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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
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To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

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subject:"Swift"
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16161 results found.

  1. EP250827a: Gemini-South optical counterpart detection
  2. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  3. EP250821a: Gemini GMOS Redshift Confirmation
  4. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  5. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  6. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  7. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  8. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  9. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  10. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  11. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  12. GRB 250823A: COLIBRÍ optical observations
  13. GRB 250823A: SVOM/VT optical observation
  14. GRB 250823A: NOT optical observations
  15. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  16. GRB 250823A: Fermi GBM Observation
  17. GRB 250823A: LCOGT Optical Detection
  18. GRB 250823A: BOOTES6/DPRT early optical detection
  19. GRB 250823A: Liverpool Telescope optical detection
  20. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  21. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  22. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  23. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  24. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  25. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  26. GRB 250821A: Kilonova-Catcher optical upper limits
  27. EP250821a: Swift/XRT counterpart fading
  28. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  29. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  30. EP250821a: Swift/UVOT further observations.
  31. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  32. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  33. GRB 250821A: VLT/FORS2 Optical Observation
  34. GRB 250821B: SVOM/GRM observation
  35. EP250821a: SVOM/VT optical observation
  36. GRB 250821A: NOT z-band upper limit
  37. GRB 250821A: KAIT optical upper limit
  38. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  39. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  40. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  41. GRB 250821A: Swift/UVOT Upper Limits
  42. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  43. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  44. GRB 250821A: LCOGT Optical Upper Limits
  45. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  46. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  47. GRB 250818B: 10 GHz VLA detection
  48. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  49. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  50. GRB 250814A: Swift/UVOT Upper Limits
  51. GRB 250813B: Swift/UVOT Upper Limit
  52. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  53. GRB 250818B: Kilonova-Catcher optical afterglow detection
  54. GRB 250818B: Liverpool Telescope optical detections
  55. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  56. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  57. GRB 250818B: Swift/UVOT Detection
  58. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  59. GRB 250818B: TRT Optical Observation
  60. GRB 250818B: SAO RAS optical observations
  61. GRB 250818B: NOT optical observations
  62. GRB 250818B: EP-FXT counterpart detection
  63. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  64. GRB 250818B: Keck redshift of the optical afterglow
  65. GRB 250818B: KAIT optical observations
  66. GRB 250818A: Swift/UVOT Upper Limits
  67. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  68. GRB 250818B: SVOM/VT optical observation
  69. GRB 250818B: Swift-XRT afterglow detection
  70. GRB 250818B: GOTO optical counterpart candidate
  71. GRB 250816A: SVOM/GRM observation of a short burst
  72. SVOM/sb25081602: detection of a likely X-ray transient
  73. GRB 250813B: Liverpool Telescope optical upper limits
  74. GRB 250814A: Further COLIBRÍ optical upper limit
  75. GRB 250814A: GRAWITA TNG NIR observations
  76. GRB 250812A: SVOM/VT optical continued observation
  77. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  78. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  79. GRB250814A: TRT optical upper limits
  80. GRB 250814B: SVOM/GRM observation
  81. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  82. GRB 250814A: KAIT optical upper limit
  83. GRB 250813B: Fermi GBM Observation
  84. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  85. GRB 250813B: NOT observations of the optical afterglow
  86. GRB 250813B: SVOM/VT optical observations
  87. Subject GRB 250813B: SVOM/MXT refined analysis
  88. GRB 250814A: COLIBRÍ optical upper limit
  89. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  90. GRB 250814A: DDOTI Optical Upper Limit
  91. GRB 250813B: EP-FXT counterpart detection
  92. GRB 250813B: Swift-XRT afterglow detection
  93. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  94. GRB 250813B: Ondrejov D50 fast decay
  95. GRB 250813B: Ondrejov D50 optical afterglow detection
  96. EP250812a: Nickel optical upper limit
  97. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  98. GRB 250812A: NTT spectroscopic redshift z = 2.57
  99. GRB250812a: STEP/T80S Indication of slow decay of afterglow
  100. EP250812a: NOT, NTT, and GS observations

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