GRB 250416C (EP250416a): Swift observation summary

This is a confirmed GRB (GRB 250416C), the afterglow is source 1 -- please see the GRB results at https://www.swift.ac.uk/xrt_products/00019721 for updated analysis

Mission:	Einstein Probe/WXT
Einstein Probe RA:	256.402°
Einstein Probe Dec:	+25.768°
Einstein Probe Err:	3.1 arcmin
T0:	2025-04-16 17:53:59 UT
Galactic:	47.13° +33.73°
Galactic N_H:	3.78× 10²⁰ cm^-2

Sun distance:	118.15°
Sun angle:	8.56 [hr] (West of Sun)
Moon distance:	53.37°
Visibility of this field.

Data analysed so far:

ObsID: 00019721001 with 2.0 ks exposure.
ObsID: 00019721002 with 1.9 ks exposure.

About tiled field analysis.

So far 1 fields have been scheduled for observations. Data are available and processed for 1 of these.

19721 — 4.0 ks of cleaned data taken between 2025-04-16 22:37:39 and 2025-04-17 16:04:29

Details of afterglow candidates

1 sources were found which matches the afterglow criteria.

#	RA (J2000)	Dec (J2000)	Err₉₀¹	Detection Flag²	Rank³	Dist from Einstein Probe/WXT pos	Exposure	Notes	Vizier
1 [details]	17h 05m 40.92s256.42050°	+25° 46′ 32.3″25.77564°	4.0′′ ^*	Good	2 (O)	1.1′	4.0 ks	The source is 3.9-σ above the RASS limit.
Mean XRT rate: 5.9 (±0.5) ×10^-2 ct s^-1 Peak XRT rate: 0.13 (±0.03) ct s^-1 RASS PSPC 3-σ upper limit: 0.02 ct s^-1 (PSPC count-rate) Mean XRT rate converted to PSPC: 0.075 (±0.007) ct s^-1 Peak XRT rate converted to PSPC: 0.17 (±0.04) ct s^-1 Mean XRT flux: 2.16 (±0.19) ×10^-12 erg cm^-1s^-1 Peak XRT flux: 4.9 (±1.1) ×10^-12 erg cm^-1s^-1 Products: Light curve \| Spectrum \| Enhanced position

¹ Radius, 90% confidence.
² Indicates how likely the source is to be real. See the LSXPS documentation.
³ T=Transient Source, O=Outbursting known source, U=Uncatalogued X-ray source, K=Known X-ray source.
^* The position was enhanced using astrometry derived from the Swift UVOT.
^† The position was astrometrically corrected using the XRT sources and the 2MASS catalogue.

Find an upper limit.

Sources found so far

So far 3 sources have been found in the XRT data. 0 sources match catalogued sources.

#	RA (J2000)	Dec (J2000)	Err₉₀¹	Detection Flag²	Rank³	Dist from Einstein Probe/WXT pos	Exposure	Notes
1 [details]	17h 05m 40.92s256.42050°	+25° 46′ 32.3″25.77564°	4.0′′ ^*	Good	2 (O)	1.1′	4.0 ks	The source is 3.9-σ above the RASS limit.
Mean XRT rate: 5.9 (±0.5) ×10^-2 ct s^-1 Peak XRT rate: 0.13 (±0.03) ct s^-1 RASS PSPC 3-σ upper limit: 0.02 ct s^-1 (PSPC count-rate) Mean XRT rate converted to PSPC: 0.075 (±0.007) ct s^-1 Peak XRT rate converted to PSPC: 0.17 (±0.04) ct s^-1 Mean XRT flux: 2.16 (±0.19) ×10^-12 erg cm^-1s^-1 Peak XRT flux: 4.9 (±1.1) ×10^-12 erg cm^-1s^-1 Products: Light curve \| Spectrum \| Enhanced position
2 [details]	17h 06m 20.72s256.58634°	+25° 39′ 11.4″25.65316°	7.2′′	Reasonable	3 (U)	12.1′	2.9 ks
Mean XRT rate: 3.1 (+1.9, -1.4) ×10^-3 ct s^-1 Peak XRT rate: 3.1 (+1.9, -1.4) ×10^-3 ct s^-1 RASS PSPC 3-σ upper limit: 9.1×10^-3 ct s^-1 (PSPC count-rate) Mean XRT rate converted to PSPC: 10 (+6, -4) ×10^-3 ct s^-1 Peak XRT rate converted to PSPC: 10 (+6, -4) ×10^-3 ct s^-1 Mean XRT flux: 4.5 (+2.8, -2.0) ×10^-14 erg cm^-1s^-1 Peak XRT flux: 4.5 (+2.8, -2.0) ×10^-14 erg cm^-1s^-1 Products: Light curve \| Spectrum
3 [details]	17h 06m 20.88s256.58702°	+25° 54′ 46.3″25.91287°	9.9′′	Poor	3 (U)	13.2′	1.9 ks
Mean XRT rate: 3.4 (+2.3, -1.6) ×10^-3 ct s^-1 Peak XRT rate: 3.4 (+2.3, -1.6) ×10^-3 ct s^-1 RASS PSPC 3-σ upper limit: 0.01 ct s^-1 (PSPC count-rate) Products: Light curve \| Spectrum

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FITS exposure map.