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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"

19804 results found.

  1. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  2. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  3. Fermi GRB 250824B: Global MASTER-Net observations report
  4. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  5. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  6. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  7. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  8. EP250821a: MeerKAT radio counterpart
  9. GRB 250823A: COLIBRÍ optical observations
  10. GRB 250823A: SVOM/VT optical observation
  11. GRB 250823A: Swift/UVOT Detection
  12. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  13. GRB 250823A: Enhanced Swift-XRT position
  14. GRB 250823A: LCOGT Optical Detection
  15. GRB 250823A: Swift detection of a burst
  16. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  17. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  18. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  19. GRB 250806A: Gemini observations of host galaxy candidate
  20. GRB 250821A: Kilonova-Catcher optical upper limits
  21. GRB 250812A: SVOM/ECLAIRs refined analysis
  22. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  23. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  24. GRB 250821A: VLT/FORS2 Optical Observation
  25. GRB 250821B: SVOM/GRM observation
  26. EP250821a: SVOM/VT optical observation
  27. GRB 250821A: NOT z-band upper limit
  28. GRB 250821A: KAIT optical upper limit
  29. GRB 250821A: Swift-XRT refined Analysis
  30. GRB 250821A: Enhanced Swift-XRT position
  31. GRB 250821A: Swift/UVOT Upper Limits
  32. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  33. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  34. GRB 250821A: LCOGT Optical Upper Limits
  35. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  36. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  37. GRB 250821A: Swift detection of a burst
  38. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  39. EP250821a: Einstein Probe detection of an X-ray transient
  40. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  41. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  42. GRB 250818B: 10 GHz VLA detection
  43. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  44. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  45. GRB 250814A: Swift/UVOT Upper Limits
  46. GRB 250813B: Swift/UVOT Upper Limit
  47. IPN triangulation of GRB 250816A (short)
  48. IPN triangulation of GRB 250814C (short)
  49. IPN triangulation of GRB 250804B (short)
  50. GRB 250818B: Kilonova-Catcher optical afterglow detection
  51. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  52. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  53. GRB 250818B: Swift/UVOT Detection
  54. GRB 250818B: SAO RAS optical observations
  55. GRB 250818B: KAIT optical observations
  56. GRB 250818A: Swift/UVOT Upper Limits
  57. GRB 250818A: Enhanced Swift-XRT position
  58. GRB 250813B: SVOM/ECLAIRs refined analysis
  59. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  60. GRB 250814A: Further GRAWITA TNG NIR observations
  61. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  62. GRB 250818A: Swift detection of a burst
  63. GRB 250816A: SVOM/GRM observation of a short burst
  64. GRB 250813B: Liverpool Telescope optical upper limits
  65. GRB 250814A: Further COLIBRÍ optical upper limit
  66. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  67. GRB 250814A: GRAWITA TNG NIR observations
  68. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  69. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  70. GRB250814A: TRT optical upper limits
  71. GRB 250814B: SVOM/GRM observation
  72. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  73. GRB 250814A: P200/WIRC observations of the afterglow candidate
  74. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  75. GRB 250814A: KAIT optical upper limit
  76. GRB 250814A: Swift-XRT refined Analysis
  77. GRB 250814A: Possible afterglow candidate from P200/WIRC
  78. GRB 250813B: Fermi GBM Observation
  79. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  80. GRB 250814A: J-band upper limit from WINTER
  81. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  82. GRB 250813B: NOT observations of the optical afterglow
  83. GRB 250814A: COLIBRÍ optical upper limit
  84. GRB 250813A: AstroSat CZTI detection
  85. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  86. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  87. GRB 250814A: DDOTI Optical Upper Limit
  88. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  89. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  90. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  91. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  92. GRB 250813B: SVOM detection of a bright long burst
  93. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  94. EP250812a: Nickel optical upper limit
  95. EP250812a: NOT, NTT, and GS observations
  96. GRB 250812A: Swift/UVOT Detection
  97. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  98. EP250812a: Liverpool Telescope upper limits
  99. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  100. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate

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