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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"
body:"GRB"
submitter:"Judith Racusin"

16153 results found.

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

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