek HST WFC3/IR F140W imaging to obtain a final late-time point on the afterglow light curve to constrain any break, and an image after the afterglow has faded, to provide a subtraction template and characterisation of the host galaxy. This would make it the first galaxy at z>6 detected in emission for which detailed absorption line abundances for multiple species are available.We will obtain two vists for observations of GRB 210905A. The first will aim to capture light from the afterglow while the second will search for the host galaxy. Both visits will use F140W. The first will be a two orbit visit while the second will require a 4-orbit exposure. We will use a standard 4 point dither pattern for the 2 orbit visit and a 8-point dither pattern for the 4 orbit visit, acquiring two exposures per orbit.Our collaboration has been highly successful at identifying and studying high-z GRBs using many telescopes, including HST. This includes discovery (or co-discovery) of all of the known z>6 GRBs. We have also been at the forefront of utilising GRB afterglow spectroscopy to probe ISM and IGM properties, as well as performing multiwavelength GRB host galaxy studies in emission, particularly at high redshift and with HST (e.g. Tanvir+2012; McGuire+2016; Tanvir+2018). We were also the group that located the afterglow and found the redshift for GRB 210905A, and have been conducting substantial ground follow-up. We note that some of the proposers also have an ongoing HST c29 program to target candidate high-z GRBs (GO 16738), however that program is for grism spectroscopy of afterglows in cases where a spectroscopic redshift has not been possible from the ground, and has no provision in it for light curve monitoring or deep host searches.GalaxiesStellar Populations and the Interstellar Medium3falsefalsefalsefalsefalsetruefalsefalseSUPPORTEDGALAXYSTARBURSTJ2000J2000H(AB)~27WFC3/IRImagingNoNoF140WWFC3/IRImagingNoNoF140WPOS-TARGDITHER0.173LINE0.112falsefalse81.785423.884WFC3-UVIS-DITHER-BOX1falsePOS-TARGDITHER0.572LINE0.365falsefalse74.653418.528WFC3-IR-DITHER-BOX-MIN2false/Users/nrt3/Desktop/Proposals/HSTc29/210905A_mid/OP-cache/GO16918-v01.xmlThe scheduling data was generated by CASM 31.0.CASM was run in Phase II mode.1650824951000250.44(Tic-Visit
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